The ν7, ν8, and ν11 bands of propynal, C2HCHO, in the 650 cm−1 region

The infrared spectrum of propynal, C2HCHO, is studied at high resolution (0.003 cm−1) in the range 570-640 cm−1. The relatively intense ν11 (CC-H out-of-plane bend, 693 cm−1) and ν7 (CC-H in-plane bend, 651 cm−1) fundamental bands are linked by a strong a-type Coriolis interaction. The somewhat weaker ν8 (CCO in-plane bend, 614 cm−1) fundamental has a significant Fermi-type interaction with the “dark” background state 3ν9 (∼618 cm−1). About 1400 lines are assigned and analyzed in terms of a four-state fit in order to obtain accurate band origins, rotational and centrifugal distortion parameters, and Fermi and Coriolis interaction parameters. This represents the first systematic high-resolution infrared study of propynal.