Photoionisation through isolated Rydberg states interacting with a broad state

When a Rydberg series interacts with a broad underlying state, the Fano parameters of the Rydberg states vary in a systematic way with detuning from the centre of the broad state. The authors derive the general theoretical form of the variation, and show that the asymmetry parameter q may change sign up to four times as a function of detuning. Relevant data are discussed.