Knowledge Bank

A time-of-flight technique has been used to study the velocity and energy distributions of the metastable H(2S) and D(2S) atoms produced by the electron-impact dissociation of $H2,D2$ and HD: $H2+e-\to H(2S)+H+e-$, etc. The Franck-Condon and the Winans-Stueckelberg approximations were used to quantitatively determine the potential energy curves for the excited molecular states which yield the observed metastable atoms. This dissociation process produces two groups of metastables [fast” and slow”$]1,2$, which have kinetic energy peaks at 5.4 and 0.1 eV. The slow atoms were found to originate in the $D1\Pi u$ and the $B\prime 1\Sigma u+$ states, as has been previously $reported.2$ The fast metastables originate in a state whose potential energy is: V(R) = 34.9/R + 11.0 eV, for: 1.0 $\le$ R $\le$ 1.8 au. This state has recently been identified by $Misakian2$ as a $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi u$ with a dissociation limit of 24.9 eV. We have compared the velocity and energy distributions of the metastables resulting from the dissociation of $H2$ and $D2$, and also of HD, in which this reaction had not previously been studied. In general, we found that the metastable spectra exhibit the expected isotopic dependence. In contrast with previously published $data1,2$, the energy distributions of the slow metastable atoms are found to agree with those predicted by theory.