Optical Electronegativities

Abstract

Recent quantum-mechanical investigations have clarified certain properties of the exact wavefunctions (which never are explicitly known in many — electron systems). Thus, all the observable quantities pertaining to a given stationary state can be described by the first -order density matrices (or rather operators), i. e. the density of electrons having each of the two possible spin directions in our three -dimensional space, and the analogous second -order density operators describing the relative distribution of two electrons consi — dered at the time, in a six-dimensional space (1–3). Hence, if we concen — trate our interest on the groundstate alone, or a single excited state, we have only a basis for talking about individual orbitals in an indirect way (introducing natural spin orbitals) except in the case of systems with positive total spin S where the density of uncompensated spin is observable in principle. On the other hand, if we consider transitions from the groundstate to the various excited energy levels, we get another, but not necessarily consistent, picture of the individual orbitals.