High-Resolution Spectroscopy and Ab Initio Calculations on HfCl

Abstract

The emission spectrum of HfCl has been investigated in the 3000–18 500 cm−1 region at high resolution using a Fourier transform spectrometer. The bands were excited in a microwave discharge through a flowing mixture of HfCl4 and helium. Two bands near 17 140 and 17 490 cm−1 were also measured in absorption using laser excitation spectroscopy. In this instance the molecules were created by laser ablation in a molecular beam apparatus. The observed bands have been classified into two electronic transitions, [7.6]4Δ3/2–X2Δ3/2 and [17.1]2Δ3/2–X2Δ3/2 involving a common lower state. A rotational analysis of the 0–0 and 1–1 bands of [7.6]4Δ3/2–X2Δ3/2 and 0–0, 1–1, and 1–0 bands of the [17.1]2Δ3/2–X2Δ3/2 transitions has been carried out and the equilibrium spectroscopic constants have been determined. The ground state principal molecular constants are Be = 0.1097404(54) cm−1, αe = 0.0004101(54) cm−1, and re = 2.290532(57) Å. Ab initio calculations have been performed on HfCl and spectroscopic properties of the low-lying electronic states have been predicted. The ground state is predicted to be a regular 2Δ state arising from the valence electron configuration, 1ς22ς23ς21π41δ1. On the basis of our ab initio calculations, we assign the observed transitions as [7.6]4Δ3/2–X2Δ3/2 and [17.1]2Δ3/2–X2Δ3/2.