Chlorosyl Nitrite (OClNO): An Elusive Intermediate in the Photochemistry of Nitryl Chloride

Nitryl chloride (ClNO₂) is a reactive trace gas in the troposphere that plays an important role in atmospheric chlorine chemistry. Previous studies on the photochemistry of ClNO₂ reveal dissociation and isomerization to cis- and trans-chlorine nitrite (ClONO); however, evidence for the formation of the high-energy isomeric chlorosyl nitrite (OClNO) remains controversial since its first claimed identification about 50 years ago. Here, we report the direct observation of the cis- and trans-conformers of OClNO in the photochemistry of ClNO₂ in solid Ar-matrices at 10 K. In addition to the characterization of OClNO by using matrix-isolation IR (with ¹⁸O- and ¹⁵N-isotope labeling) and UV-vis spectroscopy, spontaneous trans → cis conformational conversion via quantum tunneling with further photoisomerization to ClONO has been observed. Our results underscore the role of OClNO as a potent intermediate in the atmospheric chlorine chemistry at low temperatures.