Continuum and magnetic dipole absorption of the water vapor-oxygen mixtures from 0.3 to 3.6Â THz

The measurement of absorbance in water vapor-oxygen mixtures is reported for the far-IR region from 10 to 120 cm−1 (0.3-3.6 THz). The experiments were performed in a temperature-stabilized multipass absorption cell coupled to a far-infrared Fourier transform spectrometer with a liquid-He-cooled bolometer detector. The absorbance components due to both the H2O-O2 continuum and the oxygen magnetic dipole discrete lines have been measured in the temperature range from 294 to 333 K with a spectral resolution of 0.03 to 0.07 cm−1. In the range up to 2.5 THz, the H2O-O2 continuum demonstrates a nearly quadratic dependence of absorbance on frequency, while in the 3.43 THz window deviation from this dependence was detected. The series of rotational lines associated with magnetic dipole transitions was measured in pure oxygen. In the mixture of 1.36 kPa of water vapor and 79.2 kPa of oxygen, a comparable contribution from continuum and discrete lines associated with magnetic dipole transitions of O2 was observed. The absorption coefficient of 0.066 (dB/km)/(kPa THz)2 and its temperature exponent of 4.7 were measured for the H2O-O2 continuum. Experimental continua data compared to theoretically predicted values exhibit good agreement. The modeling of the resonant water vapor spectrum was performed using a Van Vleck-Weisskopf lineshape with a 215 cm−1 far-wing cut-off and the HITRAN2004 database.