A Study of the X 2Sigma+ and A 2Pi States of SiO+ Using Fast-Ion-Beam Laser Spectroscopy

We have observed for the first time the (4, 4), (4, 3), and (5, 4) bands of the B 2Sigma+-X 2Sigma+ system of SiO+ using laser-induced fluorescence spectroscopy on a fast SiO+ beam. These data contain avoided crossings between the X 2Sigma+ and A 2Pi states, as well as a few extra lines belonging to the (3, 2), (4, 2), and (5, 3) bands of the B 2Sigma+-A 2Pi system. They enlarge considerably a previously measured data set consisting of almost 1400 lines of the (0, 0), (1, 1), (2, 2), (3, 3), (1, 0), (2, 1), and (3, 2) bands of the B-X system and 66 lines of the (2, 0) Omega = (1/2) subband of the B 2Sigma+-A 2Pi system. The entire data set of 2378 assigned lines has been fit simultaneously to a model Hamiltonian in which many closely overlapped levels of the X and A states are handled by direct diagonalization. The newly observed avoided crossings between the X and A states allow the determination of many A-state parameters with increased precision, several for the first time, including the spin-orbit splitting. The analysis confirms our earlier reinterpretation of older photoelectron spectroscopy data and allows the accurate prediction of the frequencies of strong infrared transitions between the X and A states, which have astrophysical significance. Copyright 1998 Academic Press.