Nuclear Size and Shape Effects in Chemical Reactions. Isotope Chemistry of the Heavy Elements

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1、3676J.Am.Chem.Soc.1996,118,3676-3680NuclearSizeandShapeEffectsinChemicalReactions.IsotopeChemistryoftheHeavyElementsJacobBigeleisenContributionfromtheDepartmentofChemistry,StateUniVersityofNewYorkatStonyBrook,StonyBrook,NewYork11794-3400ReceiVedDecember5,1995XAbstract:Thetheoryofthe

2、isotopicenrichmentfactorisextendedtoincludehyperfinesplittingandthenuclearfieldshift.Itisshownthathyperfinesplittingisanorderofmagnitudetoosmalltoexplaintheanomalyinthe238U/235UseparationintheU(III)-U(VI)exchangereaction.TheªanomalousmasseffectºinthisreactionandtherelatedU(IV)-U(VI)

3、exchangereactionsareshowntoberelatedtothenuclearfieldshiftoftheelectronenergylevels.Calculationsoftheeffectsoftheseshiftsexactlyreproducetheodd-evenstaggeringintheU(IV)-U(VI)exchangereactionandtheseparationfactorsfortheeven-evennuclei.IntheU(IV)-U(VI)exchangereactionsthenuclearfield

4、effectisthreetimesaslargeastheabsolutevalueandofoppositesigntothevibrationalenergyterm.ItisthenuclearfieldshiftwhichleadstoapreferenceoftheU(IV)fortheheavyisotopeineachoftheseexchangereactions.Arevisionofthereducedpartitionfunctionratiosofuraniumionsinsolution,whichtakesintoaccountt

5、henuclearfieldshift,ispresented.Backgroundlogarithmsofthereducedpartitionfunctionratiosoftwochemi-calspeciesisjustthelogarithmoftheisotopefractionationfac-Isotopeshiftsintheelectronicspectraofatomsandmolecules2tor.ThefieldshiftsdonotscalewithäM/M.Sincevibrationalarewell-known.1,2The

6、rearetwotypesofshifts:(1)themassisotopeeffectsintheheavyelementsscalewithäM/M2,anshift,whichresultsfromthecouplingofthemotionofthenucleianomalousmasseffectinisotopechemistrymaybeasignatureandtheelectrons,and(2)thefieldshift,whichresultsfromtheoftheeffectoffieldshiftsonisotopechemist

7、ry.Whenthedifferenceinnuclearsizesandshapesofisotopes.Onlythequantumeffectsrelatedtomolecularvibrationsarenotsmall,implicationsofthemassshiftonisotopechemistryhavebeeni.e.E(vib)gkT,onemayencounteranomalousmasseffects.consideredtothisdate.ConventionalwisdomhasbeenthatTheconditionswhe

8、nsuchanomalousmasse