Molecular Beam Laser Spectroscopy of ReF: Rotational and Hyperfine Analyses of Two Bands near 557 nm

Abstract

An extensive survey of the electronic spectrum of the ReF molecule has been carried out in the region 15 150-29 600 cm −1 using laser-induced fluorescence spectroscopy. The ReF molecules were produced by chemical reaction in a laser-generated plasma and cooled by supersonic expansion. Both isotopomers 185Re 19F (37.1%) and 187Re 19F (62.9%) were studied. The observed bands are interpreted as transitions involving two different lower Ω = 0 states and a number of different excited electronic states. Using a ring dye laser, two of the bands were recorded at 100-MHz resolution, which was sufficient to resolve hyperfine structure. The analysis of these bands shows that both arise from Ω = 0 ← Ω = 0 transitions involving a common lower state a ( v″) and two strongly interacting upper states b( v′) and c( v′ = 2), located at, respectively, 17 931 and 17 966 cm −1 above a. The b( v′) state exhibits an avoided crossing with an unidentified state. Dispersed fluorescence studies reveal the presence of two low-lying states located at 2750 and 4240 cm −1 above the a state. The energy difference between the two low-lying Ω = 0 states is not known; neither is it known which one is the ground state. The observed hyperfine structure is attributed to electric quadrupole effects.