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

We have observed the Hanle effect in the ²Σ (v=0) excited state of the free radical OH in lines which originate from sublevels with rotational quantum numbers $K=3,4,5$. 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 $g[K=3]=0.176(23)$, $g[K=4]=0.141(15)$, and $g[K=5]=0.118(11)$.