Reaction-Path Dynamics Calculations of the NH₃ + O(³P) Hydrogen Abstraction Reaction

Abstract

Molecular orbital theory was used to study the stationary points on the reaction-path of the hydrogen abstraction reaction between ammonia and an oxygen atom. In the C s symmetry, this reaction proceeds over two potential energy surfaces, 3 A′ and 3 A′′, with a hydrogen-bonded complex in the exit channel. From the analysis of the reaction-path curvature, we find qualitatively that excitation of the NH 3 stretch and bend modes might enhance the forward rate constants and that the OH stretch and NH 2 bend modes of the products could appear vibrationally excited, although, as a result of the randomization of the energy favored by the deep hydrogenbonded well, these modes will appear less vibrationally excited than those in other direct reactions. The total forward thermal rate constants were calculated from the sum of the calculated rate constants for the two surfaces using variational transition-state theory with semiclassical transmission coefficients over a wide temperature range, 500-2000 K. The calculated rate constants show reasonable agreement with experimental data, with a more pronounced curvature in the Arrhenius plot than in the experimental data.

Ab initio modeling of organophosphorus combustion chemistryElectronic supplementary information (ESI) available: Optimized geometric parameters for transition states. See http://www.rsc.org/suppdata/cp/b4/b402742f/

“…However, at the HF level (HF/6-31G(d 0 )), the highly polar nature of the reaction coordinate, O dÀ -H d1 -O dÀ , causes the magnitude of the imaginary frequency to be unusually large. Similar problems have earlier been observed and discussed for other polar reaction coordinates such as N-H-O (NH 3 þ O reaction), 42 O-H-O (H 2 O þ OH reaction), 43 and CF 3 -H-O (CF 3 þ OH reaction). 44 The evaluation of second derivatives at higher levels of correlation can help to overcome this problem in polar reaction coordinates.…”

“…However, it has been demonstrated in the N-H-O transition state that frequencies obtained at the B3LYP level (1456 cm À1 without scaling) are in good agreement with those at the MP2 (Full) level (1724 cm À1 without scaling) with all electron correlation. 42 Consequently, we optimized the geometry and calculated the frequencies for TS 6 at the B3LYP/CBSB7 level. The B3LYP/CBSB7 O-H bond lengths along the reaction coordinate are included in Fig.…”

Laboratory-Scale Investigation of UV Treatment of Ammonia for Livestock and Poultry Barn Exhaust Applications

“…Regardless of the primary reaction(s) of NH 3 , it is almost certain that the first nitrogenous intermediate is the amino radical, NH 2 (Cohen, 1987; DeMore et al, 1997; Espinosa‐Garcia, 2000; Seinfeld and Pandis, 2006; Tyndall et al, 1991). As with N 2 O formation, the detailed pathways of NH 2 oxidation remain a matter of some debate in the literature (Alfassi, 1998; Inomata and Washida, 1999; Levine, 1985; Seinfeld and Pandis, 2006; Tyndall et al, 1991; Warneck, 2000).…”

Ab initio and kinetic calculations for the reactions of Cl with SiHnCl4−n (n=1,2,3,4)

“…[31][32][33][34] In the present study, the rate constants have been obtained using interpolated CVT state theory method with SCT effect correction. All the kinetic calculations have been carried out using the POLYRATE 9.1 program.…”