Academic Staff - Dr T. Thirunamachandran - Theoretical Chemistry

Chiral discrimination Intermolecular forces Molecular quantum electrodynamics Multiphoton processes Optical activity

tel: +44 (0)20 7679 4701 fax: +44 (0)20 7679 7463 internal: 24701 email: t.thirunamachandran@ucl.ac.uk

Dr. Thiru deceased on 13. October 2008

Molecular quantum electrodynamics deals with both radiation-molecule and molecule-molecule inter-actions. Current research interests centre around the applications of quantum electrodynamics to optical activity, intermolecular forces, energy transfer and multiphoton processes. Our interests also include the development of simple methods within the framework of quantum electrodynamics that are suitable for applications in chemical physics.

Intermolecular Forces

From the point of view of quantum electrodynamics, intermolecular interactions arise from an exchange of virtual photons. A theory based on such an exchange leads to a direct understanding of retardation effects. A well-known example is the Casimir potential, showing an inverse seventh power dependence on distance for large intermolecular separations instead of an inverse sixth power predicted by elementary quantum mechanics. The theory is being extended to interactions involving molecules in excited states and to many-body interactions. An interesting extension of the theory is the calculation of discriminatory interaction energies between optically active molecules, i.e. energies dependent on the relative handedness of the molecules. Modifications to intermolecular interactions in the presence of an incident radiation field are also being investigated. A study of excitation transfer between molecules in a medium is in progress.

Multiphoton Processes

With the advent of lasers, particularly tunable lasers, there has been considerable activity, both experimental and theoretical, in a variety of multiphoton processes. Such processes provide valuable information about molecular properties such as hyperpolarizabilities. They also provide a means of determining the symmetry properties of energy levels not accessible by one-photon transitions. Current studies include circularly polarized luminescence and laser-induced optical activity.

Applications of the Heisenberg Formalism

In studies of time-dependent phenomena in chemical physics, the Schrödinger formulation of quantum mechanics is widely employed. However, in many cases the Heisenberg formulation provides additional valuable insight. The method has been applied to a wide range of phenomena, including energy transport and induced circular dichroism. A form of response theory based on the response of a molecule to the electromagnetic fields of other molecules is being developed. The theory will then be applied to many-body forces.

Selected Publications

1. DP Craig and T Thirunamachandran, Molecular Quantum Electrodynamics, (Dover NY) 1998.
2. A Salam and T Thirunamachandran, A new generalization of the Casimir-Polder potential to higher electric multipole polarizabilities. J Chem Phys 1996 104 5094.
3. R Passante, EA Power and T Thirunamachandran, Radiation-molecule coupling using dynamic polarizabilities. Phys Lett A 1998 249 77.
4. EA Power and T Thirunamachandran, Two derivations of the Feynman formulae for the fields of a moving charge. J Mod Optics 1999 46 1869.
5. EA Power and T Thirunamachandran, Time dependence of operators in minimal and multipolar nonrelativistic quantum electrodynamics. Phys Rev A 1999 60 4927.

This page last modified 9 August, 2010