Laboratory of Low Temperature Microwave Spectroscopy
esrlab@orange.ichtj.waw.pl  
Head: Prof. Jacek Michalik  
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Research activity


The research activity of the Laboratory concerns the paramagnetic transient species - free atoms, radicals and small metal clusters produced radiolytically in solids. Their structures, stabilization sites and reactivities are studied by Electron Paramagnetic Resonance ( EPR ).

The major area of research involves the radiation - induced agglomeration of silver in molecular sieves. In angstrem size of cages and channels of molecular sieves silver atoms and clusters are stabilised at higher temperature than in non - porous materials. Owing to that the influence of silver loading, presence of different cations and molecular adsorbates on agglomeration process can be followed up in more detailed way.
For example, we proved that in zeolite rho the cationic silver clusters are formed gradually during thermal annealing by the reactions between silver atoms and clusters and Ag+ cations until silver tetramer Ag43+ stable at room temperature is formed. In contrast in Ag - solidates the paramagnetic silver cluster - Ag65+ hexamer is produced directly during radiolysis at 77K. The proposed mechanism involves the electron capture by the assembly of six Ag+ cations in the same cage.
The stabilization of small organic radicals in zeolites is other research topic. The radicals produced by g - irradiation of zeolites with adsorbed methane, ethane, ethylene etc. show in some cases unique stability at room temperature. The aim of the studies is to understand the mechanism of radical stabilization.
In Na - A zeolite -CH3 radicals are observable at room temperature. By analysing the EPR spectra we proved that in A zeolite two types of •CH3 radicals are formed : free - rotating radicals and radicals interacting with Na+ cations.
The EPR studies of radicals in the systems of biological importance concern the secondary radiation reactions in sulphur - containing carboxylic acids, amino acids and peptides. The investigations are carried out with close cooperation with Pulse Radiolysis Laboratory and aim to better understanding of the mechanism of radiation damages in living organisms.
The EPR studies of radiation - induced polycrystalline methionine - containing peptides showed that radical processes strongly dependent on the peptide structure i.e.: the location of methionine residue with respect to the terminal functions and the nature of the neighbouring amino acids located at the N - and C - terminus of methionine.
Carbon - centered anion - radicals, •CO2-, •CO3-, •CO33 in biological (bones, tooth enamel) and synthetic carbonate - apatities are studied in order to apply the stable EPR signals for dosimetry of ionising radiation.
The better understanding of the nature and the trapping site of stable paramagnetic centers is essential for correct dose estimation. For example, in teeth enamel the dosimetric signal of CO2- is overlapped with CO33- which requires the necessary correction for the calibration of CO2- signal intensity vs radiation dose.
The Conduction Electron Spin Resonance (CESR) experiments are carried out to prove that electron resonance technique might be useful tool to measure the size of metallic nanoparticles.

The EPR studies of radicals in polymers modified by accelerated electron beam aim to understand the role of radiation - induced radicals in degradation or cross - linking processes of polymer chains.