| Proton Transfer Dynamics and Cluster Ion Fragmentation in Phenol/Ammonia CLusters |
24 AUG 93 |
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| Authors:
M. Hineman; D. F. Kelley; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF BIOCHEMISTRY
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 | Excited-state proton transfer dynamics are reported for the PHENOL(NH3)n cluster system. Excited state proton transfer is shown to occur for this system by isotopic substitution of the hydroxyl proton and ammonia protons. The observed dynamics slow from 80 ps to 600 ps upon cluster deuteration. The effects of cluster vibrational energy and ammonia concentration in the expansion gas are also studied. The results of these experiments are compared with a ... |
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| Solvation Effects on Reactive Intermediates: The Benzyl Radical and Its Clusters with Ar, N2, CH4, C2H6, and C3H8 |
11 DEC 92 |
50 pages |
| Authors:
R. Disselkamp; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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 | Mass resolved excitation spectra are presented for the benzyl radical and its clusters with Ar, N2, CH4, C2H6, and C3H8. The cluster spectra exhibit small red shifts (< 50 cm-1) relative to the unclustered benzyl radical for the D sub 1 (1(2) A sub 2) reverse transition D sub 0 (1(2) B sub 2) and D sub 2 (2(2) B sub 2) reverse transition D sub 0 (1(2) B sub ... |
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| Solvation Effects on Reactive Intermediates: the Benzyl Radical and Its Clusters with Ar, N sub 2, CH sub 4, C sub 2 H sub 6, and C sub 3 H sub 8 |
04 NOV 92 |
49 pages |
| Authors:
R. Disselkamp; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Mass resolved excitation spectra are presented for the benzyl radical and its clusters with Ar, N2, CH4, C2H6, and C3H8. The cluster spectra exhibit small red shifts (< 50 cm-1) relative to the unclustered benzyl radical for the D1(1(2)A2) <-- DO(1(2)B2) and D2(2(2)B2) <-- DO(1(2)B2) electronic transition regions. A unique set of low energy van der Waals modes is observed for these clusters for each excited electronic state investigated. The ... |
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| Benzyl Alcohol-Water and -Ammonia Clusters: Ion Fragmentation and Chemistry |
10 SEP 92 |
35 pages |
| Authors:
S. Li; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Benzyl alcohol/ammonia alpha, alpha-dimethylbenzyl alcohol/ammonia and benzyl alcohol/water cluster ion fragmentation and chemistry are studied for isolated cold clusters by means of one- and two-colors mass resolved excitation spectroscopy, nozzle/laser timing delay adn deuteration experiments. Experiments lead to an identification of parent clusters for all fragment ion clusters observed. Fragmentation reactions depend on cluster size, structure, and (weakly) on the vibrational energy deposited in the ion. Specifically, for benzyl alcohol+(NH3)1 ... |
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| Vibrational Dynamics of Aniline (N2)1 Clusters in Their First Excited Singlet State |
04 FEB 92 |
24 pages |
| Authors:
E. R. Bernstein; M. F. Hineman; S. K. Kim; D. F. Kelley; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| The vibrational dynamics of van der Waals (vdW) clusters have recently attracted considerable experimental and theoretical attention. The most extensively studied vdW clusters consist of a chromophore molecule and one or more solvent molecules. The cluster is excited by absorption of a photon to a chromophore vibronic state which can then relax by three different pathways: fluorescence or radiationless processes (intersystem crossing or internal conversion); intra cluster vibrational redistribution of ... |
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| Solvation Effects on the Electronic Structure of 4-N,N- Dimethylaminobenzonitrile: Mixing of the Local Pi(pi) and Charge Transfer States |
04 FEB 92 |
34 pages |
| Authors:
E. R. Bernstein; Q.-y. Shang; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| The effect of polar solvents acetonitrile and water on the electronic excited states of 4-N,N-dimethylaminobenzonitrile (DMABN), is studied through the optical spectroscopy of small clusters of DMABN/solvent. The clusters are created in a supersonic jet expansion. The results of mass resolved excitation spectroscopy (MRES), fluorescence excitation (FE), dispersed emission (DE), and photo-depletion studies demonstrate that the solvent molecule can bind to DMABN at two distinct sites for the 1:1 cluster. ... |
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| Excited State Proton Transfer in 1-Naphthol/Ammonia Clusters |
04 FEB 92 |
27 pages |
| Authors:
