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The electron effective attenuation length (EAL) in free, neutral ethane clusters has been determined at 40 eV kinetic energy by combining carbon 1s x-ray photoelectron spectroscopy and theoretical lineshape modeling. More specifically, theory is employed to form model spectra on a grid in cluster size (N) and EAL (λ), allowing N and λ to be determined by optimizing the goodness-of-fit Χ²(N, λ) between model and observed spectra. Experimentally, the clusters were produced in an adiabatic-expansion setup using helium as the driving gas, spanning a range of 100-600 molecules in mean cluster size. The effective attenuation length was determined to be 8.4?±?1.9 Å, in good agreement with an independent estimate of 10 Å formed on the basis of molecular electron-scattering data and Monte Carlo simulations. The aggregation state of the clusters as well as the cluster temperature and its importance to the derived EAL value are discussed in some depth. [ABSTRACT FROM AUTHOR]

Free neutral methanol clusters produced by adiabatic expansion have been studied by photoelectron spectroscopy and line shape modeling. The results show that clusters belonging to two distinct size regimes can be produced by changing the expansion conditions. While the larger size regime can be well described by line shapes calculated for clusters consisting of hundreds of molecules, the smaller size regime corresponds to methanol oligomers, predominantly of cyclic structure. There is little contribution from dimers to the spectra. [ABSTRACT FROM AUTHOR]

Vibrationally resolved C1s and S2p photoelectron spectra of the thiophene molecule have been recorded using monochromated synchrotron radiation at photon energies of 330 eV and 210 eV, respectively. The photoelectron bands contain complex vibrational structures which are analyzed using ab initio and curve-fitting procedures. The analysis is in good agreement with the experimental spectrum which enables identification of two chemically shifted carbon 1 s core hole states. We were also able to determine the molecular-field splitting of the S2p [sub 3/2] ionic state to about 99 meV. The molecular-field splitting was moreover calculated using second-order Moller-Plesset perturbation theory, confirming the result from the fitting procedure. [ABSTRACT FROM AUTHOR]

The effective attenuation length (?) is determined to 5.7 ± 1.1 Å at an electronic kinetic energy of 30 eV for carbon disulfide, CS2, from sulphur 2p photoelectron spectroscopy and lineshape modelling of CS2 clusters at a temperature of 150-170 K. The present approach is based on exploring the relation between ? and the cluster-monomer chemical shift and width of the cluster peak. A priori knowledge of the cluster temperature is required. [ABSTRACT FROM AUTHOR]

Mixed CH4/CF4 clusters as well as pure clusters of CF4 were produced by adiabatic expansion and studied by carbon 1s (C1s) X-ray photoelectron spectroscopy. Evidence is presented that CH4 and CF4 do indeed form binary clusters in CH4/CF4 coexpansion experiments and that these clusters exhibit radial structure; i.e., CF4 is primarily found in the bulk. The interpretation of the photoelectron spectra is supported by calculations of C1s ionization energies based on theoretical clusters models. [ABSTRACT FROM AUTHOR]

Chemisorption of 1,1-dichloroethene (Cl2C=CH2) to a Si(111)-7×7 surface was studied by means of X-ray photoelectron spectroscopy using synchrotron radiation, recording chlorine 2p and carbon 1s spectra. For carbon 1s, spectral assignment of the chemisorbed species is based on quantum chemical calculations of chemical shifts in model compounds. The results confirm the identity of covalently bonded 1-chlorovinyl (–CCl=CH2) and vinylidene ((...)C=CH2) adspecies. Upon chemisorption at room temperature it was found that about one-third of the molecules break one C–Cl bond while about two-thirds of the adsorbates break two C–Cl bonds. We do not, however, find evidence for isomerization of (...)C=CH2 to di-bonded vinylene (–CH=CH–). [Copyright &y& Elsevier]

High-resolution carbon 1s photoelectron spectroscopy of propyne (HC triple bond CCH3) shows a spectrum in which the contributions from the three chemically inequivalent carbons are clearly resolved and marked by distinct vibrational structure. This structure is well accounted for by ab initio theory. For 3,3,3-trifluoropropyne (HC triple bond CCF3) and ethynylsulfur pentafluoride (HC triple bond CSF5), the ethynyl carbons show only a broad structure and have energies that differ only slightly from one another. The core-ionization energies can be qualitatively understood in terms of conventional resonance structures; the vibrational broadening for the fluorinated compounds can be understood in terms of the effects of the electronegative fluorines on the charge distribution. Combining the experimental results with gas-phase acidities and with ab initio calculations provides insights into the effects of initial-state charge distribution and final-state charge redistribution on ionization energies and acidities. In particular, these considerations make it possible to understand the apparent paradox that SF5 and CF3 have much larger electronegativity effects on acidity than they have on carbon 1s ionization energies.