Collision-induced infrared absorption of hydrogen in H₂-He and H₂-Ne mixtures at different temperatures

The collision-induced fundamental infrared absorption band of hydrogen in H₂-He and H₂-Ne mixtures at 77°K, 195°K, 273°K and 298°K has been studied for gas densities up to 530 amagat for several base densities of hydrogen. In each of these mixtures the enhancement absorption profiles show, in addition to the usual splitting of the Q branch into the main Qp and QR components, a splitting of the S(1) line into the Sp(1) and SR(1) components at all the experimental temperatures, and a secondary splitting of the main Qp component into the Qp(3) and QR(3) components at 273°K and 298°K. The profiles of H₂-He at 77°K also show a splitting of the S(0) line into Sp(0) and SR(0). Integrated absorption coefficients were measured and binary and ternary absorption coefficients were derived. Van Kranendonk's theory of the 'exp-4' model for the induced dipole moment was applied to the experimental binary absorption coefficients. The quadrupolar parts of these coefficients were calculated from the known molecular parameters. These were then subtracted from the experimental values to obtain the overlap parts. The overlap parameters λ and ρ, giving respectively the magnitude and range of the overlap moment, were determined for each of the mixtures by obtaining the best fit of the calculated overlap part of the binary absorption coefficient as a function of temperature to the experimental values of the overlap parts. The values of λ and ρ are as follows: -- Mixture λ ρ -- H₂-He 5.6 x 10⁻³ 0.24Å -- H₂-Ne 9.0 x 10⁻³ 0.29