New experimental observations in the collision-induced infrared spectra of molecular hydrogen.

Chang, Kai-siung (1974) New experimental observations in the collision-induced infrared spectra of molecular hydrogen. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

This work describes several new experimental observations made by the author in the collision-induced infrared absorption spectra of molecular hydrogen at liquid nitrogen and room temperatures for densities up to 660 amagat. The experiments were carried out with a 2 m low-temperature high-pressure absorption cell of the transmission type. The spectral region investigated extends from 3500 to 10,000 cm⁻¹. -- Collision-induced vibration-rotation U transitions (ΔJ = +4) of the hydrogen molecule in its fundamental band have been observed for the pure gas at 77 K for densities in the range 430 - 660 amagat and for the binary mixtures, hydrogen-xenon, and hydrogen-krypton at 298 K for total gas densities ~ 450 amagat. The high frequency tail of the quadrupolar S transitions which overlaps the U transitions has been separated from the experimental profiles by the method of profile analysis. The spectrum of the U transitions is interpreted in terms of the hexadecapolar induction mechanism. From the experimental integrated binary absorption coefficients of the U transitions, appropriate values of the hexadecapole moment matrix elements of the hydrogen molecule are derived. -- Spectra of the collision-induced first overtone band of hydrogen in binary mixtures with krypton and xenon at 298 K for densities up to ~ 450 amagat have been recorded for the first time. From an analysis of the profiles of the enhancement of absorption, the frequency shifts δν₀ and the half-widths δ have been determined. Unusual occurrence of some H₂ double transitions was observed. The observed frequency shifts of the quadrupolar lines are negative and level off at high densities, qualitatively in the same way, but with larger shifts, as those observed in the fundamental. The observed half-widths of the quadrupolar lines were found to increase with the density of the inert gas, and to be quite sensitive to the base density of the hydrogen. Both observed line-shifts and half-widths are expected to have larger values than the true ones because of overlapping double transitions obscuring the single transition lines. -- During the above mentioned experiments with hydrogen, it was observed that especially in the spectral region 6800 - 7400 cm⁻¹ more light reached the detector with compressed hydrogen in the cell than when the cell was evacuated. The spectral profiles of this phenomenon in the region 6800 -7400 cm⁻¹ and their density dependence have been determined and it is speculated that upper states are populated by collision-induced absorption in the region of the first overtone and the subsequent radiative emission transitions follow the same selection rules that are known for collision-induced absorption.

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