E. R. Bernstein; M. F. Hineman; G. A. Brucker; D. F. Delley; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Proton transfer is a central mechanistic and kinetic step in a large number of important reactions. Reactions involving proton transfer are strongly affected by the surrounding solvent: several studies of proton transfer mechanisms and dynamics in bulk condensed phases have appeared encompassing solvent, pH, and isotope effects. In these studies the effects observed can be related to the bulk properties of the solvent. The individual effects of solvent molecules and ... |
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| Toluene-Ammonia Cluster: Ion Fragmentation and Chemistry |
04 FEB 92 |
26 pages |
| Authors:
E. R. Bernstein; S. Li; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| The Toluene ammonia cluster system is studied by mass resolved excitation spectroscopy: like the toluene water system, an extensive ion chemistry is found to exist generating ammonia solvated protons and (solvated) benzyl radicals. Extensive cluster fragmentation is observed even ar threshold ionization energies. Nozzle deuteration studies are applied to elucidate the extensive ion chemistry of this cluster system. Proton transfer cluster fragmentation reactions in this system are assisted by solvation ... |
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| Mass Resolved Excitation Spectroscopy of Benzyl and Phenylnitrene Radicals |
30 JUL 91 |
15 pages |
| Authors:
E. R. Bernstein; H. S. Im; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Two-color mass resolved excitation spectra are obtained for the benzyl and phenylnitrene radicals. The spectrum previously assigned to the benzyl radical is generated by a species with mass 91 amu. This finding is consistent with the proposed benzyl radical structure. The origin of transition lies at 21,997 cm-1. The ionization energy for the benzyl radical is ca. 7.236 eV. The phenylnitrene radical spectrum is associated with a species of 90 ... |
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| Normal Mode Analysis of van der Waals Vibrations |
07 MAR 91 |
37 pages |
| Authors:
S. Li; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Two algorithms are presented for calculation of the van der Waals modes of weakly bound clusters. Both methods rely on the harmonic normal mode approximation and a chosen intermolecular potential. These calculational techniques differ specifically in the form of the force field employed: one method uses the total (both intra- and inter- molecular) force field for the cluster and the other uses only the intermolecular force field. Both methods require ... |
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| Excited State Proton Transfer in the S1 State of 2-Allylphenol, 2- Propenylphenol and 2-Propylphenol and Their van der Waals Clusters with Water and Ammonia |
07 MAR 91 |
33 pages |
| Authors:
S. K. Kim; S. C. Hsu; S. Li; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Excited state intramolecular and intermolecular proton transfer reactions in cold, isolated 2-allylphenol, 2-propenylphenol and 2-propylphenol and their clusters with water and ammonia are investigated employing a combination of spectroscopic techniques (mass resolved excitation, threshold photo-ionization, dispersed emission), a semi-empirical MNDO calculation (MOPAC 5) and a potential energy calculation of cluster structure. Threshold photo- ionization spectroscopy proves to be useful for the identification of molecular conformers in these systems but has ... |
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| Excited State Intermolecular Proton Transfer in Isolated Clusters: 1- Naphthol/Ammonia and Water |
07 MAR 91 |
39 pages |
| Authors:
S. K. Kim; S. Li; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| The excited singlet state intermolecular proton transfer reaction in jet-cooled clusters of 1-naphtho1/ammonia and water is investigated employing mass resolved excitation, threshold photo-ionization, and emission spectroscopy. The 1-naphthol(NH3)3 cluster for which proton transfer is indicated has a threshold photo-ionization energy roughly 2000 cm-1 below the other 1- NAPHTHOL(NH3)3 cluster configurations. These results are employed to explain the previous discrepancy between static spectroscopic experiments and picosecond time resolved dynamic experiments concerning ... |
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| Supersonic Jet Studies of Benzyl Alcohols: Minimum Energy Conformations and Torsional Motion |
13 MAY 90 |
54 pages |
| Authors:
Hoong-Sun Im; E. R. Bernstein; Jeffrey I. Seeman; Henry V. Secor; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Supersonic jet mass resolved excitation spectroscopy is employed to determine the minimum energy conformations of benzyl alcohol and a series of nine methyl-, ethyl-, fluoro-, and aminobenzyl alcohols. The interpretation of the time-of-flight mass spectra (TOFMS) of these molecules leads to the assignment of specific molecular geometries for each system. The minimum energy conformation of the -CH2O moiety is determined to be perpendicular relative to the plane of the aromatic ... |
