High‐resolution infrared spectroscopy of 2‐fluoroethanol in a molecular beam

The high‐resolution infrared spectrum of 2‐fluoroethanol (2FE) in a molecular beam was obtained in the region of 2990–2977 cm−1. This spectral region contains the asymmetric CH stretch of the fluorinated carbon. Excitation of the CH stretch has previously been observed to photochemically isomerize 2FE from the Gg’ to the Tt conformation. The high‐resolution spectrum of this transition provides the information necessary to quantitatively evaluate the amount of vibrational mode‐coupling between the asymmetric CH stretch and the torsional reactive coordinate. Minimal amounts of vibrational mode coupling were observed in the spectrum which is consistent with the slow photoisomerization rate. The correlation of the amount of mode coupling and the isomerization rate supports the conclusion that mode‐selective vibrational coupling plays an important role in the photochemical dynamics. It is further suggested that the strong intramolecular attractive interactions limit the magnitude of the vibrational mode coupling.