High-resolution spectroscopy of refractory molecules at low temperature. The e3Π–a 3Δ band system (β-system) of ZrO

Abstract

The band origins of the e³Π–a³Δ system of ZrO have been investigated using the combined techniques of chemical reaction in laser-produced plasma, supersonic cooling and laser-induced fluorescence. Rotational temperatures of ca. 35–45 K have been observed. Each of the three main sub-bands, ³Π₂–³Δ₃, ³Π₁–³Δ₂ and ³Π₀–³Δ₁, has been fully analysed at a Doppler-limited resolution of 120 MHz. Lambda-type doubling has been observed for all three sub-bands, and nuclear hyperfine structure has been resolved for ⁹¹ZrO. Data for all five isotopic species are reported. Effective molecular constants (B″, D″, ν_0–0,B′, D′) have been derived for (1) the e-and f-term series of each sub-band and (2) the entire system. In light of these results the multiplet splittings are re-assessed, the electronic configurations of ZrO in the a³Δ and e³Π states are discussed, and the nature and location of nearby perturbing states are predicted.