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| Spectroscopic Observation of Individual sp3-Nitrogen Stereoisomers. Supersonic Jet Studies of 2-Aminobenzyl Alcohol |
13 MAY 90 |
12 pages |
| Authors:
Jeffrey I. Seeman; Henry V. Secor; Hoong-Sun Im; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Conformational analysis of the trivalent nitrogen atom is conceptually complicated because of the presence of two dynamic processes, nitrogen inversion and internal rotation about various single bonds. Experimental investigations of this subject are further entangled because these conformational interconversions have very low barriers and are rapid on the time scale of most experimental observations. Evaluation of the sterodynamics of these systems has typically required one of three tricks to slow ... |
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| Low Temperature Elastic and Dielectric Properties of Incommensurate Barium Sodium Niobate |
15 DEC 89 |
47 pages |
| Authors:
W. F. Oliver; J. F. Scott; R. Nowak; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| We have performed dielectric and Brillouin spectroscopic measurements on incommensurate (IC) Ba(2)NaNb(5)O(15) from ca. 15 K to room temperature and have related our measurements to earlier studies of birefringence and x-ray and neutron crystallography, with special emphasis upon the structural phase transition near 105 K and 40 K. The 105 K transition is from Ccm2(1) to a modulated structure, which appears to be a reentrant phase also found at atmospheric ... |
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| Observation and Geometry Assignment of the Conformation of Benzyl Alcohol in the Gas Phase |
15 DEC 89 |
15 pages |
| Authors:
Jeffrey I. Seeman; Henry V. Secor; Hoong-Sun Im; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Supersonic molecular jet laser spectroscopy is used to establish the perpendicular conformation of benzyl alcohol and a number of sterically unencumbered derivatives in the gas phase. Benzyl alcohol and its derivatives have vast synthetic utility, are frequently found in natural products, and play a central role in numerous mechanistic investigations. In spite of this chemical importance, the conformational preference of the -CH2OH group relative to the aromatic ring has not ... |
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| 7-Azaindole and Its Clusters with Ar, CH4, H2O, NH3, and Alcohols: Molecular Geometry and Nature of the First Excited Singlet Electronic State |
15 DEC 89 |
44 pages |
| Authors:
Seong K. Kim; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Mass resolved excitation vibronic spectra of jet-cooled 7-azaindole and its clusters with Argon, Methane, Ammonia, H2O, D2O, and Methyl Alcohol, Ethyl Alcohol are reported and analyzed with regard to molecular and cluster geometry and the nature of the first excited sinlet state. Large changes in the various spectra are observed upon clustering and upon deuteration of 7- azaindole. The observed vibronic spectra of both 7-azaindole and its clusters can be ... |
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| Spectroscopy and Structure of Jet Cooled Alpha-Methylstyrene |
15 DEC 89 |
30 pages |
| Authors:
V. H. Grassian; E. R. Bernstein; Henry V. Secor; J. I. Seeman; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| The ground (S0) and excited (S1) state geometries of alpha- methylstyrene (2-phenylpropene,2) are investigated by mass resolved excitation spectroscopy. In contrast to styrene, which has an intense spectral S1-S0 origin transition, alpha-methylstyrene exhibits a weak origin transition and a long progression in a low frequency torsional mode, with an energy level spacing of approx. 69/cm. The intensity maximum of this progression occurs at the eighth peak position, indicating that the ... |
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| Determination of the Minimum Energy Conformation of Alkyl Substituted Pyrazines |
15 DEC 89 |
33 pages |
| Authors:
Hoong-Sun Im; E. R. Bernstein; J. I. Seeman; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Supersonic jet laser spectroscopy has been utilized to identify the minimum energy conformers of substituted aromatic molecules in the gas phase. These determinations have been performed based on the observation that each conformer produces its own origin transition for the excitation. Thus the counting of origin transition in the mass resolved excitation spectrum reveals the number of conformers present for a given system. Conformational preferences for methyl, ethyl, isopropyl and ... |
