$\Lambda$-doublet spectra of diatomic radicals and their dependence on fundamental constants

TL;DR

This paper investigates the $ ext{Lambda}$-doublet spectra of diatomic radicals, highlighting their high sensitivity to variations in fundamental constants like alpha and beta, especially in molecules like OH and CH.

Contribution

It demonstrates how spin decoupling affects $ ext{Lambda}$-doublet sensitivity coefficients, revealing enhanced sensitivity in certain molecular states.

Findings

Sensitivity coefficients for OH $ ext{Lambda}$-doublet lines reach around 10^3.

Decoupling of electron spin causes sign changes and increased sensitivity.

Sensitivity varies with total angular momentum J and coupling cases.

Abstract

$\Lambda$-doublet spectra of light diatomic radicals have high sensitivity to the possible variations of the fine structure constant alpha and electron-to-proton mass ratio beta. For molecules OH and CH sensitivity is further enhanced because of the J-dependent decoupling of the electron spin from the molecular axis, where J is total angular momentum of the molecule. When $\Lambda$-splitting has different signs in two limiting coupling cases a and b, decoupling of the spin leads to the change of sign of the splitting and to the growth of the dimensionless sensitivity coefficients. For example, sensitivity coefficients for the $\Lambda$-doublet lines J=9/2 of the $\Pi_{1/2}$ state of OH molecule are on the order of $10^3$.