A method for the variational calculation of hyperfine-resolved rovibronic spectra of diatomic molecules

TL;DR

This paper introduces a variational method implemented in extsc{Duo} for calculating hyperfine-resolved rovibronic spectra of diatomic molecules, accounting for multiple hyperfine interactions and validated against experimental data.

Contribution

It presents a novel variational algorithm for hyperfine-resolved spectra calculation integrated into extsc{Duo}, improving accuracy over effective Hamiltonian methods.

Findings

Results for NO and MgH agree with experimental data.

The method accurately reproduces hyperfine-resolved spectra.

The approach is validated against PGOPHER calculations.

Abstract

An algorithm for the calculation of hyperfine structure and spectra of diatomic molecules based on the variational nuclear motion is presented. Hyperfine coupling terms considered are Fermi-contact, nuclear spin-electron spin dipole-dipole, nuclear spin-orbit, nuclear spin-rotation and nuclear electric quadrupole interactions. Initial hyperfine-unresolved wavefunctions are obtained for given set of potential energy curves and associated couplings by variation solution of the nuclear-motion Schr\"odinger equation. Fully hyperfine-resolved parity-conserved rovibronic Hamiltonian matrices for a given final angular momentum, $\bm{F}$, are constructed and then diagonalized to give hyperfine-resolved energies and wavefunctions.Electric transition dipole moment curves can then be used to generate a hyperfine-resolved line list by applying rigorous selection rules.The algorithm is implemented in \textsc{Duo}, which is a general program for calculating spectra of diatomic molecules. This approach is tested for NO and MgH,and the results are compared to experiment and shown to be consistent with those given the well-used effective Hamiltonian code PGOPHER.