Magnetic dipole transitions in the OH $A\,^2\Sigma^+ \leftarrow X\,^2\Pi$ system

TL;DR

This study observes magnetic dipole transitions in the OH radical's electronic system, using advanced spectroscopy techniques, and finds these transitions are significantly stronger than previously believed, aligning with theoretical predictions.

Contribution

The paper provides the first experimental observation of magnetic dipole transitions in the OH radical and confirms theoretical predictions about their relative strength.

Findings

Magnetic dipole transitions are only 2.580 times weaker than electric dipole transitions.

Experimental data confirms theoretical predictions about transition strengths.

Advanced Stark deceleration and microwave spectroscopy enable precise control of hyperfine states.

Abstract

We report on the observation of magnetic dipole allowed transitions in the well-characterized $A\,^2\Sigma^+ - X\,^2\Pi$ band system of the OH radical. A Stark decelerator in combination with microwave Rabi spectroscopy is used to control the populations in selected hyperfine levels of both $\Lambda$-doublet components of the $X\,^2\Pi_{3/2},v=0,J=3/2$ ground state. Theoretical calculations presented in this paper predict that the magnetic dipole transitions in the $\nu'=1 \leftarrow \nu=0$ band are weaker than the electric dipole transitions by a factor of $2.58\times 10^3$ only, i.e., much less than commonly believed. Our experimental data confirm this prediction.