Variational analysis of HF dimer tunneling rotational spectra using an ab initio potential energy surface

TL;DR

This study uses an accurate ab initio potential energy surface to perform variational calculations of HF dimer spectra, achieving high accuracy and enabling the assignment of previously uncharacterized spectral lines.

Contribution

It introduces a highly precise variational analysis of HF dimer spectra using an ab initio PES, improving spectral assignment accuracy and extending understanding of excited vibrational states.

Findings

Calculated energy levels agree within 50 MHz of experimental data

Successfully assigned 3 new J-branches in HF dimer spectra

Extended spectral analysis to higher vibrational and rotational states

Abstract

A very accurate, (HF)$_2$ potential energy surface (PES) due to Huang et al. (J. Chem. Phys., 150, 154302 (2019)) is used to calculate the energy levels of the HF dimer by solving the nuclear-motion Schr\"{o}dinger equation using variational program WAVR4. Calculations on an extended range of rotational states show very good agreement with experimental data. In particular the known empirical rotational constants for the ground and some observed excited vibrational states are reproduced with an accuracy of about 50 MHz. This level of accuracy is shown to extend to higher excited inter-molecular vibrational states $v$ and higher excited rotational quantum numbers $(J,K_a)$. These calculations allow the assignment of 3 new $J$-branches in an HF dimer tunneling-rotation spectra recorded 30 years ago. These branches belong to excited $K_a$ = 4 state of the ground vibrational state, and $K_a$ = 0 states of excited inter-molecular vibrational states.