C. Cauletti

Photoelectron spectra of metallocenes

Abstract The He(II) spectra of the unsubstituted metallocenes {M(η-C 5 H 5 ) 2 }, M  V, Cr, Mn, Fe, Co, Ni and Ru, and of {Mn(η-C 5 H 4 Me) 2 } are reported; both He(I) and He(II) spectra of some decamethylmetallocenes {M(η-C 5 Me 5 ) 2 }, where M  Mg, V, Cr, Mn, Fe, Co and Ni, are also given. Intensity changes between the He(I) and He(II) spectra are shown to provide a reliable guide to band assignment. A ligand field treatment of the decamethylmanganocene cation, including limited configuration interaction, gives values for Δ 2 , B and C ; these values are also in good agreement with the photoelectron spectra of {M(η-C 5 Me 5 ) 2 } where M  V, Cr and Fe. Overlap between the ligand and metal “ d ” band structures prevents complete assignment in the cases of Co and Ni.

General trends in the molecular physics of azabiphenyls

Some phenylpyridines and bipyridines have been studied by UV photoelectron spectroscopy and quantum-chemical methods. This study, together with some new computations on the previously reported bipyrimidines, has allowed a comprehensive analysis of general trends along the whole series of biphenyl-like molecules. Several physico-chemical characteristics have been considered in this respect, including geometric structure, conformational behaviour, relative stabilities, dipole moments and ordering of ionic states. The results obtained have been analysed in terms of conjugative and steric interactions by means of fragment analysis. On these grounds simple thumb-rules have been suggested, which may prove useful for a better understanding of polyphenyl-like molecules.

Photoionization branching ratios and asymmetry parameters for inner- and outer-valence shells of H2S in the 18–70 eV energy range

Abstract Branching ratios, asymmetry parameters and relative partial cross sections have been obtained for photoionization of the outer and the inner valence shells of H 2 S. These measurements were made in the photon energy range 18–70 eV using synchrotron radiation. Our results are compared to a set of calculations using a developed extension of the self-consistent field- X α scattered-wave method to the continuum states. This comparison shows a qualitative agreement between the experimental and calculated β curves of the outer valence shells. The largely predominant sulfur 3 p contribution to the outer valence orbitais 2 b 1 , 5 a 1 , 2 b 2 is revealed in the corresponding β curves by a Cooper minimum also predicted in the same energy range for the β( 3p ) of the atomic sulfur. This comparison also shows discrepancies in the branching ratios curves and we suggest that this theoretical framework is better adapted to predict photoionization processes in the outer valence shells than in the inner ones.

Photoelectron spectra of bis-cyclopentadienyl metal dihalides

Abstract He(I) and HE(II) photoelectron spectra are reported for (η-C5H5)2MX2 (M = Ti; X = F, Cl, Br, I: M = Zr, Hf; X = Cl, Br: M = Ta; X = Cl, Br) and (η-MeC5H4)2MX2 (M = Nb, X = Cl: M = Mo; X = Cl, Br, I). A substantial variation is found in the ordering of the halogen and cyclopentadienyl ionizations, the order being dependent on the metal as well as on the halogen. The compounds may be divided into three classes, namely, those in which the electrons in cyclopentadienyl e1 orbitals ionize at a lower energy than those occupying halogen pπ orbitals, those in which halogen pπ electrons have lower ionization energy than cyclopentadienyl e1 electrons and those in which the corresponding electrons arise from extensively delocalized molecular orbitals with significant contributions from both these categories of fragment orbital.

Final state multiple structures in photoionization of the inner valence shell of H2S: angular distribution in the 40–70 e V photon energy range

Abstract Using Synchrotron Radiation in the 40–70 eV photon energy range, we have obtained well resolved photoelectron spectra of the inner valence shell of H2S and studied the behaviour of the corresponding asymmetry parameters. Our results show that the present and currently accepted theoretical interpretation using Greens function is qualitatively but not quantitatively valid in this case; in the binding energy range where two prominent peaks are predicted we have observed at least six peaks. Nevertheless, the analysis of the asymmetry parameter results suggests that the essential part of the spectrum can be described as corresponding to levels with somewhat mixedorbital with dominant s-type character. Therefore, a breakdown of the molecular orbital model is evident.

