RESONANCES AND CHAOS IN THE COLLINEAR COLLISION SYSTEM (HE, H-2(+)) AND ITS ISOTOPIC VARIANTS

The collinear atom-diatom collision system provides one of the simples t instances of chaotic or irregular scattering. Classically, irregular scattering is manifest in the sensitive dependence of post-collision variables on initial conditions, and quantally, in the appearance of a dense spectrum of dynamical resonances. We examine the influence of k inematic factors on such dynamical resonances in collinear (He, H-2(+) ) collisions by computing the transition state spectra for collinear ( He,HD+) and (He,DH+) collisions using the time-dependent quantum mecha nical approach. The nearest neighbor spacing distribution P(s) and the spectral rigidity Delta(3)(L) for these resonances suggest that the d ynamics is predominantly irregular for collinear (He,HD+) and predomin antly regular for collinear (He, DH+). These findings are reinforced b y a significantly larger ''correlation hole'' in ensemble averaged sur vival probability [[(t)]] values for collinear (He, HD+) than for coll inear (He,DH+). In addition we have also examined measures of classica l chaos through the dependence of the final vibrational action, n(f), on the initial vibrational phase phi(i) of the diatom, and Poincare su rfaces-of-section They show that (He, HD+) collisions are partly chaot ic over the entire energy range (0-2.78 eV) while (He, DH+) collisions , in contrast, are highly regular at collision energies below the clas sical threshold for reaction. Above the threshold, the scattering rema ins regular for initial vibrational states v = 0 and 1 of DH+.