EXPERIMENTAL AND THEORETICAL VIBRATIONAL OVERTONE SPECTRA OF V-CH=3,4,5, AND 6 IN FORMALDEHYDE (H2CO)

We present the first photoacoustic absorption spectra of higher C-H st retching overtones in formaldehyde up to the visible spectral region. The analysis of the coarse rotational structure on the basis of asymme tric rotor simulations provides band centers up to the fifth overtone (nu(CH) = 6). A two dimensional normal coordinate model for the C-H st retching degrees of freedom explains the observed polyad structure of the spectrum using ab initio (MP2/6-311G*) potential energy and elect ric dipole functions. The observed intensity distribution reflects the increasing local mode character of higher overtone wave functions wit hin the normal coordinate subspace. (C) 1996 American Institute of Phy sics.