Salam, Agha Akbar; (1993) Intermolecular interactions using molecular quantum electrodynamics. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The physical theory describing the interaction of electromagnetic radiation with atoms and molecules, molecular quantum electrodynamics, is applied to problems in intermolecular interactions and optical activity. After an outline of the basic Coulomb gauge theory in Chapter 1, the quantum electrodynamical Maxwell field operators in the vicinity of a molecule are derived in Chapter 2 in both the multipolar and minimal-coupling frameworks in the Heisenberg picture. The electromagnetic field operators are expanded in powers of the transition moments, correct up to second order in the sources with the interaction Hamiltonian including electric dipole and quadrupole, magnetic dipole and diamagnetic coupling terms. The Maxwell field operators in the multipolar form are then used in Chapter 3 to calculate the Thompson energy density and the Poynting vector associated with the electromagnetic field. The equivalence of the expectation value of both these operators obtained using the minimal-coupling Maxwell fields in the electric dipole approximation is demonstrated. The energy of interaction between two neutral molecules in ground or excited electronic states is determined in Chapter 4 using molecular response theory. The response of a polarisable test body to the electric displacement and magnetic fields of a second source molecule is calculated. Discriminatory interaction energies dependent upon the handedness of the pair of molecules are found. The energy shift is expressed in terms of pure and mixed multipole polarisabilities and is valid for all separation distances beyond overlap of electronic wavefunctions for molecules with fixed relative and random orientations. The near- and far-zone behaviour is also examined. In the final Chapter a theory for the chiroptical phenomenon molecule induced circularly polarised luminescence is presented. The difference in the rate of emission of a left-/right-circularly polarised photon from an achiral molecule through intermolecular interaction with a chiral species is calculated.

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