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| Determination of the Minimum Energy Conformations of Benzyl Alcohol and 2-Phenethyl Alcohol |
14 DEC 89 |
39 pages |
| Authors:
Hoong-Sun Im; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Supersonic jet mass resolved excitation spectroscopy is employed to determine the minimum energy conformation of the alcohol group with respect to the benzene ring for benzyl alcohol (BA) and 2-phenethyl alcohol (2-PEA). The mass resolved excitation spectra of these molecules are presented and assigned. The C-O bond orientation in BA is determined to be perpendicular to the benzene ring (tau (Cortho-Cipso-C alpha-O) = 90deg) and in 2-PEA it is determined ... |
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| Spectroscopy and Structure of Jet-Cooled Alpha-Methylstyrene |
01 JUN 89 |
35 pages |
| Authors:
V. H. Grassian; E. R. Bernstein; Henry V. Secor; Jeffrey I. Seeman; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| The sterically hindered styrene derivative, alpha-methylstyrene (2- phenyl-propene), is studied by 1-color time-of-flight mass spectroscopy (TOFMS). In contrast to styrene, which has an intense spectral origin transition in the TOFMS, alpha-methylstyrene exhibits a weak origin transition. A progression in a low frequency torsional mode, with an energy level spacing of approx. 69/cm, is built on the origin. The intensity maximum of this progression occurs at the eighth peak position, indicating ... |
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| Monte Carlo Simulations of Small Solute/Solvent Clusters: Cluster Properties and Phase Transitions |
01 JUN 89 |
41 pages |
| Authors:
S. Li; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Atom-atom L-J (6-12-1) potentials are employed to calculate the cluster configurations of all local energy minima of benzene(N2)n and (N2)n clusters for n=1, 2,.....10 and some benzene(Ar)n and N2(Ar)n clusters. The number of configurations increases exponentially and the binding energy range increases linearly with the number of solvent molecules for these clusters. Monte Carlo simulations are performed on the temperature behavior of the cluster potential energy, intermolecular distance, and some ... |
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| Vibrational Dynamics of Aniline (Ar)1 and Aniline (CH4)1 Clusters |
01 JUN 89 |
37 pages |
| Authors:
M. R. Nimlos; M. A. Young; E. R. Bernstein; D. F. Kelley; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
|
| The first excited electronic state (S1) vibrational dynamics of aniline(Ar)1 and aniline(CH4)1 van der Waals (vdW) clusters have been studied using molecular jet and time resolved emission spectroscopic techniques. The rates of intramolecular vibrational energy redistribution (IVR) and vibrational predissociation (VP) as a function of excess vibrational energy are reported for both clusters. For vibrational energy in excess of the cluster binding energy, both clusters are observed to dissociate. The ... |
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| A Study of Non-Rigid Aromatic Molecules by Supersonic Molecular Jet Spectroscopy: Observation and Spectroscopic Analysis of the Stable Conformations of Various Alkylbenzenes |
01 JUN 89 |
23 pages |
| Authors:
J. I. Seeman; H. V. Secor; P. J. Breen; V. H. Grassian; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
|
| The technique of supersonic molecular jet laser spectroscopy was used to determine the stable conformations of a series of alkylbenzenes. This study demonstrates, for the first time, the sensitivity of molecular jet spectroscopy in determining both the number of stable conformation as well as the geometry of various ethyl, propyl, and butyl substituents relative to the aromatic ring. Different rotamers with low barriers to interconversion, >5 kcal/mol. can be isolated ... |
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| Supersonic Jet Studies of Fluorene Clustered with Water, Ammonia and Piperidine |
01 JUN 89 |
37 pages |
| Authors:
H. S. Im; V. H. Grassian; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
|
| Mass resolved excitation spectroscopy and dispersed emission spectroscopy are employed to study van der Waals (vdW) clusters of jet cooled fluorene with ammonia, water and piperidine. For fluorene(H20)1 and fluorene(NH3)1 clusters, cluster geometries and binding energies can be suggested based on the experimental results and Lennard-Jones (LJ) potential (6- 12-1) energy calculations. As the number of solvent molecules in the cluster is increased, spectra of the clusters become more complex ... |
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| Determination of the Minimum Energy Conformation of Allylbenzene and Its Clusters with Methane, Ethane, Water and Ammonia |
01 JUN 89 |
38 pages |
