Friedman Jeffrey F, Stevens Amy E, Miller Thomas M, Viggiano A A
Department of Physics, University of Puerto Rico, Mayaguez, Puerto Rico.
J Chem Phys. 2006 Jun 14;124(22):224306. doi: 10.1063/1.2202851.
Rate constants were measured for electron attachment to MoF(6), ReF(6), and WF(6) 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 MoF(6) on surfaces as the gas temperature is increased. The electron attachment rate constant for MoF(6) is (2.3+/-0.8)x10(-9) cm(3) s(-1) at 297 K; only MoF(6) (-) 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 ReF(6) occurs with a rate constant of (2.4+/-0.8)x10(-9) cm(3) s(-1) at 297 K; only ReF(6) (-) is produced. MoF(6) (-) reacts with ReF(6) to form ReF(6) (-) on essentially every collision, showing definitively that the electron affinity of ReF(6) is greater than that of MoF(6). A rate constant of (5.0+/-1.3)x10(-10) cm(3) s(-1) was measured for this ion-molecule reaction at 304 K. The reverse reaction is not observed. The reaction of Ar(+) with MoF(6) was found to produce MoF(5) (+)+F, with a rate constant of (1.8+/-0.5)x10(-9) cm(3) s(-1). WF(6) attaches electrons so slowly at room temperature that the attachment rate was below detection level (< or =10(-12) cm(3) s(-1)). By 552 K, the attachment rate constant reaches a value of (2+/-1)x10(-10) cm(3) s(-1).
使用流动余辉朗缪尔探针装置，在133帕的氦气中测量了电子与MoF(6)、ReF(6)和WF(6)的附着速率常数。该实验颇具难度，原因在于这些分子易于在进料管线表面形成氧化物杂质，并且随着气体温度升高，MoF(6)会在表面发生热分解。MoF(6)的电子附着速率常数在297 K时为(2.3±0.8)×10⁻⁹立方厘米·秒⁻¹；在297 - 385 K的温度范围内仅形成MoF(6)⁻。速率常数随温度升高，直至分解明显时达到峰值。电子与ReF(6)的附着速率常数在297 K时为(2.4±0.8)×10⁻⁹立方厘米·秒⁻¹；仅产生ReF(6)⁻。MoF(
