THz laser study of self-pressure and temperature broadening and shifts of water vapor lines for pressures up to [formula omitted

Abstract

The self-broadened linewidths of pure rotational lines of water vapor have been investigated in the temperature range 263– 340 K over a pressure range from 30– 1400 Pa using an optically pumped THz photomixer spectrometer having a relative precision of ≈10 −5 cm −1 . The lineshapes of several lines between 12 and 52 cm −1 were well fit by Lorentzian profiles over the spectral interval spanning ±5 FWHM. The Lorentzian FWHM linewidths varied between 6.6×10 −6 and 1.06×10 −6 cm −1 Pa −1 (0.67 and 1.07 cm −1 atm −1 ) and were found to depend on the J, K a and K c quantum numbers as well as temperature. The observed pressure-induced shifts, δν( P), ranged from 1.3×10 −7– 4.5×10 −7 cm −1 Pa −1 (0.013– 0.046 cm −1 atm −1) . The measured linewidths also exhibited a ( T 0/ T) n power law dependence on temperature. The best fit exponent n varied from 0.56 to 0.81, dependent on rotational line. A decrease in δν( T) with increasing temperature is also observed, varying between 2×10 −8 and 5×10 −8 cm −1 Pa −1 (2×10 −3 and 5×10 −3 cm −1 atm −1 ) over the 300– 340 K temperature range.