The Vibrational and Electronic Spectra of Ethynylbenzene

Abstract

<p> The infrared and Raman spectra of ethynylbenzene-h6, -d1, -d5 and -d6 have been analysed, and the fundamental frequencies assigned.</p> <p> Vibrational analyses of the electronic spectra of ethynylbenzene-h6, -d1, -d5 and -d6 in the 2900-2500 Å region have been carried out. The transition is identified as an allowed A~1B2<--X~1A1 transition. A very strong "forbidden" component, which borrows intensity from a B~1A1<--X~1A1 transition by vibronic interactions, also appears in the spectrum.</p> <p> Semi-empirical LCAO-SCF-MO-CI calculations predict the lowest singlet excited state to be of B2 symmetry, at an energy above the ground state close to the experimental values.</p> <p> Rotational band contour analysis substantiates the observation that both A- and B-type bands are present in the electronic spectrum. Ethynylbenzene remains planar and shows little geometrical change on electronic excitation.</p>