Near dissociation states for H$_2^+$-He on MRCI and FCI potential energy surfaces

TL;DR

This paper develops a new analytical potential energy surface for H$_2^+$-He using advanced quantum chemistry methods and calculates ro-vibrational states, enabling precise spectral line assignments for near-dissociation states.

Contribution

It introduces a novel RKHS-based PES for H$_2^+$-He combining MRCI and FCI data, and computes ro-vibrational states for detailed spectral analysis.

Findings

Assignment of the 15.2 GHz line to a $J=2$ $e/f$ parity doublet in ortho-H$_2^+$-He.

Identification of the 21.8 GHz line as a $J=0$ to $J=1$ transition in para-H$_2^+$-He.

Development of a smooth connection between short-range and long-range PES regions.

Abstract

A new analytical potential energy surface (PES) has been constructed for H$_2^+$-He using a reproducing kernel Hilbert space (RKHS) representation from an extensive number of $ab initio$ energies computed at the multi-reference and full configuration interaction level of theory. For the MRCI PES the long-range interaction region of the PES is described by analytical functions and is connected smoothly to the short-range interaction region, represented as a RKHS. All ro-vibrational states for the ground electronic state of H$_2^+$-He are calculated using two different methods to determine quantum bound states. Comparing transition frequencies for the near-dissociation states for $ortho$- and $para$-H$_2^+$-He allows assignment of the 15.2 GHz line to a $J=2$ $e/f$ parity doublet of $ortho$-H$_2^+$-He whereas the experimentally determined 21.8 GHz line is only consistent with a $(J=0)$ $\rightarrow$ $(J=1)$ $e/e$ transition in $para$-H$_2^+$-He.