Ab Initio and RRKM Studies of the Reactions of C, CH, and ¹CH₂ with Acetylene

Abstract

We present ab initio calculations of geometries, energies, and normal mode frequencies for complexes and saddle points along the minimum energy reaction path for the reaction C + HCCH → C3H2 → C3H + H. We also present ab initio calculations along the minimum energy reaction path in the entrance channel for the reactions C + HCCH, CH + HCCH, and 1CH2 + HCCH. These results and those presented earlier by Walch are used to calculate rate constants for the reactions of C, CH, and 1CH2 with acetylene, using variational RRKM theory. The rate constants obtained agree well with experimental results for all three reactions. Unimolecular lifetimes for intermediate complexes associated with each reaction path are also presented. Among the more stable C3 isomers are propargyl and propargylene, which have lifetimes of 25 and 1900 ps, respectively, under thermal reaction conditions.

Accurate quantum mechanical calculation for the N+OH reaction

“…19,20 More recently, such surfaces have been calculated with high-level ab initio methods by Schatz and co-workers for the three lowest energy surfaces 1 AЈ, 3 AЉ, and 1 AЉ of HNO. 21 The quasiclassical trajectory ͑QCT͒ calculations on these PESs agreed satisfactorily with the available experimental data. 22 Up to now, to the best of our knowledge, no accurate quantum mechanical calculations have been performed for the above-given reactions.…”

Accurate time dependent wave packet calculations for the N + OH reaction

“…In this study, the WP calculations using the MADWAVE3 code for the N + OH(v = 0, j = 0) → NO + H reaction have been performed for total angular momentum J ≥ 0, using an ab initio PES built by Guadagnini et al 20 State-to-state ICSs have been obtained for the first time using an accurate quantum mechanical method. The WP results have been compared with QCT calculations.…”

“…The first ab initio potential energy surface (PES) for the N + OH → NO + H reaction was built by Guadagnini et al 20 This PES was based on complete active space self-consistent field (CASSCF)/internally contracted configuration interaction calculation and fitting of the 800 ab initio points obtained at the (multireference configuration interaction) MRCI/cc-pVTZ level. It was found that the N + OH → NO + H reaction has no barrier relative to the entrance channel and a double well along the reaction path, corresponding to HON and HNO configuration geometries.…”

“…It was found that the N + OH → NO + H reaction has no barrier relative to the entrance channel and a double well along the reaction path, corresponding to HON and HNO configuration geometries. It has been shown that, initially, this reaction leads to the formation of a HON complex, 20 bound by 3.07 eV relative to the entrance channel. Because of the open shell character of the reactants, there are several electronic states correlating to the N( 4 S) + OH( 2 ) entrance channel, namely, 3 A , 3 A , 5 A , and 5 A .…”

“…The aim of the present work is to study the state-to-state dynamics of the N + OH→ NO + H reaction at collision energies below 0.5 eV on the PES built by Guadagnini et al 20 Using an accurate quantum WP method, total and product vibrational state-resolved ICSs have been obtained and compared with QCT results. For J = 0, the state-to-state reaction probabilities are also compared with the TIQM calculations.…”