| Autor: |
Marlton SJP; School of Chemistry, The University of Melbourne, Victoria, Australia3010., Buntine JT; School of Chemistry, The University of Melbourne, Victoria, Australia3010., Watkins P; School of Chemistry, The University of Melbourne, Victoria, Australia3010., Liu C; School of Chemistry, The University of Melbourne, Victoria, Australia3010., Jacovella U; Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d'Orsay, 91405Orsay, France., Carrascosa E; Bruker Daltonics GmbH & Co. KG, Fahrenheitstrasse 4, 28359Bremen, Germany., Bull JN; School of Chemistry, Norwich Research Park, University of East Anglia, NorwichNR4 7TJ, United Kingdom., Bieske EJ; School of Chemistry, The University of Melbourne, Victoria, Australia3010. |
| Abstrakt: |
Carbon aggregates containing between 10 and 30 atoms preferentially arrange themselves as planar rings. To learn more about this exotic allotrope of carbon, electronic spectra are measured for even cyclo[ n ]carbon radical cations ( C 14 + - C 36 + ) using two-color photodissociation action spectroscopy. To eliminate spectral contributions from other isomers, the target cyclo[ n ]carbon radical cations are isomer-selected using a drift tube ion mobility spectrometer prior to spectroscopic interrogation. The electronic spectra exhibit sharp transitions spanning the visible and near-infrared spectral regions with the main absorption band shifting progressively to longer wavelength by ≈100 nm for every additional two carbon atoms. This behavior is rationalized with a Hückel theory model describing the energies of the in-plane and out-of-plane π orbitals. Photoexcitation of smaller carbon rings leads preferentially to neutral C 3 and C 5 loss, whereas rings larger than C 24 + tend to also decompose into two smaller rings, which, when possible, have aromatic stability. Generally, the observed charged photofragments correspond to low energy fragment pairs, as predicted by density functional theory calculations (CAM-B3LYP-D3(BJ)/cc-pVDZ). Using action spectroscopy it is confirmed that C 14 + and C 18 + photofragments from C 28 + rings have cyclic structures. |
