First high resolution analysis of the ν21 band of propane CH3CH2CH3 at 921.382cm−1: Evidence of large amplitude tunneling effects

A high resolution (0.0015 cm −1 ) IR spectrum of propane, C 3 H 8 , has been recorded with synchrotron radiation at the French light source facility at SOLEIL coupled to a Bruker IFS-125 Fourier transform spectrometer. A preliminary analysis of the ν 21 fundamental band (B 1 , CH 3 rock) at 921.382 cm −1 reveals that the rotational energy levels of 21 1 are split by interactions with the internal rotations of the methyl groups. The AA, EE and AE + EA components of this A-type band have their band centers at 921.3724(38), 921.3821(33) and 921.3913(44) cm −1 , respectively. These torsional splittings most probably are due to anharmonic and/or Coriolis resonance couplings with nearby highly excited states of both internal rotations of the methyl groups. In addition, several vibrational–rotational resonances were observed that affect the torsional components in different ways.