Photodetachment in a cavity: From rectangles to parallel plates

Simple analytic formulas are presented for photodetachment cross sections of H− inside a rectangular cavity using semiclassical closed-orbit theory. The formulas predict oscillations in the spectrum and correlate the oscillations with closed orbits of the system. Explicit fully-quantum-mechanical formulas are also derived. We compare the results from closed orbit theory and quantum-mechanical calculations. We also show how the photodetachment cross section formulas for a rectangular cavity can be reduced to those for a cavity consisting of two plates.