Ab initio calculations to support accurate modelling of the rovibronic spectroscopy calculations of vanadium monoxide (VO)

TL;DR

This paper presents ab initio calculations of dipole moments and spin-orbit couplings for VO, enabling the creation of a comprehensive line list with over 277 million transitions for astrophysical spectroscopy.

Contribution

The study develops a new set of ab initio data and a detailed VO line list considering multiple electronic states, improving spectral modeling accuracy for astrophysical applications.

Findings

Generated a new VO line list with 277 million transitions.

Identified optimal methods for calculating off-diagonal dipole moments.

Enhanced understanding of VO's electronic structure for spectral analysis.

Abstract

Accurate knowledge of the rovibronic near-infrared and visible spectra of vanadium monoxide (VO) is very important for studies of cool stellar and hot planetary atmospheres. Here, the required ab initio dipole moment and spin-orbit coupling curves for VO are produced. This data forms the basis of a new VO line list considering 13 different electronic states and containing over 277 million transitions. Open shell transition, metal diatomics are challenging species to model through ab initio quantum mechanics due to the large number of low-lying electronic states, significant spin-orbit coupling and strong static and dynamic electron correlation. Multi-reference configuration interaction methodologies using orbitals from a complete active space self-consistent-field (CASSCF) calculation are the standard technique for these systems. We use different state-specific or minimal-state CASSCF orbitals for each electronic state to maximise the calculation accuracy. The off-diagonal dipole moment controls the intensity of electronic transitions. We test finite-field off-diagonal dipole moments, but found that (1) the accuracy of the excitation energies were not sufficient to allow accurate dipole moments to be evaluated and (2) computer time requirements for perpendicular transitions were prohibitive. The best off-diagonal dipole moments are calculated using wavefunctions with different CASSCF orbitals.