Electronic states ozone molecule

By including electron correlation in the wave function the UHF method introduces more biradical character into the wave function than RHF. The spin contamination part is also purely biradical in nature, i.e. a UHF treatment in general will overestimate the biradical character. Most singlet states are well described by a closed-shell wave function near the equilibrium geometry, and in those cases it is not possible to generate a UHF solution which has a lower energy than the RHF. There are systems, however, for which this does not hold. An example is the ozone molecule, where two types of resonance structure can be drawn. Figure 4.8. 

Then the O atoms, which are reactive radicals with two unpaired electrons, react with the more abundant 02 molecules to form ozone. The ozone molecules are created in such a high-energy state that their vibrational motions would quickly tear them apart unless another molecule, such as 02 or N2, collides with them first. The other molecule, indicated as M, carries off some of the energy ... 

D) is an electronically excited oxygen atom. It can decay back to a ground state oxygen atom ( P) (which will regenerate an ozone molecule), or else it can react with water to produce two OH radicals ... 

My answer would be, using an analogy between molecules and human beings, that it is neither nice nor possibly easy to use brute force on the molecules. However, often the molecules may be in a state where they do not really know what they want to do. Then we might use some very mild means to seduce them to do what we would wish them to do. As an early example for such mild seduction I might quote the theoretical scheme for potentially mode selective infrared laser chemistry of ozone [1, 2], which predates some of the more widely publicized subsequent schemes using excited electronic states. 

The photochemical processes of triatomic molecules have been extensively studied in recent years, particularly those of water, carbon dioxide, nitrous oxide, nitrogen dioxide, ozone, and sulfur dioxide, as they are important minor constituents of the earth s atmosphere. (Probably more than 200 papers on ozone photolysis alone have been published in the last decade.) Carbon dioxide is the major component of the Mars and Venus atmospheres. The primary photofragments produced and their subsequent reactions are well understood for the above-mentioned six triatomic molecules as the photodissociation involves only two bonds to be ruptured and two fragments formed in various electronic states. The photochemical processes of these six molecules are discussed in detail in the following sections. They illustrate how the knowledge of primary products and their subsequent reactions have aided in interpreting the results obtained by the traditional end product analysis and quantum yield measurements. 

Fig. 7.1.1 Photodissociation (at a fixed bending angle) for a symmetric triatomic molecule like ozone. The vibrational ground state is superimposed on the potential energy surface of the electronic ground state an illustration of a true (direct) unimolecular reaction. (Note that in this figure all potential energies above a fixed cut-off value Amax have been replaced by Bmax, in the electronic ground state as well as in the excited electronic state.)...

The first type of hidden JTE defined above is generated by an excited state with a strong JTE. A straightforward example of such a hidden JTE, the ozone molecule O3, was considered recently [11]. Ab initio calculations of the electronic structure of this molecule were performed by a number of authors. Eigure 2 shows some of the results obtained by means of high-level ab initio calculations for the ground state with geometry optimization [12-14]. 

A complete description of the rate of a photolytic reaction should include the electronic states of the product molecules. / contains contributions from photons of all wavelengths that lead to a reaction. The flux of photons and the likelihood that photon absorption will lead to a reaction depend on the wavelength of the radiation. In the ozone example, / is sensitive to the flux of ultraviolet [A (wavelength) < 320 nm] radiation and thus / increases with height in the atmosphere, varies with time of day, and becomes zero at night. 

A similar kind of behavior of the diabatic electronic states has been found, e.g. for the ozone and hydrogen disulphide molecules. This may be a surprising feature of the diabatization procedure but, in practice, is often imavoidable. However, since the adiabatic states are well separated... 

The ground electronic state of ozone, O3, a Cgv molecule, has A, symmetry. If z-polarized light excites an allowed transition to an excited state, what is the symmetry species of the excited state ... 

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