Collision-induced fundamental band of H2 in H2He and H2Ne mixtures at different temperatures

The collision-induced fundamental infrared absorption band of hydrogen in binary mixtures H₂He and H₂Ne at 77, 195, 273, and 298 K has been studied with absorption path lengths of 27 and 105 cm 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 Q_P and Q_R components, a splitting of the S(1) line into the S_P(1) and S_R(1) components at all the experimental temperatures and a secondary splitting of the main Q_P component into the Q_P(3) and Q_R(3) components at 273 and 298 K. The profiles of H₂He at 77 K also show a splitting of the S(0) line into S_P(0) and S_R(0). Integrated absorption coefficients were measured and binary and ternary absorption coefficients were derived. Van Kranendonk's theory of the ‘exponential-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 and 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, ρ, and μ(σ) (the overlap induced dipole moment at the Lennard-Jones intermolecular diameter σ) are as follows:

Mixture	λ	ρ	μ(σ)
H2He	5.6 × 10?3	0.24 Å	2.92 × 10?2ea0
H2Ne	9.0 × 10?3	0.29 Å	4.85 × 10?2ea0
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