Classical dynamics above dissociation

Classical Dynamics Above Dissociation ABA I/>cal Mode Systems with Two Degrees of Freedom... 

Figure 5. Island chain in the Base (M oiodel problem. The presence of such classical resonances prevented Hase from carrying out EBK quantization for this model of H-C-C dynamics above dissociation. See Table III. Reproduced from ref. ( ). Copyright 1983, American Chemical Society.

Comparisons between state-specific quantum mechanical and classical calculations have been made for four systems, HO2 [60], NO2 [271], HNO [39], and HCO [51]. For the first three systems the quantum dynamics is statistical state-specific and the classical dynamics is in essence irregular above the dissociation threshold HCO is an example of mode-specific quantum mechanical behavior and the classical phase space is certainly not completely chaotic. 

The most illuminating consequence of multi-dimensional vibrational dynamics in polyatomic molecules are fluctuations of resonance widths. In particular, narrow resonances can often be found far above the first dissociation threshold. We have seen that in systems with one degree of freedom the sequence of resonance states is rather short. Since the excitation energy is deposited directly into the reaction coordinate, the complex breaks apart very quickly and the resonances become broad even close to the dissociation threshold. In polyatomic molecules, energy can be temporarily stored in additional degrees of freedom. The lifetime is then determined not only by the total energy, but also by the rate with which the excitation can be redistributed and transferred to the dissociation bond (see the discussion of the classical phase space structure in Sect. 8). 

The main purposes of the present studies are the characterization of the dynamics and the calculation of rate information for the early stages of nucleation. We have studied clusters of four, five, and six atoms. Most of the calculations were done for collisional formation of a quasibound cluster and its subsequent dissociation as illustrated in equation (1). In these calculations, all the energy of the system is initially in the relative translational motion of A and An that is, the geometry of the target cluster A is that (or close to that, see above) for the classical minimum of the summed pairwise potential. To test the validity of the assumption that initially placing the total energy of the system in translation does not affect the results, a series of calculations were done for the decay of internally hot clusters, that is. 

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