Orientation and alignment depolarization in OH(X 2Pi)+Ar/He collisions.
Orientation and alignment depolarization in OH(X 2Pi)+Ar/He collisions.
复制标题
OH(X 2Pi) Ar/He 碰撞中的定向和排列去极化。
DOI：
10.1063/1.2967861
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
R. Toboła
中科院分区：
文献类型：
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作者：
Grant Paterson;S. Marinakis;M. Costen;K. McKendrick;J. Kłos;R. Toboła
用双色偏振光谱（PS）研究了热条件下（298 K）OH（X（2）Pi（3/2），v=0，J=1.5- 6.5，e）与He和Ar碰撞中的转动角动量（RAM）的退极化.在非对角OHA（2）Sigma（+）-X（2）Pi（1，0）带上分别使用圆偏振或线偏振脉冲激发实现OHRAM的取向或排列。基态OH（X）RAM极化的演化，专门使用一个独立的，线性偏振脉冲调谐到对角OH A（2）Sigma（+）-X（2）Pi（0，0）带探测。对于OH（X）+Ar，PS信号衰减速率常数k（PS）随转动量子数的增加而减小，但对于OH（X）+He，PS信号衰减速率常数k（PS）并不单调变化。测量的k（PS）等于和k（RET）+k（λ）+k（dep），其中k（RET）、k（λ）和k（dep）分别是旋转能量转移、λ-二重态变化碰撞和旋转弹性去极化（OH（X）角动量的取向或排列，如所指定的）的速率常数。可以利用k（RET）和k（λ）的先验知识从测量的k（PS）中提取k（dep）的值。由于k（RET）和k（λ）是以前没有提供的Ar与OH（X，v=0）的碰撞，我们进行了精确的，完全量子力学的散射计算上的一个新的势能面（PES）在这里提出的第一次。原始实验结果表明，OH（X）+Ar的k（dep）在系统上明显高于取向，而OH（X）+He的k（dep）则弱得多。在298.15 K下计算的k（RET）和k（Lambda）值与OH（X）+Ar的k（dep）的实质性贡献一致，但与OH（X）+He的k（dep）的实质性贡献不一致。这可能指向吸引力在弹性去极化中的作用。实验结果提供了对Lee等人[J.Chem.Phys.113，5736（2000）]的最新从头算OH（X）-He PES精确再现k（RET）+k（Lambda）的能力的非常灵敏的测试。
The depolarization of OH(X (2)Pi(3/2),v=0,J=1.5-6.5,e) rotational angular momentum (RAM) in collisions with He and Ar under thermal conditions (298 K) has been studied using two-color polarization spectroscopy (PS). Orientation or alignment of the OH RAM was achieved using circularly or linearly polarized pulsed excitation, respectively, on the off-diagonal OH A (2)Sigma(+)-X (2)Pi(1,0) band. The evolution of the ground-state OH(X) RAM polarization, exclusively, was probed using an independent, linearly polarized pulse tuned to the diagonal OH A (2)Sigma(+)-X (2)Pi(0,0) band. The PS signal decay rate constant k(PS) decreases with increasing rotational quantum number for OH(X)+Ar but does not vary monotonically for OH(X)+He. The measured k(PS) equals the sum k(RET)+k(Lambda)+k(dep), where k(RET), k(Lambda), and k(dep) are the rate constants for rotational energy transfer, Lambda-doublet changing collisions, and rotationally elastic depolarization (of orientation or alignment of the OH(X) angular momentum, as specified), respectively. Values of k(dep) can be extracted from the measured k(PS) with prior knowledge of k(RET) and k(Lambda). Because k(RET) and k(Lambda) were not previously available for collisions of Ar with OH(X, v=0), we performed exact, fully quantum-mechanical scattering calculations on a new potential energy surface (PES) presented here for the first time. The raw experimental results show that k(dep) is systematically markedly higher for alignment than for orientation for OH(X)+Ar but much more weakly so for OH(X)+He. Calculated k(RET) and k(Lambda) values at 298.15 K are consistent with a substantial contribution from k(dep) for OH(X)+Ar but not for OH(X)+He. This may point to the role of attractive forces in elastic depolarization. The experimental results provide a very sensitive test of the ability of the most recent ab initio OH(X)-He PES of Lee et al. [J. Chem. Phys. 113, 5736 (2000)] to reproduce k(RET)+k(Lambda) accurately.