Comprehensive Theoretical Study on Four Typical Intramolecular Hydrogen Shift Reactions of Peroxy Radicals: Multireference Character, Recommended Model Chemistry, and Kinetics

作者：Li, Yan; Wang, Ying; Zhang, Rui Ming; He, Xiao^*; Xu, Xuefei^*

来源：Journal of Chemical Theory and Computation, 2023, 19(11): 3284-3302.

DOI：10.1021/acs.jctc.3c00033

• COMPLETE BASIS-SET
• DENSITY-FUNCTIONAL THEORY
• GENERALIZED GRADIENT APPROXIMATION
• CORRELATED MOLECULAR CALCULATIONS
• MAIN-GROUP THERMOCHEMISTRY
• SEMICONDUCTOR BAND-GAPS
• GAUSSIAN-BASIS SETS
• PRESSURE RATE RULES
• NONCOVALENT INTERACTIONS
• ATMOSPHERIC OXIDATION

Intramolecular hydrogen shift reactions in peroxy radicals(RO2 (center dot) -> (center dot)QOOH)playkey roles in the low-temperature combustion and in the atmosphericchemistry. In the present study, we found that a mild-to-moderatemultireference character of a potential energy surface (PES) is widelypresent in four typical hydrogen shift reactions of peroxy radicals(RO2 (center dot), R = ethyl, vinyl, formyl methyl,and acetyl) by a systematic assessment based on the T (1) diagnostic, %TAE diagnostic, M diagnostic,and contribution of the dominant configuration of the reference CASSCFwaveC (0) (2)). To assessthe effects of these inherent multireference characters on electronicstructure calculations, we compared the PESs of the four reactionscalculated by the multireference method CASPT2 in the complete basisset (CBS) limit, single-reference method CCSD-(T)-F12, and single-reference-basedcomposite method WMS. The results showed that ignoring the multireferencecharacter will introduce a mean unsigned deviation (MUD) of 0.46-1.72kcal/mol from CASPT2/CBS results by using the CCSD-(T)-F12 method ora MUD of 0.49-1.37 kcal/mol by WMS for three RO2 (center dot) reactions (R = vinyl, formyl methyl, and acetyl)with a stronger multireference character. Further tests by single-referenceKohn-Sham (KS) density functional theory methods showed evenlarger deviations. Therefore, we specifically developed a new hybridmeta-generalized gradient approximation (GGA) functional M06-HS forthe four typical H-shift reactions of peroxy radicals based on theWMS results for the ethyl peroxy radical reaction and on the CASPT2/CBSresults for the others. The M06-HS method has an averaged MUD of 0.34kcal/mol over five tested basis sets against the benchmark PESs, performingbest in the tested 38 KS functionals. Last, in a temperature rangeof 200-3000 K, with the new functional, we calculated the high-pressure-limitrate coefficients of these H-shift reactions by the multi-structuralvariational transition-state theory with the small-curvature tunnelingapproximation (MS-CVT/SCT) and the thermochemical properties of allof the involved key radicals by the multi-structural torsional (MS-T)anharmonicity approximation method.

• 单位
  清华大学