Electron attachment to MoF6, ReF6, and WF6; reaction of MoF6- with ReF6 and reaction of Ar+ with MoF6.

Rate constants were measured for electron attachment to MoF₆, ReF₆, and WF₆ in 133 Pa of helium gas using a flowing-afterglow Langmuir-probe apparatus. The experiment is a thorny one because the molecules tend to form oxide impurities on feedline surfaces and because of thermal decomposition of MoF₆ on surfaces as the gas temperature is increased. The electron attachment rate constant for MoF₆ is (2.3±0.8)×10^-9 cm³ s^-1 at 297 K; only MoF₆^- is formed in the temperature range of 297–385 K. The rate constant increases with temperature up to the point where decomposition becomes apparent. Electron attachment to ReF₆ occurs with a rate constant of (2.4±0.8)×10^-9 cm³ s^-1 at 297 K; only ReF₆^- is produced. MoF₆^- reacts with ReF₆ to form ReF₆^- on essentially every collision, showing definitively that the electron affinity of ReF₆ is greater than that of MoF₆. A rate constant of (5.0±1.3)×10^-10 cm³ s^-1 was measured for this ion-molecule reaction at 304 K. The reverse reaction is not observed. The reaction of Ar⁺ with MoF₆ was found to produce MoF₅⁺+F, with a rate constant of (1.8±0.5)×10^-9 cm³ s^-1. WF₆ attaches electrons so slowly at room temperature that the attachment rate was below detection level (<=10^-12 cm³ s^-1). By 552 K, the attachment rate constant reaches a value of (2±1)×10^-10 cm³ s^-1. [ABSTRACT FROM AUTHOR]