Detailed benchmark ab initio mapping of the potential energy surfaces of the X + C₂H₆ [X = F, Cl, Br, I] reactions

Abstract

We provide benchmark relative energies for the stationary points of three different channels of the halogen atom + ethane reactions.

Benchmark ab initio characterization of the abstraction and substitution pathways of the OH + CH4/C2H6 reactions

“…4). For the halogen + C 2 H 6 systems we reported a higher-energy front-side attack MS pathway as well, 14 however, for OH + C 2 H 6 MS FS TS is not found, though its existence cannot be ruled out. Nevertheless, we have found a H 3 CÁ Á ÁCH 3 OH complex in the product channel of MS with D e (D 0 ) values of 0.69(0.38) kcal mol À1 .…”

“…2 shows, MS is slightly exothermic DE(DH 0 ) = À0.94(À2.20) kcal mol À1 and goes over a classical (adiabatic) Walden-inversion barrier of 39.89(39.60) kcal mol À1 height. Thus, similarly to the halogen + C 2 H 6 reactions, 14 MS is both thermodynamically and kinetically favored over HS. At the central MS W TS the O-C-C atoms are nearly collinear and the forming O-C and breaking C-C bonds are stretched by 0.407 and 0.413 Å, respectively, relative to their corresponding equilibrium values in the product and reactant (Fig.…”

“…39 In this study we focus on the high-level ab initio characterization of the PES of the OH + CH 4 /C 2 H 6 reactions providing benchmark structures and energies for the stationary points, thereby complementing our recent work on atom (F, Cl, Br, I) + CH 4 /C 2 H 6 systems. [13][14][15] Several aspects of the present study move beyond the previous work: (1) unlike most of the early work except ref. 38, we use the explicitly correlated CCSD(T)-F12 method 40 to obtain structures, frequencies, and energies; (2) basis sets as large as aug-cc-pV5Z (OH + CH 4 ) and aug-cc-pVQZ (OH + C 2 H 6 ) are employed; (3) post-CCSD(T) correlation effects are considered up to the CCSDT(Q) level of theory; (4) the correlation energy contribution of the core electrons is taken into account; (5) scalar relativistic corrections are determined; and (6) spin-orbit effects are computed.…”

“…Stationary-point search is performed on the basis of previous studies 14,38 and chemical intuition using the second-order Møller-Plesset perturbation theory 41 (MP2) with the aug-cc-pVDZ basis set. 42 The obtained minima and saddle points are further optimized with the explicitly-correlated coupled-cluster singles, doubles, and perturbative triples (CCSD(T)-F12b) method 40 using the aug-cc-pVDZ and aug-cc-pVTZ basis sets.…”

“…Moving beyond the reactions of atoms with alkanes, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] the reactions of the OH radical with methane (CH 4 ) and ethane (C 2 H 6 ) have been thoroughly investigated by theory and experiment to uncover the fundamental rules of polyatomic chemical reactivity. The main product channel of the OH + CH 4 /C 2 H 6 reactions results in H 2 O + CH 3 /C 2 H 5 via hydrogen-abstraction (HA).…”