Atahan Sule, Alexander Millard H
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.
J Phys Chem A. 2006 Apr 27;110(16):5436-45. doi: 10.1021/jp055860m.
We report state-to-state cross sections and thermal rate constants for vibrational and rotational relaxation of OH(2pi) by collision with H atoms. The cross sections are calculated by the coupled-states (CS) statistical method including the full open-shell character of the OH + H system. Four potential energy surfaces (PESs) ((1,3)A' and (1,3)A'') describe the interaction of OH(X2pi) with H atoms. Of these, three are repulsive, and one (1A') correlates with the deep H2O well. Consequently, rotationally and ro-vibrationally inelastic scattering of OH in collisions with H can occur by scattering on the repulsive PESs, in a manner similar to the inelastic scattering of OH by noble gas atoms, or by collisions which enter the H2O well and then reemerge. At 300 K, we predict large (approximately 1 x 10(-10) cm3 molecule(-1) s(-1)) vibrational relaxation rates out of both v = 2 and v = 1, comparable to earlier experimental observations. This anomalously fast relaxation results from capture into the H2O complex. There exists a significant propensity toward formation of OH in the pi(A') lambda-doublet level. We also report state-resolved cross sections and rate constants for rotational excitation within the OH v = 0 manifold. Collisional excitation from the F1 to the F2 spin-orbit manifold leads to an inverted lambda-doublet population.
我们报告了OH(2π)与H原子碰撞时振动和转动弛豫的态-态截面及热速率常数。截面通过耦合态（CS）统计方法计算，该方法考虑了OH + H体系的完全开壳层性质。四个势能面（PESs）（(1,3)A'和(1,3)A''）描述了OH(X2π)与H原子的相互作用。其中三个是排斥性的，一个（1A'）与深的H2O阱相关。因此，OH与H碰撞时的转动和振转非弹性散射可以通过在排斥性PESs上的散射发生，其方式类似于OH与稀有气体原子的非弹性散射，或者通过进入H2O阱然后再出射的碰撞发生。在300 K时，我们预测v = 2和v = 1的振动弛豫速率都很大（约1×10⁻¹⁰ cm³ 分子⁻¹ s⁻¹），与早期实验观测结果相当。这种异常快的弛豫是由于捕获到H2O复合物中导致的。存在显著的倾向形成π(A') λ-双重态能级的OH。我们还报告了OH v = 0流形内转动激发的态分辨截面和速率常数。从F1到F2自旋-轨道流形的碰撞激发导致λ-双重态布居反转。
