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.