THE X(2)SIGMA(+), (2)(2)SIGMA(+), AND (2)(2)PI STATES OF BALI

Fourier transform spectrometry of the thermal emission at 1 100 degree s C of (BaLi)-Li-6 and (BaLi)-Li-7 has been performed in the infrared spectral region from 4000 to 8400 cm(-1). A total of 7075 lines are as cribed to several bands, 11 for (BaLi)-Li-6, 8 for (BaLi)-Li-7, of the (2)(2) Sigma(+)-->X(2) Sigma(+) and (2)(2) Pi-->X(2) Sigma(+) systems . A consistent set of molecular constants describing the upsilon = 0, 1, 2 levels in X(2) Sigma(+) and (2)(2) Sigma(+), and upsilon = 0, 1 i n (2)(2) Pi is obtained from the simultaneous adjustment of all the da ta corresponding to upsilon-connected bands for each isotopic species. Information is also obtained for X(2) Sigma(+) (upsilon = 3) and (2)( 2) Pi(upsilon = 2) from an independant treatment of the (2-3) band in (2)(2) Pi-->X(2) Sigma(+). The standard deviation of the different fit s appears to be close to the experimental accuracy, 0.004 cm(-1). Effe ctive molecular constants at equilibrium are derived for the three sta tes. The interpretation of the evolution of different effective intera ctions with vibration and rotation, particularly the spin-orbit intera ction in the (2)(2) Pi state, leads us to invoke the presence of one o r more perturbing states. Also, the relative intensities between branc hes within the (2)(2) Sigma(+)-->X(2) Sigma(+) and (2)(2) Pi(1/2)-->X( 2) Sigma(+) bands which do not correspond to those expected for pure t ransitions are explained in terms of interference between parallel and perpendicular transition moments. Values of mu(parallel to) and mu(pe rpendicular to) can be evaluated for the (0-0) transitions. (C) 1994 A cademic Press, Inc.