Title:

Close coupling calculations of dimer energy levels

The aim of this thesis is to calculate the bound state energies of molecular dimers. The problem is formulated for a system consisting of any two diatomic molecules, treated as rigid rotors. Simplifications which arise from symmetry considerations are fully discussed. The de Vogelaere and Rmatrix propagator algorithms have been used to solve the resulting systems of coupled second order differential equations. Their numerical convergence properties are compared in test calculations on the ArHCl system. The above methods are used to calculate the bound state energies of H(_2)H(_2), using four separate ab initio potentials. The CI potential of Meyer, Schaefer and Liu (designated "M80") is found to give the best agreement with spectroscopic measurements, though a small shift in the position of the repulsive wall is indicated. The M80 potential is then used in the remaining calculations; these include the evaluation of the energies of resonances and bound states lying above the dissociation limit of the dimer, corresponding to rotationally excited H (_2). The results of these calculations are used to assess the validity of approximations made in the proposed identification of H (_2)H (_2) features in the far infrared spectra of the Jovian atmosphere. The BornOppenheimer approximation permits the use of the M80 potential to calculate the bound states and resonances of D (_2) D (_2). That some of these resonances have dual Feshbach/shape character is noted. The dimer structure, accompanying the observed near infrared S (_1)(0) and Q(_1)(0) + S(_o)(0) spectra in orthodeuterium, is modelled by treating the two D(_2) molecules as distinguishable rigid rotors. We conclude that the experiments provide evidence both for rotational splitting of the levels and for internal rotational predissociation. Alternative line assignments to those hitherto made are also suggested. We end with a general discussion in which suggestions for future work are made.
