Electron interaction with bio-molecules and clusters

Collisions between electrons and molecules initiate and drive many important chemical reactions associated with radiation physics and chemistry, environmental physics and chemistry, plasma-enhanced chemical vapor deposition, plasma processing of materials for microelectronic devices and many other applications. Moreover, life sciences are a rapidly growing area where the important role of electron driven reactions is only now beginning to be recognized. In addition, electrons and their interaction also drive key reactions in chemical synthesis, in planetary atmospheres and in plasmas used in environmental remediation applications. Moreover, electron attachment and electron ionization studies are of fundamental importance to the understanding of electron-molecule interactions and the mechanisms of negative and positive ion formation. Nonethetheless, as concluded in a recently held US workshop sponsored by US government agencies, relatively little is known about these electron-initiated processes at a microscopic level and it was recommended that a large scale effort should be mounted to solve these problems in a timely way. In the present study we plan to investigate electron attachment to clusters and electron attachment and electron ionization of bio-molecules. The present study will be based on previous experience and several exploratory studies in our laboratory concerning electron attachment and electron ionization of molecules/clusters. In the course of these studies we have developed various experimental techniques (including a trochoidal monochromator and a hemispherical monochromator both coupled in a crossed beam arrangement to a quadrupole mass spectrometer) allowing us to investigate with high energy resolution and high sensitivity electron attachment as a function of electron energy in the low energy regime. Electron impact ionization of neutrals and ions can be studied in a newly constructed three sector field mass spectrometer allowing us to determine accurate ionization cross sections, appearance energies, kinetic energy release distributions and metastable fractions. The cluster targets selected for the present study will comprise ozone cluster beams, mixed ozone/water clusetr beams, (endohedral) fullerenes and hydrogen cluster beams. In the two former cases we will either improve and extend existing knowledge or clarify existing discrepancies (also studying the temperature dependence in the case of fullerenes), whereas the hydrogen case is the first such study on this system. Except for fullerenes, the usual study with cluster beams involves interaction of electrons with beams with a broad range of cluster sizes. In the present study we plan to produce size selected neutral cluster beams, this will enable a more detailed study of the electron cluster interaction. In the case of electron attachment and electron ionization of bio-molcules we plan in contrast to earlier studies to interact the electrons with neutral beams of bio-molecules (for instance nucleobases of DNA etc.) which are produced without heating the sample (using a new molecular beam source), thereby avoiding possible excitation or fragmentation of the neutral targets produced. Electron attachment and electron ionization will be also extended to neat clusters of these bio-molecules and mixed clusters containing bio-molecules solvated in water molecules and to electron interaction with anions and cations of these various bio-molecular compounds.

Collisions between electrons and molecules initiate and drive many important chemical reactions associated with radiation physics and chemistry, environmental physics and chemistry, plasma-enhanced chemical vapor deposition, plasma processing of materials for microelectronic devices and many other applications. Moreover, life sciences are a rapidly growing area where the important role of electron driven reactions is only now beginning to be recognized. In addition, electrons and their interaction also drive key reactions in chemical synthesis, in planetary atmospheres and in plasmas used in environmental remediation applications. Moreover, electron attachment and electron ionization studies are of fundamental importance to the understanding of electron-molecule interactions and the mechanisms of negative and positive ion formation. Nonethetheless, as concluded in a recently held US workshop sponsored by US government agencies, relatively little is known about these electron-initiated processes at a microscopic level and it was recommended that a large scale effort should be mounted to solve these problems in a timely way. In the present study we have investigated in detail electron attachment and ionization of clusters (including rare gas clusters, fullerenes and atmospherical relevant molecular clusters) and electron attachment and electron ionization of bio-molecules. The present study is based on previous experience and several exploratory studies in our laboratory concerning electron attachment and electron ionization of molecules/clusters. In the course of these studies we have developed various experimental techniques (including a trochoidal monochromator and a hemispherical monochromator both coupled in a crossed beam arrangement to a quadrupole mass spectrometer) allowing us to investigate with high energy resolution and high sensitivity electron attachment as a function of electron energy in the low energy regime. Electron impact ionization of neutrals and ions has been studied successfully in two newly constructed sector field mass spectrometers allowing us to determine accurate ionization cross sections, appearance energies, kinetic energy release distributions and metastable fractions. In the frame of the present project 76 publications appeared in first rate journals in physics (Phys.Rev.Letters, Chem.Phys.Letters, J.Chem.Phys, etc.) and in chemistry (Angewandte Chemie Int.Edition, J.Phys.Chem., etc.). Moreover the principal investigator and co-workers were invited 38 times to give invited lectures at international conferences about results obtained in this FWF project. The results obtained are also relevant for radiotherapy, fusion reactor construction and material science.