Hyperfine structure of the hydroxyl free radical (OH) in electric and magnetic fields

TL;DR

This study provides a detailed analysis of the hyperfine structure of the hydroxyl radical (OH) in combined electric and magnetic fields, revealing significant effects on energy levels relevant for ultracold molecule physics.

Contribution

It offers the first comprehensive calculation including hyperfine interactions and centrifugal distortion effects for OH in combined fields, with improved accuracy over previous models.

Findings

Hyperfine interactions significantly affect energy spectra.

Electric and magnetic fields induce level crossings and repulsions.

Over 10% reduction in magnetic field strength needed for level repulsions.

Abstract

We investigate single-particle energy spectra of the hydroxyl free radical (OH) in the lowest electronic and rovibrational level under combined static electric and magnetic fields, as an example of heteronuclear polar diatomic molecules. In addition to the fine-structure interactions, the hyperfine interactions and centrifugal distortion effects are taken into account to yield the zero-field spectrum of the lowest ${}^2\Pi_{3/2}$ manifold to an accuracy of less than 2 kHz. We also examine level crossings and repulsions in the hyperfine structure induced by applied electric and magnetic fields. Compared to previous work, we found more than 10 percent reduction of the magnetic fields at level repulsions in the Zeeman spectrum subjected to a perpendicular electric field. It is important to take into account hyperfine structure when we investigate physics of OH molecules at micro-Kelvin temperatures and below.