Experimental and theoretical vibrational overtone spectra of <i>v</i>CH=3, 4, 5, and 6 in formaldehyde (H2CO)

Abstract

We present the first photoacoustic absorption spectra of higher C–H stretching overtones in formaldehyde up to the visible spectral region. The analysis of the coarse rotational structure on the basis of asymmetric rotor simulations provides band centers up to the fifth overtone (vCH=6). A two dimensional normal coordinate model for the C–H stretching degrees of freedom explains the observed polyad structure of the spectrum using ab initio (MP2/6-311G**) potential energy and electric dipole functions. The observed intensity distribution reflects the increasing local mode character of higher overtone wave functions within the normal coordinate subspace.