Helium-induced halfwidths and line shifts of water vapor transitions of the v₁ + v₂ and v₂ + v₃ bands

The collisional broadening () and shift () coefficients of more than 100 absorption rovibrational lines of the 1 + 2 and 2 + 3 bands of the water vapor molecule in a H2O-He mixture were measured with the help of a Fourier-transform spectrometer over a large range of helium pressures. The shift coefficients are mainly positive and have an unusual rotational dependence, in contrast to the line center shift induced by other mono-atomic gases. The calculations of coefficients and are performed in the framework of the semi-classical method. The rotational dependence of these shift coefficients is explained by the rotational dependence of the isotropic intermolecular potential. The influence of accidental resonances in the H2O molecule is also discussed.