| Authors:
P. J. Breen; E. R. Bernstein; Jeffrey I. Seeman; Henry J. Secor; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
|
| Supersonic molecular jet laser time of flight mass spectroscopy (TOFMS) is employed to determine the minimum energy conformation of the allyl group with respect to the benzene ring of allylbenzene, 1-allyl-2-methylbenzene and 1-allyl-3-methylbenzene. The spectra are assigned and conformations are suggested with the aid of molecular orbital molecular mechanics (MOMM-85) calculations. Based on the experimental and theoretical results, the minimum energy conformer is found to have tau(1) (C(ortho)-C(ipso)-C(alpha)-C-(beta)) = ca. ... |
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| Conformational Changes upon S1 Yields S0 Excitation in 4- Dimethylaminobenzonitrile and some of Its Chemical Analogs |
03 NOV 88 |
30 pages |
| Authors:
V. H. Grassian; J. A. Warren; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
|
| One color time of flight mass spectra (mass resolved excitation spectra) for jet cooled 4-dimethylaniline (DMA), 3-dimethylamon-obenzonitrile (3-DMABN), N,N-dimethyl-4-(trifluoromethyl) benzeamine (4-CF3-DMA) and 4-(d6- dimethylamino)benzonitrile (4-d6-DMABN), are presented and analyzed. Near the origin of the S1-So transition the low frequency modes can be assigned to motions of the dimethylamino group and the dimethylamino group torsion about the motion of the dimethylamino group and the dimethylamino group torsion about the C-ipso-N bond ... |
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| Spectroscopy and Structure of Jet-Cooled Alpha-Methylstyrene |
12 JUL 88 |
30 pages |
| Authors:
V. H. Grassian; E. R. Bernstein; J. I. Seeman; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
|
| The sterically hindered styrene derivative, alpha-methylstyrene (2- phenyl-propane), is studied by 1-color time-of-flight mass spectroscopy (TOFMS). In contrast to styrene, which has an intense spectral origin transition in the TOFMS, alpha-methyl styrene exhibits a weak origin transition. A progression in a low frequency torsional mode, with an energy level spacing of approx. 69/cm, is built on the origin. The intensity maximum of this progression occurs at the eighth peak position, ... |
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| Spectroscopy, Structure and Proton Dynamics of 2-Hydroxypyridine and Its Clusters with Water and Ammonia |
12 JUL 88 |
43 pages |
| Authors:
M. R. Nimlos; D. F. Kelley; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
|
| The two tautomeric forms of 2 hydroxypyridine (2-HP) have been studied in a supersonic jet expansion. Time-of-flight mass spectroscopy (TOFMS) and emission spectroscopy of the lactim and lactam tautomers have been studied and are reported here. The lactim spectrum is similar to an earlier TOFMS spectrum and has its origin at 36,136/cm. Evidence of mixing of the npi and pi electronic states is seen in the lactim spectrum. The mixing ... |
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| Benzene Clustered with N2, CO2, and CO: Energy Levels, Vibrational Structure and Nucleation |
12 JUL 88 |
56 pages |
| Authors:
R. Nowak; J. A. Menapace; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
|
| Two color time of flight mass spectroscopy is employed to study the van der Waals (vdW) clusters of benzene(N2)n(n<8), benzene(CO2)n(n<7), and benzene(CO)n (n=1,2) created in a supersonic molecular jet. Potential energy calculations of cluster geometries, normal coordinate analysis of vdW vibrational modes, and calculations of the internal rotational transitions are employed for the assignment of the benzene(solvent) cluster spectra. The respective vibronic and rotational selection rules for these clusters are ... |
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| A Study of Non-Rigid Aromatic Molecules by Supersonic Molecular Jet Spectroscopy: Observation and Spectroscopic Analysis of the Stable Conformations of Various Alkylbenzenes |
12 JUL 88 |
65 pages |
| Authors:
Jeffrey I. Seeman; Henry V. Secor; P. J. Breen; V. H. Grassian; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
|
| The technique of supersonic molecular jet laser spectroscopy was used to determine the stable conformations of a series of alkylbenzenes. This study demonstrates, for the first time, the sensitivity of molecular jet spectroscopy in determining both the number of stable conformations as well as the geometry of various ethyl, propyl and butyl substituents relative to the aromatic ring. Different rotamers with low barriers to interconversion, < 5 kcal/mole, can be ... |
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| Spectroscopic Studies of Phthalocyanines and Their Clusters with Small Molecules |
MAY 87 |
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| Authors:
