A study of the pressure-induced fundamental band of deuterium in pure gas and deuterium-foreign gas mixtures at low temperatures down to 77°K

The pressure-induced fundamental vibration-rotation absorption band of deuterium was studied in the pure gas for gas densities up to 175 Amagat at ice, alcohol-dry ice and liquid nitrogen temperatures respectively, and in deuterium-helium and deuterium-neon mixtures for partial foreign gas densities up to 647 Amagat at 77.3°K. The shapes of the absorption contours obtained in each case were discussed. The contours of pure deuterium exhibited sharper individual branches of the fundamental band with the decreasing temperature as expected. The magnitude of the splitting of the Q branch at a constant density decreased as the temperature was lowered, disappearing at 77.3°K in the low density region while indicating a gradual re-appearance with higher density. The enhancement absorption profiles of the band in deuterium-helium and deuterium-neon mixtures showed a marked splitting of the Q branch at 77.3°K. The distinct indication of the S(0), S(1) and S(2) lines and the density-dependence of the minima of the Q branch observed in deuterium- neon mixtures was found to be absent in deuterium-helium mixtures. Binary and ternary absorption coefficients were determined for pure deuterium and deuterium-foreign gas mixtures. Applying the theory of Van Kranendonk and using the known molecular parameters of deuterium, the binary absorption coefficients of the individual lines of the 0 and S branches and of the quadrupole part of the Q branch were calculated and hence the overlap part was estimated. Van Kranendonk's theory was used to calculate the theoretical values of the total binary absorption coefficients, α₁, of pure deuterium at various temperatures in the region 300°K - 40°K, for comparison with the available experimental values obtained from various sources including the present investigation. Theoretical variation curves of α₁ with temperature drawn for σ/ρ = 10.00, 11.80 and 7.94 are discussed