Pulsed discharge modulation technique in a supersonic jet for infrared diode laser absorption spectroscopy
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Date
1995
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Publisher
Ohio State University
Abstract
Previously, we reported a pulsed discharge modulation technique combined with infrared diode laser absorption spectroscopy in pulsed supersonic $jet^{1}.$ Using this technique, infrared absorption spectrum of the $\nu_{2}$ fundamental band of the $CH_{3}$ radical was measured. Acetone diluted to 5% with 3 atm Ar was injected in an absorption Cell through a discharge nozzle with a repetition rate of 30 Hz. Between the electrodes, 5 kHz ac high voltage pulse was applied for the duration of 1 ms, synchronized with the pulsed jet, to cause stable ac discharge of ${\sim}50$ mA. Focused diode laser beam along the Perry-type multireflection path crossed the molecular jet beam 16 times just below $(2 \sim 6mm)$. Infrared signal was demodulated by a phase sensitive detector with 1 ms time constant and averaged by a boxear integrator. We measured the $Q_{2}(2)$ and $Q_{3}(3)$ lines in the $\nu_{2}$ fundamental band of the $CH_{3}$ radical. Rotational temperature was calculated to be 80 K from the intensity ratio of the $Q_{2}(2)$ and $Q_{3}(3)$ lines. Time profile of the transient infrared absorption of the CH3 radical was measured. The time profile indicated that $CH_{3}$ was generated at the throat of the cathode and expanded into the vacuum chamber and cooled to 80 K.
Description
1. T. Imajo, K. Tanaka, T. Tanaka, $49^{th}$ Symposium on Molecular Spectroscopy, Columbus, Ohio, paper FB17 (1994).
Author Institution: Faculty of Scienc Kyushu University, 33 Hakozaki, Higashiku, Fukuoka 812, Japan.
Author Institution: Faculty of Scienc Kyushu University, 33 Hakozaki, Higashiku, Fukuoka 812, Japan.