Quantum reflection of metastable hydrogen atoms by a conducting surface

Due to the degeneracy of the n=2 states, the potential between a metastable 2S hydrogen atom and a conducting surface falls off as −1/z3 asymptotically, in contrast to the usual retarded van der Waals potentials, which fall off as −1/z4. This affects the quantum reflection amplitudes and causes the apparent space shifts, which express the time involved in the quantum reflection process, to diverge to large negative values at threshold.