Atomic and molecular2pbinding energies of P, As, and Se from many-body calculations and x-ray photoelectron spectroscopy

The 2p1/2,3/2 levels in As₄ and the 2p3/2 level in Se5,6 have been measured by x-ray photoelectron spectroscopy with the use of 1486.6-eV (AlKα) radiation. The 2p1/2 binding energies have been calculated for the atomic species, as well as for atomic phosphorus, as the difference between the total energies of the 2p1/2 hole state and the ground (neutral) state Δ SCF (Δ self-consistent field method), using the Dirac-Fock program of Desclaux, to which is added the respective correlation-energy difference between the two states. The calculated values of 140.70 eV for P2p1/2, 1368.89 eV for As2p1/2, and 1484.88 eV for Se2p1/2 include a 0.7-1.0-eV increase due to the effects of correlation, consistent with earlier work done on the K and Zn atoms. The 2p3/2 atomic binding energies were calculated similarly with the use of available Dirac-Slater Δ SCF values. When we combine these with the measured molecular binding energy of P₄, As₄, and Se5,6 we obtain corresponding $2p$ chemical shifts (atom-molecule) of 3.5, 3.0, and 2.4 eV, respectively. Comparison is also made between the atomic, molecular, and solid-state binding energies of As and Se, and it is found that the solid-state binding energy is the lowest of the three in both cases, as expected from consideration of extra-atomic relaxation.