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Related Experiment Video

Updated: Jul 6, 2026

Non-equilibrium Microwave Plasma for Efficient High Temperature Chemistry

Non-equilibrium Microwave Plasma for Efficient High Temperature Chemistry

Published on: August 1, 2017

Approach to thermal equilibrium in atomic collisions.

P Zhang¹, V Kharchenko, A Dalgarno

¹Institute for Theoretical Atomic, Molecular and Optical Physics, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA.

Physical Review Letters

|March 21, 2008

Summary

Fast atoms in a gas reach thermal equilibrium through two distinct stages. This energy relaxation process, characterized by Maxwellian distribution, is independent of atomic mass and driven by small-angle scattering.

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Area of Science:

Atomic and Molecular Physics
Chemical Physics
Statistical Mechanics

Background:

Understanding energy relaxation is crucial for modeling systems involving energetic particles in gases.
Previous studies have explored atomic collisions, but the two-stage equilibration process in thermal baths requires further elucidation.

Purpose of the Study:

To experimentally and theoretically investigate the energy relaxation dynamics of fast atoms in a thermal bath gas.
To determine the characteristic time scales and factors influencing the equilibration process.
To confirm the formation and preservation of Maxwellian energy distributions.

Main Methods:

Theoretical modeling of atomic energy relaxation in a thermal bath.
Experimental measurements using Doppler profiles of emission from excited nitrogen atoms.
Varying bath gases (helium, argon) to study mass ratio effects.

Main Results:

Identified two distinct time scales for energy relaxation: short-term Maxwellian shape formation and long-term temperature decrease.
Demonstrated that the formation and preservation of Maxwellian distribution are independent of the projectile-to-bath gas atom mass ratio.
Observed that small-angle scattering and small energy transfer dominate the collision dynamics.

Conclusions:

The two-stage energy relaxation process is a robust phenomenon in atomic systems.
The observed behavior is attributed to the nature of neutral particle collisions, favoring small energy transfers.
Experimental results confirm theoretical predictions, validating the understanding of atomic equilibration in thermal baths.