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Title:Cooling of electronically-excited He2 molecules in a microcavity plasma jet
Author(s):Su, Rui
Contributor(s):Eden, J. Gary; Houlahan, Thomas J., Jr.
Subject(s):Dynamics and kinetics
Abstract:Helium dimers in the d$^{3}\Sigma^{+}_{u}$ excited electronic state with potential energy $>$24 eV and radiative lifetime of 25 ns have been generated in a microcavity plasma jet and rotationally cooled by supersonic expansion in vacuum. The dynamic process of cooling is recorded by imaging the axis of expansion onto the slit of Czerny-Turner spectrometer, yielding spatial-temporal spectrograms of d$^{3}\Sigma^{+}_{u}$$\rightarrow$$b^{3}\Pi_{g}$ $(v', v'')=(0, 0)$ emission. Analysis of the data shows the spatial-temporal evolution of the rotational temperature to be a damped sinusoid that reaches a minimum value of 100K. This reproducible behavior is attributed to the reflection of electrons from a virtual cathode located downstream of the nozzle and indicates that the spatially-averaged electron density is 10$^{8}$ cm$^{-3}$. We present this observed rotational temperature oscillation during the supersonic cooling process as an example of the potential of our supersonic microplasma expansion as a tool to explore physical dynamics in diatomic molecules having high excitation energies and small lifetimes.
Issue Date:2016-06-24
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper/Presentation
Rights Information:Copyright 2016 by the authors
Date Available in IDEALS:2017-01-26

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