Test of the Wigner method for the photodissociation of symmetric triatomic molecules

The validity of the semiclassical Wigner method for photodissociation of symmetric triatomic molecules is studied. The photodissociation of H2O in the first absorption band using an ab initio potential energy surface and a collinear model for CO2 are considered. In both cases comparison is made with exact quantum mechanical calculations. The overall agreement with the exact results is reasonable, and the general features of the partial and total cross sections are reproduced. However, finer details such as ‘‘vibrational’’ structures superimposed on the broad absorption cross section are poorly resolved. The agreement is generally better in the case of CO2 for which the potential energy surface is more harmonic.