ON THE HEAVY ATOM QUANTUM INTERFERENCE SCATTERING PHENOMENA IN DIMOLYBDENUM(ll) DIMERS. Boris Udovic, Primoz Segedin, Faculty of Chemistry and Chemical Technology, University of Ljubljana, P.O. Box 537, 61001 Ljubljana, Slovenija

Pyramidally coordinated oxygen atoms freeze and hinder the librational motions of quadruple bonded dimolybdenum(II) dimers inside the prismatic cage of zwitterionic 3,5-diaminobenzoate tetracarboxylate units. De Broglie wavelength [[lambda]]_Mo~1.44 Å and [[lambda]]_Mo~2.10 Å were computed from vibrational spectra at 293 K and assigned to low energy components of the superimposed and periodic motions of molybdenum atoms along the principal dimer axis. The expected quantum interference fringe maxima of interdiffusing and scattering l_Mo waves were confirmed in the Fourier difference maps with observed electron density anomalies on the alternative axes inside and outside the oxygen cage at 293 K. The quantum singularities were refined at the wavelength distances [[lambda]]_Mo(2) = 1.4904(11) Å, [[lambda]]_Mo(3) = 1.4901(13) Å, [[lambda]]_Mo(4) = 2.09(5)Å, [[lambda]]_Mo(5) = 2.08(5)Å, from the vibrating molybdenum atoms Mo(1) and Mo(1)(iii) in their potential wells. The occupancy factors of the alternative sites Mo(2) and Mo(3) inside the cage were 3.8% and 4.2%, while outside the cage the alternative sites Mo(4) and Mo(5) were 0.31% and 0.25% respectively. In the prismatic cage the heavy atom random thermal energy, with its related statistical temperature, is converted into a directed kinetic energy with different velocity components which are linked to a rather localized and oriented low temperature by frozen vibrational motions of very cold metal atoms trapped in their quantum well.