On the Infrared A2Πi - X2∑+ System of Aluminium Monoxide in Relation with the Spectra of M Giant- and Mira-Type Stars

Abstract

From combinations between known ultraviolet transitions of the AlO molecule line positions in the A2Πi - X2∑+ system are tentatively proposed. Indeed, the available data on the C2Πr → X2∑+ and C2Πr → A2Πi transitions permit us to derive about 2400 energy level differences in the A-X system corresponding to the six ν-connected bands 0-0, 0-1, 0-2, 1-0, 1-1 and 1-2. A unique and consistent set of rovibrational constants is derived from a global fitting, allowing to reproduce the observed differences with a total standard deviation of 0.053 cm-1. A catalogue of vacuum line wavenumbers in the six bands is generated and can be made available on request. The synthetic spectra are expected to represent properly the true spectra at least up to J ~ 35.5 and can therefore be of usefulness for the detection of the system in the spectra of M giant- and Mira-type stars. Franck-Condon factors and r-centroïds appropriate to RKR potentials and estimates of intensities in emission are given for bands up to ν′ = 5, v″ = 8. More reliable values for the internal partition functions and dissociation constants of AlO are computed for temperatures between 1000 and 8000 K. All the known and predicted electronic states are taken into account, and present or recent values for the molecular parameters and dissociation energy are used.