The (Lb)S1←S0 transition of phenylpropyne and phenylacetylene:: an experimental and ab initio study

This work describes the first excited singlet electronic state, L-b, of phenylpropyne (PPR) and phenylacetylene (PA). Ab initio calculations have been performed for the geometry and normal modes in the So and S, states. One-photon and two-photon S, So spectra of jet cooled samples have been examined (REMPI detection) and a detailed vibronic analysis has been carried out for PPR and PA. The origin band of PPR (lambda = 279.64 nm) is one order of magnitude weaker than the origin band (lambda = 278.63 nm) of PA and the acetylenic modes are greatly reduced by the H --> CH3 substitution. These changes and the parallel PPR-PA comparison provided a way for secure vibronic assignment in both molecules, which was also aided by theoretical predictions. (C) 2004 Elsevier B.V. All rights reserved.