Dr Candadi V Sukumar

Abstract:

A new method of calculating elastic and inelastic cross sections for electron-atom and electron-ion scattering at intermediate energies is described. In this method the total wavefunction is expanded as a sum over channel functions plus a sum over L2 integrable functions. Cross sections between channels included in the first expansion are obtained by averaging the T matrix over pseudo-resonances arising from the L2 integrable functions included in the second expansion. It is shown that an appropriate averaging procedure allows for loss of flux into open channels which are omitted from the first expansion. The method is discussed in detail for a two-channel model and is shown to give good results for elastic scattering in this case when only a few L2 integrable functions are included. The method is then applied to the astrophysically important transition 2s21Se-2s2p 3Po in C III where the cross section at intermediate energies is found to be substantially below the previous best estimates.

Abstract:

A generalisation of the Jaynes-Cummings model hamiltonian describing a two-level atom interacting with a radiation field is considered. It is shown that the Heisenberg equation of motion for the atomic energy operator can be solved exactly for this model hamiltonian. © 1981.

Abstract:

We present a simple quantum model for a two-level atom interacting with initially coherent radiation. The mean atomic excitation energy, evaluated in exact closed form, exhibits rapid oscillations which periodically collapse and regenerate. The exact behaviour of the atom in a thermal field is also derived. © 1981.

Abstract:

A detailed investigation of the Regge properties of singular intermolecular potentials has been made. Inverse power potentials of the type r-s with s>2 and Lennard-Jones (12, 6) potentials are considered. Exact quantum and semiclassical calculations are carried out for collision systems for which the residue of maximum modulus is of order unity. Good agreement between the exact quantum and semiclassical results is found. The existence of non-linear as well as linear Regge trajectories is established. The accuracy and utility of some simple approximate formulae due to Brander (1966) and Tiktopoulos (1969) for the Regge properties of r-s potentials is investigated. A new approximate formula based on a complex harmonic oscillator formalism is also derived. It is shown that these approximate formulae can be used to understand the main Regge properties of singular intermolecular potentials.

Abstract:

Semiclassical and exact quantum methods have been used to make the first calculations of Regge pole positions and residues for singular complex optical potentials. The semiclassical pole positions are in excellent agreement with the quantum results. The semiclassical residues are less accurate, especially for the leading pole, but their accuracy rapidly improves as the pole number increases.