A Fermi Resonance with ν6 of Acetonitrile

The rotation-vibration spectrum of ν6 of acetonitrile measured by Nakagawa et al. has been reanalyzed by taking account of the Fermi resonance between the states |v6=1> and |v7=1, v8=1>. The previous assignment of Q branches by Amat et al. has been revised on the basis of the obtained values of band constants. The following band constants have been determined for the ν6 band: ν0=1447.9 cm−1, ζ=−0.305 and αA=0.046 cm−1. From the value of the resonance operator, the magnitude of the cubic force constant k678 has been estimated to be about 30 cm−1.