Absorption and fluorescence spectra of gaseous Se2

Abstract

The identification of the transitions in new resonance fluorescence series in 78Se2 and 80Se2 required some extension of the rotational analysis of the system B3∑–u–X3∑–g of 78Se2 to higher values of v″. Improved constants have been obtained for the ground state and these have been used to calculate Franck-Condon factors for the B—X system. A detailed study of the perturbations in B3∑–u has been made: some perturbing levels have been recognized which seem to interact both with the 0+u and 1u components. The analysis supports the value of the 1g—0+u separation, 367 cm–1, obtained from an earlier study of the absorption spectrum in the Schumann region. Moreover, if this value of the 1g—0+g separation is accepted, then the “high” value of the dissociation energy of Se2 is eliminated, and D°0(Se2)= 25 518 ± 20 cm–1. Two relatively weak fluorescence series have been observed with a lower state vibrational spacing about 15 % smaller than in the ground state. The upper state may tentatively be identified with one of the relatively weakly bound states which perturb B3sum;–u: if so, v= 0 of the lower state of the new series lies not more than about 4000 cm–1 above v= 0 of X0+g.