Reactions of Low-Energy O− Ions with D2 and H2

Total cross sections for collisions of O− and S− with hydrogen

“…13 reports a substantial isotope effect which is just the inverse of that reported in Ref. 9. The reasons for all of these discrepancies may lie in the difficult problem of determining the transmission efficiencies of the product mass analyzers in both experiments.…”

“…For example, total cross sections for reactions (3) and (4), as reported by Martin and Bailey,9 are considerably different from the corresponding rate constant measurements of Parks, 10 Fehsenfeld, II and McFarland et al 12 Additional beam studies by Tiernan et al13 are in marked disagreement with Martin and Bailey.9 Specifically, cross sections for reactions (3) and (4) from the beam measurements of Martin and Bailey exhibit a sharp threshold at a relative collision energy E = 0.39 eV, whereas the drift tube studies indicate sizeable rate constants down to thermal energies. Moreover, at E """ 0.8 eV the beam experiments of Martin and Baily indicate a cross section for reaction (3) which is an order of magnitude below that reported by Tiernan et al…”

Radiation chemistry and mass spectrometry of silanes and germanes. Progress report, June 1, 1972--May 31, 1973

“…Of course, because of the fact that the energy-spread of our ion beam is about 1 eV, we cannot rule out the possibility that, at energies lower than we could obtain experimentally, a maximum in the cross-section could occur and endothermic behavior would thus be exhibited. However, the cross-section observed is quite large for an endothermic process and this fact, coupled with the disparity of the curve 24 shown in Figure 12b with the curves typical of endothermic reactions , leads us to conclude that the actual process producing [20][21][22][23][24] SiCH4 from SiH under our conditions is exothermic; and this in turn most likely demands the participation of excited states of SiH+.…”

“…SiH2 , ions whose intensities at first increase with pressure ( Figure 1) due to reactions (2), (3), (8), (9), (14), (15), and (22). Because there is an initial increase in intensity of the precursors to SiCH4 , the.intensity-pressure curve shows an initial upward curvature.…”

“…In the methane-rich mixture ( Figure 1) the primary ions of methane are .sufficiently intense that a net formation of SiH2 by reactions (3), (9),·(15) and (22) occurs with increasing pressure until·sufficient depletion of methane primary ion intensity has taken place for the loss processes, namely reactions (31), (32) A similar argument applies to the maximum in Si (m/e 28), + shown in Figure 1, as Si is produced in the methane-rich mixtures by reactions (1), (7), and (13) and react by (27), (28) Similarly.the absence of C2H (m/e 27) formation in the monosilane-rich system was attributed earlier to competitive reaction precursor ion CH2 with monosilane, and it is now clear from Table I.that· the pertinent reactions are (13) amounts by reactions (1)-(4), (7)- (10), (13)- (16), (19), (22), (23), (26), and (34). In the monosilane-rich mixture only SiH (m/e 31), a precursors to Si2Hs , shows a net increase ( Figure 6) and this is 5,13,14 due to reactions characteristic of pure monosilane.…”