N. Correia

Theory of band shape formation in Auger and autoionization spectra of molecules. Numerical applications and new high‐resolution spectra for CO

Theory of band shape formation in Auger and autoionization decay in molecules is presented and numerically applied to spectra of the CO molecule. In particular, the role of lifetime vibrational interference in the various vibronic decay channels is elucidated. New high resolution Auger and autoionization spectra are presented. The calculated band shapes are compared with the experimental recordings. The vibronic spectra of the intermediate states in the Auger and autoionization decay are analyzed and compared with available ESCA and EELS spectra, respectively. The role of the electron correlation on the formation of the core state potential surfaces is investigated in that connection. The assignment problem of the outer part of the CO Auger spectrum is reinvestigated and the effect of interference due to hole mixing in the wave functions is pointed out. The time dependent Franck–Condon (FC) formalism used to derive the lifetime vibrational interference is shown to have a bearing on the analogy of the sudd...

X-ray photoelectron, Auger electron and ion fragment spectra of O2 and potential curves of O22+

The O22+ ion has been studied by means of electron-impact-induced and photon-induced Auger electron spectroscopy and oxygen ion fragment spectroscopy of O2. The oxygen ion kinetic energy spectrum was recorded by inverting the relevant potentials of an electron spectrometer for the detection of positive particles. The 4 Sigma - and 2 Sigma - O 1s initial core hole states have been studied using monochromatised X-ray photoelectron spectroscopy. Potential energy curves for a number of electronic states of the O22+ dication have been calculated with the complete active space SCF (CASSCF) and multireference contracted CI (MRCCI) methods with a one-particle basis set of medium size ((8s, 6p, 2d)). An analysis of the O2 Auger electron spectrum based on the computed potential curves of O22+ is presented. The autoionisation satellites are analysed and these lines correspond to molecular singly ionised final states. One line at 510.7 eV, however, is associated with an atomic-like transition. Two shake-up Auger satellites are identified by a comparison with a recent O 1s shake-up spectrum from O2.

A theoretical study of x‐ray photoelectron spectra of model molecules for polymethylmethacrylate

We explore the usefulness of the delta self‐consistent‐field (ΔSCF) approximation in connection with high‐resolution x‐ray photoelectron spectra for component and structural analysis of organic compounds. Results for core electron binding energy shifts for model molecules of the polymethylmethacrylate polymer are presented. A previously devised method for proper self‐consistent‐field solutions for core hole states in molecules is evaluated. The results indicate that chemical shifts can be obtained within a few tenths of an eV. A discussion is presented on the inherent errors in the ΔSCF approximation, the proper corrections for zero‐point vibrational energies, and the role of relaxation of core orbitals.

Gas‐phase x‐ray photoelectron spectroscopy of model molecules relating to the thermochromism in poly(3‐alkylthiophene)

Previously, a geometrical model of the thermochromism in poly(3‐alkylthiophene) was proposed, based upon an analysis of optical absorption spectra as well as ultraviolet and x‐ray photoelectron spectra (UPS and XPS). In the present contribution, the shake‐up features in the XPS C(1s) spectra of thiophene, hexyl‐substituted thiophene, and bithiophene molecules in the gas phase, are compared with the shake‐up features in previously published XPS C1s spectra of poly(3‐hexylthiophene) and poly(3‐butylthiophene). An analysis of these gas phase molecular data confirms the geometric model of electronic localization in the polymer materials proposed previously.

The x‐ray excited Auger electron spectrum of NO and potential curves and photodissociation of the NO2+ ion

A study of the NO2+ ion by means of Auger spectroscopy, fast ion beam laser spectroscopy and ab initio calculations is reported. The photon induced Auger spectrum of NO was recorded. Potential curves for a number of electronic states of NO2+ were calculated by the complete active space SCF method in order to facilitate an analysis of the Auger spectrum. A photoabsorption spectrum of NO2+ was observed by means of photofragment kinetic energy spectroscopy and assigned to the A 2Π←X 2Σ+ transition. The two different experimental methods both give a value of 38.6 eV for the appearance energy of NO2+, which is entirely consistent with recent photoionization and double charge transfer results.

