Time-of-flight study ofH(2S)andD(2S)produced by electron impact onH2andD2: Fast peaks

Time-of-flight spectra of $\mathrm{H}\mathrm{}\left(2S\right)\mathrm{}$ and $\mathrm{D}\mathrm{}\left(2S\right)\mathrm{}$ fragments from electron-bombardment dissociated ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ have been observed. Kinetic energy distributions of "fast" metastable fragments were obtained for electron-bombardment energies ranging from near the threshold for fast metastable production (less than 29 eV) to 100 eV. At low bombarding energies previously unreported structure is observed in the fast peaks for both isotopes. At high bombarding energies also there is evidence of unresolved structure in the fast peaks. The present data are compared with the results of earlier investigations. At low bombarding energies there are significant discrepancies between the present results and previous measurements. At high bombarding energies there is significant disagreement with a calculation that assumes a single dissociating state. The observed shift of the fast peak as a function of the bombarding electron energy is compared to predictions incorporating a form of the Wannier law. This comparison tends to confirm the presence of more than one dissociation channel yielding fast metastables. Several excited states of ${\mathrm{H}}_2$ and $\mathrm{H}_2^{}{}_{}{}^{+}$ are discussed as possible dissociation channels contributing to the observed kinetic energy distributions.