Resonant Auger Spectra Research Articles

Inner-valence states of CO+: comparison of photoelectron and resonant Auger spectra

We have recorded very-high-resolution photoelectron spectra of the inner-valence structure of , excited with synchrotron radiation, and have resolved fine structure never previously observed. Recently presented resonant Auger decay spectra (Sundin et al 1997 Phys. Rev. A 56 480, 1997 J. Phys. B: At. Mol. Opt. Phys. 30 4267) have established the energy of two-hole one-particle Rydberg states, and a comparison with these has been made to explain some details of the spectra.

Resonant auger spectra of TiO2 at Ti2p and O1s absorption edges

Abstract Resonant Auger measurements of TiO 2 (anatase have been performed at the Ti 2p and O 1s X-ray-absorption edges. The resonant photoelectron spectra excited at the Ti 2p absorption maxima show a strong resonance enhancement of the valence band photoemission intensity indicating the strong hybridization of the Ti 3d-level with the anion valence band. The degree of localization of the excited 3d electron in intermediate and in final Auger ionic configurations, and its influence on the decay spectra is discussed. In contrast, the resonant photoelectron spectra excited at the O 1s absorption maxima do not show resonance enhancement of the valence band which indicates that the absorption spectrum is formed by the delocalized states.

Theory of wave packet dynamics: resonant Auger spectrum of HF

The time-dependent theory of wave packet dynamics accompanying the excitation and decay in the molecular Auger process is reviewed and applied to the resonant Auger spectrum of HF. When the core-excitation is performed by an energetically non-selective source (`broad-band' excitation), many intermediate states are populated during the excitation process and their decay gives many interplaying contributions within the same energy region. To interpret the spectrum we have carried out a detailed theoretical study of all the decaying and final electronic states involved. In order to restrict the number of participating decaying states, narrow-band excitation has to be performed, so that only one intermediate decaying state is populated. We have studied in detail one particular transition between purely repulsive potential curves, where we show the effects introduced by the energetically selective excitation. By detuning the excitation energy off the resonance, very prominent interference patterns can be found. These explain the quenching of the so-called `atomic lines' and the surprising new features which appear in the case of small detuning towards higher excitation energies. The effects discussed are shown to be of a general nature. The description in the time-dependent picture allows for a novel and deeper understanding of the underlying mechanisms of these effects since the physically relevant quantities can be traced on the real time scale of the process.

High resolution study of correlation satellites in the - resonant Auger spectra of Kr

Final ionic state-configuration interaction (FISCI) between bound and final states in the Auger decay of resonantly excited Kr states has been studied by synchrotron-radiation-excited electron spectroscopy utilizing the Auger resonant Raman effect. It is found that the effects of FISCI are essentially the same as in the corresponding normal Auger spectra. Especially in the spectra the role of FISCI is to distribute the intensity from the `diagram' states to the `satellite' states without remarkably affecting the branching ratio of the `diagram' lines. Furthermore, the experimental shake probabilities are not affected by FISCI.

Controlled Interplay between Decay and Fragmentation in Resonant Auger Processes

Wave packet dynamics applied to the resonant Auger spectrum of HF bring to light novel interference effects introduced by selective excitation. By detuning the excitation energy off the resonance these effects are shown to be strongly enhanced. Besides the quenching of the so-called “atomic lines” by detuning, an unexpected prominent structure dominates the spectrum in the case of small detuning towards higher excitation energies. The underlying interference mechanisms are identified by tracing the physically relevant quantities on the real time scale of the process. [S0031-9007(97)05272-1]

Decay and dissociation dynamics of core-excited polyatomic molecules

The importance of nuclear motion in the decay and dissociation processes of the core-excited molecules is emphasized by reviewing some case studies. Discussed examples include fast dissociation of P2 p core-excited PH 3 followed by the electron emission from the core-excited fragment PH 2, molecular deformation of the B1 s core-excited state of BF 3 and its effect to the resonant Auger spectra, and symmetry breaking of the highly symmetric molecule SF 6 caused by F1 s core excitation.

