Spectroscopic Properties and Spin–Orbit Coupling of Electronic Excited States of GeCl⁺

Abstract

The electronic structure and spectroscopic properties of GeCl+ are studied by high-level ab initio calculations by considering spin–orbit coupling (SOC). The potential energy curves (PECs) and spectroscopic constants of 12 Λ–S states and 23 Ω states are calculated using the multi-reference configuration interaction plus Davidson correction method (MRCI + Q), which are in good agreement with the experiment. Based on the calculated SO matrix and the PECs of the Ω states, the interaction between the d3Π state and other states caused by the SOC and the double-potential well structure caused by the avoided crossing rule and the properties of transitions d3Π0+–X1Σ+ 0+, d3Π1–X1Σ+ 0+, and a3Σ+ 1–X1Σ+ 0+ are studied. Our results indicate that the previously observed spectra of GeCl+ in the 290–325 nm range should be assigned as the a3Σ+ 1–X1Σ+ 0+ transition. Moreover, the predissociation behavior of the d3Π state between the vibrational levels v′ = 1 and v′ = 10 is discussed, and the radiative lifetimes of transitions d3Π0+–X1Σ+ 0+ and d3Π1–X1Σ+ 0+ are evaluated on the order of microseconds, while a3Σ+ 1–X1Σ+ 0+ is on the order of milliseconds. We estimate that the strongest bands of a3Σ+ 1–X1Σ+ 0+ are the 0–16, 0–17, and 0–18 bands. This study will promote our understanding of the detailed electronic structure and spectra of the GeCl+ radical cation.