Potential energy surface and rovibrational calculations for the ${\rm Mg}^+$ Mg +–${\rm H}_2$H2 and ${\rm Mg}^+$ Mg +–${\rm D}_2$D2 complexes
Authors: Dryza V. , Bieske E. J. , Buchachenko A. A. , Kłos J. 
Published: January 2011

A three-dimensional potential energy surface is developed to describe the structure and dynamical behavior of the \documentclass[12pt]{minimal}\begin{document}${\rm Mg}^+$\end{document} Mg +–\documentclass[12pt]{minimal}\begin{document}${\rm H}_2$\end{document}H2 and \documentclass[12pt]{minimal}\begin{document}${\rm Mg}^+$\end{document} Mg +–\documentclass[12pt]{minimal}\begin{document}${\rm D}_2$\end{document}D2 complexes. Ab initio points calculated using the RCCSD(T) method and aug-cc-pVQZ basis set (augmented by bond functions) are fitted using a reproducing kernel Hilbert space method [Ho and Rabitz, J. Chem. Phys. 104, 2584 (1996)] to generate an analytical representation of the potential energy surface. The calculations confirm that \documentclass[12pt]{minimal}\begin{document}${\rm Mg}^+$\end{document} Mg +–\documentclass[12pt]{minimal}\begin{document}${\rm H}_2$\end{document}H2 and \documentclass[12pt]{minimal}\begin{document}${\rm Mg}^+$\end{document} Mg +–\documentclass[12pt]{minimal}\begin{document}${\rm D}_2$\end{document}D2 essentially consist of a \documentclass[12pt]{minimal}\begin{document}${\rm Mg}^+$\end{document} Mg + atomic cation attached, respectively, to a moderately perturbed \documentclass[12pt]{minimal}\begin{document}${\rm H}_2$\end{document}H2 or \documentclass[12pt]{minimal}\begin{document}${\rm D}_2$\end{document}D2 molecule in a T-shaped configuration with an intermolecular separation of 2.62 Å and a well depth of \documentclass[12pt]{minimal}\begin{document}$D_e$\end{document}De = 842 \documentclass[12pt]{minimal}\begin{document}$\,{\rm cm}^{-1}$\end{document} cm −1. The barrier for internal rotation through the linear configuration is 689 \documentclass[12pt]{minimal}\begin{document}$\,{\rm cm}^{-1}$\end{document} cm −1. Interaction with the \documentclass[12pt]{minimal}\begin{document}${\rm Mg}^+$\end{document} Mg + ion is predicted to increase the \documentclass[12pt]{minimal}\begin{document}${\rm H}_2$\end{document}H2 molecule's bond-length by 0.008 Å. Variational rovibrational energy level calculations using the new potential energy surface predict a dissociation energy of 614 \documentclass[12pt]{minimal}\begin{document}$\,{\rm cm}^{-1}$\end{document} cm −1 for \documentclass[12pt]{minimal}\begin{document}${\rm Mg}^+$\end{document} Mg +–\documentclass[12pt]{minimal}\begin{document}${\rm H}_2$\end{document}H2 and 716 \documentclass[12pt]{minimal}\begin{document}$\,{\rm cm}^{-1}$\end{document} cm −1 for \documentclass[12pt]{minimal}\begin{document}${\rm Mg}^+$\end{document} Mg +–\documentclass[12pt]{minimal}\begin{document}${\rm D}_2$\end{document}D2. The H–H and D–D stretch band centers are predicted to occur at 4059.4 and 2929.2 \documentclass[12pt]{minimal}\begin{document}$\,{\rm cm}^{-1}$\end{document} cm −1, respectively, overestimating measured values by 3.9 and 2.6 \documentclass[12pt]{minimal}\begin{document}$\,{\rm cm}^{-1}$\end{document} cm −1. For \documentclass[12pt]{minimal}\begin{document}${\rm Mg}^+$\end{document} Mg +–\documentclass[12pt]{minimal}\begin{document}${\rm H}_2$\end{document}H2 and \documentclass[12pt]{minimal}\begin{document}${\rm Mg}^+$\end{document} Mg +–\documentclass[12pt]{minimal}\begin{document}${\rm D}_2$\end{document}D2, the experimental B and C rotational constants exceed the calculated values by ∼1.3%, suggesting that the calculated potential energy surface slightly overestimates the intermolecular separation. An ab initio dipole moment function is used to simulate the infrared spectra of both complexes.