High resolution infrared absorptivities of chlorine nitrate (ClONO2) are required in order to quantitatively evaluate, by examination of infrared spectra obtained recently from balloon‐borne spectrometers, the possible occurrence of this compound in the stratosphere. In the present study, infrared absorptivities for four absorption bands of gaseous ClONO2have been measured at 0.0625 cm−1spectral resolution with a Fourier transform infrared (FT‐IR) system. Spectra were obtained at two pressures (0.05 and 1.05 torr) of pure ClONO2and with 125 torr of N2added to a 0.50 torr sample. Absorptivities for a range of spectral resolutions (0.0625, 0.125, 0.25 and 0.50 cm−1) have been calculated from t