Mrugała Felicja, Kraemer Wolfgang P
Institute of Physics, Nicolaus Copernicus University, Grudziadzka 5, PL 87-100 Torun, Poland.
J Chem Phys. 2005 Jun 8;122(22):224321. doi: 10.1063/1.1924453.
The paper presents a theoretical study of the low-energy dynamics of radiative association processes in the He+ + H2 collision system. Formation of the triatomic HeH2(+) ion in its bound rotation-vibration states on the potential-energy surfaces of the ground and of the first excited electronic states is investigated. Close-coupling calculations are performed to determine detailed state-to-state characteristics (bound <-- free transition rates, radiative and dissociative widths of resonances) as well as temperature-average characteristics (rate constants, photon emission spectra) of the two-state (X <-- A) reaction He+(2S) + H2(X1sigma(g)+) --> HeH2(+)(X2A') + h nu and of the single-state (A <-- A) reaction He+(2S) + H2(X1sigma(g)+) --> HeH2(+)(A2A') + h nu. The potential-energy surfaces of the X- and A-electronic states of HeH2(+) and the dipole moment surfaces determined ab initio in an earlier work [Kraemer, Spirko, and Bludsky, Chem. Phys. 276, 225 (2002)] are used in the calculations. The rate constants k(T) as functions of temperature are calculated for the temperature interval 1 < or = T < or = 100 K. The maximum k(T) values are predicted as 3.3 x 10(-15) s(-1) cm3 for the X <-- A reaction and 2.3 x 10(-20) s(-1) cm3 for the A <-- A reaction at temperatures around 2 K. Rotationally predissociating states of the He+-H2 complex, correlating with the upsilon = 0, j = 2 state of free H2, are found to play a crucial role in the dynamics of the association reactions at low temperatures; their contribution to the k(T) function of the X <-- A reaction at T < 30 K is estimated as larger than 80%. The calculated partial rate constants and emission spectra show that in the X <-- A reaction the HeH2(+)(X) ion is formed in its highly excited vibrational states. This is in contrast with the vibrational state population of the ion when formed via the (X <-- X) reaction He(1S) + H2(+)(X2sigma(g)+) --> HeH2(+)(X2A') + h nu.
本文对He⁺ + H₂碰撞体系中辐射缔合过程的低能动力学进行了理论研究。研究了在基态和第一激发电子态势能面上三原子HeH₂⁺离子在其束缚转动 - 振动态的形成。进行了密耦计算，以确定双态（X ← A）反应He⁺(²S) + H₂(X¹σg⁺) → HeH₂⁺(X²A') + hν和单态（A ← A）反应He⁺(²S) + H₂(X¹σg⁺) → HeH₂⁺(A²A') + hν的详细态 - 态特征（束缚←自由跃迁速率、共振的辐射和离解宽度）以及温度平均特征（速率常数、光子发射光谱）。计算中使用了HeH₂⁺的X和A电子态的势能面以及在早期工作[Kraemer, Spirko, and Bludsky, Chem. Phys. 276, 225 (2002)]中从头算确定的偶极矩面。计算了温度区间1 ≤ T ≤ 100 K内速率常数k(T)随温度的变化。预测在约2 K的温度下，X ← A反应的最大k(T)值为3.3×10⁻¹⁵ s⁻¹ cm³，A ← A反应的最大k(T)值为2.3×10⁻²⁰ s⁻¹ cm³。发现与自由H₂的υ = 0，j = 2态相关的He⁺ - H₂复合物的转动预解离态在低温缔合反应动力学中起关键作用；在T < 30 K时，它们对X ← A反应的k(T)函数的贡献估计大于80%。计算得到的部分速率常数和发射光谱表明，在X ← A反应中，HeH₂⁺(X)离子是在其高激发振动态形成的。这与通过（X ← X）反应He(¹S) + H₂⁺(X²σg⁺) → HeH₂⁺(X²A') + hν形成离子时的振动态布居情况相反。
