Low temperature reaction dynamics for CH₃OH + OH collisions on a new full dimensional potential energy surface

Abstract

Is the rise of the rate constant measured in laval expansion experiments of OH with organic molecules at low temperatures due to the reaction between reactants or to the formation of complexes with the buffer gas?. This question has importance for understanding the evolution of prebiotic molecules observed in different astrophysical objects. Among these molecules methanol is one of the most widely observed, and its reaction with OH has been measured by several groups showing a fast increase of the rate constant under 100K. Transition state theory doesn’t reproduce this behavior and here dynamical calculations are performed on a new full dimensional potential energy surface developed for this purpose. The calculated classical reactive cross sections show an increase at low collision energies due to a complex forming mechanism. However, the calculated rate constant at temperatures below 100 K remains lower than the observed one. Quantum effects are likely responsible for the measured behavior at low temperatures.

Experimental Studies of Gas-Phase Reactivity in Relation to Complex Organic Molecules in Star-Forming Regions

“…[214][215][216][217] by several different groups. The reaction was first studied at low temperature by the Leeds group, who measured the rate coefficient by OH LIF at 63 K and 80 K. They found the rate coefficient for the reaction between OH and methanol was almost two orders of magnitude larger at…”

Astrochemistry as a Gateway to Teaching and Learning Threshold Concepts in Physical Chemistry

“…Reaction between the hydroxyl radical (OH) and methanol (CH 3 OH), one of the most abundant organic molecules in space, is almost two orders of magnitude larger at 63K than previously measured at ~200K [55,56].…”

Gas phase reaction kinetics of complex organic molecules at temperatures of the interstellar medium: The OH + CH3OH case

“…The same year, a quasi-classical trajectory QCT calculation was published by Roncero et al 2018. As the methods excludes collisions with a third body, their results can be compared to the LPL data obtained by Gao et al Although they found higher rate constants than Gao et al QCT calculations were not able to reproduce the experimental temperature dependence.…”

“…the LPL calculations by Nguyen et al underestimated the experimental values with a significant exception at 10 K for which the agreement was very good. Finally, it is worth mentioning the very recent calculations from del Mazo-Sevillano et al 2019 which are an extension of the initial work by Roncero et al in 2018. The authors used a combination of the Ring Polymer Molecular Dynamics (RPMD) method and TST technique in order to calculate the temperature evolution of the rate constant considering quantum effects.…”

“…All these results have been obtained using CRESU reactors (French acronym for Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in Uniform Supersonic Flows), a well-established technique for the study of gas-phase reaction kinetics at very low temperatures (Potapov et al 2017). From a theoretical point of view the interest for reactions involving COMs has considerably grown recently and several reactions mentioned in Table 1 have been investigated at interstellar temperatures with a special attention paid on OH + CH 3 OH (Shannon et al 2013;Gao et al 2018;Roncero et al 2018;Ocaña et al 2019;Nguyen et al 2019;del Mazo-Sevillano et al 2019) because of its potential importance in the formation of CH 3 O (see next section). In the present paper we will review the recent experimental and theoretical works carried out concerning this reaction and will comment about its significance for the chemistry of molecular clouds.…”