Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
J Phys Chem A. 2010 Oct 28;114(42):11109-16. doi: 10.1021/jp102334t.
Rotational relaxation rates for HBr(v = 1) colliding with helium atoms at room temperature have been measured using a time-resolved optical-optical double resonance technique. Rotational state selective excitation of v = 1 for rotational levels in the range J = 1-9 was achieved by stimulated Raman pumping. The population decay in the prepared states and the transfer of population to nearby rotational states was monitored via 2 + 1 resonance-enhanced multiphoton ionization (REMPI) spectroscopy using the g(3)Σ(-)-X(1)Σ(+) (0-1) band. Collision-induced population evolution for transfer events with |ΔJ| ≤ 8 was observed at pressures near 0.7 Torr. The experimental data were analyzed using fitting and scaling functions to generate state-to-state rotational energy transfer rate constant matrices. Total depopulation rate constants were found to be in the range (1.3 to 2.0) × 10(-10) cm(3) s(-1). As a test of current computational methods, state-to-state rotational energy transfer rate constants were calculated using ab initio theory. The total removal rate constants were in good agreement with the measured values, but the transfer probabilities for events with |ΔJ| ≥ 3 were underestimated. Inspection of the anisotropic characteristics of the potential energy surface did not yield an obvious explanation for the discrepancies, but it is most likely that the problem stems from inaccuracies in the potential surface.
室温下 HBr(v=1)与氦原子碰撞的转动弛豫速率已使用时间分辨光-光双共振技术进行了测量。通过受激拉曼泵送，实现了 v=1 的转动态选择性激发，激发范围为 J=1-9 的转动能级。通过 2 + 1 共振增强多光子电离 (REMPI) 光谱，在制备态中的粒子数衰减和向附近转动态的粒子数转移被监测，该光谱使用 g(3)Σ(-)-X(1)Σ(+) (0-1) 带。在接近 0.7 托的压力下，观察到 |ΔJ| ≤ 8 的转移事件引起的碰撞诱导粒子数演化。使用拟合和缩放函数分析实验数据，生成状态到状态的转动能量转移率常数矩阵。总去活率常数在 (1.3 到 2.0) × 10(-10) cm(3) s(-1) 的范围内。作为对当前计算方法的检验，使用从头算理论计算了状态到状态的转动能量转移率常数。总去除率常数与测量值吻合良好，但 |ΔJ| ≥ 3 的转移概率被低估。对势能面各向异性特征的检查并没有给出明显的差异解释，但最有可能的问题是由于势能面的不准确性。
