Electronic spectra of positively charged carbon clusters—C2n+ (n = 6–14)

Abstract

Electronic spectra are measured for mass-selected C2n+(n = 6–14) clusters over the visible and near-infrared spectral range through resonance enhanced photodissociation of clusters tagged with N2 molecules in a cryogenic ion trap. The carbon cluster cations are generated through laser ablation of a graphite disk and can be selected according to their collision cross section with He buffer gas and their mass prior to being trapped and spectroscopically probed. The data suggest that the C2n+(n = 6–14) clusters have monocyclic structures with bicyclic structures becoming more prevalent for C22+ and larger clusters. The C2n+ electronic spectra are dominated by an origin transition that shifts linearly to a longer wavelength with the number of carbon atoms and associated progressions involving excitation of ring deformation vibrational modes. Bands for C12+, C16+, C20+, C24+, and C28+ are relatively broad, possibly due to rapid non-radiative decay from the excited state, whereas bands for C14+, C18+, C22+, and C26+ are narrower, consistent with slower non-radiative deactivation.

Electronic Spectroscopy of Monocyclic Carbon Ring Cations for Astrochemical Consideration

“…The electronic spectra of C 2 n + –He ( n = 6–14) complexes are presented in Figure , showing a linear increase in the wavelength of the origin bands with increasing ring size. A similar result for C 2 n + –N 2 has been reported in ref and provides confidence that the same molecular structures are probed in both experiments. The observed spectra are believed to be the lowest energy doublet electronic transitions of these open-shell carbon cations, and in most cases, the pattern is dominated by a strong origin band.…”

“…The C 2 n + ( n = 6–14) species reported in ref are of interest in the context of the DIBs because their wavelength range (400–1400 nm) spans the region where the majority of them are found. The measured bandwidths show an alteration with 2 n , and the narrowest absorptions have widths of 10–20 cm –1 in the visible, making them appealing targets for further laboratory and observational studies.…”

“…For example, for C 18 + –He, the weighted average of three points gives 7991 Å compared with the data point at maximum intensity, 7988 Å. In comparison with the C 2 n + –N 2 data reported in ref , the C 4 n +2 + –He absorptions lie to the red and are shifted by between 3 and 26 cm –1 . Both blue and red shifts are observed for the C 4 n + –He in comparison to the values listed in Table 1 of ref .…”

“…Buntine et al very recently presented results using an instrument that combines ion mobility with spectroscopic characterization in a cylindrical ion trap at 25 K, reporting N 2 tagged data of C 2 n + monocyclic rings, with n = 6–14. These beautiful experiments are a breakthrough in attempts to attain the electronic spectra of carbon cations and reveal that the lowest energy doublet electronic transitions shift linearly to longer wavelengths with increasing n . The behavior thus resembles that observed for linear chains by Maier and colleagues, with examples being C n and the neutral and positively charged polyacetylenes HC n H …”

The combination of laser photodissociation, action spectroscopy, and mass spectrometry to identify and separate isomers

“…A subsequent experimental arrangement that combines IMS and cryogenic PD action spectroscopy has presented the electronic spectra of several cyclic carbon cluster ions. 158,159…”