Rotational Mode-Specificity in the Cl + C₂H₆ → HCl + C₂H₅ Reaction

Abstract

We perform rotational mode-specific quasi-classical trajectory simulations using a high-quality ab initio analytical potential energy surface for the Cl( 2 P 3/2 ) + C 2 H 6 → HCl + C 2 H 5 reaction. As ethane, being a prolate-type symmetric top, can be characterized by the J and K rotational quantum numbers, the excitation of two rotational modes, the tumbling ( J , K = 0) and spinning ( J , K = J ) rotations of the reactant is carried out with J = 10, 20, 30, and 40 at a wide range of collision energies. The impacts of rotational excitation on the reactivity, the mechanism, and the post-reaction distribution of energy are investigated: (1) exciting both rotational modes enhances the reactivity with the spinning rotation being more effective due to its coupling to the C–H stretching vibrational normal modes (C–H bond elongating effect) and larger rotational energies, (2) rotational excitation increases the dominance of direct rebound over the stripping mechanism, while collision energy favors the latter, (3) investing energy in tumbling rotation excites the translational motion of the products, while the excess spinning rotational energy readily flows into the internal degrees of freedom of the ethyl radical or, less significantly, into the HCl vibration, probably due to the pronounced rovibrational coupling in this case. We also study the relative efficiency of vibrational and rotational excitation on the reactivity of the barrierless and thus translationally hindered title reaction.

Automated full-dimensional potential energy surface development and quasi-classical dynamics for the HI(X1Σ+) + C2H5 → I(2P3/2) + C2H6 reaction

“…This work is a continuation of our previous studies on the analytical PES developments for the reactions HX + C 2 H 5 2 X + C 2 H 6 (X = F, 30,31 Cl, [32][33][34] ). In the present work we have developed a full-dimensional spin-orbit-corrected PES for the HI + C 2 H 5 -I + C 2 H 6 reaction using the ROBOSURFER program package and the MSA of the permutationally invariant polynomial method for fitting the ab initio energy points, and the dynamics of the title reaction were studied in detail by performing QCT simulations.…”

“…As a class of elementary reactions, atom transfer or metathesis reactions of HX + C 2 H 5 ↔ X + C 2 H 6 (X = F, Cl, Br, I) have become benchmark systems to study the dynamics and mechanisms of post-six-atom polyatomic chemical reactions. These exothermic reactions have attracted a lot of attention from both experiment and theory for the forward processes (X = Br, I) 1–9 and backward processes (X = F, Cl), 10–34 whose activation energies have been found to have small positive or negative values. 35…”

“…33 Later, the impacts of rotational excitation on the reactivity, mechanism, and post-reaction distribution of energy of Cl + C 2 H 6 were also investigated. 34 A full-dimensional spin–orbit-corrected analytical PES for the HBr + C 2 H 5 reaction and a quasi-classical dynamics study on the new PES were reported very recently. 9…”

“…33 Later, the impacts of rotational excitation on the reactivity, mechanism, and post-reaction distribution of energy of Cl + C 2 H 6 were also investigated. 34 A full-dimensional spin-orbit-corrected analytical PES for the HBr + C 2 H 5 reaction and a quasi-classical dynamics study on the new PES were reported very recently. 9 Investigations of the HI + C 2 H 5 -I + C 2 H 6 reaction began with the measurement of rate constants as a function of temperature to determine the Arrhenius parameters in a tubular reactor coupled to a photoionization mass spectrometer.…”

Stretching-mode specificity in the Cl + CH3D(v1-I, v1-II, and v4 = 1; |jK〉) reactions: dependency on the initial |jK〉 selectivity

“…[19][20][21][22] Several theoretical studies have also addressed the rotational-mode specificity in a few polyatomic reactions. 15,[23][24][25][26][27][28][29][30][31][32][33][34] Depending on the system, the rotational excitation of the reagent can either promote or hinder the overall reactivity. Even the type of the rotational motion matters, for instance, the spinning (K = AEj) or the tumbling (K = 0) motion.…”