分子排列回波探测碰撞引起的旋转速度变化
Molecular alignment echoes probe collision-induced rotational-speed changes
摘要：
我们表明，在N2 O-He气体混合物中由两个激光脉冲与各种延迟引起的对准回波的衰减与压力带来的碰撞引起的转速变化的详细信息。测量和计算表明，当回波出现较晚时，碰撞会更有效地降低回波幅度。我们定量地解释了这种行为的经典的旋转相空间的诱导的第一个脉冲和渐进缩小的细丝随着时间的推移。因此，回波衰减的变化反映了碰撞以各种量改变分子旋转速度的能力，从而能够对由分子间力引起的耗散模型进行精细测试。
英文摘要：
We show that the decays with pressure of the alignment echoes induced in N2O-He gas mixtures by two laser pulses with various delays bring detailed information on collision-induced changes of the rotational speed. Measurements and calculations demonstrate that collisions reduce the echo amplitude all the more efficiently when the echo appears late. We quantitatively explain this behavior by the filamentation of the classical rotational phase space induced by the first pulse and the progressive narrowing of the filaments with time. The variation of the echo decay thus reflects the ability of collisions to change the molecules' rotational speed by various amounts, enabling refined tests of models for the dissipation induced by intermolecular forces.
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