Study of TwoElectron Systems in a Radiation Field Using Interparticle Coordinates
Abstract
We provide a general formulation of the energy eigenvalue problem for a twoelectron system interacting with a monochromatic radiation field, using the interparticle coordinates to describe the internal motion, with electron correlation fully incorporated. No restriction is placed on the total orbital angular momentum of the system. The solution of the Schrodinger wave equation for a twoelectron system is obtained by expanding the atomic wavefunction on a set of basis functions that are eigenfunctions of the total orbital angular momentum operator. The angular dependence of the wave function is determined a priori. The derivation of the interaction of the twoelectron system with a radiation field is carried out in both length and velocity gauges. The timeindependent Schrodinger equation is solved by using the RayleighSchrodinger expansion of the quasienergy, and alternatively, using an effective Hamiltonian that is the representation of the Hamiltonian on a finite set of basis vectors that are successive terms in the RayleighSchrodinger expansion of the Floquet wavefunction. We have applied this formulation to the calculation of accurate second and fourthorder ac shifts and widths of both the negative hydrogen ion and helium. In addition, by constructing a 3level model Hamiltonian from the zeroth, first, and secondorder perturbed wavefunctions, we have obtained estimates of the ac shifts and widths of the negative hydrogen ion in the nonperturbativefield regime, where the atomfield interaction is relatively strong. Using this model for the negative hydrogen ion, we have explored photodecay in the autoionizing resonance region below the twoelectron escape threshold, and stabilization (against ionization) at frequencies above the threshold for twoelectron escape. Furthermore, we have gained some insight into the properties of electron correlation in ground states of the negative hydrogen ion and helium by plotting the unperturbed spatial probability distribution of the two electrons. We also present accurate results of calculations of oscillator strengths of helium for singlet and triplet transitions nS→ mP with n,/ m<= 5, and nP→ mD with n,/ m<= 4.
 Publication:

Ph.D. Thesis
 Pub Date:
 1997
 Bibcode:
 1997PhDT.........3Y
 Keywords:

 SCHRODINGER EQUATION;
 WAVE FUNCTION;
 QUASIENERGY;
 Physics: Atomic, Physics: Astronomy and Astrophysics