Intramolecular Lineshape Narrowing in the Overtone Spectrum of Benzene

Abstract

Recently, BRAY and BERRY [1] have systematically explored the overtone spectra of gas phase benzene and certain deuterated benzene derivations (H5, H2, H1). They found that above 14000 cm^-1 only absorptions assignable to CH local mode stretching overtones were evident and that these absorption features exhibited particularly striking lineshapes. Generally, all observed overtones were relatively structureless bands having nearly Lorentzian profiles. Even the very slight asymmetries of some of the lower overtones disappeared with increasing overtone excitation (v). The apparent linewidths were remarkably broad (~100 cm^-1, corresponding to dynamical processes having sub-picosecond timescales) and varied only slowly with overtone excitation or deuterium substitution. The overtone dependence of the line width was rather curious: the H1 line width increases with v but for all other species (H2, H5, H6) the linewidth narrows with v.