The infrared A2PI(i)-X2SIGMA+ band system of AlO has been recorded with Fourier transform techniques using an electrodeless 2450-MHz discharge as a source. Transitions involving upsilon = 0-3 of X2SIGMA+ and upsilon = 0-10 of A2PI(i) have been observed. Local perturbations affect the different levels of the A2PI(i) state, and all these perturbations are shown to be caused by vibrational levels of the X2SIGMA+ state. Extra lines originating from the nominal upsilon = 7, 8 levels of X2SIGMA+ are observed in the proximity of the A2PI(i) (upsilon = 2) <-> X2SIGMA+ (upsilon = 7) and A2PI(i) (upsilon = 3) <-> X2SIGMA+ (upsilon = 8) crossings. In total, data from 23 vibrational bands are included in the analysis. The spin splittings of the X2SIGMA+ state are strongly dependent of upsilon''. The X2SIGMA+ state also shows clearly noticeable nuclear hyperfine effects, manifested by numerous hyperfine-induced DELTAJ = +/-2 branches. A global deperturbation has been performed for upsilon = 0-8 of A2PI(i) and for the corresponding intersecting levels upsilon = 5-11 of X2SIGMA+. The X2SIGMA+ state has been fitted both with and without hyperfine parameters. The inclusion of the hyperfine interaction was found to be necessary in order to describe the X2SIGMA+ ground state adequately. The anomalous intensity distributions among branches terminating at different vibrational levels of the X2SIGMA+ state are discussed. The strong B2SIGMA+-X2SIGMA+ system has been recorded with FTS techniques, and the contradictory results of Mahieu et al. and Lagerqvist et al. regarding the gamma value of the B2SIGMA+ state are discussed in the light of the new parameterization of the X2SIGMA+ state, and the spin component assignments presented in the work of Lagerqvist et al. have been reestablished. (C) 1994 Academic Press, Inc.
