Quenching of theCΠu3metastable state ofH2andD2by an electric field

The quenching of the $\nu =0\mathrm{} C{}_{}{}^3{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ metastable state of ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ by a static electric field has been measured using the time-of-flight technique. Neutral ground-state molecules effusing from a source slit are immediately excited to the $C{}_{}{}^3{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ metastable state by a pulse of antiparallel magnetically focused electrons. After passing through a uniform electric field region 0.5 m long, the velocity distribution of this thermal beam of metastable molecules is then preferentially detected at the end of the time-of-flight region, 1.825 m from the electron gun. The number of $C{}_{}{}^3{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ molecules arriving at the detector in specific velocity intervals with the electric field off is compared to the number with the field on, to determine the quenching rate ($=k{E}^2$). The result for the quenching constant $k$ is the same for both para- and ortho-${\mathrm{H}}_2$, as well as for ${\mathrm{D}}_2$, and with $E$ in kV/cm is $k=8.6\mathrm{}\pm 0.3$.