Park Kisam, Light John C
Department of Chemistry, University of Chicago, Chicago, Illinois 60637, USA.
J Chem Phys. 2007 Jan 28;126(4):044305. doi: 10.1063/1.2430711.
The ortho-para conversion of H(3) (+) and H(2) in the reaction H(3) (+)+H(2)-->(H(5) (+))()-->H(3) (+)+H(2) in interstellar space is possible by scrambling the five protons via (H(5) (+))() complex formation. The product distribution of the ortho-para conversion reaction can be given by ratios of cumulative reaction probabilities (CRP) calculated by microcanonical statistical theory with conservation of energy, motional angular momentum, nuclear spin, and parity. A statistical method to calculate the state-to-state reaction probabilities for given initial nuclear spin species, rotational states, and collision energies is developed using a simple semiclassical approximation of tunneling and above-barrier reflection. A new calculation method of branching ratios for given total nuclear spins and scrambling mechanisms is also developed. The anisotropic long-range electrostatic interaction potential of H(2) in the Coulomb field of H(3) (+) is taken into account using the first-order perturbation theory in forming the complex. The CRPs and the product distribution of the ortho-para conversion reaction at very low energies with reactants in their ground vibronic and lowest rotational states for given initial nuclear spin species are presented as a function of collision energy assuming complete proton scrambling or incomplete proton scrambling. The authors show that the product distribution at very low energies (or very low temperatures) differs substantially from the high energy (or high temperature) limit branching ratios.
在星际空间中，反应H(3) (+)+H(2)-->(H(5) (+))()-->H(3) (+)+H(2) 中H(3) (+)和H(2) 的正 - 仲转换可通过经由(H(5) (+))() 复合物的形成使五个质子发生重排来实现。正 - 仲转换反应的产物分布可以由通过微正则统计理论计算的累积反应概率（CRP）的比率给出，该理论考虑了能量、运动角动量、核自旋和宇称的守恒。利用一种简单的隧穿和势垒上反射的半经典近似，开发了一种计算给定初始核自旋种类、转动状态和碰撞能量下态 - 态反应概率的统计方法。还开发了一种针对给定总核自旋和重排机制的分支比的新计算方法。在形成复合物时，使用一阶微扰理论考虑了H(2) 在H(3) (+)的库仑场中的各向异性长程静电相互作用势。对于给定的初始核自旋种类，给出了在反应物处于基振转和最低转动状态时，极低能量下正 - 仲转换反应的CRP和产物分布作为碰撞能量的函数，假设存在完全质子重排或不完全质子重排。作者表明，极低能量（或极低温度）下的产物分布与高能量（或高温）极限分支比有很大不同。
