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A preliminary study of neutral titanium emission behind reflected shock waves in TiCl4-Ar mixtures
NOTES
AND
DISCUSSION
The Editors of the Journal of Quantitative Spectroscopy and Radiative Transfer welcome the submittal of brief? original contributions on timely topics. These manuscripts will generally be publishedpromptly and without editorial review if the.y are submitted through one of the Associate Editors of JQSRT.
1. Qsant.
Spectrosc.
Radial.
Transfer.
Vol. 2. pp. 245-246.
Pergamon Press Ltd.
Printed in Great Britain
A PRELIMINARY STUDY OF NEUTRAL EMISSION BEHIND REFLECTED SHOCK TiCl,-Ar MIXTURES*
TITANIUM WAVES IN
W. L. SHACKLEFORD Daniel and Florence Guggenheim Jet Propulsion Center, California Institute of Technology Pasadena, California (Received 16 November 1961) TITANIUM TETRACHLORIDEis
one of a number of volatile metal halides and carbonyls which may be used as a source of metal atoms in shock-tube measurements of atomicf-numbers. Recently, WILKERSON~~)has employed mixtures of chromium carbonyl and neon in a shock tube to measure the&numbers for transitions of Cr I and Cr II. In our investigations, mixtures of TiCl, and argon, varying in TiCl, mole fraction from 0.005 to l-00, were subjected to incident and reflected shock waves corresponding to incident shock Mach numbers in the range 4 < M, < 7.2. Time integrated spectra of the visible radiation emitted axially through the end of the tube were photographed. The more dilute mixtures (containing about 1 per cent Tic&) yielded spectra showing several multiplets of neutral titanium at the highest Mach numbers used. Under these conditions, the gas behind the reflected shock was completely dissociated and partially ionized at a temperature of about 8000°K. Weaker shocks and shocks in mixtures containing higher TiCI, concentrations produced only background and impurity radiation (because of the lower shock temperatures). A l-in. i.d. stainless steel shock tube with a 4*5-ft test section was used. Helium served as driver gas. The spectrum was photographed with Kodak Royal-X Pan film, using an ARL 1-5-m grating spectrograph. The low speed (J/30) of the spectrograph made it impossible to observe spectral lines in the linear region of the curves of growth, as is required in quantitative work. The darkening on the photographic plate was produced by * Supported by the USAF Office of Scientific Research under Contract AF 49(638)-984 with the California Institute of Technology. 245
‘
246
W.L.
SHACKLEFORD
the light emitted from the gases behind both the incident and reflected shock waves, with practically all of the line radiation coming from the hotter reflected shock region. Relative intensities of selected lines were measured using standard techniques. A tungsten strip lamp of known temperature was used to relate the calibration curves at different wavelengths. These measurements showed that the observed spectral lines were heavily self-absorbed, and, therefore, were not suitable for color temperature off-number measurements. It was not possible to reduce self-absorption significantly by using less Tic14 without causing the lines to diminish in intensity to the background level. By (a) using the known conditions behind the reflected shock wave, (b) estimating an effective optical depth for our experiments, and (c) noting that the spectral lines were in the square-root region of the curves of growth, a lower limit was obtained for thef-number of the transition ysGs’+ a5Fz (A = 5007.22 A): j-iiOO7.22> 2x
lo+.
On the basis of various theoretical estimates and an examination of available experimental data, ALLEN@) has recommended the valuefsse7,ss = 8.5 x 10m2. Titanium tetrachloride has properties which appear to make it of doubtful usefulness in quantitative spectroscopic studies. The vapor reacts vigorously with moisture to produce HCl and mixed hydroxides and chlorides of titanium. Because of the tendency to react with components of the system, it is difficult to obtain controlled concentrations of Tic14 that are so low that emission spectrum lies in the linear part of the curves of growth. Results of the studies on Tic14 are presented in greater detail (SHACKLEFORD(~ Acknowledgement-The
author is indebted
to Dr. S. S. PENNER for helpful discussions. REFERENCES
1. T. WILKERS~N and 0. LAPORTE,The Use of the Shock Tube as a Spectroscopic Sourcewith an Application to the Measurement of gf-values for Litis of Neutral and Singly Ionized Chromium, University of Michigan, Ann Arbor, Michigan, Report No. 02822-3-T (1961). 2. C. W.-ALLEN, Mon. iot. Roy, Ash. sot. 121,299(1960). 3. W. L. SHACKLEFORD.Preliminarv Studies on the Suectrum of Ti I Emitted Behind Reflected Shock Waves in TiCL-Ar hkixtures, Technical Report No. !?A, Contrkt AF 49(638)-984, Califirnia Institute of Technology, Pasadena (1961).
