Ab initio study on the spectroscopic and radiative properties of lithium monocarbide

High-level electronic structure calculations were conducted for LiC molecule and compared to other theoretical results. The potential energy curves (PECs) for the 18 states originating from the first three dissociation channels of LiC molecule were calculated by the internally contracted multireference configuration interaction (icMRCI) method. The spectral constants, vibrational energy levels are reported. The transition properties for the a²Π, b²Δ, c²Σ^-, d²Σ⁺, and 2²Π states are discussed. In addition, the spin-orbit coupling (SOC) effects were taken into account in the electronic transition d²Σ⁺ - a²Π. The b²Δ and c²Σ^- states had radiative lifetimes of approximately 0.03-16.83 and 0.86-8.06 ms, respectively. The d²Σ⁺ and 2²Π states had radiative lifetimes of approximately 1.94 - 64.83 and 0.31 - 16.59 µs, respectively. Between these transitions, the emissions from the d²Σ⁺ - a²Π, 2²Π - c²Σ^-, 2²Π - b²Δ, and 2²Π - a²Π systems were strongest, while the emissions from the c²Σ^- - a²Π, b²Δ - a²Π, and 2²Π - d²Σ⁺ systems were weaker. The d²Σ⁺_1/2 state had radiative lifetimes of approximately 3.75 - 29.81 µs. Among the spontaneous emissions of the transitions generated by the d²Σ⁺_1/2 state, the emissions from the d²Σ⁺_1/2 - a²Π_1/2 and d²Σ⁺_1/2 - a²Π_3/2 systems were relatively strong and easily observed experimentally. The radiative lifetime variation law with the rotational quantum number for the d²Σ⁺_1/2 state at rotational quantum number J ≤ 70 and vibrational quantum number ν ≤ 15 is also presented in this paper. In addition, almost all the strong emissions of the transitions were distributed in the infrared region. It is expected that the results of this study will serve as a helpful reference for future experimental and theoretical studies.