Electron spin resonance of the C6, C8, and C1 molecules

Abstract

Electron-spin-resonance (ESR) signals attributed to the linear C6, C8, and C10 molecules in their lowest 3Σ states, presumably their ground states, have been observed in solid neon and argon matrices at 4 K. There is evidence of two forms of the C10 molecule, perhaps indicating two slightly bent structural isomers. Laser vaporization of graphite and 13C-enriched graphite produced a high proportion of these larger molecules. Hyperfine interaction in the 13Cn molecules was small and resolved only for C6, indicating cumulene-type bonding with the unpaired spins in pπ orbitals, as in C4. The zero-field-splitting parameters ‖D‖ were found to be 0.363, 0.783, and 0.190 cm−1, respectively, in solid neon. The increase in ‖D‖ through C8 is attributed to a corresponding variation in the spin–orbit coupling with low-lying states, principally the 1Σ+g, as the chains lengthen. Gross orbital spin populations and 1Σ+g– X 3Σ−g energy differences were obtained from Hartree–Fock calculations in order to interpret the hfs and ‖D‖ data, respectively. Electron correlation was included via second and third order Mo/ller–Plesset perturbation theory. The possibility of quasilinear or nonlinear character in these chains is briefly considered. Relative concentrations of the linear and cyclic forms of these molecules in the vapor and in matrices were estimated from thermodynamics using their theoretically derived properties.

Vibrational spectra of cyclic C6 in solid argon

“…%~). This ordering of isomer energies agrees with earlier predictions by Raghavachari and Binkley [3], Linear C 8 was first identified by Van Zee et al [7] in electron-spin-resonance studies of laser-vaporized graphite trapped in solid neon. Szczepanski et al [8] subsequently used theoretical results to interpret their own infrared spectroscopic measurements of carbon clusters trapped in argon matrices, concluding that absorptions at 2071.5 and 1710.5 cm" 1 could originate from linear C 8 .…”

Infrared laser spectroscopy of jet-cooled carbon clusters

“…Recent experiments [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] as well as high level ab initio calculations [19][20][21][22][23][24][25][26][27][28][29][30] have largely vindicated the description originally put forth by Pitzer and Clementi [31] in 1959. Clusters with odd numbers of carbons possess linear singlet ground states, whereas even numbered clusters have two low-lying isomers, a triplet linear form and a singlet cyclic form.…”

The origin of white luminescence from silicon oxycarbide thin films

“…7 Besides, no evidence for the presence of such sp 2 -C clusters was found in the EPR measurements reported herein, despite the fact that their corresponding signals are well documented in the analysis of thin a-C:H layers. [19][20][21] Therefore, the observed white luminescence from the SiC x O y samples may not be associated with the above-mentioned defect centers and a possible C phase separation within the SiC x O y matrix.…”