A dynamical (e,2e) investigation into the ionization of the outermost orbitals of R-carvone

We report an experimental and theoretical investigation into the dynamics of electron-impact ionization of R-carvone. Experimental triple differential cross sections are obtained in asymmetric coplanar kinematic conditions for the ionization of the unresolved combination of the three outermost molecular orbitals (41a-39a) of R-carvone. These cross sections are compared with theoretical cross sections calculated within a molecular 3-body distorted wave (M3DW) framework employing either a proper orientation average or orbital average to account for the random orientation of the molecule probed in the experiment. Here, we observe that the overall scattering behavior observed in the experiment is fairly well reproduced within the M3DW framework when implementing the proper average over orientations. The character of the ionized orbitals also provides some qualitative explanation for the observed scattering behavior. This represents substantial progress when trying to describe the scattering dynamics observed for larger molecules under intermediate-impact energy and asymmetric energy sharing scattering conditions.

Elastic differential cross sections for C₄F₆ isomers in the 1.5-200 eV energy electron impact: similarities with six fluorine containing molecules and evidence of F-atom like scattering

We report absolute elastic differential cross sections for electron interactions with the C4F6 isomers, hexafluoro-1,3-butadiene (1,3-C4F6), hexafluoro-2-butyne (2-C4F6), and hexafluorocyclobutene (c-C4F6). The incident electron energy range is 1.5-200 eV, and the scattered electron angular range for the differential measurements varies from 15° to 150°. In all cases the absolute scale of the differential cross section was set using the relative flow technique, with helium as the reference species. Atomic-like behaviour in these scattering systems is shown here for the first time, and is further investigated by comparing the elastic cross sections for the C4F6 isomers with other fluorinated molecules, such as SF6 and CnF6 (n = 2, 3, and 6). We note that for all the six-F containing molecules, the scattering process for electron energies above 30 eV is indistinguishable. Finally, we report results for calculations of elastic differential cross sections for electron scattering from each of these isomers, within an optical potential method and assuming a screened corrected independent atom representation. The level of agreement between these calculations and our measurements is found to be quite remarkable in all cases.

Dissociative electron attachment to gas phase glycine: exploring the decomposition pathways by mass separation of isobaric fragment anions

Dissociative electron attachment to gas phase glycine generates a number of fragment ions, among them ions observed at the mass numbers 15, 16 and 26 amu. From stoichiometry they can be assigned to the chemically rather different species NH(-)/CH(3)(-)(15 amu), O(-)/NH(2)(-)(16 amu) and CN(-)/C(2)H(2)(-)(26 amu). Here we use a high resolution double focusing two sector mass spectrometer to separate these isobaric ions. It is thereby possible to unravel the decomposition reactions of the different transient negative ions formed upon resonant electron attachment to neutral glycine in the energy range 0-15 eV. We find that within the isobaric ion pairs, the individual components generally arise from resonances located at substantial different energies. The corresponding unimolecular decompositions involve complex reaction sequences including multiple bond cleavages and substantial rearrangement in the precursor ion. To support the interpretation and assignments we also use (13)C labelling of glycine at the carboxylic group.

Laser desorption electron attachment time-of-flight mass spectrometry: a new approach to detection of involatile compounds

We report initial results of a new method for obtaining mass spectra of involatile compounds: laser desorption electron attachment time-of-flight mass spectrometry. With this approach, laser desorbed neutral molecules are entrained in a molecular beam and subsequently ionized by low energy electron attachment. Mass analysis is carried out by a linear time-of-flight. We present a description of the apparatus and a number of examples of our early results on: van der Waals condensates of SF6, Fullerenes, derivatized Fullerenes, perfluorinated polyethers, polyphenylethers, and 5-bromouracil.

Bridging the cluster-to-bulk divide: electron attachment time-of-flight mass spectrometry reveals geometrical shell closings in (SF6) (n) clusters (n = 2 - 550)

We report electron attachment time-of-flight mass spectra of SF (6) clusters over a wide range of cluster sizes, revealing a simple pattern of geometrical shell closings which persists from large clusters (n approximately 500) to as small as perhaps n = 14. Quantitative structural properties of these nanocrystallites are derived. These observations, made possible by an extraordinarily gentle ionization method and mass spectral analysis, suggest that bulk crystalline packing may be important for much smaller molecular clusters than previously observed, confirming theoretical predictions.