J. A. Menapace; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| VAN DER Waals clusters of free base phthalocyanine (H2Pc) and magnesium phthalocyanine (MgPc) with small hydrocarbons (CnH2n+2 (n = 1, 2, 3)), hydrogen bonding solvents (H2O, MeOH, EtOH), and CO2 are studied in the gas phase using supersonic molecular jet spectroscopy. Flourescence excitation spectra of the cluster systems are characterized in the O regions of the cluster S1, S0 transitions. Forbidden low frequency cluster chromophore out-of-plane vibronic transitions are induced ... |
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| The Spectroscopy and Structure of 2-Hydroxyquinoline |
MAY 87 |
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| Authors:
M. R. Nimlos; D. F. Kelley; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| 2-Hydroxyquinoline (2-H) is known to exist as two tautomeric forms which are nearly equal in energy. These tautomers are referred to as the lactim and lactam (or enol and keto) forms which are interconverted by simple hydrogen atom transfer between the oxygen of the OH group and the ring nitrogen. The spectroscopy of 2HG is of interest because of this tautomerization. Similar proton transfer processes which are important in many ... |
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| On the van der Waals Modes of Solute/Solvent Clusters: Benzene-Methane, -Deuteromethane, and -Carbon Tetrafluoride |
MAY 87 |
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| Authors:
J. A. Menapace; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Clusters of benzene (CD4)1 and (CF4)1 are created in a supersonic molecular jet and are studied by two-color time-of-flight mass spectroscopy. The clusters' S1 - So intermolecular vibronic structures are characterized by calculational modeling of the clusters' intermolecular motion. The calculations include: 1) an intermolecular normal coordinate analysis (NCA) which treats all six van der Waals modes under a harmonic oscillator assumption; and 2) a three dimensional hindered rigid rotor ... |
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| Torsional Motion in Aromatic Molecules. Conformational Analysis of Methyl-, Ethyl, and n-Propylbenzenes |
MAY 87 |
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| Authors:
P. J. Breen; J. A. Warren; E. R. Bernstein; J. I. Seeman; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
|
| Supersonic molecular jet spectroscopy is used to obtain information on the torsional motion in methyl, ethyl and n propyl substituted benzenes. Dispersed emission and time of flight mass spectral results are evaluated for toluene, the three xylenes, diethylbenzene and normal propyltoluene. The aromatic ring methyl groups in meta and paraxylene can be considered as independent free rotors while in o-xylene they are considerably more hindered in these two states and ... |
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| Supersonic Molecular Jet Studies of the Pyrazine and Pyrimidine Dimers |
01 JUN 86 |
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| Authors:
J. Wanna; J. A. Menapace; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Mass selected optical spectra for the first excited singlet pi states of the pyrazine and pyrimidine dimers are presented. The species are created in a pulsed supersonic jet expansion. The spectra are analyzed based on ionization energy, vibronic structure and relative energy with respect to the isolated monomer (cluster spectroscopic shift). Calculations of binding energy and geometry for these dimers are carried out employing a lennard-jones (6-12-1) and hydrogen bonding ... |
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| Calculation of the Vibronic Structure of Solute/Solvent van der Waals Clusters |
01 JUN 86 |
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| Authors:
J. A. Menapace; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Calculations of the eigenvectors and eigenvalues for the van der Waals clusters benzene (Ar)1, (CH4)1, (H2O)1, and (NH3)1, and s-tetrazine (Ar)1 are presented. The calculations are based on an atom-atom Lennard-Jones (6-12-1- 10-12) potential function, which includes hydrogen bonding, and a normal coordinate analysis. The clusters are treated as giant molecules. The results of these calculations are then used to assign the van der Waals vibronic spectra of the above ... |
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| On the Pyrazine and Pyrazine-Pyrimidine Dimers |
01 JUN 86 |
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| Authors:
J. Wanna; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Spectra of the pyrazine-d sub 4, pyrazine-h sub 4-pyrazine-d sub 4- pyrimidine dimer are obtained and analyzed with the help of Lennard-Jones- hydrogen-bonding (LJ-HB) potential energy calculations. The pyrazine isotopic hetero- and homo-dimers possess nearly identical spectra with the exception that the perpendicular dimer features are displaced to the red by approx. 11 cm. Exchange or exciton interactions in this system are vanishingly small (less than 1/cm). The geometrics suggested ... |
