Time-fhght spectra of H(2S) and D(2$) fragments from electron-bombardment dissociated H, and D, have been observed. Kinetic energy distributions of "fast" metastable fragments were obtained for electronbombardment 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 H, and H, are discussed as possible dissociation channels contributing to the observed hnetic energy distributions.
A cylindrically symmetric electron-bombardment ion source is described that has been useful in beam experiments with molecular ions. Measurements indicate that the ions have a kinetic-energy spread (full-width at half-maximum) of 0.5-1.0 eV, a current of several microamperes, and a population distribution that is consistent with vibrational and rotational factors resulting from single-electron-impact ionization. The source exhibits low noise ( less, similar twice the theoretical shot-noise limit) and has a compact and easily serviceable construction.
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