Mechanisms of the electron-impact-induced glycine molecule fragmentation J. Tamuliene a,⇑ , L.G. Romanova b , V.S. Vukstich b , A.V. Snegursky b a Vilnius University, Institute of Theoretical Physics and Astronomy, 12 A. Goštauto str., 01108 Vilnius, Lithuania b Institute of Electron Physics, Ukr. Nat. Acad. Sci., 21 Universitetska str., 88017 Uzhgorod, Ukraine article info Article history: Available online 8 February 2012 abstract Fragmentation of the glycine (C 2 H 5 NO 2 ) molecule by low-energy electron impact has been studied both experimentally and theoretically. The main emphasis has been given to the mechanisms of the initial molecule fragment production including formation of the doubly-charged CH 2 NHCO 2+ fragment. A spe- cial attention has been paid to the energy characteristics of the ionic fragment yield. The geometrical parameters of the initial molecule rearrangement have also been analyzed. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction The studies of the damages in biological systems, including ami- no acids, resulted from the influence of ionizing radiation, are being the hot topic of a series of investigations within last decades [1]. The majority of the above damages are not usually due to the primary high-energy radiation but results from the effect of the secondary low-energy charged particles produced in the course of ionization. Amino acids are known as the building blocks of the human body proteins responsible for forming antibodies to struggle against bac- teria and viruses, constructing the hormonal system and transfer- ring oxygen throughout the human organism. It is well-known that glycine, which is one of the non-essential amino acids, helps involving oxygen into hormone production mechanism and, thus, strengthens the immune system of live tissues [1]. The studies of amino acids in the gas phase are of great signif- icance in biology for understanding and determining their proper- ties. Such knowledge is fundamental to understanding the complex structure of their polymers, say, proteins and peptides. Further- more, this information is important for a number of modern fields of biological science, e.g., for biological astrophysics and photo- chemistry as well as for various nano-bio-technological applica- tions. The structures of these molecules can be accessed in different ways. Here we would like to emphasize that the complex gas-phase experimental investigations and the relevant theoretical calculations allow an unambiguous experimental data interpreta- tion to be obtained, which, in turn, may serve to prove theoretical models. In our recent papers [2,3], we reported the experimental data on the thermal and electron-impact fragmentation of the gly- cine molecule. The present paper deals with the continuation of our previous studies on fragmentation of this molecule induced by the collisions with low-energy monoenergetic electrons [2,3]. 2. Experimental The experimental apparatus and method applied are described in detail in Refs. [3,4]. The experimental technique is related to the crossed-beam method involving mass separation of the collision products by means of a modernized magnetic mass spectrometer that allows the reaction products to be selected with respect to their mass-to-charge ratio [4]. Here we would like to mention that our apparatus is capable of studying ionic fragments within the 1– 720 a.m.u. mass range with high sensitivity (10 16 A) and mass resolution (m/Dm = 1100). The beam of the molecules under study was formed by an effusion source with a resistively heated oven providing the target molecule concentrations of about 10 10 cm 3 . The operating temperature of the molecular beam source was var- ied up to 150 °C and controlled by a thermocouple. The experimen- tal conditions excluded molecular cluster formation in the beam. An original three-electrode electron gun provided an electron cur- rent of 30–50 lA over the energy range under study (0–150 eV). The parent and fragment ions produced were detected after mass separation by means of an electrometer. The data acquisition and processing were controlled by a PC. The electron energy scale cal- ibration was carried out against known ionization thresholds for an argon atom and nitrogen molecule with the accuracy not worse than ±0.1 eV [3]. The glycine molecule mass spectrum was mea- sured at the 70 eV electron energy, the appearance energies for positively charged fragment ions were determined using technique described in Refs. [2,3] within the 5–30 eV energy range. 3. Theoretical The structure of the molecule and its fragments has been stud- ied by using the generalized gradient approximation for the ex- change-correlation potential in the density functional theory (DFT) as it is described by the Becke’s three-parameter hybrid func- tional, using the non-local correlation provided by Lee, Yang, and 0301-0104/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.chemphys.2012.01.019 ⇑ Corresponding author. E-mail address: jelena.tamuliene@tfai.vu.lt (J. Tamuliene). Chemical Physics 404 (2012) 36–41 Contents lists available at SciVerse ScienceDirect Chemical Physics journal homepage: www.elsevier.com/locate/chemphys