High-resolution FTIR spectroscopy of the x11 and x2 + x7 bands of ethylene-d4

The Fourier transform infrared spectrum of the x11 band of ethylene-d4 (C2D4) has been recorded with an unapodized resolution of 0.006 cm-1 in the frequency range 2150 to 2250 cm-1. The x11 band, with a band centre of about 2201 cm-1, was found to be perturbed by the nearby x2 + x7 band centred at about 2235cm-1 by a b-type Coriolis interaction. By fitting a total of 772 infrared transitions of x11 using a Watsonʹs Areduced Hamiltonian in the Ir representation with the inclusion of b-type Coriolis interaction term, two sets of constants, up to quartic distortion constants for the x11 = 1 state, and principal rotational constants for the x2 + x7 = 1 dark state, were derived. The inertia defect of the x11 state was found to be 0.0693 +/- 0.0004u ?2.