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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Rotational Changes Accompanying Vibrational Transfer in Low-Energy Collisions between Benzene and H_2, D_2, and CH_4
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Rotational Changes Accompanying Vibrational Transfer in Low-Energy Collisions between Benzene and H_2, D_2, and CH_4

机译：苯与H_2，D_2和CH_4之间的低能碰撞中伴随振动传递的旋转变化

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摘要

We have examined the changes in rotation that occur simultaneously with a change in vibrational state within a large polyatomic. Specifically, a variety of rotational-level population distributions have been prepared in the 6~1 vibrational level of ~1B_(2u) benzene, and the rotational distributions within 0~0 that result from collisions with H_2, D_2, or CH_4 have been observed by measuring the rotational contour of the band in emission. The experiments were performed in the collision region of a supersonic free jet expansion at a translational temperature of 34 K (H_2 and D_2) or 18 K (CH_4). It is demonstrated that rotational-energy transfer within 6~1 and 0~0 does not obscure the rotational changes accompanying the vibrational change. For a particular collision partner, the final rotational distributions in 0~0 are essentially the same for all initial 6~1 distributions. However, the final 00 rotational distributions are quite different for the different collision partners. The observed rotational contours are fit reasonably well by a thermal distribution with 0~0 rotational temperatures of 19, 41, and 93 K for H_2, D_2, and CH_4, respectively. The rotational contours were also fit using an exponentially decaying momentum gap model to evolve the initial 6~1 rotational distribution to the final 0~0 distribution. As an illustration, for an initial J, K distribution with average J and K values of 8 and 6, respectively, the changes in these average values are (written as (ΔJ-bar,ΔK-bar )) (3, 1), (8, 4), and (16, 9) for the thermal distribution fits for H_2, D_2, and CH_4, respectively. The corresponding values for the momentum gap model are (4, 0), (10, 1), and (19, 8). The modeling shows that the |ΔK| changes are much larger for CH_4 than for H_2 and D_2. A possible reason for the relaxed K restriction with CH_4 may be that a broad range of collision geometries leads to 6~1 → 0~0 vibrational-energy transfer with this partner. The 0~0 distributions for D_2 are broader than for H_2, illustrating that the reduced mass and rotational-level spacings play an important role in determining the rotational changes that occur.
机译：我们已经检查了旋转的变化，该变化是在大型多原子内部与振动状态的变化同时发生的。具体而言，在〜1B_（2u）苯的6〜1振动能级下已准备了多种旋转能级分布，并观察到了与H_2，D_2或CH_4碰撞导致的0〜0范围内的旋转能级。通过测量发射带的旋转轮廓。在超音速自由射流膨胀的碰撞区域中，在34 K（H_2和D_2）或18 K（CH_4）的平移温度下进行实验。结果表明，在6〜1和0〜0之间的旋转能量传递不会掩盖伴随振动变化的旋转变化。对于特定的碰撞伙伴，对于所有初始6〜1分布，0〜0的最终旋转分布基本上是相同的。但是，对于不同的碰撞伙伴，最终的00旋转分布是完全不同的。对于H_2，D_2和CH_4，通过0〜0旋转温度分别为19、41和93 K的热分布，可以很好地拟合观察到的旋转轮廓。还使用指数衰减动量间隙模型拟合旋转轮廓，以将初始的6〜1旋转分布演变为最终的0〜0分布。作为说明，对于平均J和K值分别为8和6的初始J，K分布，这些平均值的变化表示为（记为（ΔJ-bar，ΔK-bar））（3，1），热分布的（8、4）和（16、9）分别适合H_2，D_2和CH_4。动量差距模型的对应值为（4，0），（10，1）和（19，8）。建模显示|ΔK| CH_4的变化远大于H_2和D_2。 CH_4放松K限制的可能原因可能是，广泛的碰撞几何形状导致与该伙伴的6〜1→0〜0振动能量转移。 D_2的0〜0分布比H_2的宽，说明减小的质量和旋转水平间距在确定发生的旋转变化中起重要作用。

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