Rotational analysis of the ν_6, ν_8, ν_3 + ν_4 interacting infrared system of C_2D_6 between 960 cm~(-1) and 1180 cm~(-1)

摘要

The Fourier transform infrared spectrum of C_2D_6 (FWHM ≈ 0.0030 cm~(-1)) has been investigated in the region of the ν_6(A_(2u)) and ν_8(E_u) fundamentals, from 960 cm~(-1) to 1180 cm~(-1). A strong x,y Coriolis interaction between ν_6 and ν_8, 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 ν_8, a z Coriolis-type resonance of ν_3 + ν_(A_(1u)) and ν_6 occurs at K ≤ 6, and an x,y Coriolis-type resonance of ν_8( — l, K— 1) and ν_3 + ν_4(K) occurs at K = 7 and 8. A further coupling of ν_8 (4- /, K— 2) and ν_3 + ν_4(K) has been observed as well. The vibration-rotation constants of ν_6, ν_8 and ν_3 + ν_4, and several interaction parameters, have been determined by the least-squares fit of the available data, with an overall standard deviation σ = 4.6 x 10~(-4) cm~(-1) in the fit of 1661 observed transition wavenumbers. A torsional splitting is observed only in the level ν_8( -l,K=8,J= 20), resonant with 2ν_4 + ν_9( - l, K = 11, J = 20) in which two torsional quanta ν_4 are excited. Many other J components of ν_8(—l,K= 8) are broadened by this interaction. Rules on the symmetries of the allowed perturbing operators and of their torsional components in ethane-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.