Near-threshold electron impact excitation functions of high-n states of Ar, Kr, Xe, H2, N2and CO

Excitation functions of Rydberg states lying within a band of n values that is typically from approximately 16 to 46 have been measured with high energy resolution. All the excitation functions are found to have a sudden threshold onset, the sharpness of which is consistent with the high-n excitation cross sections having finite values at threshold. This behaviour, and also the details of the energy dependences of the excitation functions near to, but above the threshold, are interpreted in terms of the high-n states being formed by the evolution of the collision complex along the Wannier ridge.