Vibrational and Rotational Energy Distributions in a Hot Cl2 Molecular Beam

Abstract
Vibrational and rotational energy distributions of a hot Cl2 (Cl2 *) molecular beam, which is used for a semiconductor device etching process, is studied by a laser-induced fluorescence method. The Cl2 * beam is produced by free jet expansion of a Cl2 gas heated in a quartz furnace. It is found that the hot molecular beam is a transition flow between a continuum free jet and an effusive flow. The vibrational and rotational energy distributions can be described by Boltzmann functions of well-defined temperatures. The vibrational temperature is rather close to the furnace exit temperature, while the rotational temperature is cooled to 150–250 K during the isentropic free expansion. These results show that furnace exit temperature is crucial to the production of a highly reactive hot molecular beam of large vibrational energy.

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