PRESSURE DEPENDENCE OF THE STIMULATED RAMAN Q-BRANCH SPECTRUM OF $D_{2}$ DILUTED IN He, A, AND $N_{2}$
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Date
1984
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Ohio State University
Abstract
Foreign gas broadening and shifting of the vibrational Q-branch lines of $D_{2}$ has been measured by use of high resolution (10 MHz) CW-stimulated Raman spectroscopy. The foreign gases studied were He, A, and $N_{2}$ with $D_{2}$ present at 0.1 mole fraction (or less). The measurements were done at $296\pm 0.5$ K in the range 0.25 to 3.75 amagat. The (0-1) Q(3) and Q(4) lines were measured with the following results for the shifting and broadening (T = HWHM) coefficients: [FIGURE]$$He N_{2} A He N_{2} A 3 +7.6 -5.9 -9.5 1.67 2.95 3.04 4 +6.4 -5.5 -9.0 1.44 2.55 2.78$$ The Q-lines of $D_{2}$ show large collision (Dicke) narrowing with the minimum line widths approximately 0.4 times the Doppler width. The spectral profiles are shown to be Lorentzian for the $condition^{1}$ $q^{1}$ $(=momentum transfer \times mean free path) \leq 0.5$. Deviations from Lorentzian lineshapes are observed for $q_{1} \geq 0.7$. For the Lorentzian lineshape region ($P>0.25$ amagat for A and $N_{2}; P>0.6$ amagat for He) the linewidth (HWHM) versus density (amagat) is well described by $\Gamma = D_{0}/P + (\partial \Gamma/\partial P)P$ with $D_{0}(cm^{2}$/s-amagat) the self-diffusion constant at 1 amagat for $D_{2}$ in the mixture and the pressure broadening coefficients given above. The self-diffusion constant for the mixture can be expressed, in the ideal gas limit, in terms of the diffusion of $D_{2}$ in pure $D_{2}$ and the diffusion of $D_{2}$ in the foreign gas. For He and $N_{2}$ we find the last mentioned diffusion constant to be in good agreement (3\% and 6\%, respectively) with literature values of the mutual diffusion $coefficient^{2}$, whereas for A our value is 24\% lower than the reported $value^{2}$.
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$^{1}$ S.G. Rautian and I.I. Sobelman, Sov. Phys. Uspek. 9, 701 (1967). $^{2}$ B.A. Ivakin and P.E. Suetin, Sov. Phys. Tech. Phys. 8, 748 (1964).
Author Institution: U.S. National Bureau of Standards, Temperature and Pressure Division
Author Institution: U.S. National Bureau of Standards, Temperature and Pressure Division