International Journal of Mass Spectrometry and Ion Physics最新文献

Given an accurate control of chemical composition, structure and thickness, monomolecular layers of fatty acids are used as model systems to study biological processes. Assembled as multimolecular layers on solid supports, these systems are used to prove the feasibility of secondary-ion mass spectrometry (SIMS) to investigate organic surfaces.

A simple model can be applied to explain the observed sputtering phenomena. The yield of this process is, for the organic systems, approximately as large as that for inorganic systems, but the damaged cross-section is considerably larger. The latter determines the dependence of the intensities of various signals on the primary-ion dose. Yet it could be shown that the chemical composition of the organic system can be determined with a depth resolution of better than 25 Å.

The temperature dependence of the reaction of Cl⁺ with H₂ has been the subject of several recent studies. The interest in this reaction derives mainly from its importance in modeling chlorine chemistry in interstellar clouds. New data on this reaction are reported that suggest the reaction has a weak negative temperature dependence in agreement with recent flow tube studies. Data for the HD and D₂ isotopic species show the same trend. New data on the HCl⁺ + H₂ reaction are also reported.

Collisional enhancement of the SiC₂H₇⁺ intensity in the reaction of SiH₃⁺ ions of 2.6 eV laboratory kinetic energy with C₂H₄ is due to moderation of the reactant-ion energy rather than removal of excess energy from the (SiC₂H₇⁺)* collision complex. The effectiveness of (CD₃)₄Si, CH₄, CO₂, N₂, D₂ and Ar as kinetic energy moderators was studied at a constant C₂H₄ pressure of 2.5 × 10⁻⁴ torr and at moderator pressures up to 5 × 10⁻³ torr. The most important property determining moderator efficiency is molecular complexity, i.e. number of vibrational degrees of freedom. The moderator (CD₃)₄Si is not efficient, despite its large number of vibrational degrees of freedom, because it undergoes a rapid reaction with SiH₃⁺ to produce (CD₃)₃Si⁺ ions.

The decrease in the ²⁴¹Pu/²⁴⁰Pu isotope ratio and in the ratio of the isotope ratios (²⁴¹Pu/²⁴⁰Pu)/(²⁴⁰Pu/²³⁹Pu) due to the β-decay of ²⁴¹Pu was measured by high-precision isotope mass spectrometry over a period of six years on a 93% isotopically enriched sample. The resulting value for the ²⁴¹Pu half-life is 14.33 ± 0.02 years.

The need for accurate isotope abundance values (θ) in reactor neutron activation analysis is discussed. A comparison of literature θ-values for target isotopes of low abundance is made and this shows a considerable scattering of data. Although the k₀ standardization method can offer some help in nuclear data evaluation, it must be concluded that, for some 14 analytically interesting minor isotopes, more reliable θ-values are required: ³⁶S, ⁵⁰Ti, ⁵⁸Fe, ⁶⁴Ni, ⁷⁴Se, ⁸⁴Sr, ¹¹²Sn, ¹²²Sn, ¹²⁴Sn, ¹³⁰Ba, ¹⁶²Er, ¹⁷⁴Hf, ¹⁹⁸Pt, ¹⁹⁶Hg.

The relative cross-sections for charge transfer to hydrogen chloride, hydrogen bromide and water vapour together with the mass spectrum of HBr were obtained with several reactant ions.

The Q(RE) functions resembled the corresponding photoelectron spectra, confirming earlier statements that the PE peaks can be treated as experimental FC factors.

The influence of electronic and/or vibrational excitation, as well as of the kinetic energy of the reactant ions, on the hydrogen bromide mass spectrum has been demonstrated.

A new ion source has been designed and tested for performing thermal ionization isotopic analyses with a quadrupole mass spectrometer. Significantly improved performance in comparison to the commercial source was obtained.