Rotational analysis of thev6,v8,v3+v4interacting infrared system of C2D6between 960 cm-1and 1180 cm-1

Abstract

The Fourier transform infrared spectrum of C2D6 (FWHM ≈ 0⋅0030 cm-1) has been investigated in the region of the ν6(A2u) and ν8(Eu) fundamentals, from 960 cm-1 to 1180 cm-1. A strong x, y Coriolis interaction between ν6 and ν8, with K level crossing, generates large displacements of the rotational components of both vibrational states, tuning them to additional local resonances in several spectral regions. Beyond l resonances with Δl = ±2, Δk = ∓ 1 within ν8, a z Coriolis-type resonance of ν8 + ν4 (A1u) and ν6 occurs at K⩽6, and an x, y Coriolis-type resonance of ν8 (- l, K-1) and ν3 + ν4 (K) occurs at K = 7 and 8. A further coupling of ν8 (+ l,K - 2) and ν3 + ν4 (K) has been observed as well. The vibration-rotation constants of ν6, ν8 and ν3 + ν4, and several interaction parameters, have been determined by the least-squares fit of the available data, with an overall standard deviation σ = 4. x 6 10-4cm-1 in the fit of 1661 observed transition waveνmbers. A torsional splitting is observed only in the level ν8(-l, K = 8,J = 20), resonant with 2ν4 + ν9 (- l, K = 11, J = 20) in which two torsional quanta ν4 are excited. Many other J components of ν8 (- l, K = 8) are broadened by this interaction. Rules on the symmetries of the allowed perturbing operators and of their torsional components inethane-like molecules are determined. In the high-barrier limit, we find it useful to factorize the torsional operators into functions of torsional coordinate and momentum operators and trigonometric functions of the torsional angle. Application of these rules to the coupling operators active in this spectrum is made.