High resolution, vibrationally resolved, near-edge x-ray absorption fine structure ͑NEXAFS͒ spectra at the C 1s and N 1s ionization thresholds of pyridine and deuterated d 5-pyridine in the gas phase have been recorded. The high resolution of 65 meV ͑150 meV͒ at the C s ͑N 1s͒ ionization thresholds reveals vibrational structures in the spectra. Detailed ab initio and density functional theory ͑DFT͒ calculations were performed to interpret the experimental spectra and to assign the observed peaks. In particular we focused on the previously unexplained intensity ratio for the two components of the C 1s→1* transition. For this transition the vibrational structure is included through a linear coupling model in the DFT calculations and leads to the experimentally observed ϳ2:3 intensity ratio between the two * components in the C 1s spectrum rather than the ϳ3:2 ratio obtained without vibrational effects. After inclusion of relaxation effects in the excited states, in addition to the vibrational effects, both theoretical methods yield almost perfect agreement with experiment.

An experimental and theoretical study of ground-state photoionization of neon is presented in the photon energy range between 44 and 53 eV. This portion of the spectrum is characterized by a singly excited Rydberg series 2s2p 6 np, and by overlapping doubly excited Rydberg series 2s 2 2p 4 3snp and 2s 2 2p 4 3pnl (lϭs,d).With the use of synchrotron radiation of Х3 meV spectral resolution, numerous hitherto unobserved resonances were resolved, including some which exhibit relativistic effects. To identify resonances observed here and in earlier works, we employed numerical calculations, which combine the eigenchannel R-matrix method, multichannel quantum defect theory, and the recoupling frame transformation. These nearly ab initio methods account for most of the observed features in the spectrum, including a class of spin-induced relativistic effects.

High-resolution photoabsorption spectra of CO B.lld NO below the 0 Is ionization threshold are presented. For both molecules, the vibrational finestructure of the 0 ls-t 'II"• a.nd 0 ls-1 Ryd (Rydberg) excitations could be resolved, allowing a derivation of the vibrational energies and intra.moleculal' distances of the core-excitation states in CO and NO from Ftanck-Condon analyses. The spectral features of the 0 ~s-1 Ryd region in CO are reassigned on the basis of the new experimental results. The results obtained for the 0 ls-1 3s Rydberg state in NO support the idea of a WP.akt>.nihg of the molecular bond upon an 0 15-J. ionization process.

Using synchrotron radiation and high-resolution electron spectroscopy, we have directly observed and identified specific photoelectrons from K^{-2}V states in neon corresponding to simultaneous 1s ionization and 1s→valence excitation. The natural lifetime broadening of the K^{-2}V states and the relative intensities of different types of shakeup channels have been determined experimentally and compared to ab initio calculations. Moreover, the high-energy Auger spectrum resulting from the decay of Ne^{2+}K^{-2} and Ne^{+}K^{-2}V states as well as from participator Auger decay from Ne^{+}K^{-1}L^{-1}V states, has been measured and assigned in detail utilizing the characteristic differences in lifetime broadenings of these core hole states. Furthermore, post collision interaction broadening of Auger peaks is clearly observed only in the hypersatellite spectrum from K^{-2} states, due to the energy sharing between the two 1s photoelectrons which favors the emission of one slow and one fast electron.

Direct measurements of Ar^{+} 1s^{-1}2p^{-1}nl double-core-hole shake-up states are reported using conventional single-channel photoemission, offering a new and relatively easy means to study such species. The high-quality results yield accurate energies and lifetimes of the double-core-hole states. Their photoemission spectrum also can be likened to 1s absorption of an exotic argon ion with a 2p core vacancy, providing new information about the spectroscopy of both this unusual ionic state as well as the neutral atom.