Determination of the Rate Constants for the Radical−Radical Reactions NH2(X̃2B1) + NH(X3Σ−) and NH2(X̃2B1) + H(2S) at 293 K

Abstract

The rate constant for the reactions NH2((2)B1) + NH(X(3)Sigma-) and NH2((2)B1) + H((2)S) were measured over a pressure range from 2 to 10 Torr in CF4, or Ar gases at 293 +/- 2 K. The radicals were produced by the 193 nm photolysis of NH3 dilute in the carrier gas. Both radicals were monitored simultaneously following the photolysis laser pulse using high-resolution time-resolved absorption spectroscopy. The NH2 radical was monitored using the (1)2(21) <-- (1)3(31) rotational transition of the (0,7,0)(2)A1 <-- (0,0,0) (2)B1 vibronic band near 675 nm, and the NH radical was monitored using the (1)R3(4) rotational transition on the 1-0 vibrational transition near 3084 nm. The data was analyzed using model simulations of the NH2 and NH temporal concentration profiles. The rate constants for the NH2 + NH and NH2 + H reactions were found to be (9.6 +/- 3.2) x 10(-11) and (7.7 +/- 14) x 10(-15) cm3 molecule(-1) s(-1), respectively, where the uncertainty includes an estimate of both systematic and random errors. The measurements were independent of the nature of the diluents, CF4 or Ar, and total pressure.