Interferometric Line Shape Modulation in Alkali-Halide Photoabsorption

Abstract

An ab initio calculation of the photoabsorption spectrum of ground state LiF below the ionic ${\mathrm{Li}}^{+}+{\mathrm{F}}^{\ensuremath{-}}$ threshold predicts a periodic modulation of the predissociation line shapes. Specifically, we predict a periodic reversal of Fano's line shape asymmetry parameter $q$. In this case, reversal of the $q$ parameter occurs because of the interference of vibrational wave functions propagating alternatively along diabatic and adiabatic potentials. The interference modulates the predissociation spectrum giving rise to both extremely long-lived resonances and broad window resonances. These anomalous resonances occur periodically on an energy scale greater than the Rydberg energy spacing and are finite in number.