Effect of the avoided crossing on the rovibrational energy levels, resonances, and predissociation lifetimes within the ground and first excited electronic states of lithium fluoride

TL;DR

This study models the rovibrational energy levels, resonances, and predissociation lifetimes of lithium fluoride's ground and first excited states, achieving high-precision spectral predictions up to 7800 cm$^{-1}$ above dissociation.

Contribution

It introduces a detailed ab initio approach incorporating diabatic and adiabatic potentials to accurately compute LiF spectra and resonance features, improving spectral line predictions.

Findings

Accurately reproduces observed transition frequencies within experimental uncertainties.

Provides extensive line lists for rovibrational transitions up to high quantum numbers.

Analyzes the effects of avoided crossings on energy levels and lifetimes.

Abstract

We investigate the LiF spectrum up to $7800$ cm$^{-1}$ above the first dissociation limit. The ab initio calculations of the adiabatic potentials and other molecular functions are performed in a wide range of interatomic separations, $r=1$-17 bohr. We consider the model of two interacting electronic states including both the bound states and the resonances of two kinds, the tunneling resonances and the predissociative ones. The Born-Oppenheimer potentials are modeled with use of two functions imitating the diabatic terms whereas the coupling between them was set constant equal to the half of the minimum separation between the adiabatic terms, and then we define the final diabatic terms and the final diabatic coupling via the adiabatic potentials and the angle of the adiabatic-to-diabatic basis rotation obtained by integration of the nonadiabatic coupling matrix element. The energies of the bound states, as well as the positions and widths of the resonances are calculated. The observed transition frequencies are reproduced with the standard deviation of 0.0009 cm$^{-1}$ for $^7$LiF, 0.0006 cm$^{-1}$ for $^6$LiF, and within the experimental uncertainties for the most of the lines. The line lists for the bound-bound $X$-$X$ rovibrational transitions are calculated for quantum numbers $v\le50,\Delta v\le15,J\le170$ ($J\le200$ for the 0-0 and 1-0 bands).