Tunable diode laser study of the ν2 infrared band of fluoroketene: Confirmation of anomalously low C=O stretching frequency

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Abstract
The short-lived molecule fluoroketene (FHCCO) was generated by laser pyrolysis of fluoroacetyl chloride in a static multipass cell to record the first high-resolution infrared spectrum of its ν 2 fundamental band. More than 400 transitions between 2143 and 2160 cm−1 were assigned and analyzed to yield very accurate rotational and centrifugal distortion constants for the upper vibrational state. The ν 2 band origin of fluoroketene lies at 2147.826 93 cm−1, which is surprisingly low compared to the band origins of other ketenes. This result is confirmed by matrix isolation Fourier transform infrared spectroscopy of all four monohaloketenes.