Diode-Laser Measurements of N₂-Broadening Coefficients in the ν₂ Band of HCN at Low Temperature

N-broadening coefficients have been measured for 28 lines of HCN at 203 K in the P, Q, and R branches of the ν band, using a tunable diode-laser spectrometer. Semiclassical calculations of these collisional broadenings have been performed using two intermolecular anisotropic potentials as well as two isotropic potentials to describe the trajectory model: one is the Lennard-Jones potential, and the other is a spherical average of the atom-atom model. The parameters of the atom-atom model and those of the Lennard-Jones potentials have been calculated for HCN by fitting experimental values of second viral coefficients. The calculated broadening coefficients are significantly larger, especially for the lines with J > 10, than the experimental data. By comparing the results obtained at room and low temperatures. the temperature dependence of line widths has been determined both theoretically and experimentally.