Hooker, W.

Lapp, M.

Penner, S. S.

Weber, D.

English

Caltech Authors - Main

Reprinted from THE JOURNAL OF CHEMICAL PHYSICS, Vol. 25, No.5, 1087, November, 1956 
Printed in U. S. A. 
Multiple-Path Technique for the Determination 
of Physico-Chemical Data Behind Shock Fronts* 
W. HOOKER. M. LAPP. D. WEBER. AND S. S. PE"NER 
Daniel and Florence Guggenheim Jet Propulsion Center, California Institute 
of Technology Pasadena, California 
(Received August 27. 1956) 
I N connection with current experimental studies on carbon formation and gas emissivities at elevated temperatures behind 
shock fronts, we are utilizing single-path and double-path emission 
and absorption measurements. l For observations behind shock 
fronts (observation times of less than about 200/Lsec), we have 
adopted a procedure involving simultaneous spectral recording of 
an unchopped single-path beam and of a chopped double-path 
beam. 
<D lingle b •• m 
~ double beom 
A schematic diagram of the experimental arrangement for 
emission studies is sketched in Fig. 1. A slotted air turbine wheel 
making 120000 rpm permits frequency modulation of the double-
path beam at a rate of 5/Lsec, which is sufficiently rapid for our 
particular shock-tube applications. The mechanical chopper is to 
be preferred to a Kerr cell shutter2 because the losses are minimized 
and because a much wider wavelength range can be covered. The 
single and double-path beams are observed simultaneously on the 
same detector and are used only to establish the intensity ratio at 
various wavelengths as a function of time. Hence errors associated 
with any variations in the receiving system, other than a loss of 
linearity, will not affect the observed results. 
Shock fube ero .. section 
Interpretation of the measurements is based on the fact that, 
under suitably chosen conditions, the spectral intensity ratio for 
the double- and single-path experiments is a unique function of the 
product PApL. Here P A is the spectral absorption coefficient, p 
equals the partial pressure of emitter or absorber, and L is the cell 
length. For chemical reaction rate studies, P A and L are known 
through independent calibrations and analysis; hence the partial 
pressure of emitter (or absorber) p is determined by the experi-
mental data. In gas emissivity measurements, p and L are known 
and the measured intensity ratio determines the spectral absorp-
tion coefficient P A• 
* The work on chemical reactions is supported by the U. S. Air Force. 
Office for Advanced Studies. under Contract AF 18 (603).2; the gas emis-
sivity measurements are being performed with support from the U. S. Navy, 
Office of Kaval Research. under Contract NOIlr.220(03). NR 015 401. 
1 A similar procedure has been employed previously for emission studies 
on flames. See S. S. Penner and E. K. Bjornerud. J. Chern. Phys. 23. 143 
(1955) . 
2 F. Harshbarger. J. Chern. Phys. 24. 1261 (1956). 
collimator 
FIG. 1. Schematic diagram of the optical system used for the simultaneous 
determinations of single-path and double-path intensities. The axis of the 
shock tube is normal to the plane of the paper. 


Multiple-path technique for the determination of physico-chemical data behind shock fronts

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Multiple-path technique for the determination of physico-chemical data behind shock fronts

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