M. P. Keane

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.

Vibronic and electronic states of doubly charged H2S studied by Auger and charge transfer spectroscopy and by ab initio calculations

Doubly ionic states of H2S are investigated by means of Auger and double charge transfer spectroscopy. From the kinetic energy distribution of H− ions arising from double charge‐transfer of protons impinging on gaseous H2S several singlet state energies of H2S2+ have been resolved in the 30 to 50 eV energy region. The most intense experimental peak is narrow proving that the doubly ionized ground state is stable or quasi‐stable. The LII,IIIVV Auger electron spectrum exhibits a number of well‐defined structures which exhibit vibrational fine structure in the outermost bands. The assignments of the charge transfer states and of the Auger bands are given by ab initio MCSCF electronic structure calculations. We also present vertical double ionization energies, optimized geometries and normal coordinate analysis for the neutral, single and double ionized states. A vibrational analysis of the resolved Auger bands is carried out by employing a recently derived theory for vibrational decay of short‐lived core hol...

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.

Semiempirical configuration interaction calculations of shake‐up satellites in formaldehyde, benzene, and benzaldehyde

The core photoionization shake‐up spectra of benzaldehyde, benzene, and formaldehyde are discussed using a new computational package based on the method of intermediate neglect of differential overlap (INDO) including configurational interaction (CI). The computations include all singly excited and a large selection of the doubly excited states in the CI. The inclusion of the doubly excited states leads to a reduction of the overall intensities and to an elimination of artificial intensity in high and low shake‐up peaks. A reassignment of one of the structures in the benzene spectrum has been made. In the case of benzaldehyde, where the shake‐up spectrum is assigned for the first time, the calculated spectrum shows very good agreement with experiment for C1s ionization, whereas the O1s spectrum shows larger deviations due to a stronger core–valence interaction. By utilizing information from analogous calculations on the smaller molecules benzene and formaldehyde, however, it is possible to assign also the O1s spectrum in this case.

Isotope effects in the auger electron spectra of HBr and DBr

Abstract High-resolution Auger electron spectra of HBr and DBr are presented. Extensive vibrational structure has been resolved in the bands corresponding to the 6σ 2 3π 2 final state electron configuration. An isotope effect is observed in all the bands. A Franck-Condon analysis of the potential curves for the 3d core ionized state and the 3π 2 3 Σ − , 3π 2 1 Δ and 3π 2 1 1Σ + states has been p giving equilibrium bond distances of 1.53, 1.66, 1.69 and 1.76 A, respectively. An approximately linear correlation is found between the equilibrium bond distances and the 0–1 vibrational spacings in HBr, HBr + (3π −1 ) and the different electronic states of HBr 2+ (3π −2 ). The adiabatic electron binding energies for the doubly ionized molecule with π −2 configuration are determined to be 32.87, 33.97 and 35.27 eV for the 3Σ − , 1 Δ and 1 Σ + states, respectively.

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.