Simulation of Ã(2)A(1)←X̃(2)E laser excitation spectrum of CH3O and CD3O

A theoretical calculation of the laser-induced fluorescence excitation spectrum from X̃(2)E→Ã(2)A1 is carried out for CH3O and CD3O using a transition dipole moment surface expanded up to second order. The vibronic form of these operators is obtained using symmetry arguments. The Ã(2)A1 vibrational levels are calculated using Van Vleck perturbation theory, and the latter is used to adjust harmonic constants of the potential to match experimental fundamentals. The CH3O fit force field is tested on CD3O. For both molecules the transition energies are well reproduced, but there are systematic differences between experimental and theoretical intensities. The origins of these differences are discussed.