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| Hydrogen Bonded and Non-Hydrogen Bonded vdWs (van der Waals) Clusters: Comparison Between Clusters of Pyrazine, Pyrimidine and Benzene with Various Solvents |
01 JUN 86 |
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| Authors:
J. Wanna; J. A. Menapace; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
|
| Solute-solvent clusters of pyrazine, pyrimidine and benzene (solutes) and CnH2n+2 (n=1, 2), NH3 and H20 (solvents) are studied by the techniques of supersonic molecular jet spectroscopy and two-color time of flight mass spectroscopy (2-color TOFMS). Spectral shifts, van der Waals (vdW) modes, dissociation energies, and vdW mode-solute mode vibronic couplings are characterized for most of the observed clusters. Based on these data and previous results for hydrocarbon systems, cluster geometries ... |
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| On the Phase Transition of N-Isopropylcarbazole |
MAY 86 |
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| Authors:
R. Nowak; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| The elastic properties of N-isopropylcarbazole (NIPC), a pyroelectric molecular crystal, are investigated by Brillouin scattering. The full elastic constant tensor is determined at 295 K and the temperature dependence of the elastic constants are given. The major experimental finding reported is the anomaly of the LA a-axis mode governed by the c sub 11 elastic constant. This mode exhibits a pronounced downward bending on both sides of the nonferroic, first ... |
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| The S sub 0 to S sub 2 Laser Photoexcitation Spectrum and Excited State Dynamics of Jet-Cooled Acetophenone |
MAY 86 |
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| Authors:
J. A. Warren; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| The S2 from S0 photoexcitation spectrum of jet cooled acetophenone is presented. The observed homogeneously broadened linewidths indicate S2 lifetimes < or = 0.26 fs while the measured emission lifetimes range from 540 + or - 30 ns for S0 O0 superscript 0 excitation to 130 + or - 50 ns for S2 12 1/2 excitation. The dynamics revealed by the spectrum are discussed in terms of the known photochemical ... |
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| Calculations of the Geometry and Binding Energy of Aromatic Dimers: Benzene, Toluene, and Toluene-Benzene |
15 APR 85 |
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| Authors:
Mark Schauer; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Calculations of the geometries and energies of the benzene, toluene, and toluene-benzene dimers using a combination of atom-atom and multipolar potentials are presented and discussed. An exponential-six atom-atom potential plus a molecular quadrupole-quadrupole interaction term gives the reported parallel displaced C2h benzene dimer geometry. The excited state behavior of the benzene dimer can be qualitatively understood based on this calculation. The toluene-benzene dimer is well modeled by these terms in ... |
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| Molecular Jet Study of Van Der Waals Complexes of Flexible Molecules: n- Propyl Benzene Solvated by Small Alkanes |
01 APR 85 |
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| Authors:
K. S. Law; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| A combination of atom-atom potential calculations and experimental molecular jet spectroscopic studies is used to elucidate the geometry and binding energy of n-propul benzene/methane, ethane, and propane clusters. Two color time-of-flight mass specttoscopy data and calculations are presented for both trans and gauche configurations of n-propul benzene with up to three hydrocarbon molecules of solvation. Cluster shifts and geometry are treated in detail for the observed and calculated systems. Solvation, ... |
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| Molecular Jet Study of Solvation of Pyrazine by Small Hydrocarbons |
19 MAR 85 |
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| Authors:
J. Wanna; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Supersonic molecular jet two-color time of flight mass spectroscopy studies are reported for pyrazine solvated by methane, ethane, and propane. The results parallel those obtained for benzene and toluene solvated by these molecules. The presence of nitrogen atoms and lone pair electrons in the aromatic system has only a small effect on the cluster structure. Lennard-Jones potential calculations are presented along with the experimental data. Cluster shifts and binding energies ... |