Angle‐resolved photoelectron spectroscopic study of the outer‐ and inner‐valence shells of NH3 in the 20–80 eV photon energy range

We report here highly resolved photoelectron spectra of the outer‐ and inner‐valence shells of NH3, together with the corresponding angular distribution parameter. The measurements were made in the 20–80 eV photon energy range, using synchrotron radiation as an ionizing source. In the inner‐valence region, three spectral features were evidenced, and namely a main component at 27.4 eV and two weaker features at 31.4 and 35.4 eV. The spectral feature at 35.4 eV was not evident in the previous (e, 2e) measurements. Our experimental findings are compared with three different sets of calculations performed by the Green’s function method. The best agreement is found with one of them which predicts three main lines and some low‐intensity components. From the angular distribution measurements, we conclude that the nature of the spectral feature at 31.4 eV is different from the one of the main component at 27.4 eV.

Photoionization energetics and dynamics of gas‐phase SnCl2 by synchrotron radiation photoemission and configuration interaction calculations

The photoionization from outer‐ and inner‐valence shells of SnCl2 vapor, induced by means of molecular effusive beam technique and dispersed synchrotron radiation as an ionizing source, reveals new spectroscopic and dynamical aspects in this molecule. Spectral features related to states with main Cl 3s contribution are observed for the first time in a molecule with Cl‐metal bonds. The corresponding ionization energy (IE) is 22.61 eV. A breakdown of the one‐particle model is exhibited in the inner‐valence spectral region. These experimental findings are compared with the theoretical predictions obtained by performing configuration interaction (C.I.) calculations for the molecular ionic states. A strongly resonant behavior in the cross section of some main lines and satellites is experimentally pointed out by tuning the excitation photon energy through resonances localized at 25.03 and 26.11 eV. CI calculations for the transition energies relative to 4d excitations have been carried out and explain the afor...

Coordinative bond and d-shell ionisations in the UV photoelectron spectra of bis(β-diketonato) cobalt(II) and copper(II) complexes, and their thioanalogues

Abstract The analysis of UV photoelectron spectra of the title compounds, as well as of their Ni(II) analogues, is presented, with particular regard to the identification of d -ionisation bands. The spectra are assigned on the grounds both of a framework of interpretation similar to that usually applied to β-diketonato metal complexes, and of a systematic comparison between He(I) and He(II) data.

Photoionization of the outer- and inner-valence shells of PH3 in the photon energy range 30–90 eV

Abstract We measured the Binding Energy Spectrum and the angular distribution parameter β for both outer- and inner-valence shells of PH 3 , by using synchrotron radiation as ionizing source. The photoionization of the 4a 1 inner-valence orbital, mainly P 3 s in character, gives rise to a multiple structure rather than a single peak. This structure is related to the so-called “breakdown of the one-electron picture”. We obtained highly-resolved spectra of this region in the photon energy range 40–90 eV. The angular distribution measurements evidenced different localization of the 5a 1 and 2e outer-valence orbitals, as expected, and suggested a lower bonding character of the e orbital with respect to the corresponding orbital in NH 3 , previously studied.

Study of the electronic structure of some alkyltin derivatives by means of uv photoelectron spectroscopy

Abstract He(I) photoelectron spectra (UPS) provide data on the orbital energy levels in the valence shells of the following compounds: R 3 SnOR (R = methyl), R 3 Sn(acac) (R = methyl, ethyl, acac = acetylacetonate), R 2 SnCl 2 (R = methyl, n-butyl), R 2 Sn(acac) 2 (R = methyl, n-butyl, acac = acetylacetonate), R 2 Sn(Tacac) 2 (R = methyl, Tacac = trifluoroacetylacetonate). The results are discussed in the light of comparisons with the UPS spectra of simple tin compounds and of the β-diketonates of other metals.