Characterization of free jet expansion of SF6 molecules

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Abstract
In this work we present experimental measurements of the mean velocity of SF6 molecules in a pulsed-free jet as a function of the distance from the expansion orifice. A pyroelectric detector was used to measure the time of flight of the molecules in the jet. A comparison of the experimental results with theoretical values for the mean velocity taking the temperature dependence of the specific-heat ratio into account leads to the conclusion that the freezing of rotational, vibrational, and translational temperature is reached at considerable distances from the expansion orifice.