Spectroscopic Properties and Spin-Orbit Coupling of Electronic Excited States of GeCl

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.