Photo-fragmentation spectroscopy of benzylium and 1-phenylethyl cations
- Physique des Interactions Ioniques et Moleculaires, UMR CNRS 7345, Aix-Marseille Université, Avenue Escadrille Normandie-Niémen, 13397 Marseille Cedex 20 (France)
- Institut des Sciences Moléculaires d’Orsay, CNRS UMR 8214, Université Paris Sud 11, 91405 Orsay Cedex (France)
The electronic spectra of cold benzylium (C{sub 6}H{sub 5}-CH{sub 2}{sup +}) and 1-phenylethyl (C{sub 6}H{sub 5}-CH-CH{sub 3}{sup +}) cations have been recorded via photofragment spectroscopy. Benzylium and 1-phenylethyl cations produced from electrosprayed benzylamine and phenylethylamine solutions, respectively, were stored in a cryogenically cooled quadrupole ion trap and photodissociated by an OPO laser, scanned in parts of the UV and visible regions (600–225 nm). The electronic states and active vibrational modes of the benzylium and 1-phenylethyl cations as well as those of their tropylium or methyl tropylium isomers have been calculated with ab initio methods for comparison with the spectra observed. Sharp vibrational progressions are observed in the visible region while the absorption features are much broader in the UV. The visible spectrum of the benzylium cation is similar to that obtained in an argon tagging experiment [V. Dryza, N. Chalyavi, J. A. Sanelli, and E. J. Bieske, J. Chem. Phys. 137, 204304 (2012)], with an additional splitting assigned to Fermi resonances. The visible spectrum of the 1-phenylethyl cation also shows vibrational progressions. For both cations, the second electronic transition is observed in the UV, around 33 000 cm{sup −1} (4.1 eV) and shows a broadened vibrational progression. In both cases the S{sub 2} optimized geometry is non-planar. The third electronic transition observed around 40 000 cm{sup −1} (5.0 eV) is even broader with no apparent vibrational structures, which is indicative of either a fast non-radiative process or a very large change in geometry between the excited and the ground states. The oscillator strengths calculated for tropylium and methyl tropylium are weak. Therefore, these isomeric structures are most likely not responsible for these absorption features. Finally, the fragmentation pattern changes in the second and third electronic states: C{sub 2}H{sub 2} loss becomes predominant at higher excitation energies, for both cations.
- OSTI ID:
- 22253633
- Journal Information:
- Journal of Chemical Physics, Vol. 140, Issue 2; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
Similar Records
Electronic state spectroscopy of diiodomethane (CH{sub 2}I{sub 2}): Experimental and computational studies in the 30 000–95 000 cm{sup −1} region
Infrared spectrum of the strongly coriolis coupled v{sub 2} and v{sub 4} vibrational states of CH{sub 3}{sup +}