Creation of Population Inversions in theΛDoublets of OH by the Photodissociation ofH2O at 157 nm: A Possible Mechanism for the Astronomical Maser

Abstract

Water molecules are photolyzed by a ${\mathrm{F}}_2$ laser at 157 nm. The nascent OH (${}_{}{}^2{}_{}{}^{}\Pi _{\frac{3}{2}}^{}{}_{}{}^{}, v=0\mathrm{}$) rotational state distribution, probed via laser-induced fluorescence, reveals a strong preference for populating the upper $\Lambda$-doublet component. The population inversion is found to be a function of both the initial temperature of the ${\mathrm{H}}_2$O as well as the final rotational state in which the OH radical is formed. These results may provide a simple mechanism for the astronomical OH maser observed by others.