Photon stimulated ion desorption of condensed acetonitrile molecules induced by core excitation

Photon stimulated ion desorption (PSID) of condensed acetonitrile molecules induced by carbon and nitrogen core excitation has been examined to elucidate the Auger process following resonant core excitation and the ion desorption mechanism related to this Auger process using total electron yield, total ion yield, resonant Auger electron spectra. Resonant Auger electron spectra show a strong dependence on the character of excitation. In particular, these Auger spectra are drastically changed between the carbon 1s to theπ * CN excitation and that of the C H * excitation. The spectrum of the total ion yield divided by the total electron yield shows that the desorption efficiency is largely increased at the resonant excitation of carbon 1s electron in the CH 3 group to C H * orbital. The results of the resonant Auger spectra and the Auger electron-photoion coincidence (AEPICO) measurements at various resonant excitations are discussed in relation to the bonding/anti-bonding character and localized character of the excited state and the Auger final state.

Resonant Auger decay in the L2,3-MM spectrum of Ar excited by electron bombardment

The L 2,3 -MM Auger spectrum of argon was measured using electron beam excitation. A weak structure on the high energy side of the main transitions was identified as corresponding to the resonant Auger transitions by comparing these spectral structures with individual resonant Auger spectra excited by monochromatic synchrotron radiation.

Vibrationally resolved decay spectra of CO at the C and O K-edges: experiment and theory

The resonant Auger spectrum of CO has been measured at both the C and O K-edges. At the C resonance the decay spectrum was recorded selectively at the energies of the = 0, 1 and 2 vibrational states. Vibrational fine structure was not only resolved on the participator but also on the spectator lines. For the O resonance the photon energy bandwidth was sufficiently low that different, vibrationally distinct regions of the absorption profile could be selected. Ab initio calculations and their detailed analysis are presented for both the C and O decay spectra. At the C resonance the calculation explicitly accounts for the vibrational fine structure including vibrational-lifetime interference effects. The appearance of the spectator part of the spectrum is shown to be strongly influenced by the existence of unbound states and diabatic interactions. The nodal structure of the vibrational wavefunction of the core-excited state is reflected in the decay spectrum.

Assignment of fine structure in the HBr absorption spectrum at the Br3d→Rydberg resonances using the Auger resonant Raman effect

High-resolution resonant Auger electron spectra of HBr are reported at the Br $3d\ensuremath{\rightarrow}5p$ and Br $3d\ensuremath{\rightarrow}4d$ resonances. Subnatural linewidths of \ensuremath{\sim}40 meV, due to the Auger resonance Raman effect, reveal complex multiplet features. By recording spectra at closely spaced energies, the resonant Auger spectra from the resonantly excited core Br $3d$ to $4d,$ $5p\ensuremath{\sigma},$ and $5p\ensuremath{\pi}$ Rydberg states are obtained. The well-resolved resonant Auger spectra are used to confirm the assignments of the complex unresolved Br $3d\ensuremath{\rightarrow}$Rydberg photoabsorption spectrum.

Theoretical analysis of line shapes in resonant Auger electron spectra

General expressions for predicting line shapes in resonant Auger electron spectra are derived. These formulas take into account explicitly the interference effects due to the presence of several resonances embedded in the continua of different final states having finite lifetimes and include also the effects due to the finite bandwidth of the incident radiation and the finite resolving power of the electron spectrometer. The characteristic features of the Auger resonant Raman effect are derived analytically. The theory is applied to the analysis of high resolution resonant Auger spectra recently measured at the VUV beam line at Elettra, Sincrotrone Trieste.

Angular distributions of resonant and non-resonant Auger electrons as a test case for the validity of the spectator model: the argon case

Resonant Auger spectra following Ar selective excitation with synchrotron radiation are reported with low- and high-photon resolution. The angular distribution of the resonant Auger lines, in particular the Ar excitation, was analysed in order to test the validity of the spectator model in its various forms. It is shown that this model in its strict form holds well for the Ar excitation and in its `shake modified' gross form also for the nd excitations in the case of n > 3.

Theoretical analysis of line shapes in resonant Auger electron spectra

General expressions for predicting line shapes in resonant Auger electron spectra are derived. These formulas take into account explicitly the interference effects due to the presence of several resonances embedded in the continua of different final states having finite lifetimes and include also the effects due to the finite bandwidth of the incident radiation and the finite resolving power of the electron spectrometer. The characteristic features of the Auger resonant Raman effect are derived analytically. The theory is applied to the analysis of high resolution resonant Auger spectra recently measured at the VUV beam line at Elettra, Sincrotrone Trieste.

