Maluendes S A, McLean A D, Herbst E
Molecular Research Institute, Palo Alto, CA 94304, USA.
Astrophys J. 1992 Oct 1;397(2):477-81. doi: 10.1086/171804.
Gas-phase chemical models of deuterium fractionation in dense interstellar clouds utilize a small number of exothermic reactions to achieve fractionation. Although HD is a major repository of deuterium, it appears not to exchange deuterium with many molecular ions. Useful semiquantitative reasons have been given for the unusual lack of reactivity of exothermic ion-HD deuterium exchange systems, but quantum chemical studies are needed to understand these ideas in more detail and to determine if the lack of reactivity pertains at very low temperatures not studied in the laboratory, or whether tunneling can drive the reactions. Accordingly, the potential energy surfaces of three representative ion-molecule exchange reactions involving protonated ions (H3+, CH3+, HCO+) and HD have been investigated with ab initio quantum chemical techniques. Our results generally confirm the semiquantitative picture as to which reactions are likely to occur and show that tunneling at low temperatures is unlikely to alter this picture.
致密星际云中氘分馏的气相化学模型利用少量放热反应来实现分馏。虽然HD是氘的主要储存库，但它似乎不会与许多分子离子进行氘交换。对于放热离子-HD氘交换系统异常缺乏反应性，已经给出了有用的半定量解释，但需要进行量子化学研究以更详细地理解这些观点，并确定这种反应性的缺乏是否适用于实验室未研究的极低温度，或者隧道效应是否能驱动反应。因此，我们使用从头算量子化学技术研究了涉及质子化离子（H3+、CH3+、HCO+）和HD的三个代表性离子-分子交换反应的势能面。我们的结果总体上证实了关于哪些反应可能发生的半定量情况，并表明低温下的隧道效应不太可能改变这一情况。
