Experimental study of the line mixing coefficient for 118.75 GHz oxygen line

The oxygen fine structure line 1- at 118.75GHz was studied by two spectrometers at low (0.2-3.5Torr) and high (atmosphere) pressures in air and pure oxygen. Improvement in the spectrometer with BWO and acoustic detector included use of a powerful (more than 40 mW) radiation source. Improvement in the modern resonator spectrometer included exclusion of apparatus function by sample substitution and a wider (110-130 GHz) scanned frequency range. As a result, the 1- oxygen line was observed by both spectrometers with high (up to 450) signal-to-noise ratio which permitted precise measurements of the line parameters. The investigation separated linear- and quadratic-with-pressure displacement of the line center. The line mixing coefficient responsible for apparent quadratic dependence of the center frequency on pressure was measured experimentally for the first time for this line. The line mixing coefficient was measured at 297 K as -4.62(38) x 10(-5) Torr(-1) for pure oxygen and -5.9(29) x 10(-5) Torr(-1) for air, compared to the previously calculated value -3.1 x 10(-5) Torr(-1). Linear dependence of the line center frequency on pressure does not exceed +/-20 kHz/Torr for air and +/-10 kHz/Torr for pure oxygen. Refined values of line broadening were obtained. Integral intensity of the line was measured. A comparison with the previous investigations is presented. Inconsistencies in published data about pressure line shifts of oxygen molecule spectral lines are discussed. (C) 2003 Elsevier Inc. All rights reserved.