Excited state normal vibrations and force field of ethynylbenzene

Abstract

Accurate vibrational frequencies of ethynylbenzene and three of its deuterated isomers in first excited state (1B2) have been used in the determination of intramolecular force constants and the assignments of vibrational frequencies have been discussed in the light of calculated potential energy distributions. The vibrational modes corresponding to normal frequencies ν30 and ν31 exhibit mode scrambling on ring deuteration. Evidence of Duschinsky mixing in going from ground to the excited state has been found in the vibrational modes ν6, ν13, ν31 and ν34 which are active in one photon absorption and also in ν30 which is active in two photon excitation spectrum.