RATE-CONSTANT MEASUREMENTS OF C2H WITH CH4, C2H6, C2H4, D2, AND CO

The rate constants for the reactions of the ethynyl radical (C2H) with CH4, C2H6, C2H4, D2, and CO have been determined by following the time decay of a C2H infrared transient absorption line originating from the ground vibronic state using diode laser spectroscopy. The C2H was created by excimer laser flash photolysis (ArF, 193 nm) of CF3CCH. Relaxation of excited states of C2H was achieved by buffering the photolysis cell with ≈20 Torr of He buffer and ≈130 mTorr of SF6. When possible, the dependence of the reaction rate on helium pressure was investigated over the range of 8-70 Torr. Second-order rate constants of 3.0 (2) × 10-12, 1.3 (3) × 10-10, 3.6 (2) × 10-11, 2.3 (3) × 10-13 cm3 molecule-1 s-1 were obtained for the reactions of C2H with CH4, C2H4, C2H6, and D2, respectively. A third-order rate constant of 2.4 (6) × 10-30 cm6 molecule-2 s-1 was obtained for the reaction of C2H with CO. © 1990 American Chemical Society.