Doubly charged valence states of formaldehyde, acetaldehyde, acetone, and formamide studied by means of photon excited Auger electron spectroscopy and ab initio calculations

The doubly ionized states in formaldehyde, acetaldehyde, acetone, and formamide have been studied by means of x‐ray excited core (C1s, N1s, O1s)–valence–valence Auger electron spectroscopy. Assignments of the spectra have been made using ab initio Hartree–Fock, Green’s function, and configuration interaction (CI) calculations. A molecular orbital analysis has been carried out for the high kinetic energy part of the spectra. The breakdown of the single particle picture is found to be important over a large energy interval in the spectra. The results obtained illustrate the usefulness of Auger electron spectroscopy in characterizing the doubly ionized states even in the case of large molecular systems. The first double ionization energies for the four molecules presented have been determined to be 33.8, 30.3, 28.0, and 30 eV, respectively.

Experimental and theoretical study of the N1s and C1s shake-up satellites in pyridine and aniline

Abstract High-resolution monochromatised X-ray photoelectron spectroscopy (XPS) shake-up spectra of both N1s and C1s ionisation of pyridine and aniline are reported. The shake-up energies and intensities have been assigned by means of semi-empirical INDO/CI calculations, the intensities being calculated using the sudden approximation. The results of the calculations for carbon ionisation are found to be of the same high standard as in the earlier studies. For the case of the aromatic nitrogen in pyridine, the results are of the same standard as in the carbon case, whereas in the case of the aliphatic nitrogen in aniline the results are less satisfactory.

X-ray induced electron yield spectrum of thin films of 1,3-trans-butadiene and 1,3,5-trans-hexatriene

Abstract The electron yield spectrum, also commonly referred to as near-edge X-ray absorption spectra (NEXAFS), of 1,3-trans-butadiene and 1,3,5-trans-hexatriene in the 280–330 eV photon-energy region are reported. The spectra were obtained by measuring the total yield of electrons as a function of photon energy. The results for butadiene are compared with earlier inner shell electron energy loss (ISEELS) data. A reassignment of the C1s → π* transitions was made using multiconfiguration self consistent field (MCSCF) calculations and recent X-ray photoelectron measurements of the C1s line in butadiene. It was found that even the first core excited states are strongly influenced by electron correlation. The first structure in the electron-yield spectrum was assigned to transitions from 1s orbitals on the non-equivalent carbon atoms to the first corresponding states of π symmetry. The electron-yield spectrum of 1,3,5-trans-hexatriene was assigned in analogy with the results for 1,3-trans-butadiene. The vibrational fine structure was revealed in the spectra of both molecules.

The C1s core shake-up spectra of alkene molecules : an experimental and theoretical study

The C1s core photoelectron spectra of a series of alkene molecules, ethene, propene, 1‐butene, cis and trans 2‐butene, 2‐methyl‐propene, and 1‐pentene are discussed. The experimental spectra are assigned using intermediate neglect of differential overlap‐configuration interaction (INDO‐CI) calculations and comparative discussions. It is shown that hyperconjugation is a useful concept in the assignment of the transitions. INDO‐CI is shown to give a reasonable description of the low energy part of the spectra. The results are used in the discussion of molecular models for the interpretation of the electronic structure of polyacetylene.

The N 1s core electron shake-up and the shake-up Auger satellite spectrum of the N2 molecule

The shake-up Auger satellite spectrum associated with the N 1s Auger spectrum of N2 is recorded using monochromatized X-ray excitation. As many as 11 structures are observed in the spectrum. Assignments in terms of participator and spectator processes are discussed based on data from normal Auger and shake-up spectra and from a simple one-particle model. The interpretation is assisted also by a new N 1s photoelectron shake-up spectrum showing several hitherto unobserved details. A new X-ray excited normal Auger electron spectrum of N2 is also presented.