Precise measurement of pressure broadening parameters for water vapor with a terahertz time-domain spectrometer

The pressure broadening parameters γN2 and γO2of pure rotational transitions of water vapor with nitrogen and oxygen as foreign gases, respectively, were measured with a terahertz time-domain spectrometer (THz-TDS) in the frequency region from 0.5 to 3.5 THz. A White-type multi-pass cell was introduced in the THz-TDS system to precisely measure the absorption spectra of water vapor. The parameters of 36 lines were determined for both N2 and O2, of which 25 parameters for γN2and 28 parameters for γO2were the first laboratory experimental data. The quantum number dependence of the parameters was experimentally observed for the first time due to the good signal-to-noise ratio of this system compared with the conventional Fourier transform infrared spectrometer (FT-IR) experiments.