Abstract
Recently, femtosecond laser techniques have been developed that are capable of bringing gas molecules to extremely fast rotation in a very short time, while keeping their translational motion relatively slow. Here we study collisional equilibration dynamics of this new state of molecular gases. We show that the route to equilibrium starts with a metastable ‘gyroscopic stage' in the course of which the molecules maintain their fast rotation and orientation of the angular momentum through many collisions. The inhibited rotational–translational relaxation is characterized by a persistent anisotropy in the molecular angular distribution, and is manifested in the optical birefringence and anisotropic diffusion in the gas. After a certain induction time, the ‘gyroscopic stage' is abruptly terminated by an explosive rotational–translational energy exchange, leading the gas towards the final equilibrium. We illustrate our conclusions by direct molecular dynamics simulation of several gases of linear molecules.
Highlights
Femtosecond laser techniques have been developed that are capable of bringing gas molecules to extremely fast rotation in a very short time, while keeping their translational motion relatively slow
Our study provides the first modelling of the collisional kinetics of molecular SRs by direct molecular dynamics (MD) simulation methods
To get a deeper insight into the collisional relaxation of SRs, we investigated the process of isotropization of the molecular orientation, and of the direction of the rotational angular momentum
Summary
Femtosecond laser techniques have been developed that are capable of bringing gas molecules to extremely fast rotation in a very short time, while keeping their translational motion relatively slow. The optical centrifuge method was recently used[19] to investigate the effects of ultrafast molecular rotation on the initial short-lasting relaxation stage of collisional decoherence of the quantum Raman transitions in molecular nitrogen At ambient conditions, this stage lasts o1 ns The classical approach seems to be an appropriate tool for studying molecules at room temperature, excited to the quasi-classical rotational states with the angular momentum of tens to hundreds of ‘ It has already been successfully used for analysis of the laser experiments on molecular alignment at dissipative conditions[20,21,22]. The Supplementary Movie 1 shows in an animated way a very similar relaxation dynamics in a gas of O2 molecules
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