Electronic absorptions of the benzylium cation

Abstract

The electronic transitions of the benzylium cation (Bz(+)) are investigated over the 250-550 nm range by monitoring the photodissociation of mass-selected C(7)H(7)(+)-Ar(n) (n = 1, 2) complexes in a tandem mass spectrometer. The Bz(+)-Ar spectrum displays two distinct band systems, the S(1)←S(0) band system extending from 370 to 530 nm with an origin at 19,067 ± 15 cm(-1), and a much stronger S(3)←S(0) band system extending from 270 to 320 nm with an origin at 32,035 ± 15 cm(-1). Whereas the S(1)←S(0) absorption exhibits well resolved vibrational progressions, the S(3)←S(0) absorption is broad and relatively structureless. Vibronic structure of the S(1)←S(0) system, which is interpreted with the aid of time-dependent density functional theory and Franck-Condon simulations, reflects the activity of four totally symmetric ring deformation modes (ν(5), ν(6), ν(9), ν(13)). We find no evidence for the ultraviolet absorption of the tropylium cation, which according to the neon matrix spectrum should occur over the 260 - 275 nm range [A. Nagy, J. Fulara, I. Garkusha, and J. Maier, Angew. Chem., Int. Ed. 50, 3022 (2011)].

Hydrogen-adduction to open-shell graphene fragments: spectroscopy, thermochemistry and astrochemistry

“…However, these shifts have been shown to be small for similar molecules 49,53,54 and spectra of Ar-tagged molecular cations have proved useful in determining if the observed excitation spectra are relevant to astronomical spectroscopy.…”

“…While the calculations were carried out for the bare radical cation, it is assumed that the energy shift due to argon-tagging is small compared with the differences in predicted energy, as in past studies. 49,52 …”

Photo-fragmentation spectroscopy of benzylium and 1-phenylethyl cations

“…This progression has already been discussed elsewhere. 14,16,47 Apart from the 0-0 transition which is a single band, all other vibrational bands are split by c.a. ~10 cm -1 .…”

“…The benzylium cation has been calculated extensively in two recent papers 14,47 using different methods (TD-DFT mostly). It has a C 2v structure in the ground state and the vertical energies and the oscillator strengths calculated at the RI-CC2/cc-pVTZ level are presented in and a fourth mode observed at 1350 cm -1 , which is tentatively assigned to 2 quanta in  30…”

Infrared detection of the 1,3-dimethyl cyclopentadienyl cation, an isomer of protonated toluene

“…Similar measurements for C 3 H 5 + found it to have both allyl and 2-propenyl cation structures [14]. C 7 H 7 + ions are known to adopt the benzylium and tropylium ion structures, although limited spectroscopy is available for this system [15][16][17][18][19]. Protonated benzene was shown by Olah and coworkers to have only the -protonated form [20,21], and recent gas phase IR measurements confirmed this, revealing the full vibrational spectrum [22][23][24][25].…”