M 3-alignment of gold by 0.16-5 MeV proton impact ionization

The alignment of theM ₃ subshell of gold following proton impact ionization was studied with projectile energies in the range from 160 keV up to 5MeV. The experiments were performed by measuring the polarization of emittedM X-rays be means of a 5 in. Johansson crystal spectrometer. A good agreement of the experimental data and the results of theoretical SCA calculations was found.     

The electron impact and chemical ionization mass spectra of dimethyltrisulfide

Summary The mass spectra obtained by electron impact ionization (EI) of dimethyltrisulfide, both at constant sample pressure and during elution from a GC column, are essentially identical, with the molecular ion Me₂S ₃ ⁺ providing the basis peak. Masses heavier than the molecular ion are not observed. Chemical ionization, using nitrogen, methane or isobutane, gives rise to numerous ions of larger mass than that of the molecular ion. Particularly characteristic are sulfonium type structures Me₃S _n ⁺ , with n=3–6. In addition, radical cations of the type Me₃S_nCH ₂ ⁺ and protonated trisulfide, Me₂S₃H⁺, are observed, even with N₂ as ionizing gas, together with a variety of ions of lower hydrogen content. Further, a large number of ion types of lower mass than the parent molecule are formed. The mass distribution of ions in the spectrum is found to be highly dependent on the partial pressure of dimethyltrisulfide in the ion source. These phenomena were investigated and accounted for semiquantitatively.

---

Die EIund CI-Massenspektren des Dimethyltrisulfids

Zusammenfassung Dimethyltrisulfid liefert nach Elektronenstoßionisation bei konstantem Probendruck und bei GC-Probeneinlaß im wesentlichen identische Massenspektren. Das Molekülion Me₂S ₃ ⁺ stellt dabei den Basispeak dar. Größere Massen als die des Molekülions wurden nicht beobachtet. Bei chemischer Ionisation unter Verwendung von Stickstoff, Methan oder Isobutan als Reaktantgas entstehen zahlreiche Ionen mit höherer Masse als der des Molekülions. Charakteristisch sind hierbei sulfoniumartige Strukturen Me₃S _n ⁺ mit n=3–6. Daneben beobachtet man Radikalkationen des Typs Me₂S_nCH ₂ ⁺ und protoniertes Trisulfid Me₂S₃H⁺ auch bei Ionisation mittels N₂ sowie Ionenarten mit einem geringeren Wasserstoffgehalt. Weiterhin wird eine größere Anzahl von Ionenarten gebildet, deren Massen kleiner sind als die des Stammoleküls. Die Massenverteilung der Ionen im Spektrum hängt außerordentlich stark vom Partialdruck des Dimethyltrisulfids in der CI-Quelle ab. Diese Abhängigkeiten wurden semiquantitativ untersucht und dargestellt.

     

Angular distributions in the double ionization of noble gases by electron impact

Electron-impact double ionization of noble gases is investigated theoretically for the case of high incident energies (5 keV). An ab initio calculation is made including partial correlation in the initial state as well as in the final state. The results of the calculations are compared with those of other theories and with the first available (e, 3e) experimental data on krypton 4p ⁶.     

The influence of basis sets on wave function tails

Wave function tails are analyzed quantitatively by investigating the dependence of exterior electron density (EED ) on basis sets; the EED is defined as the integrated electron density outside the repulsive molecular surface. Ab initio MO calculations with large scale basis sets were performed to establish the benchmark order of EED values for valence orbitals of some simple molecules. It is found that very popular basis sets, such as 4-31G, which are determined by energy optimization, are inferior in describing the wave function tails to some similar size basis sets, such as MIDI -4, which are obtained by least-squares fit to near Hartree-Fock atomic functions. Further the EED values for atomic 2s functions are shown to be unfavorably smaller than those for atomic 2p functions when the same value is used for the exponent α in the GTO basis sets. This indicates that the frequently used constraint α_s = α_p is not appropriate for describing wave function tails with medium-size basis sets. Deficiencies in the energy-optimized basis sets are found to become more serious for molecules including heavier atoms.     

Total ionization and electron attachment cross sections of CCl2F2 by electron impact

The absolute total ionization cross sections from threshold to 250 eV and dissociative attachment cross sections from zero to 10 eV have been measured for the CCl₂F₂ (dichloro-difluoro-methane) molecule by using a parallel plate condenser type ionization chamber. The maximum of the ionization cross-section curve was found to be at an energy of about 90 eV with a cross section of 1.44 × 10^?19 m². The attachment cross-section curve shows three peaks, the most intense being at zero electron energy with a cross-section value of 1.80 × 10^?20 m², and the other two at energies of 0.6 eV and 3.5 eV, respectively. The maximal relative error in cross-section values is 0.08, for electron energies larger than 0.4 eV.     

