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Title:Electronic Spectroscopy Of cis- And trans-meta-vinylbenzyl Radicals
Author(s):Reilly, Neil J.
Contributor(s):Hewett, Daniel M.; Flores, Jonathan; Ross, Sederra D.
Abstract:The electronic spectra of the resonance-stabilized radical C$_9$H$_9$ isomers \textit{cis}- and \textit{trans-meta}-vinylbenzyl (MVB), generated in a supersonically cooled discharge of \textit{m}-vinyltoluene, have been investigated using resonant two-colour two-photon ionization (R2C2PI) and laser-induced fluorescence. The $D_0-D_1$ band origins of the \emph{cis} and \emph{trans} conformers are at 19037\,\wn\ and 18939\,\wn, respectively. Adiabatic ionization energies near 7.17\,eV were determined for both conformers from two-colour ion-yield scans. Dispersed fluorescence (DF) was used to conclusively identify the \emph{cis} conformer: ground-state \emph{cis}-MVB eigenvalues calculated from a Fourier series fit of a computed (B3LYP/6-311G++(d,p) vinyl torsion potential are in excellent agreement with torsional transitions observed in the 19037\,\wn\ DF spectrum. Features arising from \textit{cis-} or \textit{trans-}MVB in the R2C2PI spectrum were distinguished by optical-optical holeburning spectroscopy and vibronic assignments were made with guidance from DFT and TDDFT calculations. There is a notable absence of mirror symmetry between excitation and emission spectra for several totally symmetric modes, whereby $a'$ fundamentals that are conspicuous in emission are nearly absent in excitation, and \emph{vice-versa}. This effect is largely ascribed to interference between Franck-Condon and Herzberg-Teller contributions to the electronic transition moment, as the former is carried with a different sign in excitation $vs.$ emission, while the latter is not. Rampant HT activity among $a'$ modes is attributed to the low symmetry ($C_s$) of the molecule, which permits intensity-borrowing from several relatively bright electronic states of $A''$ symmetry.
Issue Date:2021-06-23
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Date Available in IDEALS:2021-09-24

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