Nonadiabatic calculations of the oscillator strengths for the helium atom in the hyperspherical adiabatic approach

Energies and wavefunctions are calculated for the bound states of the heliu m atom in the hyperspherical adiabatic approach by the full inclusion of no nadiabatic couplings. We show that the use of appropriate asymptotic radial boundary conditions not only allows the efficient calculation of energies accurate up to a few ppm for the ground state but also gives increasingly p recise results for high-lying excited states with a unique set of equations . The accuracy of the wavefunctions is demonstrated by the calculation of o scillator strengths in the length form for transitions between stares ii S- 1(e) and (n + 1) P-1(0) up to n = 29, in agreement with variational calcula tions.