Spectroscopic Properties of MgH₂, MgD₂, and MgHD Calculated from a New ab Initio Potential Energy Surface

A three-dimensional potential energy surface for the ground electronic state of MgH2 has been constructed from 9030 symmetry-unique ab initio points calculated using the icMRCI+Q method with aug-cc-pVnZ basis sets for n = 3, 4, and 5, with core-electron correlation calculated at the MR-ACPF level of theory using cc-pCVnZ basis sets, with both calculations being extrapolated to the complete basis set limit. Calculated spectroscopic constants of MgH2 and MgD2 are in excellent agreement with recent experimental results: for four bands of MgH2 and one band of MgD2 the root-mean-square (rms) band origin discrepancies were only 0.44 and 0.06 cm-1, respectively, and the rms relative discrepancies in the inertial rotational constants (B[v]) were only 0.0196% and 0.0058%, respectively. Spectroscopic constants for MgHD were predicted using the same potential surface.本研究构建了MgH₂（氢化镁）电子基态的三维势能面，该势能面基于9030个具备对称性唯一性的从头算（ab initio）单点能构建而成。上述单点能采用icMRCI+Q方法，结合aug-cc-pVnZ基组（n=3、4、5）计算得到；同时采用cc-pCVnZ基组，在MR-ACPF理论级别下完成芯电子关联效应的计算，并将两类计算结果外推至完全基组极限。计算得到的MgH₂与MgD₂（氘化镁）的光谱常数与近期实验结果高度吻合：针对MgH₂的4个谱带与MgD₂的1个谱带，其带源的均方根（rms）偏差仅分别为0.44 cm⁻¹与0.06 cm⁻¹；而惯性转动常数(B[v])的均方根相对偏差仅分别为0.0196%与0.0058%。本研究基于该势能面，进一步预测了MgHD的光谱常数。