Diode-Laser Study of Rotational Temperature and Absorption Line Shape in Supersonic Free Jets

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Abstract
Infrared spectra of NNO and OCS have been studied in a supersonic free jet by using a diodelaser spectrometer. The sample gas of the molecules of 1 bar pressure was injected into a vacuum chamber (p ≈ 10−5 mbar) through a nozzle with a magnetic valve. The molecular beam was pulsed ( ≈ 82 Hz) by controlling the magnetic valve. Near the nozzle and for low values of the quantum number J the rotational temperature was determined to range between 29 and 3 K. For NNO we have observed the unusual line shapes in detail. They are caused by superposition of absorption signals of molecules in the jet and the background.