The autoionisation widths of He I below the N=3 He⁺threshold

Abstract

The saddle-point technique is extended to calculate autoionisation energies and widths of helium below the n = 2 and the n = 3 hydrogenic thresholds. The width of the lowest 'P" state below the n = 3 threshold is determined to be 114.2 meV, but the experimental value of Dhez and Ederer is (1323~ 14) meV. The width of the lowest 'Po state below the n = 2 threshold is 0.0366 eV, which agrees with the experimental value of 0.0384*0.004 eV given by Madden and Codling.

Observation of the (2p,nd)1Podouble-excitation Ry

“…Since the lifetime of a state n in a given Rydberg series is oc/7* 3 , with the effective quantum number n*=n-}j. ip -quantum defect) [13], reduced widths (V n n* } ) can be introduced. Theory predicts the reduced widths of the (sp,2n -) and (2p,nd) series to be smaller by factors of = 10 2 and up to = 10 4 , respectively, than the one o( the (sp,2n + ) series [6,12], The extremely narrow widths of the (2p,nd) states, with the theoretical predictions for the lowest (2p,3d) state ranging from 4.2xl0 -5 meV [6] via ^4.5xl0~4 meV [12,14,15] to 3.0xlO~3 meV [5], make it difficult to observe these states.…”

“…After the initial pioneering experimental [l] and theoretical [2] work, progress in this field was relatively slow due to severe spectroscopic limitations, in particular of available photon sources in the 60-to 80-eV range. In recent years, however, considerable attention has been paid to these states, as well as to related states in H~, from both the theoretical [3][4][5][6][7] and the experimental [8] point of view.…”

“…In photoexcitation, the dipole-selection rule allows only X P° final states, which reduces the number of observable Rydberg series to three [10]: Only two of them, the (sp,2n + ) x P° and the (sp,2n~) x P° series could be observed until now [3,8], while the third (2p,nd) l P° series was missing [11]. This situation has led to considerable confusion, since the various theoretical calculations are characterized by substantial discrepancies with respect to the energies and widths of the (2p,nd) ] P° states [5][6][7][11][12][13][14][15].In the present Letter we report on the first observation of the four lowest states of the (2p,nd) ] P° series by high-resolution photoabsorption spectroscopy using synchrotron radiation. With a resolving power of E/AE = 16000 combined with high photon flux, the (sp, 2n + ) x P° and (sp,2n -) l P° series were in addition resolved up to the n =20 and the n = 11 state, respectively.…”

Toward a soft X-ray Fourier-transform spectrometer

“…Even the latest 4 meV resolution is not sufficient to determine any of the line-shape parameters for these extremely narrow resonances. Such values are crucial for the test of theories, which disagree by two orders of magnitude with respect to the width of the 2(-1,0)~ state, for example, the calculated values ranging from 4x1Q-5 to 3xiQ-3 meV [15,16]. Such experimental evidence as there is presently [14] agrees with neither of these values.…”

Theoretical investigations on the dynamical correlation in double excitations of helium by theR-matrix method

“…In Burke and McVicar's calculation [7] in 1965, resonance states other than the normally known plus-minus series appeared. Sequently, atomic theoreticians developed various methods to deal with doubly excited states of helium, including configuration-interaction (CI) methods [56][57][58][59][60], hyperspherical coordinate methods [9,[61][62][63][64][65][66][67][68][69][70][71][72][73][74], close-coupling approximations [7,75,76], R-matrix methods [77][78][79][80][81][82][83][84], complex coordinate method [85][86][87][88][89][90], saddle-point technique [91][92][93][94][95], Feshbach projection formalism [8,[96][97][98]…”