The Role of the Lone Pairs in Hydrogen Bonding
The Role of the Lone Pairs in Hydrogen Bonding
The Role of the Lone Pairs in Hydrogen Bonding
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Monday, February 5 10:00-10:30<br />
High-resolution Compton pr<strong>of</strong>iles<br />
Pekka Suortti<br />
Department <strong>of</strong> Physical Sciences, PL 64, FIN-00014 Hels<strong>in</strong>ki University, F<strong>in</strong>land and European Synchrotron<br />
Radiation Facility, BP 220, F-38043 Grenoble, France, e-mail: Pekka.Suortti@hels<strong>in</strong>ki.fi, suortti@esrf.fr<br />
Compton scatter<strong>in</strong>g has played a decisive role <strong>in</strong> some developments <strong>of</strong> modern physics, first <strong>in</strong> <strong>in</strong>terpretation<br />
<strong>of</strong> photon scatter<strong>in</strong>g and conservation laws, <strong>the</strong>n <strong>in</strong> giv<strong>in</strong>g direct evidence that electrons <strong>in</strong><br />
solids obey Fermi-Dirac statistics. <strong>The</strong> history <strong>of</strong> Compton scatter<strong>in</strong>g is that <strong>of</strong> a dialogue between experiment<br />
and <strong>the</strong>ory at <strong>the</strong> deepest level, and <strong>the</strong>ory and experiment have taken <strong>the</strong> lead alternately.<br />
In this work <strong>the</strong> development <strong>of</strong> focus<strong>in</strong>g crystal spectrometers for Compton scatter<strong>in</strong>g studies from<br />
1930s to present is reviewed. <strong>The</strong> design pr<strong>in</strong>ciples have stayed <strong>the</strong> same, but <strong>the</strong> efficiency has improved<br />
much ow<strong>in</strong>g to <strong>the</strong> availability <strong>of</strong> large perfect crystal analyzers and efficient detectors. <strong>The</strong> reflectivity<br />
and energy resolution <strong>of</strong> <strong>the</strong> crystal can be tailored to <strong>the</strong> needs <strong>of</strong> <strong>the</strong> experiment by <strong>the</strong> asymmetric<br />
cut, thickness and bend<strong>in</strong>g radius <strong>of</strong> <strong>the</strong> crystal, and <strong>the</strong> response function <strong>of</strong> <strong>the</strong> spectrometer can be<br />
calculated precisely. <strong>The</strong> spectrometers at synchrotron radiation beaml<strong>in</strong>es achieve better than 0.1 a.u.<br />
momentum resolution, and several statistically accurate Compton spectra can be acquired <strong>in</strong> one day.<br />
<strong>The</strong> latest developments <strong>in</strong>clude spectrometers that operate <strong>in</strong> <strong>the</strong> 100 keV range, and count rates are<br />
enhanced by us<strong>in</strong>g wide energy bands and dispersion compensation. Experimental momentum density <strong>of</strong><br />
crystall<strong>in</strong>e LiH is compared with results <strong>of</strong> a Hartree-Fock calculation <strong>in</strong> terms <strong>of</strong> directional Compton<br />
pr<strong>of</strong>iles and reciprocal form factors. <strong>The</strong> agreement is excellent, and <strong>the</strong> residual differences are attributed<br />
to electron-electron correlation, which is not <strong>in</strong>cluded <strong>in</strong> <strong>the</strong> H-F calculation. <strong>The</strong> correlation energy<br />
is calculated from <strong>the</strong> second moment <strong>of</strong> <strong>the</strong> difference between experimental and <strong>the</strong>oretical Compton<br />
pr<strong>of</strong>iles.<br />
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