Electron attachment reactions of perfluoroalkyl transition metal carbonyls: Rate constants and product analysis

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Abstract
Absolute rate constants for electron attachment reactions of CF3Mn(CO)5, CF3Co(CO)4, and C2F5Co(CO)4 have been measured in a gas flow system with electron cyclotron resonance (ECR) detection. Free electrons were generated by Penning ionization of argon gas by helium metastables produced in a low power radio-frequency discharge. The pressure was 2.3–2.5 Torr. The rate constants at 293 K in units of cm3 molecule−1 s−1 are (3.5±0.6)×10−7 for CF3Mn(CO)5; (2.0±0.4)×10−7 for CF3Co(CO)4; and (1.8±0.3)×10−7 for C2F5Co(CO)4. Negative ion mass spectra indicate that nondissociative attachment is important at thermal electron energy. The cross section for nondissociative capture falls rapidly with increasing electron energy. Dissociative product channels are also observed. Electron capture rate constants for several additional molecules are presented and compared with values from the literature. The rate constants in units of cm3 molecule−1 s−1 are 2.8×10−7 for SF6; 3.7×10−7 for CCl4; 3.1×10−7 for CFCl3; 1.8×10−9 for CF2Cl2; 1.5×10−8 for CF3Br; 3.8×10−9 for CHCl3; and 1.2×10−8 for C2F3Cl3.