Comparison of Three Isoelectronic Multiple-Well Reaction Systems: OH + CH₂O, OH + CH₂CH₂, and OH + CH₂NH

Abstract

Methylenimine (CH2NH) has been predicted to be a product of the atmospheric photo-oxidation of methylamine, but its atmospheric reactions have not been measured. In this paper, we report potential energy surfaces (PESs) and rate constants for OH + CH2NH and its isoelectronic analogues OH + CH2O and OH + CH2CH2, which are more fully understood. The PESs were computed using the BHandHLYP/aug-cc-pVTZ and CCSD(T)/aug-cc-pVTZ levels of theory. Canonical variational transition state theory and Rice-Ramsperger-Kassel-Marcus and master equation modeling were used to calculate temperature- and pressure-dependent rate constants, with particular emphasis on the OH + reactant entrance channels and the effects of prereactive complexes. The computed results are in reasonable agreement with experimental data where they can be compared and also with the results of previous theoretical calculations. The results show that to some extent OH radicals both add to the carbon center double bond in CH2NH and abstract methylene hydrogen atoms, as in the OH + CH2O and OH + CH2CH2 reactions, respectively, but the dominant pathway is abstraction of the hydrogen from N-H. The computed rate constants are suitable for both atmospheric and combustion modeling.

State-of-the-Art Thermochemical and Kinetic Computations for Astrochemical Complex Organic Molecules: Formamide Formation in Cold Interstellar Clouds as a Case Study

“…If we add zero-point corrections, this complex is found to be more stable than the precursors by 22.2 kJ/mol. In the paper by Akbar Ali et al18, CCSD(T)/aug-cc-pVTZ calculations gave a ZPE-corrected relative energy of -19.8 kJ/mol for this compound. Two transition states, TS0 a or TS0 b , with relative electronic energies of -4.5 and -4.1 kJ/mol (5.0 and -3.3 with ZPE corrections here, 2.8 and -2.8 in Ref 18), respectively, can follow this first step and govern hydrogen abstraction and addition of OH to the π bond of methanimine, leading to the intermediates RI1 ( RI1z or RI1e ) and to H 2 CN + H 2 O, respectively.…”

“…In the paper by Akbar Ali and coworwers ,18 optimized geometries of several compounds at both the BHandHLYP/aug-cc-pVTZ and CCSD(T)/aug-cc-pVTZ levels of theory have been reported. Thanks to these data, a validation of our B2PLYP-D3/m-aug-cc-pVTZ geometries is possible.…”

Bimolecular recombination reactions: K-adiabatic and K-active forms of the bimolecular master equations and analytic solutions

“…7,10 In so revealing features of the kinetics, in such situations, tracing the evolution of the time dependence of the populations may be important. In the context of unimolecular theory, 1-3 the two typical approaches to this problem are the lowest-eigenvalue matrix approach 1,[7][8][9][10] and the stochastic approach, 6,[11][12][13][14] introduced earlier in this section. In the present paper, recurrence relations [43][44][45] are also given for the time dependent populations of the K-active and K-adiabatic master equation cases, for single and multiple well and reaction channels.…”

“…6 In the atmosphere or in other chemical systems, the buffer gas may react with the vibrationally excited species, as well as deactivate it, and such processes may also be investigated by master equations. 6 The usual treatments of master equations for studying a unimolecular or bimolecular process utilize either an eigenvalue method 1,[7][8][9][10] or a stochastic based approach, 6,[11][12][13][14] for obtaining a unimolecular dissociation rate constant k uni or bimolecular recombination rate constant k rec using detailed balance. Presently, both methods are available for the K-active case, where K is the component of the total angular momentum along the axis of least moment of inertia of the recombination product.…”

Quantum chemical and master equation study of OH + CH2O → H2O + CHO reaction rates in supercritical CO2 environment

“…reported potential energy surface with a barrier of 5.3 kcal/mol for R1 at the MP4(SDTQ)/6‐311++G(3df,3pd) theory level. Akbar Ali and Barker reported a potential energy surface for the R1 reaction using CCSD(T)/aug‐cc‐pVTZ//CCSD(T)/aug‐cc‐pVTZ theory level and found an activation barrier of 3.5 kcal/mol. They also carried out rate calculations at the temperature interval of 200–400 K using canonical transition state theory with Eckart asymmetric tunneling corrections.…”