Coming to Terms with Term States

In multielectron atoms or molecules, quantized electronic energy states known as term states provide a framework for interpreting absorption and emission spectra. Enumerating the term states associated with any particular electron configuration is possible using time-honored procedures, but the underpinnings of the methods do not always receive the attention they deserve. Rounding out the discussion with another approach to term states would provide added perspective. In particular, for systems involving two electrons distributing among two orbitals one can begin by identifying plausible wave functions. The states generated are few in number but noteworthy in that analogous states occur in a host of systems, including helium, titanocene, and molecular hydrogen. Parallels among the systems become evident from the forms of the wave functions.