Ab Initio Study Predicts That Enigmatic Isonitrosyl Fluoride Should Be Stable at Low Temperatures yet Unnoticeable Due to Its Photoreactivity

Isonitrosyl fluoride F–ON remains an undetected molecule despite multiple attempts to generate it and successful identification of other isonitrosyl halides (X–ONs) via phototransformations of corresponding X-NOs. We investigated this problem using ab initio methods and found no evidence of instability of F–ON at low temperatures of 8–10 K. Instead, experimental observation of F–ON is likely challenged by the (1) different nature of photoexcitation of F-NO and its quantum yield being lower than those of other X-NOs and (2) the presence of a bright charge-transfer transition in the F–ON spectrum that likely overlaps with the weak band of F-NO used for photoexcitation. Formation of F–ON via symmetry-prohibited photoexcitation of F-NO is followed by its immediate photodecomposition to the charge-transfer excited state and its conversion to F-NO upon de-excitation. Thus, F–ON should be readily observable using non-photochemistry methods such as microwave spectroscopy.