Cold collisions of complex polyatomic molecules

TL;DR

This paper presents a classical trajectory simulation method to study atom-molecule collisions at low temperatures, revealing insights into complex formation and the importance of molecular shape in buffer-gas cooling efficiency.

Contribution

It introduces a new classical trajectory approach for large asymmetric-top molecules and analyzes how molecular shape influences collision dynamics at cryogenic temperatures.

Findings

Naphthalene-helium complexes have short lifetimes, hindering stable cluster formation.

Increasing helium density could enhance cold molecule production.

Molecular shape significantly affects collision outcomes, more than degrees of freedom.

Abstract

We introduce a method for classical trajectory calculations to simulate collisions between atoms and large rigid asymmetric-top molecules. Using this method, 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.