Simulating rotationally inelastic collisions using a direct simulation Monte Carlo method

• Published in: Molecular physics Vol. 113; no. 24; pp. 3972 - 3978
• Main Authors: Schullian, O., Loreau, J., Vaeck, N., Avoird, A. van der, Heazlewood, B.R., Rennick, C.J., Softley, T.P.
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 17.12.2015; Taylor & Francis Ltd
• Subjects: Collision dynamics; Computer simulation; Cooling; Direct simulation Monte Carlo; Direct simulation Monte Carlo method; Gas cooling; inelastic scattering; Mathematical models; molecular beam; Monte Carlo methods; Monte Carlo simulation; Populations; rotational population
• ISSN: 0026-8976; 1362-3028
• DOI: 10.1080/00268976.2015.1098740

A new approach to simulating rotational cooling using a direct simulation Monte Carlo (DSMC) method is described and applied to the rotational cooling of ammonia seeded into a helium supersonic jet. The method makes use of ab initio rotational state changing cross sections calculated as a function of collision energy. Each particle in the DSMC simulations is labelled with a vector of rotational populations that evolves with time. Transfer of energy into translation is calculated from the mean energy transfer for this population at the specified collision energy. The simulations are compared with a continuum model for the on-axis density, temperature and velocity; rotational temperature as a function of distance from the nozzle is in accord with expectations from experimental measurements. The method could be applied to other types of gas mixture dynamics under non-uniform conditions, such as buffer gas cooling of NH 3 by He.