Computation-based Science and Technology Research Center, The Cyprus Institute, 20 Konstantinou Kavafi Street, Nicosia 2121, Cyprus.
Laboratoire Univers et Particules de Montpellier, UMR-CNRS 5299, Université de Montpellier, Place Eugène Bataillon, 34095 Montpellier, France.
Phys Chem Chem Phys. 2018 Nov 7;20(41):26752-26763. doi: 10.1039/c8cp05398g. Epub 2018 Oct 16.
The reaction between D and H plays an important role in astrochemistry at low temperatures and also serves as a prototype for a simple ion-molecule reaction. Its ground X[combining tilde]A' state has a very small thermodynamic barrier (up to 1.8 × 10 eV) and the reaction proceeds through the formation of an intermediate complex lying within the potential well with a depth of at least 0.2 eV, thus representing a challenge for dynamical studies. In the present work, we analyze the title reaction within the temperature range of 20-100 K by means of ring polymer molecular dynamics (RPMD) and quasi-classical trajectory (QCT) methods over the full-dimensional global potential energy surface developed by Aguado et al. [A. Aguado, O. Roncero, C. Tablero, C. Sanz and M. Paniagua, J. Chem. Phys., 2000, 112, 1240]. The computed thermal RPMD and QCT rate coefficients are found to be almost independent of temperature and fall within the range of 1.34-2.01 × 10 cm s. They are also in very good agreement with previous time-independent quantum mechanical and statistical quantum method calculations. Furthermore, we observe that the choice of asymptotic separation distance between the reactants can markedly alter the rate coefficient in the low temperature regime (20-50 K). Therefore it is of utmost importance to correctly assign the value of this parameter for dynamical studies, particularly at very low temperatures of astrochemical importance. We finally conclude that the experimental rate measurements for the title reaction are highly desirable in future.
D 和 H 之间的反应在低温下的天体化学中起着重要作用，并且作为简单的离子-分子反应的原型。其基态 X[波浪号]A'态具有非常小的热力学势垒（高达 1.8×10 eV），反应通过形成位于势能阱中的中间复合物进行，该势能阱的深度至少为 0.2 eV，因此对动力学研究构成了挑战。在目前的工作中，我们通过使用环聚合物分子动力学（RPMD）和准经典轨迹（QCT）方法，在 Aguado 等人开发的全维全局势能表面上，在 20-100 K 的温度范围内分析了标题反应。[A. Aguado、O. Roncero、C. Tablero、C. Sanz 和 M. Paniagua，J. Chem. Phys.，2000，112，1240]。计算得到的热 RPMD 和 QCT 速率系数几乎与温度无关，并且落在 1.34-2.01×10 cm s 的范围内。它们也与以前的非时间相关量子力学和统计量子方法计算非常吻合。此外，我们观察到反应物之间的渐近分离距离的选择可以显著改变低温区（20-50 K）的速率系数。因此，对于动力学研究，特别是在天体化学重要的极低温度下，正确指定该参数的值非常重要。我们最后得出结论，未来非常需要对标题反应进行实验速率测量。
