Frontiers of positron and positronium chemistry in condensed media

Our work proves that positron annihilation spectroscopy is an excellent too l to follow the structural changes in chemical species. We present four exa mples to support the above statement. The sizes of defects in electrodeposi ted chromium layers were studied and estimated on the basis of positron lif etime spectra decomposed into two components. Vacancies, di-vacancies and v acancy-clusters could be identified in the electrodeposites. The changes of the size distribution of the free volume units in poly(methylmetacrylate) on the dependence of molecular weight and dispersity were described by the correlation between the lifetime of ortho-Ps and the free volume units in p olymers. It was found that the free volume is affected by both the molecula r weight and dispersity. The effect of dispersity was explained by the samp le preparation technique, namely by the application of high pressure. The o rtho-para conversion of ortho-Ps was used to follow the partial spin-crosso ver in [Fe(1-ethyl-1H-tetrazole)(6)](BF4)(2). The spin-crossover temperatur e was identified to be 105 K. A conformal structural transformation was fou nd in [Zn(1-propyl-1H-tetrazole)(6)](BF4)(2) between 170 and 90 K by positr onium lifetime measurement and the role of (BF4)(2-) anion, in this transfo rmation, was proved by F-19 NMR spectroscopy.