Determination of the Rate Constant for the NH₂(X²B₁) + NH₂(X²B₁) Recombination Reaction with Collision Partners He, Ne, Ar, and N₂at Low Pressures and 296 K. Part 1

Abstract

The recombination rate constant for the NH(2)(X(2)B(1)) + NH(2)(X(2)B(1)) → N(2)H(4)(X(1)A(1)) reaction in He, Ne, Ar, and N(2) was measured over the pressure range 1-20 Torr at a temperature of 296 K. The NH(2) radical was produced by 193 nm laser photolysis of NH(3) dilute in the third-body gas. The production of NH(2) and the loss of NH(3) were monitored by high-resolution continuous-wave absorption spectroscopy: NH(2) on the (1)2(21) ← (1)3(31) rotational transition of the (0,7,0)A(2)A(1) ← (0,0,0) X(2)B(1) vibronic band and NH(3) on either inversion doublet of the (q)Q(3)(3) rotational transition of the ν(1) fundamental. Both species were detected simultaneously following the photolysis laser pulse. The broader Doppler width of the NH(2) spectral transition allowed temporal concentration measurements to be extended up to 20 Torr before pressure broadening effects became significant. Fall-off behavior was identified and the bimolecular rate constants for each collision partner were fit to a simple Troe form defined by the parameters, k(0), k(inf), and F(cent). This work is the first part of a two part series in which part 2 will discuss the measurements with more efficient energy transfer collision partners CH(4), C(2)H(6), CO(2), CF(4), and SF(6). The pressure range was too limited to extract any new information on k(inf), and k(inf) was taken from the theoretical calculations of Klippenstein et al. (J. Phys. Chem A 2009, 113, 10241) as k(inf) = 7.9 × 10(-11) cm(3) molecule(-1) s(-1) at 296 K. The individual Troe parameters were: He, k(0) = 2.8 × 10(-29) and F(cent) = 0.47; Ne, k(0) = 2.7 × 10(-29) and F(cent) = 0.34; Ar, k(0) = 4.4 × 10(-29) and F(cent) = 0.41; N(2), k(0) = 5.7 × 10(-29) and F(cent) = 0.61, with units cm(6) molecule(-2) s(-1) for k(0). In the case of N(2) as the third body, it was possible to measure the recombination rate constant for the NH(2) + H reaction near 20 Torr total pressure. The pure three-body recombination rate constant was (2.3 ± 0.55) × 10(-30) cm(6) molecule(-2) s(-1), where the uncertainty is the total experimental uncertainty including systematic errors at the 2σ level of confidence.

An experimental, theoretical and kinetic-modeling study of the gas-phase oxidation of ammonia

“…The experimental literature reports either experimental measurements of ammonia decomposition at high temperatures (higher than 2000 K) 12,58 or of NH 2 + H recombination rates at room temperature, but a systematic temperature-and pressure-dependent study is not available to the authors' knowledge. 62,63 In order to fit both high-and low-temperature data sets, a single exponential energy transfer model was adopted, with a ΔE down of 130 (T[K]/ 298) 0.8 cm −1 . At 1 atm, the calculated rate constant is about a factor of 2 slower than the Davidson et al 12 high temperature experimental decomposition rate, a factor of 2 larger than the high-temperature Baulch recommendation, 58 and in excellent agreement with the recent recombination measurement of Altinay and MacDonald, 63 on whose data ΔE down was fitted in the present study.…”

“…62,63 In order to fit both high-and low-temperature data sets, a single exponential energy transfer model was adopted, with a ΔE down of 130 (T[K]/ 298) 0.8 cm −1 . At 1 atm, the calculated rate constant is about a factor of 2 slower than the Davidson et al 12 high temperature experimental decomposition rate, a factor of 2 larger than the high-temperature Baulch recommendation, 58 and in excellent agreement with the recent recombination measurement of Altinay and MacDonald, 63 on whose data ΔE down was fitted in the present study. Experimental and theoretical data are compared in Fig.…”

“Third‐body” collision parameters for hydrocarbons, alcohols, and hydroperoxides and an effective internal rotor approach for estimating them

“…More generally and despite some systematic experimental studies (eg, Refs. [42][43][44][45][46][47][48][49][50][51][52][53][54], it remains difficult to anticipate how collision efficiencies vary with the temperature and identity of the bath gas M as well as the size and chemical structure of the unimolecular reactant A.…”

Experimental and numerical studies of the ignition of ammonia/additive mixtures and dimethyl ether burning velocities

“…In the present work, the rate coefficients for the reaction forming hydrazine, NH2 + NH2 (+M) = N2H4 (+M) (R3.1), were reevaluated; this re-evaluation was performed by P. Glarborg and is included here for completeness. Both Glarborg et al [30] and Klippenstein et al [31] relied on the theoretical work of Klippenstein et al [87], which was in good agreement with the low temperature measurements of the reaction [88][89][90][91][92]. At elevated temperature, the reaction has been studied over a wide range of pressure in shock tubes.…”

“…Similarly, the rate constants reported by Meyer et al [94] were multiplied by a factor of 2/3. Figure 3.2 compares data for the low-pressure limit of R 3.1; i.e., the low temperature experimental data of Khe et al [88] and Altinay and Macdonald [92], the theoretical value by Klippenstein et al [87], and data derived from low-pressure measurements of the reverse rate constant by Diesen [93] and Meyer et al [94], converted through the equilibrium constant. The data in Fig.…”