The electron impact and chemical ionization mass spectra of some glycidyl ethers

The electron impact and chemical ionization mass spectra of a number of aliphatic and aromatic glycidyl ethers are reported. For electron impact spectra, partial fragmentation pathways have been determined by metastable linked scan techniques.     

On the vibrational dependence of electron impact ionization of diatomic molecules

The dependence of the Na₂ electron impact ionization rate is measured as a function of vibrational excitation in a crossed molecule-electron beamm arrangement at collision energiesE _coll ≤ 3 eV above the ionization threshold. Specific vibrational distributions in theX ¹∑ _g ⁺ state with average vibrational energies of 0.17 eV, 0.276 eV, and 0.349 eV, are prepared via Franck-Condon pumping using a narrow-band cw laser. Enhancement of the ionization rate is observed only at impact energies near the ionization threshold where the ionization rate increases linearly as a function of vibrational excitation. Analysis of the experimental data is based on three model calculations. The first of these calculations equates vibrational energy with kinetic energy and agrees well with the experimental data. A second, more refined model allows for differences in state-to-state ionization rates and uses Franck-Condon factors to estimate transition probabilities, but leads to a less favorable agreement. The third one employs a semi-classical formulation of the Franck-Condon principle. It provides the best agreement with the experimental data. In contrast with an earlier study of electron impact ionization of diatomic molecules [20], we find no evidence of dynamical modification of the ionization rate, due to vibrational motion of the nuclei, at the present level of accuracy of our data and analysis.     

Measurement of impact parameter dependent probabilities and total cross sections for targetK-shell ionization by He+ ions

We have measured the impact parameter dependent K-shell ionization probabilitiesP _K (b) of Ca, Cr and Cu from collisions with 4.04 MeV He⁺ ions by particle-K X ray coincidences. A dependence on the target thickness was investigated to study a possible influence of multiple collisions onP _K (b). We measured the total cross section σ _K forK vacancy production simultaneously withP _K (b) and σ _K agrees within 30% with the integratedP _K (b). A comparison of theP _K (b) and σ _K with SCA calculations of Trautmann et al. using RHFS wavefunctions for united atom and separated atom states is discussed.     

An improved Born approximation for the electron impact ionization of atomic hydrogen

A two-electron continuum wave function satisfying exact asymptotic boundary conditions (see [1]) is simplified in the high energy limit for asymmetric kinematics. The long range correlation between the fast escaping electron and the target atom in a low continuum state is properly taken into account, and corrects therefore the major shortcoming of the ordinary Born approximation. This improved Born approximation has been employed to calculate triply differential ionization cross sections at intermediate energies.     

Solvation dynamics of electron produced by two-photon ionization of liquid polyols. III. Glycerol

The solvation dynamics of excess electrons in glycerol have been measured by the pump-probe femtosecond laser technique at 333 K. The electrons are produced by two-photon absorption at 263 nm. The change in the induced absorbance is followed up to 450 ps in the spectral range from 440 to 720 nm. The transient signals of electron solvation have been analyzed by two kinetic models: a stepwise mechanism and a continuous relaxation model, using a Bayesian data analysis method. The results are compared with those previously published for ethylene glycol (J. Phys. Chem. A 2006, 110, 175) and for propanediols (J. Phys. Chem. A 2007, 111, 4902). From the comparison, it is pointed out that solvation dynamics in glycerol is very fast despite its high viscosity. This is interpreted as the existence of efficient traps for the electrons in glycerol with low potential energy. The small shift of the absorption band of the excess electron indicates that the potential of these traps is very close to that corresponding to the fully solvated electron.     

Disintegration of 1-silalactones under the influence of electron impact

It is shown that the paths of fragmentation of 1-silalactones under the influence of electron impact are determined by the ring size and remain virtually unchanged when the methyl groups attached to the silicon atom are replaced by a chlorine atom or an ethyl group. The possibility of the identification of isomeric silalactones on the basis of their mass spectra was established.     

Identification of the hydrolysis products of AlCl3.6H2O by electrospray ionization mass spectrometry

The hydrolysis reactions of AlCl3 in 0.1 M aqueous solutions at pH 3.27-4.20 were monitored by electrospray ionization time-of-flight mass spectrometry (ESI-ToF MS) as a function of time. The cationic and anionic ESI mass spectra of aluminum(III) solutions gave strong evidence of the presence of a variety of monomeric and polymeric complexes. Competition between the OH- and Cl- ligands within the same aluminum core was observed. The influence of the sample cone voltage on the product distribution was also explored. The optimum sample cone voltage for the cationic spectra was 70 V. For the anionic spectra no optimum sample cone voltage was found and the appearance of the anionic spectra was strongly dependent on the sample cone voltage within the whole range explored.