New measurements of the water vapor continuum in the region from 0.3 to 2.7 THz

We present a spectroscopic study of the water vapor continuum absorption in the far-IR region from 10 to 90cm(-1) (0.3-2.7THz). The experimental technique combines a temperature-stabilized multipass absorption cell, a polarizing (Martin-Puplett) interferometric spectrometer, and a liquid-He-cooled bolometer detector. The contributions to the absorbance resulting from the structureless H2O-H2O and H2O-N-2 continua have been measured in the temperature range from 293 to 333 K with spectral resolution of 0.04-0.12 cm(-1). The resonant water vapor spectrum was modeled using the HITRAN04 database and a Van Vleck-Weisskopf lineshape function with a 100cm(-1) far-wing cut-off. Within experimental uncertainty, both the H2O-H2O and H2O-N-2 continua demonstrate nearly quadratic dependencies of absorbance on frequency with, however, some deviation near the 2.5 THz window. The absorption coefficients of 3.83 and 0.185 (dB/km)/(kPaTHZ)(2) were measured for self- and foreign-gas continuum, respectively. The corresponding temperature exponents Were found to be 8.8 and 5.7. The theoretically predicted foreign continuum is presented and a reasonable agreement with experiment is obtained. (c) 2007 Elsevier Ltd. All rights reserved.