Electronic spectra of the SH⁺ and SD⁺ molecular ions

The A 3Π-X 3Σ- emission systems of SH+ and SD+ have been observed free of impurity lines in a special d.c. discharge source. Seven bands have been analysed and accurate rotational constants have been obtained for the levels v = 0 and 1 of the A 3Π and v = 0, 1 and 2 of the X 3Σ- states of SH+ and SD+. The fine structure of the two states, characterized by (i) large (∼ 5 cm-1) spin-splitting of the X state, (ii) large Λ doubling of the A 3Π0 component and (iii) anomalous spin-orbit splitting of the A state, has been shown to originate mainly from second-order spin-orbit interactions. Finally, the radiative and non-radiative properties of the A state of SH+ are discussed in the framework of a crude quantum calculation of the predissociation rates for the lowest vibrational levels, in connection with the laser predissociation spectrum data described in the following paper (Edwards, Maclean, Sarre).