Vibrational energies for the X 1A1, Ã 1B1, and B 1A1 states of SiH2/SiD2 and related transition probabilities based on global potential energy surfaces

Transition probabilities were evaluated for the X 1A1-à 1B1 and à 1B1-B 1A1 systems of SiH2 and SiD2 to analyze the X→Ã→B photoexcitation. The Franck–Condon factors (FCFs) and Einstein's B coefficients were computed by quantum vibrational calculations using the three-dimensional potential energy surfaces (PESs) of the SiH2(X1A1,Ã1B1,B1A1) electronic states and the electronic transition moments for the X-Ã, X-B, and Ã-B system. The global PESs were determined by the multireference configuration interaction calculations with the Davidson correction and the interpolant moving least-squares method combined with the Shepard interpolation. The obtained FCFs for the X-à and Ã-B systems exhibit that the bending mode is strongly enhanced in the excitation since the equilibrium bond angle greatly varies with the three states; the barrier to linearity is evaluated to be 21 900 cm–1 for the X state, 6400 cm–1 for the à state, and 230–240 cm–1 for the B state. The theoretical lifetimes for the pure bending levels of the à and B states were calculated from the fluorescence decay rates for the Ã-X, B-Ã, and B-X emissions