Two resonances in the photodetachment spectrum of H, one just below the n = 3 threshold and the other just below the n =4 threshold, were observed decaying into H {n'=2)+e. The n =3 resonance shows a preference for the n'=2 channel when compared with total-detachment measurements. Fanoline-shape fits give central energies of 12.652+0.003 eV for H * (3) and 13.338+0.004 eV for H **(4). These values are in good agreement with current theoretical calculations. PACS number(s): 32.80.Fb, 31.50.+w, 32.80.Cy

Laser photodetachment on a relativistic H beam has revealed several series of resonances in which both electrons are excited. These "bound states in the continuum" appear as dips in the partial production cross sections of various excited states of neutral hydrogen. We present here a detailed account of the experimental observation of the resonances and the results of fits of the measured yields to sets of Fano profiles. A simple analytic formula for the energy-level spacing in this quantum-mechanical three-body system is verified.In this paper we report the observation of several series of high-lying 'P resonances in the photodetachment cross section of H . The energy levels of these doubly excited states are shown to obey a simple and elegant analytic formula. We discuss here in greater depth the results presented earlier. '

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Several series of doubly excited resonances have been observed in H ~ photodetachment, appearing as dips in the production cross section of excited neutral hydrogen. At least three resonances are clearly visible converging on each of the thresholds /! ™5, 6, 7, and 8. The data support recent theoretical calculations for the energies of doubly excited resonances and verify a Rydberg-dipole formula for the main resonance positions.PACS numbers: 32.80.FbThe dipole potential of an excited hydrogen atom polarized by a second electron will support series of resonances associated with the relevant hydrogenic state. The resonances that lead to the threshold of the outgoing channel H(n)+e~ can be observed in the continuum above the H(« -1 ) + e ~ threshold. These doubly excited resonances may be classified by "+" and " -" quantum numbers, * which emphasize whether the wave function is approximately odd (for -) or even (for 4-) under radial exchange ri«-*/*2. By combining a modified Rydberg formula 2 for the energy of the lowest resonance in each series with a recursion formula 3 for the energies of successive resonances within a series, we obtain an analytic expression for the energies (in eV) of all of the +type X P resonances in H ~ associated with all of the hydrogenic thresholds: 4Here £+ is the double-detachment threshold energy, R is the Rydberg constant, a n is a parameter associated with the hydrogenic threshold of principal quantum number n, TJ = 1 -a includes a screening factor, n is a quantum defect, and m =/*, n + 1, n +2,. . .. The cross section in the vicinity of a resonance at energy EQ and of width T, which is embedded in a continuum, is described by a Fano profile 5 o = o b + o a (q + e) 2 /(\+e 2 ) ,where e=*2(E -EQ)/T.