Absolute photoionization cross section profiles and asymmetry parameters of Ne, Ar and Kr have been calculated at the time-dependent local density approximation level. We employed a very accurate B-spline finite basis set and the modified Sternheimer approach, which is a first-order perturbative scheme particularly suited to finite basis set calculations. The gradient-dependent van Leeuwen and Baerends (VLB) exchange-correlation potential has been used, since it has the correct Coulombic behaviour at large distances which is a necessary condition for the existence of the Rydberg states. A simple modification of the boundary conditions considerably improves the number of terms of the Rydberg series. The resonance parameters obtained by fitting the calculated Fano profiles with a suitable analytic expression are compared with the experimental parameters.

We report theoretical calculations of the total and partial cross section and asymmetry parameter for He photoionization up to the N = 3 threshold. Multichannel continuum wavefunctions are obtained via a least squares solution of the Schrödinger equation employing a basis set expansion based on a primitive B-spline radial basis and a general configuration interaction form. This allows use of a mixed full CI and close-coupling expansion in a completely general approach to improve correlation description in the continuum channels. The present algorithm correctly describes the full range of phenomena encountered with full details and a remarkable accuracy both on non-resonant cross sections and resonance structures. An accuracy of better than 0.001 Mb is estimated both on total and partial cross sections, also Fano resonance parameters compare very well with the best methods available based on Hylleraas type wavefunctions and complex coordinate rotation.

A recently proposed algorithm for the determination of the continuum wavefunction employing a 8-spline basis set expansion and a least-squares approach is extended to a full multichannel formulation employing a general close coupling expansion of the continuum wavefunction. Photoionization of the He atom up to the n = 4 threshold and Uup to the n = 3 threshold are described with a pure close coupling wavefunction (16 and 9 channels respectively), and an accurate full CI expansion for the ground state. Excellent agreement with previous accurate calculations is obtained for total and partial cross sections, resonance parameters and angular distributions. For He a nine-channel wavefunction allows photoionization to be described up to 2 keV. Modification of the boundary conditions to describe long Rydberg series is successfully tested, The proposed algorithm appears to be a general and flexible approach for the description of multichannel continuum wave. functions by basis set expansion.

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Near-threshold inner-shell photoionization of neon has been studied by measuring threshold photoelectron spectra in the energy regions of the 1s ' main line and the 1s2p'nl satellite states. The measured linewidth (0.22+0.03 eV) of the 1s -+3@ transition is more consistent with the observation of the 1s hole state linewidth than previous determinations.Features, assigned as doubly excited states and conjugate shakeup transitions, have been discerned in the 1s2p'nl satellite spectrum. PACS number(s): 32.80.HdThe high sensitivity and energy resolution of threshold photoelectron spectroscopy (TPES) have made this technique a unique tool to study photoionization of valence and inner valence shells of a,toms [1 -3] and molecules [4 -6]. Recently, the application of TPES has been extended to the photoionization of inner shells of the rare gases [7,8] and small molecules [9,10]. This paper de-