The influence of the stretch modes on the classical highly excited bend motion with Darling–Dennison coupling in acetylene Original Research Article

The detail mode characters of the C–H bends with Darling–Dennison coupling in the bath of the stretches of acetylene are analyzed in the coset representative space SU(2)/U(1). Besides the local and normal modes, the precessional mode [Mol. Phys. 53 (1984) 961; J. Chem. Phys. 105 (1996) 10743] is also reproduced. The analysis shows that the excitation of the C–C stretch will lead to more trans local modes for high excitation of the bend. This is prone to the isomerization of acetylene to vinylidene.