Full-dimensional automated potential energy surface development and dynamics for the OH + C2H6 reaction

Abstract

We develop a full-dimensional analytical potential energy surface (PES) for the OH + C2H6 reaction using the Robosurfer program system, which automatically (1) selects geometries from quasi-classical trajectories, (2) performs ab initio computations using a CCSD(T)-F12/triple-zeta-quality composite method, (3) fits the energies utilizing the permutationally-invariant monomial symmetrization approach, and iteratively improves the PES via steps (1)−(3). Quasi-classical trajectory simulations on the new PES reveal that hydrogen abstraction leading to H2O + C2H5 dominates in the collision energy range of 10−50 kcal/mol. The abstraction cross sections increase and the dominant mechanism shifts from rebound (small impact parameters and backward scattering) to stripping (larger impact parameters and forward scattering) with increasing collision energy as opacity functions and scattering angle distributions indicate. The abstraction reaction clearly favors side-on OH attack over O-side and the least-preferred H-side approach, whereas C2H6 behaves like a spherical object with only slight C−C-perpendicular side-on preference. Collision energy efficiently flows into the relative translation of the products, whereas product internal energy distributions show only little collision energy dependence. H2O/C2H5 vibrational distributions slightly/significantly violate zero-point energy and are nearly independent of collision energy, whereas the rotational distributions clearly blue-shift as collision energy increases.

Vibrational Mode-Specific Dynamics of the OH + C2H6 Reaction

“…Excitation of the CH stretching modes (ν 1 , ν 5 , and ν 7 ) clearly increases the reaction probabilities, again in accordance with the ICSs. As we have recently discussed in our previous work, the scattering angle distributions are connected to the shape of these opacity functions. At the lowest collision energy, the probabilities show a monotonic decrease with increasing impact parameter until approximately b = 4 and then the curves rapidly drop off.…”

“…In the same year, we also started to investigate the title reaction using high-level ab initio methods such as CCSD­(T)-F12b, CCSDT­(Q), and MRCI showing that, besides the H 2 O + C 2 H 5 channel, hydrogen- and methyl-substitution can also occur at higher collision energies resulting in the H + C 2 H 5 OH and CH 3 + CH 3 OH products, respectively . Based on the benchmark ab initio characterization of the stationary points of the multichannel OH + C 2 H 6 reaction, in 2022 we developed a full-dimensional coupled-cluster-quality analytical PES, which allowed efficient dynamics investigations using the quasi-classical trajectory (QCT) method . The dynamics simulations for the ground-state OH­(ν = 0) + C 2 H 6 (ν = 0) reaction showed that the reactivity of the hydrogen- and methyl-substitution channels is negligible besides hydrogen abstraction in the collision energy range of 10–50 kcal/mol.…”

“…The dynamics simulations for the ground-state OH­(ν = 0) + C 2 H 6 (ν = 0) reaction showed that the reactivity of the hydrogen- and methyl-substitution channels is negligible besides hydrogen abstraction in the collision energy range of 10–50 kcal/mol. Following our previous work, here we perform mode-specific dynamics simulations for the OH + C 2 H 6 → H 2 O + C 2 H 5 reaction utilizing our analytical ab initio PES and the QCT method. The dynamics results obtained for different excited initial vibrational states at various collision energies provide new insights into the validity of the Polanyi rules for a reactive system with 24 vibrational degrees of freedom.…”

Crossed-Beam Imaging of the Reaction of OH with Propanol Isomers

“…Those for the 1-propanol reaction, in which we detect abstraction at both α- and β-sites, are much more broadly scattered. Recently, Czakó and co-workers have reported a classical trajectory study of the OH + ethane reaction over a broad collision energy range . They also reported large vibrational excitation in the H 2 O product, and a shift from rebound dynamics to stripping dynamics as the collision energy is increased from 10 to 50 kcal mol –1 .…”

Direct and steady state rate constants of C2H6 + X (X = H, Cl, OH): influence of the van der Waals well

“…Apart from methane, ethane is the most commonly adopted hydrocarbon, and numerous studies have been performed involving various reactions, such as C( 1 D) + C 2 H 6 , 9 C 2 H + C 2 H 6 , 10 N( 2 D) + C 2 H 6 , 11 Mu + C 2 H 6 , 12 C 4 H + C 2 H 6 , 13 H + C 2 H 6 , 14 F + C 2 H 6 , 15,16 Cl + C 2 H 6 , 17,18 Br + C 2 H 6 , 19 I + C2H6, 20 O + C 2 H 6 , 21 and OH + C 2 H 6 . 22,23 In particular, most of these reactions possess van der Waals wells in the reactant and product valleys, and the depth of the wells varies with the reactions. [24][25][26][27] Considering that the depth the of van der Waals well may have a critical impact on the reaction rate constant, three different reactions (i.e.…”