Collision Broadening of Rotational Absorption Lines. VI. Pressure Broadening of Microwave Absorption Spectra Involving Oxygen

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Abstract
The pressure broadening of microwave absorption lines by collisions involving O2 has been investigated using a method presented earlier for analyzing and evaluating microwave linewidth parameters under conditions where impact‐theory assumptions are valid. A value of (1.16 ± 0.12) D· Å was obtained for the molecular quadrupole moment of O2 from linewidth data for broadening of NH3 inversion lines by O2. This value is in reasonably good agreement with values determined by other methods, and should constitute an upper limit to the true value since only dipole–quadrupole interaction was considered in the linewidth calculations, This value of the molecular quadrupole moment of O2 was used to calculate linewidth parameters for H2O–O2 broadening, OCS–O2 broadening, N2O–O2 broadening, O2–O2 self‐broadening, and the broadening of the 9– line of O2 by various foreign gases. These results are in general smaller than the experimental values, suggesting that the effects of higher‐order interactions are important in collisions with O2.