Level-Crossing Spectroscopy in Molecules: Application to the OH Free Radical

Abstract

We have observed the Hanle effect in the ${}_{}{}^2{}_{}{}^{}\Sigma \mathrm{}(v=0\mathrm{})\mathrm{}$ excited state of the free radical OH in lines which originate from sublevels with rotational quantum numbers $K=3,4,5\mathrm{}$. From the widths of each of these experimental signals we can calculate the $g$-factor-lifetime product and, since the lifetime of the state has been measured previously, our observations yield the values $g[K=3\mathrm{}]=0.176\mathrm{}\left(23\right)\mathrm{}$, $g[K=4\mathrm{}]=0.141\mathrm{}\left(15\right)\mathrm{}$, and $g[K=5\mathrm{}]=0.118\mathrm{}\left(11\right)\mathrm{}$.