Ionization Mechanism of Chromium in Cr–Ar Mixtures

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Abstract
Time‐resolved emission measurements have been performed behind reflected shocks in mixtures of Cr(CO)6 and Ar, for wavelength regions including the 3421.2‐ and 3422.7‐Å transitions of Cr(II) and the 3976.7‐, 3983.9‐, and 3991.7‐Å transitions of Cr(I); a single measurement was performed for the 4254.4‐Å resonance line of Cr(I). Under the experimental conditions used in our studies, self‐absorption was not important, except possibly for the resonance line of Cr(I) at 4254.4 Å. The observed time—intensity data in the three spectral regions are consistent with the following excitation and ionization model of Cr in an Ar bath at temperatures of about 7000°K: (a) Cr(I) is excited by collisions with electrons and/or atoms to levels which lie approximately 3.1 eV above the ground level; (b) excitation to more highly excited levels of neutral chromium occurs very rapidly; (c) ionization occurs from the excited electronic states of Cr(I) by rate‐controlling processes that involve inelastic collisions with either electrons or neutral atoms.
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