Knowledge Bank

Instantaneous multiple-mode correlation functions and the semiclassical spectral method have been investigated as means of diagnosing the onset of chaotic vibrations in classical models of acetylene (ethyne). Correlation function methods provide an objective, computation ally efficient, temporally resolving criterion which should be generaliz able to larger molecules. Trajectories were performed on the potential energy surface of Halonen, Carter, and $Child1$, which reproduces experimental bond lengths, angles, and frequencies, and yields an acceptable geometry and energy for the metastable vinylidene structure. Examination of individual trajectories show that there is participation in chaotic vibrations by flux near the vinylidene configuration. We have surveyed semiclassical initial conditions through overtones of all the normal mode types, and some combinations thereof. Relatively small differences in thresholds for chaos were observed