W PCy 3 CO 3 -H2 Complex

Dikydrogen Transfer and Symmetry in the Light ofNMR Spectroscopy 

The high temperature limit of the rates was chosen as 4x10 s , according to the Eyring equation. 

This chapter presents some effects symmetry has on the rates and mechanisms of chemical reactions. The reaction kinetics of low mass groups like dihydrogen or dideuterium, in particular at low temperatures, is strongly influenced by quantum mechanical tunneling processes and the Fermi postulate of the symmetry of the 

Finally, we wish to note that hydrogen is not the only small molecule, where molecular exchange symmetry causes the existence of a para- and an ortho- spin isotopomer. Water is another important example. In the gas phase it exists as para- or ortho-water. They are distinguishable by IR. Their concentration ratio is used in astronomy as a remote temperature sensor. The spin conversion mechanisms of these isotopomers are still an open field for future studies [98, 99]. 

This research has been supported by the Deutsche Forschungsgemeinschaft, Bonn, and the Fonds der Chemischen Industrie (Frankfurt). 

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