F. B. Yousif

Generation of an H3+(v = 0) beam and its diagnosis from the observation of its polar dissociation in collision with He

Abstract Ground state H 3 + ions in their lowest vibrational level were produced, and the initial vibrational state of the H 3 + ions was qualitatively observed as a function of the source pressure. Quantitatively, the polar dissociation channel was studied in order to verify the initial vibrational state of the ions. The energy distributions of H + and H − , generated from the collisional dissociation of H 3 + in He at 9 keV of projectile energy, resulting from the polar dissociating channel, were measured in coincidence. The good agreement between the center of mass energy threshold of the proton distributions from the polar dissociation process and the theoretical potential curves for the adiabatic Born-Oppenheimer energies of the H 3 + ions confirms the vibrational cooling of the H 3 + beam by operating the ion source at high pressure. We conclude that the process is effectively originated from H 3 + ( v =0).

One-photon excitation and dissociation of both weakly bound rotational excited states and vibrational excited states of HD2+ and photofragment branching ratio D+/H+ of the final predissociative states

The presence of weakly bound rotationally excited initial states of HD2+ lying just below the lowest dissociation limit has been observed as well as quasi-bound, predissociative final states above the dissociation limit resulting from one-photon excitation of those weakly bound states. The excitation of the initial weakly bound and possibly only few quasi-bound states took place with 1064 nm laser radiation. The possibility of one-photon excitation of the vibrationally excited initial HD2+ ions is considered. The centre-of-mass kinetic energy distributions of the D+ and H+ fragment were used to identify the possible initial and final states involved in the transitions leading to these fragments. The fragment ratio D+/H+ is shown to be critically dependent on the ion source pressure. A strong preference is observed for the D+ + HD dissociation channel over the H+ + D2 channel at high source gas pressures. The centre-of-mass energy of the resulting H+ and D+ fragments was found to agree with predicted theoretical values, and suggest that among initially excited HD2+ ions, only a few of these lie initially above the lowest dissociation limit.

Negative ion motion in mixtures of CH/sub 4/ and Ar with low SF/sub 6/ content

This paper deals with the measurement of the mobility of negative ions in the mixture SF/sub 6/-CH/sub 4/-Ar, with SF/sub 6/ contents of up to 50%. The Pulsed Townsend Technique was used to produce electronic and ionic avalanches over the low E/N range in which ionization is either negligible or absent, and attachment processes are significant. The E/N range of measurement was 1 to 100 Td. The structure of the measured signals strongly suggests that there is only one negative ion, most likely formed by resonant attachment. A test of the measured mobilities with Blancs law provides further support to ascribe the drifting species to SF/sub 6//sup -/.

H3+ and D3+ ground state beams production with a filament-type ion source

H3+ and D3+ molecular ions in their ground state have been produced by using a filament-type ion source. This was achieved by increasing the ion source pressure up to 0.82 Torr. These molecular ion beams were used in collision with He to study the polar dissociation of H3+ and D3+. The polar dissociating channel for H3+ with He was used to qualitatively verify the internal vibrational energy of the initial H3+ ions by observing the protons in coincidence with H− fragments. Variation of the source pressure influenced the vibrational population of the initial H3+ ions, and this was reflected in the distribution of the coincident H+ and H− fragments resulting from H3+ ions in their ground state.