ELECTRONIC SPECTRA OF RhH AND RhD

Abstract

Electronic transitions have been observed with LIF techniques in a supersonic molecular beam of He doped with $H_{2}$ and $D_{2}$ and laser-ablated Rh vapor. Bands of RhH have been found near 464.73 and 438.38 nm, which are assigned as (0,0) and (1,0) vibrational bands of a ${^{3}}\Delta_{3} - X^{3} \Delta_{3}$ electronic transition. There is a sudden disapperance of the rotational structure in the (1,0) band of RhH above $J^{\prime}=7$ and the spectra associated with higher vibrational levels in the excited states are missing. These observations are attributed to predissociation. Its onset agrees with an ab intio calculation of $22 664-23 955 cm^{-1a}$ and the estimate of $20 650 \pm 1 750 cm^{-1}$ from $thermochemistry.^{b}$ The RhH(0,0) band also shows irregular A-doubling. The corresponding (0,0) and (1,0) transitions in RhD appear at 463.40 and 443.02 nm. Analyses of the spectra indicate that the ground state of RhH is an inverted ${^{3}}\Delta$ state, which is believed to derive from the electronic configuration $\ldots \delta^3 \pi^{1} \sigma^{1}$ and provide the following RhH molecular constants($cm^{-1}: B^{\prime \prime}_{0}= 6.546[r^{\prime \prime}_{0}= 0.1610 nm], B^{\prime}_{0}=6.175, B^{\prime}_{1}= 5.823, \omega^{\prime \prime}_{e}= 1927, \omega^{\prime \prime}_{e}x^{\prime \prime}_{e}= 35.7, \omega^{\prime}_{e}=1645, \omega^{\prime}_{e}x^{\prime}_{e}= 174$. The observed ground state symmetry and internuclear distance agree with ab initio $predictions.^{a}$ Six additional bands have been found for RhD: near $445.15 nm(\Omega^{\prime} =3 - \Omega^{\prime \prime}=3), 428.05 nm(\Omega^{\prime} =3 - \Omega^{\prime \prime}=3)427.83 nm(\Omega^{\prime} =3 - \Omega^{\prime \prime}=3), 424.40 nm(\Omega^{\prime} =2 - \Omega^{\prime \prime}=3), 422.58 nm(\Omega^{\prime} =3 - \Omega^{\prime \prime}=3),$ and $409.24 nm(\Omega^{\prime} =4 - \Omega^{\prime \prime}=3)$.