EGAS41 - Swansea University

41 st EGAS CP 92 Gdańsk 2009
Mass-spectrometric studies of electron-impact dissociative
ionization of glycine molecule
V.S. Vukstich, A.I. Imre, O.A. Sitalo, A.V. Snegursky ∗
Institute of Electron Physics, Ukrainian National Academy of Sciences, 21 Universitetska
street, Uzhgorod 88017, Ukraine
∗ Corresponding author: sneg@mail.uzhgorod.ua
We have developed a mass-spectrometric apparatus based on the magnetic mass-analyzer
intended for studying ionization of atoms and single/dissociative ionization of polyatomic
molecules by low-energy electron impact. A primary emphasis was given to the production
of ionic fragments following dissociation of complex molecules, mainly those having
biological relevance. Such data are of specific interest in view of tracing the possible effects
occurring in the live tissue under the influence of ionizing radiation accompanied by the
production of slow secondary electrons, which, in turn, cause a series of structural transformations
in the cells resulted in degradation of constituent elements of human/animal
body [1]. Amino acids, which glycine belongs to, are one of the basic building blocks of
the live body. Moreover, recent investigations have shown that amino acids are present
in various space objects (say, meteorites and/or comets), proving, thus, the idea of life
”import” to the Earth [2]. Of special interest is the fact that such molecules take an active
part in constructing live cells and repairing damaged tissues, in particular, in forming
antibodies, which fight against the viruses and bacteria that destroy the immune system
of living organism. Experiment was carried out using a crossed-beam technique combined
with mass separation of electron-molecule interaction products. The measuring procedure
was fully automated using the PC control. Besides measuring the mass-spectra of
the initial molecule, we have determined the energy dependences of the ionized fragment
yield with the 0.3 eV energy step and the 0.2 − 0.5 eV (FWHM) energy resolution from
the threshold up to 150 eV using a specially-designed electron gun instead of the conventional
one used in the original version of mass-spectrometer ion source. It has been found
that the main ionic fragments of the initial C 2 H 5 NO 2 molecule are CH 4 N + , CH 3 N + and
CH 2 N + , which can be produced in various isomer states. Since the initial molecule may
undergo strong fragmentation due to the thermal processes, special studies of possible
temperature-induced fragmentation of the glycine molecule were carried out allowing one
to choose the regime of molecular beam generation, minimizing, thus, the influence of
thermal effects. Application of special least-square fitting procedure [3] enabled the absolute
values of the appearance potentials for the above fragments to be found. Out data
demonstrate fairly good agreement with the results of recent photoioniozation studies [4].
More detailed analysis of experimental data and possible mechanisms of electron-impact
glycine molecule fragmentation will be presented at the conference.
References
[1] B.D. Michael, P.A. O’Neill, Science 287, 1603 (2000)
[2] Ed. A. Brack, The Molecular Origins of Life (Cambridge University press, Cambridge,
UK, 1998)
[3] G. Hanel, B. Gstir, T. Fiegele et al., J. Chem. Phys. 116, 2456 (2002)
[4] H.-W. Jochims, M. Schwell, J-L. Chotin, J. Chem. Phys. 298, 279 (2004)
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