A STUDY OF THE X-(2)SIGMA(-(2)-PI STATES OF SIO+ USING FAST-ION-BEAM LASER SPECTROSCOPY() AND A)

We have observed for the first time the (4, 4), (4, 3), and (5, 4) ban ds of the B-2 Sigma(+) - X-2 Sigma(+) system of SiO+ using laser-induc ed fluorescence spectroscopy on a fast SiO+ beam. These data contain a voided crossings between the X-2 Sigma(+) and A 2 Pi states, as well a s a few extra lines belonging to the (3, 2), (4, 2), and (5, 3) bands of the B-2 Sigma(+) - A(2) Pi system. They enlarge considerably a prev iously 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-2 Sigma (+) - A(2) Pi system. The entire data set of 2378 assigned lines has b een fit simultaneously to a model Hamiltonian in which many closely ov erlapped levels of the X and A states are handled by direct diagonaliz ation. The newly observed avoided crossings between the X and A states allow the determination of many A-state parameters with increased pre cision, several for the first time, including the spin-orbit splitting . The analysis confirms our earlier reinterpretation of older photoele ctron spectroscopy data and allows the accurate prediction of the freq uencies of strong infrared transitions between the X and A states, whi ch have astrophysical significance. (C) 1998 Academic Press.