Statistical theory of Fano resonances in atomic and molecular photoabsorption

A statistical theory of Fano resonances is presented for highly excited atomic and molecular systems with a classical chaotic limit. The probability distribution of the Fano parameter, which characterizes the asymmetry profile of a single resonance, is derived both for the case when the quantum system obeys time-reversal symmetry and when time-reversal symmetry is broken. Applications of the theory to photodissociation spectra of molecules and autoionization of Rydberg atoms are discussed.