Models of three and four body electron attachment to O2 molecules
1982; Elsevier BV; Volume: 66; Issue: 1-2 Linguagem: Inglês
10.1016/0301-0104(82)88007-5
ISSN1873-4421
Autores Tópico(s)Mass Spectrometry Techniques and Applications
ResumoThe recent work of Kokaku et al. using different gas pressures suggests the existence of a deviation from the Bloch—Bradbury two-step electron attachment process for several O2, M gas mixtures. These authors suggest a four-body attachment mechanism whereas on the basis of observations at different temperatures Shimamori and Fessenden find evidence of single-step three body attachment in pure O2 gas and in O2 binary mixtures with N2, CO and n-C4H1O. Some considerable ambiguity exists for the interpretation of the pressure dependent data. Much depends on the value of k1(0), the rate coefficient for the process e + O2k1(0)O 2−*. It is difficult to distinguish empirically a single Bloch—Bradbury two-step process with a high k1(0) value from a Bloch—Bradbury process with a low k1(0) to which is added another attachment mechanism. Collisional detachment of the electron further complicates the interpretation. These complications are examined in some detail and it is concluded that k1(0) is still about the order of magnitude 5 × 10−11 cm3/s originally suggested by Shimamori and Hatano but who assumed the simple two-step mechanism alone. This value is consistent with the analysis of electron beam experiments. The pressure dependence is concluded to be due to a single-step process for O2− and O2−* production added to the two-step process. There is also a probable contribution from collisional detachment. Physical reasons why this rather than the four-body attachment hypothesis should be expected are given. The mechanisms possible for single-step attachment are discussed. One previously unrecognized mechanism is charge transfer from low energy <100 meV M−* resonances. Evidence for these ions exists for all O2, M mixtures showing high pressure deviations from Bloch—Bradbury saturation.
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