Small Carbon Clusters (Cn(0), Cn(+), Cn(-)) from Acyclic and Cyclic Precursors. Neutralization-Reionization Mass Spectrometry and Theory

Authors: Aberra Fura; Frantisek Turecek; Fred W. McLafferty; CORNELL UNIV ITHACA NY BAKER LAB

Abstract:

Ab initio calculations of isomeric carbon clusters C sub n(0) and C sub n(+), n = 2-4, yield structures and energies similar to previous reports, although five (not two) C4(+) structures have local energy minima. Dissociative ionization of structurally varied precursors was used to prepare C3 and C4 ionic and neutral isomers; however, their mass spectra from collisionally activated dissociation (CAD) and neutralization-reionization (NR) under a wide variety of conditions are indistinguishable, indicating only one isomer or the same mixture of isomers. Likewise, CAD and NR spectra of C4(+) and C4(0) from (13) CH2=CHCH=(13)CH2 and C3(+) and C3(0) from CH2=(13)CHCH3 show complete (13)C/(12) C scrambling. CAD cross sections are consistent with C4(+) - C6(+) ions as mainly linear isomers and C7(+) ions from cyclic precursors as mainly cyclic. Product abundances from the unimolecular dissociation of C sub (0), C sub n(-), and C sub n(+) allow the selection of thermodynamic data that should be of higher relative accuracy, such as 11.4 eV for the C3 ionization energy from reported values of 10.0-13.0 eV.

Limitations:

APPROVED FOR PUBLIC RELEASE