An excited state ab initio and multidimensional Franck-Condon analysis of the A B-1(2) - X (1)A(1) band system of fluorobenzene

摘要

This work combines high level ab initio calculations with multidimensional Franck-Condon calculations to refine and augment previous assignments of the lower wavenumber region of the A B-1(2)<- X (1)A(1) band system of fluorobenzene. The strength of the assignment has been greatly assisted by the use of zero electron kinetic energy spectroscopy in a series of pump-probe experiments where the response of the molecule to selective excitation in specific modes prior to ionization has been studied. The net result of this analysis is the reassignment of 7 of the 12 previously assigned bands in the region below about 1000 cm(-1) using a strategy that aims to trace the origins of excited state normal modes of fluorobenzene to the well-known Wilson modes of benzene by taking full account of the Duschinsky mixing that accompanies electronic excitation. Duschinsky normal mode analyses of the ground and first excited states of fluorobenzene as well as the electronic ground state of fluorobenzene cation have shown that the common use of the benzene Wilson notation to describe normal modes of this prototypical benzene derivative is highly questionable, particularly following electronic excitation and ionization. (c) 2008 American Institute of Physics.