Study of the Rotational Structure of the Forbidden ν 8 Band of the C 2 H 2 D 2 -CIS Molecule

The spectrum of the cis-ethylene-d2 (C2H2D2-cis) molecule is recorded with a Bruker IFS 120 HR Fourier spectrometer in the region of 600–1200 cm–1 with spectral resolution of 0.0021 cm–1. As a result of analysis of the experimental spectrum, 36 transitions are first assigned, based on which seven upper energy levels of the state (ν8 = 1) are determined. The ν8 band is symmetry-forbidden, and its transitions appear in the IR spectrum only due to the strong c-type Coriolis interaction between the states (ν8 = 1) and (ν7 = 1). The parameters describing the rotational structure of the ν8 band are obtained.