THE ELECTRIC-DIPOLE MOMENTS OF SEH AND GEH IN THEIR GROUND 2-PI STATES

The relative intensities of electric and magnetic dipole transitions in the fine structure spectrum of SeH in its X 2-PI state have been measured using the technique of laser magnetic resonance (LMR). Since the magnetic moment is known in this case, the measurements can be used to determine the molecule's electric dipole moment. The permanent electric dipole moment of SeH has been measured previously from the Stark effect (mu-0 = 0.483 D). It is found that a consistent interpretation of the intensities is only possible if account is taken of mixing of excited electronic states by spin-orbit coupling (incipient Hund's case (c) behaviour). Electronic transition moments make sizable contributions to the intensities. Measurements for SeH are used to estimate the electric dipole transition moment between the A 2-SIGMA+ and X 2-PI states; the value obtained is mu-1 = 0.312 or -0.091 D. It seems likely that the discrepancy between the experimental and theoretical values for the permanent electric dipole moment of GeH in its X 2-PI state can be accounted for in the same manner.