Spectroscopic and theoretical studies of ThCl and ThCl+

Abstract

The electronic structures of ThCl and ThCl+ have been examined using laser induced fluorescence and two-photon ionization techniques. Rotationally resolved spectra, combined with the predictions from relativistic electronic structure calculations, show that the ground state of the neutral molecule is Th+(7s26d)Cl−, X2Δ3/2. Dispersed fluorescence spectra for ThCl revealed the ground state vibrational levels v = 0-10 and low energy electronic states that also originate from the atomic ion 7s26d configuration. Pulsed field ionization—zero kinetic energy photoelectron spectroscopy established an ionization energy (IE) for ThCl of 51 344(5) cm−1, and the ThCl+ vibrational term energies of the v = 1-3 levels. The zero-point level of the first electronically excited state was found at 949(2) cm−1. Comparisons with high-level theoretical results indicate that the ground and excited states are Th2+(7s6d)Cl− X3Δ1 and Th2+(7s2)Cl− Σ+1, respectively. Relativistic coupled cluster composite thermochemistry calculations yielded an IE within 1.2 kcal/mol of experiment and a bond dissociation energy (118.3 kcal/mol) in perfect agreement with previous experiments.