Refined local mode analysis of the stretching vibrational levels of C2D2

Dideuteroacetylene, C₂D₂, is a remarkable species for which the stretch-bend separability of the vibrational states is such that all the experimentally known stretching levels can be reproduced with an rms of 1.1 cm^?1 by using a simple stretching coordinate Hamiltonian model. The only two levels which deviate significantly from the calculations point out the effect of the 1/244 stretch-bend resonance previously identified. The local mode parameters retrieved from the fit of the experimental levels allow for a very satisfactory prediction of the available energy levels of the ¹²C¹³CD₂ species. A comparison between the local mode and normal mode approaches is presented.