Photoluminescence of the A2Π- X2Σ + system of the yttrium oxide molecule

Abstract

A cw dye laser, tunable in the region 570–620 nm, has been used to excite photoluminescence in the A 2Π- X 2Σ + system of the YO molecule. Two methods have been used to obtain spectra. They are ( i) photoluminescence and ( ii) spectrally selective excitation spectroscopy. The latter maintains the simplicity of photoluminescence, but has higher resolution. The spectra obtained at medium resolution (∼0.05 nm) have been surveyed and the identification of transitions has been outlined. A method was devised in which known lower state constants were used in calculating approximate upper state constants whenever the laser simultaneously excited coincident rotational transitions in the same band. From these calculations, an approximate value of α′ e was calculated which was found to be close to, but slightly larger than values previously computed from the Pekeris formula. Many examples of collisional transfer were observed. In particular, maximum transfer from 2 Π 3 2 to 2 Π 1 2 was always observed to involve an increase of one unit in the vibrational quantum number. No transfer was observed between opposite parity components of Λ doublets, in spite of their closeness in energy, indicating that the symmetry of the electronic eigenfunctions was unaffected by collisions. Reanalysis of previous high resolution data has shown that, when the contribution of Λ-doubling parameters to the separation of the 2 Π 1 2 and 2 Π 3 2 states is taken into account, the value of the spin-orbit coupling constant, A, changes significantly. It was also found necessary to include the constant, A D , to account for the effect of centrifugal distortion on the spin-orbit interaction.