Knowledge Bank

Nitric acid $(HONO2)$ isolated in solid argon at 12 K was irradiated with 193-nm emission from an ArF excimer laser. Recombination of photofragments OH and $NO2$ led to the formation of various conformers of peroxynitrous acid (HOONO). In addition to the previously reported lines due to cisperp $HOONO,1$ lines at 3285.4, 1600.3, 1395.0, 927.2, 794.3, and $616.9cm-1$ were observed; they are assigned to cis-cis HOONO. The observed vibrational frequencies and the isotopic shifts of both conformers are in agreement with recent theoretical calculations. The cis-cis HOONO was photolysed much more rapidly than the cis-perp HOONO upon irradiation of the 308-nm emission from the XeC1 laser. The mechanism of formation of different conformers of HOONO are discussed.