Experimental Study of Nonadiabatic Dynamics in Photoinduced Reactions of Complexes

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During a collision between atoms or molecules, the momentum of the heavy nuclei might be expected to supply the driving force (or energy) for a reaction to take place. Subsequently, the redistribution of electrons between the nuclei of the atoms or molecules leads to the formation or breaking of chemical bonds. This explanation is justified by the much heavier mass of the nuclei compared with electrons. However, there are examples in chemistry where it is the motion of electrons that drive the nuclei on the course of a chemical transformation. The result is the formation of a product that might otherwise have been unexpected. It is the object of this work to examine the mechanism for these processes. Two representative examples of these reactions will be described below. These involve the chemistry of a drug used to treat cancer and a rather unusual reaction mechanism.(1) Photodynamic Therapy: an experimental treatment for patients with cancer and other diseases.Oxygen molecules are absorbed in the blood and tissue of a human body. The transfer of energy to these molecules will generate a highly reactive form of oxygen that can be used for the destruction of diseased cells. This can be achieved in collisions between oxygen and another highly-energetic molecule. This other molecule is a drug that has been administered to a patient and it has been activated by the absorption of energy from light. A suitable source of light is a laser and, using a fibre-optic light guide inserted into the patient's body, the light can be delivered directly to the drug in the location of a tumor.(2) The Harpooning Reaction: the reactions of alkali metals (i.e. Li, Na, K) with halogens (fluorine, chlorine, bromine molecules).The mechanism of this reaction involves the transfer of an electron from an alkali-metal atom to a halogen molecule. This event has been referred to as harpooning because it is observed whilst the atom and molecules are widely spaced apart. The electrostatic attraction of the ion pair formed by the transfer of an electron (the harpoon ) results in the halogen molecule being reeled Into the alkali metal. This research is aimed at discovering fundamental information about the electron-transfer event and it will be extended to chemical processes involving charge-transfer from metal centres of biological molecules.In a sub-discipline of Chemistry referred to as Physical Chemistry, the principles of Physics are used to study chemical reactions. The same approach will be applied in this work using examples of chemical reactions involving molecules or mechanisms of interest in biology and medicine. This is a novel approach to the study of this field and it will provide unique and original data.