Hyperfine structure in the electronic spectrum of ReO

Abstract

Hyperfine structure in the spectrum of the molecule rhenium monoxide (ReO) has been observed for the first time by recording the [14.0] 7/2–X 5/2 (0, 0) band near 712 nm at sub-Doppler resolution using intermodulated fluorescence spectroscopy. Hyperfine splittings due to both the ¹⁸⁵Re and ¹⁸⁷Re isotopes (I = 5/2) have been resolved and assigned. A least-squares fit to the observed transitions has produced accurate values for the rotational, magnetic hyperfine and electric quadrupole constants for both electronic states. The hyperfine constants are discussed in relation to the electronic configurations of the two states. In particular, the ground state magnetic hyperfine constant is found to be consistent with a 1σ²2σ²1π ⁴1δ³3σ² (X ²Δ _i ) electronic configuration, where the 1δ orbital containing the unpaired electron is a Re 5dδ non-bonding orbital.