Semi-internal correlation in the auger electron spectrum of H₂O

The KLL Auger electron spectrum of the H₂O molecule has been studied with respect to the transitions of lowest Kinetic energy. Calculations were performed to deduce the role of semi-internal correlation in deciding energies and intensities of the transitions. Previous studies of photoelectron spectra of inner valence hole states indicate that such effects are of importance for H₂O. The relevant ionic state in the Auger spectrum of H₂O is the (2a₁)^-2 hole state, for which final ionic state correlation would be expected to be of importance. The present calculations, including a semi-internal Cl, indicate that this is indeed the case. The single particle (1s)^-1 → (2a₁)^-2 Auger transition rate is split among a number of double ionic states of which at least three have significant intensity. This leads to a satisfactory account of this previously unassigned energy region of the H₂O Auger spectrum. Transition energies involving initial and final state shake-up, shake-off were also calculated.