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

Abstract

The pressure broadening parameters γ N 2 and γ O 2 of 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 N 2 and O 2, of which 25 parameters for γ N 2 and 28 parameters for γ O 2 were 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.