Small carbon clusters (C_n~0, C_n~+, C_n~-) from

摘要

Dissociative ionization of several linear, cyclic, and branched molecules was used to generate C_3~+ and C_4~+ carbon clusters. However, mass spectra from collisionally activated dissociation (CAD) and neutralization-reionization (NR) under a wide variety conditions were indistinguishable, indicating only one isomer or same mixture of isomers. Likewise, CAD and NR spectra of C_4~+ and C_3~+ from ~(13)CH_2=CH-CH=~(13)CH_2 and CH_3-~(13)C=CH_2 show complete ~(12)C/~(13)C scrambling. CAD cross sections are consistent with C_4~+-C_6~+ ions as mainly linear isomers and C_7~+ ions from cyclic precursors as mainly cyclic. CCSD(T) ab initio and B3LYP density functional theory calculations with large basis sets yielded structures and energies for a variety of cationic, neutral, and anionic carbon clusters and transition states for some cationic rearrangements. The calculated enthalpies of formation, dissociation energies, ionization energies, and electron affinities mostly agree with currently accepted experimental data. However, CCSD(T) calculations indicate adiabatic ionization energies for C_3 (11.79eV) and C_4 isomers (10.48, 10.82, and 10.86eV) that differ > 1eV from recent measurements.