Theoretical analysis of reaction kinetics with singlet oxygen molecules

Abstract

A comparative analysis of predictive ability of three approaches to estimate the rate constants of reactions of H(2), H, H(2)O and CH(4) with electronically excited O(2)(a(1)Δ(g)) and O(2)(b(1)Σ(g)(+)) molecules is conducted. The first approach is based on a detailed ab initio study of potential energy surfaces. The second one is known as the "bond energy-bond order" method, and the third approach is a modification of the updated method of vibronic terms that makes it possible to evaluate the activation energy of reactions involving electronically excited species. The comparison showed that the estimates of the energy barrier by the updated method of vibronic terms for some reactions can be in good agreement with ab initio calculations and available experimental data. It was revealed that reactions of O(2)(b(1)Σ(g)(+)) molecules with H(2), H(2)O and CH(4) molecules and with the H atom result in the formation of electronically excited species. The reactivity of O(2)(b(1)Σ(g)(+)) molecules is smaller than that of O(2)(a(1)Δ(g)) ones, but much higher as compared to the reactivity of ground state O(2) molecules. For each reaction under study involving oxygen molecules in the excited electronic states O(2)(a(1)Δ(g)) and O(2)(b(1)Σ(g)(+)) the recommended temperature-dependent rate constants are presented.

Physics and chemistry of the influence of excited molecules on combustion enhancement

“…As was revealed on the basis of ab initio calculations [7,39,40], the principal chain-initiation reaction in the H 2 −O 2 mixture is the reaction…”

“…was also estimated in [27] using the modified model of vibronic terms (MMVT) approach [7]. It turned out that the value of k (3.16) was only somewhat greater than the value of k (3.13) .…”

“…Interest in this problem is due to the fact that both vibrationally and electronically excited molecules react much faster than non-excited ones. Theoretical [4][5][6][7][8][9] and experimental [10][11][12][13][14] studies showed that the rate constants of reactions with excited molecules can be by a factor 10 2 -10 4 higher than those with ground state molecules. Both vibrationally and electronically excited molecules can be produced with rather high efficiency in tailored electric discharge [2, [15][16][17].…”

“…[41,42]) describe a large set of experimental data with rather high accuracy. carriers of the chain mechanism [7]: Recent theoretical studies based on accurate ab initio calculations [7,9,43] showed that the rate constants of reactions with SDO were much higher than those with ground state oxygen. Shown in figure 4 is the comparison of temperature-dependent rate constants for analogous reactions of chain initiation (processes (3.1) and (3.7); figure 4a) and chain-branching (processes (3.3) and One can see that at a relatively low temperature, T = 1100 K, the rate constant of reaction (3.7) is by a factor of 3 × 10 4 greater than that for process (3.1).…”

“…The excited intermediate complex HO 2 (A ) * can be stabilized with the third body M, and, as a result, the relatively stable HO 2 (A ) molecule can form in the course of reaction (3.11). The rate constant of this reaction was estimated in [7] using the RiceRamsperger-Kassel theory. It was shown that the total rate constant k tot = k (3.9) + k (3.12) was pressure-dependent; however, such a dependence becomes notable only at pressure p ≥ 100 atm.…”