Infrared spectrum a) and difference spectrum (spectrum at time t minus spectrum at t = 0) b) of a HNCO:H₂O mixture at T = 120 K at t = 0 s, 3300 s, 21   300 s and 53 700 s. OCN⁻ has a band at 2170 cm^-1 and HOCN at 2295 cm^-1. The HNCO band has two components: one component at 2260 cm^-1 corresponding to HNCO in a H₂O environment and one component at 2234 cm^-1 corresponding to HNCO in a HNCO environment. The variation of the second component is the result of a rearrangement that can give a positive band a 2251 cm^-1 in some spectra. The bands at 2349 cm^-1 correspond to fluctuations of the gas phase CO₂.