Collision-induced spectra of molecular hydrogen in the first overtone region at 77,201 and 295 K

Van Nostrand, Edward (1983) Collision-induced spectra of molecular hydrogen in the first overtone region at 77,201 and 295 K. Masters thesis, Memorial University of Newfoundland.

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Abstract

The collision-induced absorption spectra of molecular hydrogen in its first overtone region has been recorded with a 2 m high-pressure low-temperature absorption cell for gas densities up to 940 amagat at 77, 201 and 295 K. The observed spectra in the main region consists of pure overtone (i.e. Δv=2) single transitions O₂ (J), Q₂ (J) and S₂ (J), pure overtone double transitions Q₂ (J) + Q₀ (J) and Q₂ (J) + S₀ (J) and double fundamental (i.e. Δv=1) transitions O₁ (J) + Q₁ (J). Q₁ (J) + Q₁ (J) and Q₁ (J) + S₁ (J). In addition, double transitions S₂ (J) + S₀ (J) (corresponding to a first overtone vibrational-rotational transition in one molecule and a simultaneous pure rotational transition in its collision partner) and S₁ (J) + S₁ (J) (corresponding to a simultaneous fundamental vibrational-rotational transition in each molecule of the colliding pair) have been observed for the first time for normal hydrogen at 77 K. These S + S transitions arise entirely from the contribution to the intermolecular interaction by the anisotropy of the polarizability of molecule in the quadrupole field of its collision partner. -- An analysis of the observed profiles on the basis of the theory of the quadrupole induction mechanism has been attempted using a symmetrized modified dispersion lineshape (with an extra fourth power term in the denominator) and the available matrix elements of the quadrupole moment, polarizability and anisotropy of the polarizability of the H₂ molecule; it is found that the calculated intensities of the transitions involving Δv=2 are somewhat too high. However, a reduction of the Δv=2 quadrupole moment matrix elements by a factor of 0.68 is found to give a good agreement between the calculated absorption profiles and the experimental profiles at all the three experimental temperatures. Pressure narrowing of the SΔᵥ (J) + SΔᵥ (J) transitions in the first overtone region for pure gas densities in the range 640 - 940 amagst at 77 K has been clearly observed for the first time. -- A reanalysis of the absorption profiles of the S₁ (J) + S₀ (J) transitions of the fundamental band of H₂ at 77 K obtained earlier in our laboratory is also reported.

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