Molecular dissociation energy sharing

In this contribution we demonstrate vibrationally induced molecular dissociation in two polyatomic molecules, namely chromium hexacarbonyl and diazomethane (Fig. 1), employing fs mid-infrared laser sources [1,2]. As will be shown below, in both cases the initially excited mode does not lead directly to reaction but provides the doorway to access the right combination of modes. Thus both reactions have three steps (1) Stepwise multiphoton excitation of the doorway mode, (2) sharing of energy with other modes, and (3) formation of... 

The results discussed here contain a wealth of dynamical details of the detonation wave profiles under different conditions. In particular, they show both thermal initiation and shock initiation of dissociation reactions, as well as the coupling of the reactions front, the shock front, and the thermoelastic properties of the lattice, all under highly nonequilibrium conditions. It is true that our hypothetical molecular model and the simulation of the "chemistry" of dissociation are too simple and perhaps simplistic. Nevertheless, because we were able to demonstrate by separate tests [36,37] that this model system was well behaved, we believe that many of the details, especially those relating to the mechanisms and rates of energy transfer and energy sharing, should have their counterparts in reality. As we further develop our techniques of modeling chemical reactions, we should be able to apply the MD method to the study of these details which are not easily accessible by any other method. 

MOLECULAR DYNAMICAL STUDIES OF ENERGY TRANSPORT AND ENERGY SHARING IN MOLECULAR DISSOCIATION... 

First, immediately after ionization, contact ion pairs are formed, in which no solvent molecules intervene between the two ions that are in close contact. The contact ion pair constitutes an electric dipole having only one common primary solvation shell. The ion pair separated by the thickness of only one solvent molecule is called a solvent-shared ion pair In solvent-shared ion pairs, the two ions already have their own primary solvation shells. These, however, interpenetrate each other. Contact and solvent-shared ion pairs are separated by an energy barrier which corresponds to the necessity of creating a void between the ions that grows to molecular size before a solvent molecule can occupy it. Further dissociation leads to solvent-separated ion pairs Here, the primary solvation shells of the two ions are in contact, so that some overlap of secondary and further solvation shells takes place. Increase in ion-solvating power and relative permittivity of the solvent favours solvent-shared and solvent-separated ion pairs. However, a clear experimental distinction between solvent-shared and solvent-separated ion pairs is not easily obtainable. Therefore, the designations solvent-shared and solvent-separated ion pairs are sometimes interchangeable. Eventually, further dissociation of the two ions leads to free, i.e. unpaired solvated ions with independent primary and secondary solvation shells. The circumstances under which contact, solvent-shared, and solvent-separated ion pairs can exist as thermodynamically distinct species in solution have been reviewed by Swarcz [138] and by Marcus [241],... 

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