Feshbach projection operator calculation of the potential energy surfaces and autoionization lifetimes for He(2 3S) –H and He(2 3S) –H2

Abstract

A new technique has been developed for calculating potential energy surfaces and widths for autoionizing molecular systems. The method is based on the use of the Feshbach projection operators P and Q, which are defined within the space of configurations generated from a basis set of square‐integrable orbitals. Autoionizing states are then obtained by diagonalizing a particular subblock of the finite Hamiltonian constructed by the CI procedure. These states decay because they are only approximate eigenfunctions of the full finite Hamiltonian. Their lifetimes are evaluated using continuum functions which are expanded in the basis orbitals. Such an expansion is shown to be sufficiently accurate. The present technique is compared with the stabilization method and is found to illuminate certain features of that procedure. Potential surfaces V* and widths Γ have been calculated for the Penning ionization transitions He(2 ³S)+H→He+H⁺+e⁻ and He(2 ³S)+H₂→He+H₂⁺+e⁻.