模式耦合对反常氢键系统中振动频率蓝移的影响.pdf

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1、物理化学学~E(WuliHuaxueXuebao1FebruaryAeta．一Chim．Sin．2012，28(2)，303—308303[Article]doi：10．3866／PKU．WHXB201112013www．whxb．pku．edu．cn模式耦合对反常氢键系统中振动频率蓝移的影响孔祥蕾(南开大学，元素有机化学国家重点实验室，天津300071)摘要：反常氢键所引起的NH／CH键的键长缩短被普遍地认为必然会引起其振动频率的蓝移．本文的计算结果显示非谐性效应可能会使相应的蓝移大幅度减小．其中模式耦合起着非常重要的作用．在一些例子中，这种强的相互

2、作用可能会导致一些基于谐振子模型计算所预言的气相中的蓝移频率实际上发生红移．尽管这些计算结果有待于通过相应体系中的气相红外(1R)光谱来进行确认，一些已报道的基质隔离红外光谱的实验结果已显示出对这些计算结果的支持．关键词：反常氢键：模式耦合：蓝移：红外光谱；非谐性效应中图分类号：O641EfectsofMode·ModeCouplingonVibrationalFrequencyBlueShiftinImproperH-BondedSystemsKONGXiang-Lei(StateKeyLaboratoryofElemento—OrganicChem

3、istry,NankaiUniversity,Tianjin300071，PR．China)Abstract：Bondsho~eningofNH／CHduetoimproperhydrogenbondingisalwaysthoughttobeaccompaniedbyablueshiftinitscOrresp0ndingfrequency．However,resultshereshowthatowingtoanharmonicefects，especiallythecontributionofmode—modecoupling，theblueshi

4、ftcouldbegreatlydecreased．Thestronginteractionmayeven，insomecases，causethepreviouslypredictedblue—shiftingfrequenciesbyharmonicmethodstobered—shiftedinsteadinthegasphase．Thoughtheseresultsneedtobeclearlyverifiedbyfu~herinfrared(IR)spectrumexperimentsinthegasphasefortheselectedsy

5、stems，comparisonswithpreviousIRresultsobtainedfrommatrixisolationexperimentsstronglysuppodtheresultsofthecakIations．KeyWords：Improperhydrogenbond；Mode-modecoupling；Blueshift；InfraredspectrometryAnharmoniceffect1lntroductiontems．andithasbeenpredictedthatbothC—HandN—HcarlHydrogenb

6、ondinginteractionsarethemostimportantnon—formblue—shiftingH．bondsinmanycomplexes．～Remark—covalentinteractionsinchemicalandbiologicalsystems．Re．ably,therelationshipbetweenthedissociationenergydiferenc—cently,growinginteresthasbeenattractedbytheimproperesandthestretchingfrequencys

7、hiftinsomeweakcouplingblue．shiftingH—bond．whichisthoughttobecharacterizedbyacomplexeswithbothred．andblue．shiftingH．bondshasbeendecreaseofX—H(X=C，N)bondlengthandanincreaseofitssuggestedbyDonoso—Taudaeta1．recently．However,itmuststretchingfrequency,thuscanbedistinguishedfromstandar

8、dberealizedthatmostofthosefrequencycalculations