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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.Thefieldshiftsdonotscalewith?M/M.Sincevibrationalarewell-known.1,2The
6、rearetwotypesofshifts:(1)themassisotopeeffectsintheheavyelementsscalewith?M/M2,anshift,whichresultsfromthecouplingofthemotionofthenucleianomalousmasseffectinisotopechemistrymaybeasignatureandtheelectrons,and(2)thefieldshift,whichresultsfromtheoftheeffectoffieldshiftsonisotopechemist
7、ry.Whenthedifferenceinnuclearsizesandshapesofisotopes.Onlythequantumeffectsrelatedtomolecularvibrationsarenotsmall,implicationsofthemassshiftonisotopechemistryhavebeeni.e.E(vib)gkT,onemayencounteranomalousmasseffects.consideredtothisdate.ConventionalwisdomhasbeenthatTheconditionswhe
8、nsuchanomalousmasse
