Determination of the Rate Constants for the NH2(X2B1) + NH2(X2B1) and NH2(X2B1) + H Recombination Reactions with Collision Partners CH4, C2H6, CO2, CF4, and SF6 at Low Pressures and 296 K. Part 2.

The recombination rate constants for the reactions NH2((XB1)-B-2) + NH2((XB1)-B-2) + M -> N2H4 + M and NH2((XB1)-B-2) + H + M -> NH3 + M, where M was CH4, C2H6, CO2, CF4, or SF6, were measured in the same experiment over presseure ranges of 1-20 and 7-20 Torr, respectively, at 296 +/- 2 K. The NH2 radical was produced by the 193 nm laser photolysis of NH3. Both NH2 and NH3 were monitored simultaneously following the photolysis laser pulse. High-resolution time-resolved absorption spectroscopy was used to monitor the temporal dependence of both species: NH2 on the (1)2(21) <- (1)3(31) rotational transition of the (0,7,0)A(2)A(1) <- (0,0,0)(XB1)-B-2 electronic transition near 675 nm and NH3 in the IR on either of the inversion doublets of the (q)Q(3)(3) rotational transition of the v(1) fundamental near 2999 nm. The NH2 self-recombination clearly exhibited falloff behavior for the third-body collision partners used in this work. The pressure dependences of the NH2 self-recombination rate constants were fit using Troe's parametrization scheme, k(inf), k(0), and F-cent, with k(inf) = 7.9 X 10(-11) cm(3) molecule(-1) s(-1), the theoretical value calculated by Klippenstein et al. (J. Phys. Chem. A 113, 113, 10241). The individual Troe parameters were CH4, k(0)(CH4) = 9.4 X 10(-29) and F-cent(CH4) = 0.61; C2H6, k(0)(C2H6) = 1.5 X 10(-28) and F-cent(C2H6) = 0.80; CO2, k(0)(CO2) = 8.6 X 10(-29) and F-cent(CO2) = 0.66; CF4, k(0)(CF4) = 1.1 X 10(-28) and F-cent(CF4) = 0.55; and SF6, k(0)(SF6) = 1.9 X 10(-28) and F-cent(SF6) = 0.52, where the units of k(0) are cm(6) molecule(-2) s(-1). The NH2 + H + M reaction rate constant was assumed to be in the three-body pressure regime, and the association rate constants were CH4, (6.0 +/- 1.8) X 10(-30); C2H6, (1.1 +/- 0.41) X 10(-29); CO2, (6.5 +/- 1.8) X 10(-30); CF4, (8.3 +/- 1.7) X 10(-30); and SF6, (1.4 +/- 0.30) X 10(-29), with units cm(6) molecule(-1) s,(-1) and the systematic and experimental errors are given at the 2 sigma confidence level.