Gustafsson Magnus, Monge-Palacios M, Nyman Gunnar
Department of Chemistry and Molecular Biology, University of Gothenburg, 41296 Gothenburg, Sweden.
J Chem Phys. 2014 May 14;140(18):184301. doi: 10.1063/1.4874271.
Radiative association for the formation of hydrogen fluoride through the A(1)Π → X(1)Σ(+) and X(1)Σ(+) → X(1)Σ(+) transitions is studied using quantum and classical dynamics. The total thermal rate constant is obtained for temperatures from 10 K to 20,000 K. Agreement between semiclassical and quantum approaches is observed for the A(1)Π → X(1)Σ(+) rate constant above 2000 K. The agreement is explained by the fact that the corresponding cross section is free of resonances for this system. At temperatures below 2000 K we improve the agreement by implementing a simplified semiclassical expression for the rate constant, which includes a quantum corrected pair distribution. The rate coefficient for the X(1)Σ(+) → X(1)Σ(+) transition is calculated using Breit-Wigner theory and a classical formula for the resonance and direct contributions, respectively. In comparison with quantum calculations the classical formula appears to overestimate the direct contribution to the rate constant by about 12% for this transition. Below about 450 K the resonance contribution is larger than the direct, and above that temperature the opposite holds. The biggest contribution from resonances is at the lowest temperature in the study, 10 K, where it is more than four times larger than the direct. Below 1800 K the radiative association rate constant due to X(1)Σ(+) → X(1)Σ(+) transitions dominates over A(1)Π → X(1)Σ(+), while above that temperature the situation is the opposite.
利用量子动力学和经典动力学研究了通过A(1)Π→X(1)Σ(+)和X(1)Σ(+)→X(1)Σ(+)跃迁形成氟化氢的辐射缔合过程。得到了10 K至20000 K温度范围内的总热速率常数。在2000 K以上，半经典方法和量子方法得到的A(1)Π→X(1)Σ(+)速率常数吻合。这种吻合是由于该系统相应的截面没有共振。在2000 K以下的温度，我们通过采用速率常数的简化半经典表达式（其中包括量子修正的对分布）来改善吻合度。X(1)Σ(+)→X(1)Σ(+)跃迁的速率系数分别使用布赖特 - 维格纳理论和共振及直接贡献的经典公式进行计算。与量子计算相比，对于该跃迁，经典公式似乎高估了速率常数的直接贡献约12%。在约450 K以下，共振贡献大于直接贡献，高于该温度则相反。共振的最大贡献出现在研究中的最低温度10 K，此时它比直接贡献大四倍多。在1800 K以下，由X(1)Σ(+)→X(1)Σ(+)跃迁引起的辐射缔合速率常数占主导地位，高于该温度则相反。
