Theoretical study on spectroscopic properties of 8 Λ-S and 23 Ω states for BH molecule

Abstract

In this work, the potential energy curves of eight low electronic states (X¹Σ⁺, a³Π, A¹Π, b³Σ^-, 2³Π, 1³Σ⁺, 1⁵Σ^-, and 1⁵Π) and twenty-three Ω states of BH molecule, and the transition dipole moments among the <inline-formula><tex-math id="M10">\begin{document}$ {\text{X}}{}^{\text{1}}{\Sigma}_{{{\text{0}}^ + }}^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M10.png"/></alternatives></inline-formula>, <inline-formula><tex-math id="M11">\begin{document}$ {{\text{a}}^{\text{3}}}{\Pi_{{{\text{0}}^ + }}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M11.png"/></alternatives></inline-formula>, a³Π₁, a³Π₂, and A¹Π₁ states are calculated by using the internally contracted multireference configuration interaction (icMRCI) method. In order to obtain the accurate potential energy curve, the errors caused by single and double electron excitation, core-valence correlation effects, relativistic effects and basis set truncation are corrected. The spectral and transition data of BH molecule are in good agreement with the available theoretical and experimental data. The calculation results show that the A¹Π₁(<i>υ′</i> = 0-2, <i>J′</i> = 1, +) →<inline-formula><tex-math id="M12">\begin{document}$ {\text{X}}{}^{\text{1}}{\Sigma}_{{{\text{0}}^ + }}^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M12.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M12.png"/></alternatives></inline-formula>(<i>υ′′</i> = 0-2, <i>J′′</i> = 1, –) transition has large Einstein <i>A</i>-coefficient, weighted absorption oscillator strength, and highly diagonal vibrational branching ratio<i> R</i>_{<i>υ′υ′′</i>}, and the excited state A¹Π₁(<i>υ′</i> = 0, 1) have short spontaneous radiation lifetimes. Moreover, the effects of <inline-formula><tex-math id="M13">\begin{document}$ {{\text{a}}^{\text{3}}}{\Pi_{{{\text{0}}^ + }}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M13.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M13.png"/></alternatives></inline-formula>and a³Π₁ states on A¹Π₁(<i>υ′</i> = 0) ↔ <inline-formula><tex-math id="M14">\begin{document}$ {\text{X}}{}^{\text{1}}{\Sigma}_{{{\text{0}}^ + }}^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M14.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M14.png"/></alternatives></inline-formula>(<i>υ′′</i> = 0) cycle transition can be ignored. Therefore, according to the A¹Π₁(<i>υ′</i>= 0-1, <i>J′</i> = 1, +) ↔ <inline-formula><tex-math id="M15">\begin{document}$ {\text{X}}{}^{\text{1}}{\Sigma}_{{{\text{0}}^ + }}^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M15.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M15.png"/></alternatives></inline-formula>(<i>υ′′</i>= 0-3, <i>J</i>′′ = 1, –) cycle transition, we propose to apply one main cooling laser (<i>λ</i>₀₀ = 432.45 nm) and two repumping lasers (<i>λ</i>₁₀ = 479.67 nm and <i>λ</i>₂₁ = 481.40 nm) to laser cooling BH molecules, and evaluation of the cooling effect.