Stimulated emission pumping spectroscopy of SiH2:: First observation of the spin-orbit interaction between the (X)over-tilde1 A1 and the (a)over-tilde3 B1 states

Stimulated emission pumping spectra of the (A) over tilde B-1(1)-(X) over tilde (1)A(1) transition of the SiH2 radical were observed in order to obtain information about the (a) over tilde B-3(1) state through the spin-orbit interaction. The vibrational level structure of the (X) over tilde state, which is the basis for the present observation of the triplet state, was well described with a polyad structure, in which both the 1nu(1) : 2nu(2) Fermi and the 2nu(1) : 2nu(3) Darling-Dennison anharmonic resonances were considered. In the P = 10 polyad, four sets of spin-orbit perturbations were observed for the first time. The triplet state observed at about 9640 cm(-1) from the (000) level of the 9 state was tentatively assigned as the (a) over tilde B-3(1) (030) level. An analysis of the spin-orbit interaction showed that the interaction energies of the spin-orbit coupling are 0.73-3.13 cm(-1). This value is rather smaller than that expected based on the comparison with CH2. This is considered to be due to poor overlap between the vibrational wave functions in the (a) over tilde and the (X) over tilde state. (C) 2002 Elsevier Science (USA).