Isotope exchange condensed-phase reactions

H2 + 0H [46], and has thus been associated with part of the unscavengeable H2 yield formed in water radiolysis [247]. Another (post-DEA) ion-molecule reaction, directly observed in the condensed phase for ion kinetic energies well below 5 eV, is isotope exchange... 

Exchange distillation takes advantage of the fact that condensed phase-vapor phase separation factors can be enhanced (as compared to liquid-vapor factors) by association-dissociation equilibria in one or the other phase. A good example is found in B/ B separations. At the normal boiling point of 173 K, the vapor pressure isotope effect for BF3, In a In [T( BF3)/ P("BF3)] = —0.0075, is sufficiently large for useful separation by distillation (Neetley et al., 1958). Compare this effect, however, with association-dissociation constants (f q) for reactions of the type... 

There are some items of interest here. A few basic properties are the basis for separation in two different types of basic separation processes. For example, condensability of a vapor/gas species is useful for vapor absorption as well as for membrane gas separation geometrical partitioning (or partitioning by other means between a pore and an external solution) is useful both in adsorp-tion/chromatography as well as in the membrane processes of dialysis and ultrafiltration, etc. Further, there are many cases where chemical reactions are extraordinarily useful for separation these are not identified here since chemical reactions can enhance separation only if the basic mechanism for separation exists, especially in phase equilibrium based separations. However, there are a few cases where chemical reactions, especially complexations, provide the fundamental basis for separation, as in affinity chromatography, metal extractions and isotope exchange reactions. 

The relationship between the isotope abundance ratios of the different species in the reaction is expressed as the fractionation factor a . For example, consider the oxygen isotope exchange of H2O between condensed and vapour phases ... 

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