Strong Coriolis coupling between ν5 and ν11 states of CH3CCl3 studied by millimeter-wave spectroscopy

Rotational transitions in vibrational states v5=1 and v11=1 in the oblate CH3C35Cl3 molecule have been studied at frequencies from 69 to 332 GHz. The two states belong to the second lowest wavenumber A-symmetry, and E-symmetry normal modes, and are accidentally very close in energy. They are thus strongly coupled by (x-y) Coriolis interaction, in addition to the l-type resonance in the degenerate v11=1 state. The resulting rotational transitions form three characteristic band series, which show many manifestations of strong interstate coupling. Frequencies of well over 1000 transitions have been measured and fitted to within experimental accuracy, resulting in ΔE5,11=2.41204(3) cm−1, first values of the axial constants for this molecule, C5=1709.966(7),C11=1712.462(7) MHz, and of values for the pertinent Coriolis coupling coefficients, ζ11c and ζ5,11b, which are in good agreement with results of ab initio calculations.