Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
J Chem Phys. 2012 Feb 7;136(5):054306. doi: 10.1063/1.3682982.
We introduce a method for classical trajectory calculations to simulate collisions between atoms and large rigid asymmetric-top molecules. We investigate the formation of molecule-helium complexes in buffer-gas cooling experiments at a temperature of 6.5 K for molecules as large as naphthalene. Our calculations show that the mean lifetime of the naphthalene-helium quasi-bound collision complex is not long enough for the formation of stable clusters under the experimental conditions. Our results suggest that it may be possible to improve the efficiency of the production of cold molecules in buffer-gas cooling experiments by increasing the density of helium. In addition, we find that the shape of molecules is important for the collision dynamics when the vibrational motion of molecules is frozen. For some molecules, it is even more crucial than the number of accessible degrees of freedom. This indicates that by selecting molecules with suitable shape for buffer-gas cooling, it may be possible to cool molecules with a very large number of degrees of freedom.
我们介绍了一种经典轨迹计算方法，用于模拟原子与大型刚性非对称陀螺分子之间的碰撞。我们研究了在温度为 6.5 K 的缓冲气体冷却实验中，对于像萘这样大的分子，形成分子-氦复合物的情况。我们的计算表明，在实验条件下，萘-氦准束缚碰撞复合物的平均寿命不够长，无法形成稳定的团簇。我们的结果表明，通过增加氦的密度，可能可以提高缓冲气体冷却实验中冷分子的产生效率。此外，我们发现当分子的振动运动被冻结时，分子的形状对于碰撞动力学很重要。对于某些分子，其重要性甚至超过了可及自由度的数量。这表明，通过选择适合缓冲气体冷却的具有合适形状的分子，可能可以冷却具有非常多自由度的分子。
