Knowledge Bank

Foreign gas broadening and shifting of the vibrational Q-branch lines of $D2$ has been measured by use of high resolution (10 MHz) CW-stimulated Raman spectroscopy. The foreign gases studied were He, A, and $N2$ with $D2$ 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 $D2$ 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 $condition1$ $q1$ $(=momentumtransfer\times meanfreepath)\le 0.5$. Deviations from Lorentzian lineshapes are observed for $q1\ge 0.7$. For the Lorentzian lineshape region ($P>0.25$ amagat for A and $N2;P>0.6$ amagat for He) the linewidth (HWHM) versus density (amagat) is well described by $\Gamma =D0/P+(\partial \Gamma /\partial P)P$ with $D0(cm2$/s-amagat) the self-diffusion constant at 1 amagat for $D2$ 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 $D2$ in pure $D2$ and the diffusion of $D2$ in the foreign gas. For He and $N2$ we find the last mentioned diffusion constant to be in good agreement (3% and 6%, respectively) with literature values of the mutual diffusion $coefficient2$, whereas for A our value is 24% lower than the reported $value2$.