Product branching fractions in the reaction of 3.sum.- NH (ND) with nitric oxide

Abstract

We have carried out a combined experimental and theoretical study of the reaction of N H (ND) (3Z-) with N O aimed at understanding the product distribution from that reaction. The reaction was studied at room temperature using the discharge flow technique with mass spectrometric detection of the reaction products.Measured product branching fractions at room temperature for production of N2O + H (D) were 0.8 0.4 for N H (3Z-) + N O and 0.87 f 0.17 for ND(3Z-) + NO (la statistical errors). Stationary points on the HNNO 2A' potential energy surface were characterized using the Gaussian 2 ab initio method. The initial addition of NH(3Z-) to N O on the 2A' surface is predicted to proceed without a barrier to form trans-HNNQ reaction to produce the cis isomer is predicted to have a barrier of 2.9 kcal/mol. The cis-and trans-HNNO are predicted to be at -48.9 and -56.0 kcal/mol relative to the separated reactants. Transition states with energies of -25.3 and -17.9 kcal/mol were located for dissociation of the cis isomer into H + N20 and O H + N2, respectively.The transition state for interconversion of the isomers was calculated to be at approximately -30.8 kcal/mol.The trans-HNNO was found to isomerize to the cis form before decomposing. The potential energy surface calculated explains the major features of the reaction.

Product branching fractions in the reactions of NH(a 1Δ) and NH(X 3Σ−) with NO

“…This conclusion is consistent with that of the previous studies. 2 ,5, 8 The observed time profiles of OH(v =0) were also explained by the vibrational relaxation of OH by NO with the branching fractions obtained here.…”

Combustion Chemistry of Nitrogen

“…The input parameters are listed in Table 2.6. We also explored use of a more complex reaction system, accounting separately for the cis-and trans-isomers of HNNO, as described by both Walch (1993a) and Durant (1994); the results were very similar to those presented below. We prefer the simpler analysis, since there remains considerable ambiguity as to the relative energies of the isomers, see Walch (1993a).…”

“…If this is assumed to be the case, then the computed QRRK rate coefficient expressions could be brought into better Marshall et al (1987), for this reaction is shown in Figure 2.13. Aspects of it have been addressed in several investigations (Miller and Melius 1992a;Durant 1994;Melius 1993;Walch 1993a). Although a distinction was made in some of these studies between cis-and trans-HNNO, the overall features are in each case similar to those shown in Figure 2.13.…”

Prediction of bond dissociation energies and transition state barriers by a modified complete basis set model chemistry

“…These transition states had been addressed by Durant and Rohlfing when evaluating the reliability of G2 and its G2Q derivative. 10,14 A subset of these species had been reinvestigated by Durant using DFT methods. 15 We included the hydrocarbon radical hydrogen transfer reaction between C 2 H 4 and C 2 H 5 as an additional system that previously had been treated at a high level of theory.…”

“…The geometry optimizations were performed at the QCISD/6-311G(d,p) level, which is the same as that used by Durant and Rohlfing for their G2Q formulation of G2 theory ͑ZPE corrections for the TS were taken from the QCISD frequency calculations͒. The barrier heights found at the CBS-QCI/APNO level are compared to values from G2Q, 13 G2M ͑where available͒, 4 and 17 which might be an insufficiency in the reference selection in the CCI procedure as discussed by Durant and Rohlfing, 10,14 leading to an error of 3.0 kcal in the energy of the NHϩNO asymptote. When referring the TS energy to the HϩN 2 O, the CBS-QCI/APNO and G2Q results are in excellent agreement with the CASSCF value.…”