Quéméner Goulven, Balakrishnan Naduvalath
Department of Chemistry, University of Nevada Las Vegas, Las Vegas, Nevada 89154, USA.
J Chem Phys. 2008 Jun 14;128(22):224304. doi: 10.1063/1.2928804.
We report quantum dynamics calculations of F((2)P)+HCl(v,j)-->HF(v('),j('))+Cl((2)P) and F+DCl(v,j)-->DF(v('),j('))+Cl reactions at cold and ultracold temperatures. The effect of rotational and vibrational excitations of the HCl molecule on the reactivity is investigated. It is found that, in the ultracold regime, vibrational excitation of the HCl molecule from v=0 to v=2 enhances the reactivity by four orders of magnitude. The rotational excitation from j=0 to j=1 decreases the reactivity while the rotational excitation from j=0 to j=2 increases the reactivity. The overall effect of rotational excitation was found to be much smaller than vibrational excitation. The reactivity of the F+DCl system is significantly lower than that of the F+HCl case indicating the importance of quantum tunneling at low energies. For both reactions, Feshbach resonances corresponding to Fcdots, three dots, centered HCl or Fcdots, three dots, centeredDCl triatomic states occur at low energies. We also explored the validity of the coupled-states approximation for cold collisions taking the F+HCl(v=0,j=0) reaction as an illustrative example. It is found that the coupled-states approximation is generally valid for the background scattering even at low energies but it is inadequate to accurately describe the rich resonances in the energy dependence of the cross section resulting from the decay of van der Waals complexes. It is further shown that the coupled-states approximation cannot be used for scattering in the Wigner threshold regime when the molecule is initially in a rotationally excited level.
我们报告了在低温和超低温下对F((2)P)+HCl(v,j)-->HF(v('),j('))+Cl((2)P)以及F+DCl(v,j)-->DF(v('),j('))+Cl反应的量子动力学计算。研究了HCl分子的转动和振动激发对反应性的影响。发现在超低温条件下，HCl分子从v = 0振动激发到v = 2会使反应性提高四个数量级。从j = 0到j = 1的转动激发会降低反应性，而从j = 0到j = 2的转动激发会增加反应性。发现转动激发的总体影响远小于振动激发。F+DCl体系的反应性明显低于F+HCl体系，这表明低能下量子隧穿的重要性。对于这两个反应，对应于以HCl或DCl为中心的F···三原子态的费什巴赫共振在低能时出现。我们还以F+HCl(v = 0,j = 0)反应为例，探讨了冷碰撞的耦合态近似的有效性。发现耦合态近似对于背景散射通常是有效的，即使在低能情况下，但它不足以准确描述由范德瓦尔斯复合物衰变导致的截面能量依赖性中的丰富共振。进一步表明，当分子最初处于转动激发能级时，耦合态近似不能用于维格纳阈值区域的散射。
