Quantum chemical view, initial

A Quantum Chemical View of the Initial Photochemical Event in Photosynthesis... 

The previous sections have dealt with equilibrium situations i.e., minima of the (free) energy. For the kinetics we also need to know how lateral interactions affect transition states. There has hardly been any work done on this. ° From a theoretical point of view one can in principle use quantum chemical calculations just as one would for the stable states (see Section 3.4). The kinetic experiments of Section 3.3.3 depend on the activation energies and on the difference between the lateral interactions in the transition state and the initial state of a reaction. The experiments of Sections 3.3.1, 3.3.2 and 3.3.4 do not yield any information on the effect of lateral interactions on transition states. 

In view of the accuracy of today s quantum chemical calculations, it is typically necessary to adjust the initial estimates of the potential energy surface to describe the observed kinetics of a catalytic process. Accordingly, the theoretical results presented in Table V provide only initial guesses for the entropies and enthalpies of the stable species and reactive intermediates involved in ethane hydrogenolysis on platinum. 

The interminable discussions on the interpretation of quantum theory that followed the pioneering events are now considered to be of interest only to philosophers and historians, but not to physicists. In their view, finality had been reached on acceptance of the Copenhagen interpretation and the mathematical demonstration by John von Neumann of the impossibility of any alternative interpretation. The fact that theoretical chemists still have not managed to realize the initial promise of solving all chemical problems by quantum mechanics probably only means some lack of insight on the their part. 

Electrons residing in molecular clusters can be viewed as microscopic probes of both the local liquid structure and the molecular dynamics of liquids, and as such their transitory existence becomes a theoretical and experimental metaphor for one of the major fundamental and contemporary problems in chemical and molecular physics, that is, how to describe the transition between the microscopic and macroscopic realms of physical laws in the condensed phase. Since this chapter was completed in the Spring of 1979, several new and important observations have been made on the dynamics and structure of e, which, as a fundamental particle interacting with atoms and molecules in a fundamental way, serves to assist that transformation for electronic states in disordered systems. In a sense, disorder has become order on the subpicosecond time-scale, as we study events whose time duration is shorter than, or comparable to, the period during which the atoms or molecules retain some memory of the initial quantum state, or of the velocity or phase space correlations of the microscopic system. This approach anticipated the new wave of theoretical and experimental interest in developing microscopic theories of... 

Chemical reactions in the gas phase that involve four or more atoms are of considerable current interest from both the experimental and theoretical points of view[l-6]. Of particular concern is how the initial vibrational and rotational states of AB and CD affect the reaction cross sections and product ABC ro-vibrational distributions in AB + CD ABC + D. Effects such as bond and mode selectivity and correlations between the quantum states of reactants and products are of special interest. 

Explosive decomposition of conventional EMs is based on chemical processes. In spite of this fact, very few authors in the past dealt with, and today are deahng with, the initiation mechanisms from the point-of-view of chemistry. As follows from Sect. 3, most authors of papers published in this field try to solve the problem of micro-initiation by means of quantum chemistry [1,3-5,39,56,60,74,81,85,105,106,109]. The simulations are predominantly restricted to a few selected molecules of energetic substances (NM, RDX, HMX and TATB are the dominating ones) and their crystals [1,3, 5,56,60,74], or in some cases only to hypothetical two-atom molecules [109]. 

Type I Photoinitiators Unimolecular Photoinitiators. These substances undergo an homolytic bond cleavage upon absorption of light. The fragmentation that leads to the formation of radicals is, from the point of view of chemical kinetics, a unimolecular reaction. The number of initiating radicals formed upon absorption of one photon is termed the quantum yield of radical formation... 

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