Knowledge Bank

Loosely speaking, the Franck-Condon distributions for diatonic radiative transitions from a single vibrational level of a given electronic state to all possible levels (bound and free) of a second electronic state exhibit either reflection"" or Interference"" structure. In reflection structure there is a one-to-one mapping of peaks in the initial state probability distribution into peaks in the spectrum. No such simple relationship is known for interference structure (originally called ``internal diffraction"" by $Condon1$). It can be shown that the condition for reflection structure is a monotonic difference potential in the range of internuclear distance R sampled by the initial wavefunction, whereas interference structure occurs when the initial wavefunction samples extrema in the difference potential$ ^{2}$. These conditions are discussed with application to a number of diatomic transitions. $\mathrm{<mrow\; data-mjx-texclass="ORD">\ast </mrow>}$ Work supported by the Air Force Office of Scientific Research. $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$ E. U. Condon, Phys. Rev. 32. 858 (1928). $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ J. Tellinghuisen, et al., Chen. Phys. 50. 313 (1980)