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| Molecular Jet Study of the Solvation of Benzene by Methane, Ethane, and Propane |
15 JAN 85 |
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| Authors:
Mark Schauer; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Two color time of flight mass spectroscopy studies of benzene solvated by methane, ethane, and propane in a molecular jet has been carried out. Absorption has been characterized for transitions of benzene (alkane)X(X=1, 2,3...). Atom-atom exponential-6 potentials have been employed to calculate cluster geometry and binding energy. Comparisons between calculations and experiments allow the identification of specific configurations for the cluster spectroscopic transitions. Cluster spectral shifts can also be identified ... |
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| Molecular Jet Study of the Solvation of Toluene by Methane, Ethane, and Propane |
15 JAN 85 |
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| Authors:
Mark Schauer; K. S. Law; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| The spectroscopic study of van der Waals (vdW) clusters in a molecular jet supersonic expansion has greatly increased our understanding of these species. Additionally, clusters composed of an aromatic molecule (solute) surrounded by small hydrocarbons (solvent) have been discussed as models have been focused on relatively small clusters with few solvent molecules: geometries, energetics, and energy dynamics have all been explored in these vdW systems. Two color time of flight ... |
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| Dimers of Aromatic Molecules: (Benzene)(2), (Toluene)(2), and Benzene- Toluene |
01 DEC 84 |
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| Authors:
K. S. Law; Mark Schauer; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| The optical absorption spectra of the first excited singlet states of the benzene, toluene, and toluene-benzene dimes, created in a supersonic molecular jet, are reported. The absorption spectra are detected through two- color time of flight mass spectroscopy; this method eliminates fragmentation of dimers and higher clusters and the dimer spectra are uniquely observed. The benzene dimer observed in this experiment is suggested to have a parallel stacked and displace ... |
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| Supersonic Molecular Jet Study of the Liquid State |
10 OCT 1984 |
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| Authors:
E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| The study of solvation of aromatic molecules (benzene, toluene, aniline) by small hydrocarbone (CnH2n+2, n = 2,3) in a molecular jet is discussed. The detection of the clusters is through laser induced fluorescence and time of flight mass spectroscopy. The clusters observed (up to 15 solvent molecules) are compared to liquid state systems; simple atom-atom potential calculations are employed to help assign geometry. Dynamical behavior of the clusters is characterized ... |
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| Supersonic Molecular Jet Studies of Toluene-Helium and Toluene-Methane Clusters |
15 MAY 1984 |
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| Authors:
M. Schauer; K. Law; E. R. Bernstein; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| The techniques of fluorescence excitation (FE), dispersed emission (DE), and 1- and 2-color time of flight mass spectroscopy (TOFMS) have been employed to study van der Waals clusters of toluene-helium (To1He) and toulene- methane (TolCH4) formed in a supersonic molecular jet. Spectral shifts for the toluene 1 A sub 1 to 1 B sub 2 transition have been characterized for TolHe1,2 and To1(CH4)1,2. The van der Waals stretching frequencies (V1) ... |
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| Molecular Jet Study of Aniline-Helium van der Waals Molecules and Aniline Radiationless Relaxation in the(1) B sub 2 Excited Electronic State |
16 SEP 1983 |
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| Authors:
E. R. Bernstein; K. Law; Mark Schauer; COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY
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| Fluorescence excitation (FE), dispersed emission (DE), and time of flight mass spectroscopy (TOFMS) techniques are employed to study the van der Waals molecules formed in a molecular supersonic jet of aniline and helium (AnHe sub x). It is found that AnHe1, AnHe2, and AnHe3 have absorption bands that fall under all the An(nu') vibronic features in the 1B2 electronic state of An. The features to the high energy side of ... |
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Reports by Author
