High‐resolution vib‐rotational analysis of the ν₃ and ν₄ spectral regions of chlorine nitrate

High‐resolution Fourier‐transform spectra of isotopically natural pure chlorine nitrate, ClONO 2 , were recorded with a resolution of 0.00094 cm −1 at temperatures of 190 and 297 K. An extensive vib‐rotational analysis of the ν 4 and ν 3 fundamental bands as well as the hot band, ν 4 + ν 9 − ν 9 , of the most abundant 35 Cl isotopomer was performed for the 190 K spectrum. In addition, the cold bands of the lesser abundant 37 Cl isotopomer were partially assigned. Accurate upper state rotational Hamiltonian constants were derived. In particular, the following band centers were determined: ν 0 (ν 4 ) = 780.2161(8) cm −1 , ν 0 (ν 3 ) = 809.7513(8) cm −1 , ν 0 (ν 4 + ν 9 − ν 9 ) = 778.7235(8) cm −1 for 35 ClONO 2 and ν 0 (ν 4 ) = 778.8695(8) cm −1 for 37 ClONO 2 . These constants were used to generate spectral parameters that permit a precise modeling of experimental cross sections of the ν 4 fundamental Q‐branch of 35 ClONO 2 over the temperature range of 190–297 K and atmospheric pressures up to 150 mbar. This Q‐branch is used for atmospheric retrievals.