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DIAM (Dispositif d'Irradiation d'Agrégats Moléculaires) is a new experimental setup devoted to investigate processes induced by irradiation at the nanoscale. The DIAM apparatus is based on a combination of techniques including a particle beam from high-energy physics, a cluster source from molecular and cluster physics, and mass spectrometry form analytical sciences. In this paper, we will describe the first part of the DIAM apparatus that consists of an ExB double spectrometer connected to a cluster ion source based on a continuous supersonic expansion in the presence of ionizing electrons. This setup produces high intensities of energy-and-mass selected molecular cluster ion beams (1000 s of counts s-1). The performance of the instrument will be shown through measurements of 6-8 keV beams of protonated water clusters, (H2O)nH+ (n = 0-21) and mixed protonated (or deprotonated) water-pyridine cluster ions: PyrH+(H2O)n (n = 0-15), Pyr2H+ (H2O)n (n = 0-9), and (Pyr-H)+ (H2O). [ABSTRACT FROM AUTHOR]

Abstract: We present absolute partial electron impact ionization cross sections for propene in the electron energy range between threshold and 1000eV measured with a two sector field double focussing mass spectrometer. Ion beam profiles have been measured at all electron energies by applying a deflection field method. In combination with a three-dimensional ion trajectory simulation of ions produced in the ion source ion kinetic energy distribution functions and discrimination factors can be derived form these data. Multiplication of these discrimination factors with the measured ion signals leads to relative partial cross sections. Normalization of the sum of the relative partial cross sections to an absolute total cross section gives absolute partial cross section values. The initial kinetic energy distributions of several fragment ions show the presence of two or more contributions exhibiting different electron energy dependencies. Differential cross sections with respect to initial kinetic energy of the ions are given and related to specific ion production channels. The high energetic parts of the initial kinetic energy distributions are assigned to the Coulomb explosion of doubly charged short-lived intermediates. The reaction C3H5 2+ →C2H2 + +CH3 + has been studied quantitatively in the ion source, the first field free region and the second field free region of the two sector field mass spectrometer yielding a measured mean kinetic energy release of 4.99±0.5eV, 4.85±0.5eV and 5.5±0.5eV, respectively in good agreement with a theoretical estimation. [Copyright &y& Elsevier]

Abstract: Neutral helium clusters, formed in a supersonic beam, are subjected to electron impact ionization. We report resolved size distributions of cations of size n ≤300. The distributions show the well established anomalies at n = 10 and 14, but none for larger sizes. MIKE scans of the cluster ions confirm the anomalies at n = 10 and 14, and another one at n = 7. Surprisingly broad distributions of fragment ions are observed for parent sizes 15≤ n ≤30. These findings are attributed to radiative heating. The kinetic energy released upon loss of one helium atom (KER) has been measured. The values drop below 1meV for n > 20. Neither the metastable fragment distribution nor the KER data provide evidence for the release of large, quantized energies that one would expect for relaxation of any long-lived vibronic states of the ionic core. [Copyright &y& Elsevier]

Abstract: Doubly charged ions produced by electron impact ionization of toluene (C7H8) show metastable unimolecular dissociation into two singly charged fragments. A high-resolution double focusing mass spectrometer (reversed Nier–Johnson type BE geometry) was used to monitor these decomposition reactions. We have identified four competing charge separation channels. The mass-analyzed ion kinetic energy (MIKE) technique was used to determine mean values of the kinetic energy release (KER). We obtained values of the average KER for the charge separation reactions of ranging from 2.5 to 3.5eV. [Copyright &y& Elsevier]

Abstract: The first fragmentation ratios are presented for the ionization of gas-phase DNA bases by 80keV (1.8 v 0 in Bohr velocity units) proton impact. Event-by-event determination of the projectile charge state post-collision enables branching ratios to be determined for electron capture (EC) by the projectile and for direct ionization (DI) of the target molecule (without projectile neutralization). Results are compared with similar experiments on uracil and water . In all cases, whereas both processes (EC and DI) produce the same fragment ion groups, greater fragmentation ratios are observed for EC than for DI. Moreover the fragmentation ratio is greater for thymine than for adenine, cytosine, and uracil. [Copyright &y& Elsevier]

Abstract: We present absolute partial electron impact ionization cross sections for ethylene in the electron energy range between threshold and 1000eV measured with a two sector field double focusing mass spectrometer. Ion kinetic energy distribution functions have been measured at all electron energies by applying a deflection field method. Multiplication of the measured relative cross sections by the appropriately determined discrimination factors lead to accurate relative partial cross sections. Normalization of the sum of the relative partial cross sections to an absolute total cross section gives absolute partial cross section values. The initial kinetic energy distributions of several fragment ions show the presence of two or more contributions that exhibit different electron energy dependencies. Differential cross sections with respect to the initial kinetic energy of the ions are provided and are related to specific ion production channels. The electron threshold energies for the direct and numerous other dissociative ionization channels are determined by quantum chemical calculation and these allow the determination of the total kinetic energy release and the electron energy loss for the most prominent dissociative ionization channels. [Copyright &y& Elsevier]