Full-dimensional MRCI-F12 potential energy surface and dynamics of the F(2P3/2) + C2H6 → HF + C2H5 reaction

Abstract

We report a detailed quasi-classical dynamics study on a new full-dimensional multireference spin-orbit-corrected potential energy surface (PES) for the F( 2 P3/2) + C2H6 → HF + C2H5 reaction. For the PES development the ROBOSURFER program package is applied and the MRCI-F12+Q(5,3)/aug-cc-pVDZ energy points are fitted using the monomial symmetrization approach of the permutationally invariant polynomial method. Our simulations provide substantial reaction probabilities and sharply increasing cross sections with increasing collision energy for this early-and negative-barrier reaction. Direct rebound/stripping mechanism is preferred at low/high collision energies, and the initial translational energy turns out to convert mostly into product recoil, whereas the reaction energy excites the HF vibration. Vibrational and vibrationally-resolved rotational state distributions of the HF product obtained from our computations agree well with single-collision experimental data for the vHF = 1, 2, 3 states.

First-Principles Reaction Dynamics beyond Six-Atom Systems

“…In the present Perspective we discuss how to extend the accurate first-principles full-dimensional methodologies applied successfully for six-atom systems toward larger 7–10-atom reactions. This post-six-atom age of accurate full-dimensional PES-based reaction dynamics has just recently started with the investigations of the O + C 2 H 4 , OH + CH 4 , H/F/Cl/OH + CH 3 OH, − F/Cl/O/OH + C 2 H 6 , − OH – + CH 3 I, and F – (H 2 O) + CH 3 I reactions. Furthermore, using empirical valence bond PESs the dynamics of the Cl + C 3 H 6 /C 5 H 12 reactions was also investigated. , Besides the bimolecular reactions, we should also note the pioneering work of Bowman and co-workers on CH 3 CHO photodissociation and their recent advances on efficient PES developments for many-atom systems such as CH 3 NHCOCH 3 ( N -methylacetamide) and NH 2 CH 2 COOH (glycine) .…”

“…In our group we work on all three steps of the reaction dynamics studies and in sections and we give some details about the techniques used emphasizing our efficient composite approaches toward computing accurate potential energies and our software development efforts toward reducing the amount of human labor required for constructing the fitting sets for larger, high-complexity systems. Then in section we focus on three reactions involving 7 and 9 atoms for which we developed full-dimensional ab initio PESs in 2020. ,, The three systems represent different challenges during the PES developments from the electronic structure point of view. Cl + C 2 H 6 is a less complicated case, for F + C 2 H 6 the Hartree–Fock method fails in the entrance channel, and OH – + CH 3 I suffers from a serious breakdown of the gold-standard CCSD­(T) method .…”

Benchmark ab initio stationary-point characterization of the complex potential energy surface of the multi-channel Cl + CH3NH2 reaction

“…Reactions of atoms such as H, F, and Cl with molecules from H 2 via H 2 O, NH 3 , and CH 4 to C 2 H 6 have attracted significant scientific attention from the 1970s to the present day. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Moving beyond these systems that have only equivalent H atoms, one may consider molecules with two different functional groups, thereby opening multiple hydrogen-abstraction reaction pathways. One possibility is to study the reactions of methanol (CH 3 OH), which combines the functional groups of H 2 O and CH 4 .…”

Current Status of the X + C2H6 [X ≡ H, F(2P), Cl(2P), O(3P), OH] Hydrogen Abstraction Reactions: A Theoretical Review

“…However, (i) these methods present a high computational demand because a huge amount of high-level electronic structure calculations is necessary to describe the whole reactive system, today ~100,000 points; (ii) in addition, the points calculated for a given reactive system cannot be used for another reaction, and therefore independent sets of points need to be calculated for each particular reaction, and finally, (iii) the absence of unphysical anomalies in areas far from the sampled regions cannot be ruled out. By using MO-based surfaces, in the last fourto-five years and parallel with our research, Czako et al [57][58][59][60][61][62][63][64] performed an impressive work analyzing reactions with ethane, X + C 2 H 6 → HX + C 2 H 5 ; X ≡ F( 2 P), Cl( 2 P), Br( 2 P), I( 2 P) and OH. These authors performed benchmark calculations at very sophisticated ab initio levels to develop full-dimensional potential energy surfaces and from them to characterize stationary points and calculate dynamics properties.…”

“…only suggest that the v = 0 state is the mainly populated. d Theoretical results using QCT calculations on a MO-based surface from Ref [61]…”