We studied the ml=0 photoionization channel of H(n=2, ml=0) red and blue states in a dc electric field F theoretically and experimentally in the energy region between the two ionization thresholds: the Stark-induced classical threshold at E=-2 F and the threshold of the field-free atom at E=0. We find that the ionization yield via the rapidly ionizing ml=0 channels concentrates at the two thresholds. Such concentration has not been observed in similar experiments on complex atoms due to a large degree of electron scattering from the ion core that produces significant amounts of mixing among the excitation amplitudes and among the ionization channels. Our results show that the hydrogenic Stark levels of fixed principle quantum number n become sharper as their parabolic quantum number n1 increases. On the other hand, the levels of fixed n1 get wider as their quantum number n increases. Moreover, our results show a remarkable property: The ratio of the cross sections from the red and from the blue ml=0 states of n=2 fall on a universal curve when plotted as a function of Z1, the fraction of the nuclear charge that drives the bound motion. Also, the ratio is found to be larger than 1 in two regions where Z1=0(1/4) and (1/2)(3/4), less than 1 in the rest of the Z1 regions, Z1=(1/4)(1/2) and (3/4)1, and is equal to unity at the common boundaries at Z1=(1/4), (1/2), and (3/4), thus indicating special properties of these fractional charges.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics