Shackleford, William L. (1964) I. Measurement of gf-values for singly ionized chromium using the reflected wave region of a shock tube. II. Experimental investigation of the approach to equilibrium ionization and electronic excitation in shock-heated mixtures of chromium and argon. III. Approximate spectral absorption coefficient calculations for electronic band systems belonging to diatomic molecules. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-10042002-101246
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Absolute gf-values for 21 lines of singly ionized chromium (Cr II) in the spectral region 3118-4559 [angstroms] are presented. Mixtures of Cr(CO)[subscript 6] and argon, heated by reflected shock waves to temperatures in the range 7920[degrees]K to 8730[degrees]K, were used to measure the emission intensity of ionized chromium lines. A three inch diameter shock tube was employed, with the light being observed along the shock tube axis in order to observe directly the curve of growth of each spectral line. The emitted intensities observed were converted to gf-values by means of a comparison with a calibrated tungsten strip lamp. Results are compared with values obtained from arc spectra by Corliss and Bozman[superscript 1] at the National Bureau of Standards. In general, our results are a factor of 9 below the latter measurements. Possible reasons for this discrepancy are discussed.
An experimental investigation of the approach to equilibrium ionization and electronic excitation for chromium behind shock waves in Cr(CO)[subscript 6]-argon mixtures is described. Mixtures composed of from 0.0043% to 0.036%o Cr(CO)[subscript 6] were heated by reflected shock waves to temperatures between 6170[degrees]K and 8600[degrees]K, and the emission from excited states of Cr I and Cr II was simultaneously measured by photoelectric means with a time resolution of about 3 microseconds. Relaxation toward equilibrium ionization and excited state population was observed to occur within from 12 to 60 microseconds, depending upon the temperature and chromium concentration behind the reflected shock.
In measurements in which equilibrium ionization is 95% or more, the populations of excited states of Cr I show a pronounced "overshoot" as these states become populated before ionization has depleted the supply of neutral chromium. From a study of the relaxation of Cr I and Cr II upper state populations, it is concluded that ionization proceeds by a multistep autocatalytic process dominated by collisions between chromium atoms and electrons released in prior ionization of chromium. The dependence of the relaxation rates upon the temperature behind the reflected shock wave and upon the concentration of chromium was determined. If it is assumed that the electron and atom temperatures did not differ appreciably during the relaxation period, the variation in the relaxation rate with temperature indicates a 3.1 [plus or minus] 0.3 ev activation energy for chromium ionization, which is significantly less than the ionization potential (6.74 ev).
A simplified reaction mechanism is proposed which qualitatively explains the observed relaxation behavior of Cr I and Cr II.
The spectral absorption coefficients in electronic band systems of diatomic emitters have been computed in the past by models that may be described as "the just overlapping line model" and a model "utilizing a smeared out rotational structure". Although the basic relations are obtained by utilizing somewhat different physical arguments, the resulting equations are, in fact, identical.
Spectral absorption coefficients have been calculated for the NO [...]-bands at 2000[degrees]K by using the approximate theoretical relations. The calculated results are in good agreement with estimates derived by numerical calculations in which, however, the absorption coefficient data were averaged over intervals of 2000 cm.[superscript -1].
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Degree Grantor:||California Institute of Technology|
|Division:||Engineering and Applied Science|
|Major Option:||Engineering and Applied Science|
|Thesis Availability:||Public (worldwide access)|
|Defense Date:||25 May 1964|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||07 Oct 2002|
|Last Modified:||26 Dec 2012 03:03|
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