The a4Σ−–X2Π Electronic Transition of SiF

The a4Σ−–X2Π transition of SiF at 3360 Å has been reinvestigated at high dispersion. Our new rotational line assignments show that the energy levels of the 4Σ state, which is very close to case (b) coupling, can be fitted with one rho-type doubling parameter (γ) rather than the two proposed by Hougen to account for Verma's previous results. The relative intensities of the branches have been interpreted in terms of two transition moments, whose ratio shows that the intensity of the a–X system comes mainly from the so far uncharacterized σπ22Σ+–X2Π transition. 'Equilibrium' molecular constants for the a4Σ− state have been derived from analysis of the overlapping sequence bands.