The intensity distribution in the Na2 and Li2 <i>A</i>–<i>X</i> bands

Abstract

The accuracy of the quasistatic or classical Franck–Condon approximation for unresolved bound–bound molecular bands is investigated by comparison with appropriately averaged quantum mechanical calculations. Wavelength-averaged absorption and stimulated emission cross sections are calculated for the A–X bands of Na2 and Li2, representing low resolution or collision broadened spectra, and comparisons are made with experimental spectra. These A–X bands exhibit a red edge, due to a head of heads or a classical satellite, and a comparison of quantum mechanical, classical, and semiclassical satellite shapes is made. The overall quantum mechanical band shapes agree with the classical calculation, except for approximately periodic band structures and nonclassical behavior at the satellites. The emission spectrum resulting from white light or electron excitation of Na2, is also calculated and compared to that observed in an electrical discharge. Finally, emission spectra of Na2 for thermal distributions at various temperatures are compared to the fluorescence spectrum observed from excited dimers formed by an atom–molecule excitation transfer process.