The induced infrared fundamental band of hydrogen dissolved in solid argon

Abstract

The induced infrared fundamental band of hydrogen dissolved (~1:100) in solid argon was studied with a 20-cm absorption path length at −191 °C. Transparent crystals were prepared by slow cooling of the liquid solution saturated with hydrogen at ~25 atm pressure. The H2 transitions, Q, S(0), and S(1), show similar patterns of five maxima, each of which can be analyzed as a zero-phonon line at the H2 frequency and summation and difference tones with lattice transition frequencies, 112 and 22 cm−1. The 112-cm−1 frequency is interpreted as arising from a localized lattice vibration involving an H2 molecule on a substitutional lattice site. Calculation from a model of an H2 molecule moving in the field of its argon neighbors, considered stationary, gave 109 cm−1 for this frequency. The origins of the zero-phonon lines and the 22-cm−1 lattice transition frequency are not so clear, and several possibilities are discussed. The H2 frequencies are shifted from their free-molecule values by the sum of a vibrational shift, Δνvlb = −17 cm−1, and rotational shifts corresponding to ΔB = −0.52 cm−1.