Thermal rate constants and kinetic isotope effects of the H + H2O2 reactions: barrier height and reaction energy from single- and multireference methods

Context One of the more significant sub-mechanisms of H 2 /O 2 combustion involves the reaction of hydrogen peroxide with hydrogen atoms (H + H 2 O 2 ), resulting in the production of OH + H 2 O (R1) and H 2  + HO 2 (R2) paths. Previous experimental and ab initio calculations reveal some variations...

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Published in:Journal of molecular modeling 2024-05, Vol.30 (5), p.147-147, Article 147
Main Authors: Kano, Filipe Gustavo, de Carvalho, Edson Firmino Viana, Ferrão, Luiz Fernando Araújo, Machado, Francisco Bolivar Correto, Roberto-Neto, Orlando
Format: Article
Language:English
Subjects:
Characterization and Evaluation of Materials
Chemistry
Chemistry and Materials Science
Computation
Computer Appl. in Life Sciences
Computer Applications in Chemistry
Hydrogen atoms
Hydrogen peroxide
Mathematical analysis
Molecular Medicine
Original Paper
Potential energy
Rate constants
Statistical analysis
Theoretical and Computational Chemistry
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Summary:Context One of the more significant sub-mechanisms of H 2 /O 2 combustion involves the reaction of hydrogen peroxide with hydrogen atoms (H + H 2 O 2 ), resulting in the production of OH + H 2 O (R1) and H 2  + HO 2 (R2) paths. Previous experimental and ab initio calculations reveal some variations in the barrier height for (R1). To improve the energetics of both (R1) and (R2), single reference and multireference ab initio methods are employed, and the rate constants and H/D kinetic isotope effects (KIEs) are calculated as a function of temperature. For (R1), the best results for the barrier height and reaction energies computed with the CASPT2(15,11)/aug-cc-pV6Z are 5.2 and − 70.3 kcal.mol −1 , respectively. CCSD(T)/aug-cc-pV5Z + CV (core-valence) calculations for (R2) give 9.7 and − 15.6 kcal.mol −1 to those parameters. The CVT/SCT rate constants of both paths agree well with the fitted rate constants from uncertainty-weighted statistical analysis of the 14-mechanism of H 2 /O 2 . The kinetic isotopic effect ( k H / k D ) for the reaction D + H 2 O 2  → DH + HO 2 was found to be 0.47, which is in excellent agreement with the experimental value of 0.43. Methods The structures of reactants, transition state, and products of (R1) and (R2) are calculated with the aug-cc-pVTZ basis set and M062X DFT, CCSD(T), and CASSCF methods. The barrier heights and reaction energies of (R1) and (R2) are computed using the M06-2X, CCSD(T), MRCI, and CASPT2 methods and various basis sets. The rate constants are calculated with the variational transition state theory including multidimensional tunneling corrections (VTST-MT), with potential energy surfaces built by the M06-2X/aug-cc-pVTZ approach.
ISSN:1610-2940
0948-5023
DOI:10.1007/s00894-024-05931-2