Abstract:
A detailed theoretical investigation of the large amplitude motions in the S, excited
electronic state of formic acid (HCOOH) was done. This study focussed on the the S, «-
So electronic band system of formic acid (HCOOH). The torsion and wagging large
amplitude motions of the S, were considered in detail. The potential surfaces were
simulated using RHF/UHF ab-initio calculations for the two electronic states. The energy
levels were evaluated by the variational method using free rotor basis functions for the
torsional coordinates and harmonic oscillator basis functions for the wagging coordinates.
The simulated spectrum was compared to the slit-jet-cooled fluorescence
excitation spectrum allowing for the assignment of several vibronic bands.
A rotational analysis of certain bands predicted that the individual bands are a
mixture of rotational a, b and c-type components.The electronically allowed transition
results in the c-type or Franck-Condon band and the electronically forbidden, but
vibronically allowed transition creates the a/b-type or Herzberg-Teller components. The
inversion splitting between these two band types differs for each band. The analysis was
able to predict the ratio of the a, b and c-type components of each band.
