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Excited states of molecules adsorbed on metal clusters


Over the preceding five years the applicant and his research group have developed a new version of their Table-Direct-CI program package which enables the calculation of potential energy surfaces (PES) and other properties of ground and excited electronic states of molecules adsorbed on metal surfaces. Outer layers of the meta surface are simulated by means of the embedding technique developed by Whitten and Yang for cluster sizes of 50-100 atoms. The new program system is compatible with the atomic orbital integral and core potential routines of the latter group. This software will be transferred to the host group with the objective of streamlining the computational procedures to maximize the efficiency and range of applications for its use. To this end detailed MRD-CI calculations are planned for the technologically interesting case of formaldehyde H_2CO adsorbed on a Ag(111) surface. First, the equilibrium geometries need to be determined in ground and key excited states and excitation and vibrational energies calculated for comparison with the analogous results for isolated formaldehyde. Then dissociation pathways will be considered which lead to H, HCO, O and CO fragments, again in both ground and excited states. Experimentally there has been an indication that polymerization on the metal surface occurs when HCO radicals react with other H_2CO molecules, and it is expected that the proposed calculations will be able to offer new insight into the feasibility of such processes. Excitation into the vacant PI* orbital is also thought to be involved in various photochemical reactions of this system and this mechanism should also be clarified as a result of the proposed calculations. The main objective of the transfer is to allow the host group to become familiar with the above software and to help in its further development by concentrating on the formaldehyde/Ag(111)adsorption system. Close interaction with the applicant over an extended period of time should lead to general improvements in the way such calculations are carried out. At the same time, the above application should provide insight into the photochemistry of formaldehyde on metal surfaces and a better understanding of the mechanisms for certain observed processes such as polymerisation. The main impact of the work is expected to be the availability of much more accurate PES for excited states of molecules adsorbed on metal surfaces. Analysis of the results of theoretical calculations of this kind in terms of the occupation of various molecular orbital should make it possible to formulate more realistic models for photochemical reactions on the surfaces of metals than those currently available from experimental data alone.

Funding Scheme

RGI - Research grants (individual fellowships)


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