P resonant Auger spectra in solid phosphorus compounds

P resonant Auger spectra were measured for four insulators (, , and ) and a semiconductor (GaP). Spectator Auger peaks showed both linear energy dispersion and width sharpening around the absorption edges. These peaks are attributed to the Auger resonant Raman effect. Furthermore, it was found that only for the insulators were the Auger peaks split into spectator and normal peaks. This is explained in connection with localized quasi-bound states above the P 1s ionization threshold.

Variation of the angular anisotropy in resonant Auger decay along the Mg 2p→nl excitations

Energy- and angle-resolved resonant Auger spectra were recorded on the first 12 Mg 2p\ensuremath{\rightarrow}nl resonances. Utilization of a high-resolution monochromator has allowed us to selectively excite resonant states which could not be resolved in earlier electron spectrometry measurements. The branching ratios and values of the angular anisotropy parameter \ensuremath{\mathrm{B}} were extracted for all resonances. The measurements provide a first basis for a systematic test of the spectator model for the angular anisotropy. Our experimental values are compared with ab initio multiconfiguration Dirac-Fock calculations. The sensitivity of the calculations to the configuration basis size is discussed in detail.

Decay of the , and states of Ar studied by utilizing the Auger resonant Raman effect

The 2p electrons of Ar have been excited selectively to the 4s, 3d and 4d orbitals and high-resolution de-excitation spectra have been recorded by utilizing the Auger resonant Raman effect. Fine structures in the resonant Auger spectra have been clearly resolved for the first time. The roles of shake transitions and configuration interaction between the and , n = 3 - 6 final states in producing the complicated fine structures have been discussed.

Electron correlation in the 3p44s state of Ar studied via the 2p54s resonant Auger spectra.

Electron correlation in the 3p44s state of Ar studied via the 2p54s resonant Auger spectra.

Interference Effects in the Auger Decay of the Resonantly Excited 2p3/2-13d State of Argon.

High resolution resonant Auger spectra have been measured at the VUV beam line at ELETTRA, Sincrotrone Trieste, while tuning the photon energy across the ${2p}_{3/2}^{\ensuremath{-}1}3d$ resonance of argon. A large variation of the branching ratio for decay into the spectator ${3p}^{\ensuremath{-}2}3d$ and shakeup ${3p}^{\ensuremath{-}2}4d$ channels is observed. The effect has not been seen previously in resonant inner-shell excitation and is attributed to the interference between the direct photoionization process and resonant Auger decay leading to the same final state.

Competition between direct dissociation and resonant Auger decay: a quasi-classical model applied to the [formula omitted] states of HCl, DCl and Cl 2

Resonant Auger spectra of HCl, DCl, and Cl 2 following the ( Cl 2 p 3 2 → σ ∗ excitation were studied. Both ‘molecular’ and ‘atomic’ Auger transitions are observed and assigned. The branching ratio of ‘molecular’ versus ‘atomic’ Auger transitions increases with increasing reduced mass of the target molecules. Using a quasi-classical model, we are able to deduce the principal Auger lineshape in agreement with experiment. The simultaneous occurrence of ‘atomic’ and ‘molecular’ Auger transitions is shown to be the general case for repulsive intermediate states. The kinematic model successfully describes the mass and lifetime dependence of the competition between the Auger process and dissociation.

The C 1s Auger decay spectrum of the molecule: the effects of vibrational fine structure, double excitations and shake-up transitions

Auger electron spectra of the methane molecule have been measured at various photon energies below and above the C 1s threshold. At energies corresponding to the higher Rydberg resonances the resonant Auger spectrum approaches the normal Auger spectrum both in form and peak position. Deviations from this trend are observed, however, when the core-to-Rydberg transition is accompanied by the excitation of vibrational modes. Auger spectra measured at the continuum resonance around 303 eV excitation energy display new decay features, which allows this resonance to be assigned to core-hole double excitations. Furthermore, above the C 1s threshold the satellite Auger features arising from the lowest shake-up initial states are identified.