Nonequilibrium distributions of rotational and vibrational energies in a free-jet expansion Original Research Article

The occupations of various rovibrational levels of Na2 molecules in a free jet of Ar have been determined as functions of position. For the first part of the expansion, the internal state distribution are found to be close to equilibrium; the temperatures agree with the continuum model. Further downstream, appreciable deviations from equilibrium arise; an analysis of these distributions in terms of rotational and vibrational temperatures is found to be ambiguous. However, the average rotational and vibrational energies of the molecules, determined as functions of position, are in reasonable agreement with the thermal conduction model, assuming 26 Å2 for the effective rotational inelastic cross-section and 11 Å2 for the vibrational one. The need for a more detailed analysis is argued.