AND
DISCUSSION
The Editors of the Journal of Quantitative Spectroscopy and Radiative Transfer welcome the submittal of brief? original contributions on timely topics. These manuscripts will generally be publishedpromptly and without editorial review if the.y are submitted through one of the Associate Editors of JQSRT.
1. Qsant.
Spectrosc.
Radial.
Transfer.
Vol. 2. pp. 245-246.
Pergamon Press Ltd.
Printed in Great Britain
A PRELIMINARY STUDY OF NEUTRAL EMISSION BEHIND REFLECTED SHOCK TiCl,-Ar MIXTURES*
TITANIUM WAVES IN
W. L. SHACKLEFORD Daniel and Florence Guggenheim Jet Propulsion Center, California Institute of Technology Pasadena, California (Received 16 November 1961) TITANIUM TETRACHLORIDEis
one of a number of volatile metal halides and carbonyls which may be used as a source of metal atoms in shock-tube measurements of atomicf-numbers. Recently, WILKERSON~~)has employed mixtures of chromium carbonyl and neon in a shock tube to measure the&numbers for transitions of Cr I and Cr II. In our investigations, mixtures of TiCl, and argon, varying in TiCl, mole fraction from 0.005 to l-00, were subjected to incident and reflected shock waves corresponding to incident shock Mach numbers in the range 4 < M, < 7.2. Time integrated spectra of the visible radiation emitted axially through the end of the tube were photographed. The more dilute mixtures (containing about 1 per cent Tic&) yielded spectra showing several multiplets of neutral titanium at the highest Mach numbers used. Under these conditions, the gas behind the reflected shock was completely dissociated and partially ionized at a temperature of about 8000°K. Weaker shocks and shocks in mixtures containing higher TiCI, concentrations produced only background and impurity radiation (because of the lower shock temperatures). A l-in. i.d. stainless steel shock tube with a 4*5-ft test section was used. Helium served as driver gas. The spectrum was photographed with Kodak Royal-X Pan film, using an ARL 1-5-m grating spectrograph. The low speed (J/30) of the spectrograph made it impossible to observe spectral lines in the linear region of the curves of growth, as is required in quantitative work. The darkening on the photographic plate was produced by * Supported by the USAF Office of Scientific Research under Contract AF 49(638)-984 with the California Institute of Technology. 245
‘
246
W.L.
SHACKLEFORD
the light emitted from the gases behind both the incident and reflected shock waves, with practically all of the line radiation coming from the hotter reflected shock region. Relative intensities of selected lines were measured using standard techniques. A tungsten strip lamp of known temperature was used to relate the calibration curves at different wavelengths. These measurements showed that the observed spectral lines were heavily self-absorbed, and, therefore, were not suitable for color temperature off-number measurements. It was not possible to reduce self-absorption significantly by using less Tic14 without causing the lines to diminish in intensity to the background level. By (a) using the known conditions behind the reflected shock wave, (b) estimating an effective optical depth for our experiments, and (c) noting that the spectral lines were in the square-root region of the curves of growth, a lower limit was obtained for thef-number of the transition ysGs’+ a5Fz (A = 5007.22 A): j-iiOO7.22> 2x
lo+.
On the basis of various theoretical estimates and an examination of available experimental data, ALLEN@) has recommended the valuefsse7,ss = 8.5 x 10m2. Titanium tetrachloride has properties which appear to make it of doubtful usefulness in quantitative spectroscopic studies. The vapor reacts vigorously with moisture to produce HCl and mixed hydroxides and chlorides of titanium. Because of the tendency to react with components of the system, it is difficult to obtain controlled concentrations of Tic14 that are so low that emission spectrum lies in the linear part of the curves of growth. Results of the studies on Tic14 are presented in greater detail (SHACKLEFORD(~ Acknowledgement-The
author is indebted
to Dr. S. S. PENNER for helpful discussions. REFERENCES
1. T. WILKERS~N and 0. LAPORTE,The Use of the Shock Tube as a Spectroscopic Sourcewith an Application to the Measurement of gf-values for Litis of Neutral and Singly Ionized Chromium, University of Michigan, Ann Arbor, Michigan, Report No. 02822-3-T (1961). 2. C. W.-ALLEN, Mon. iot. Roy, Ash. sot. 121,299(1960). 3. W. L. SHACKLEFORD.Preliminarv Studies on the Suectrum of Ti I Emitted Behind Reflected Shock Waves in TiCL-Ar hkixtures, Technical Report No. !?A, Contrkt AF 49(638)-984, Califirnia Institute of Technology, Pasadena (1961).