【doc】 双色飞秒脉冲场作用下吡啶分子的弛豫动力学研究

【doc】 双色飞秒脉冲场作用下吡啶分子的弛豫动力学研究 双色飞秒脉冲场作用下吡啶分子的弛豫动 力学研究 第18卷第6期 2005年12月 化学物理 CHINESEJOURNALOFCHEMICALPHYSICS Vo1.18.No.6 Dec.2005 1o03.7713/’2005/06.859.2 快报 双色飞秒脉冲场作用下吡啶分子的弛豫动力学研究冰 张建阳,刘红平.,尹淑慧,丛书林,楼南泉,王秀岩, (a.大连理工大学物理系,大连116023: b.中科院大连化学物理研究所分子反应动力学国家重点实验室,大连116023: C.武汉物理数学研究所磁共振以及原子分子物理国家重点实验室,武汉430071; d.大连海事大学物理系,大连116026) 摘要:利用自制的飞秒激光系统和飞行时间质谱仪结合泵浦.探测的方法对吡啶分子的弛豫动力学进行了研 究.用265和398nm的飞秒激光分别作为泵浦光和探测光,通过(1+2) 的共振增强多光电子电离的办法测量了 c5H5N离子强度随时间演化的情况,从而测得吡啶分子在265nm激 发的sl电子态有一寿命为(3.3?0.1)ps的 快速弛豫过程. 关键词:吡啶;泵浦一探测;寿命 中图分类号:064文献标识码:A PyridineDecayDynamicsbyTwo-colorFemtosecondPulseLaserFields ZhangJianyang”,LiuHongping,YinShuhui,CongShulin,LouNanquan,WangXiuyan (a.DepartmentofP7ics,DalianUniversityofTechnology,Dalian116023; b.StateKeyLaboratoryofMolecularReactionDynamics,DalianInstitute ofChemicalics,ChineseAcademyofSciences,Dalian116023; C.StateKeyLaboratoryofMagneticResonanceandAtomicandMolecularPs. WuhanInstituteofP7icsandMathematics,ChineseAcademyofSciences,Wuhan430071 d.DalianMaritimeUniversity,Departmentofics.Dalian116026) KeywordsPyridine,Pump—probe,Lifetime Theoriginofthefirst(S1(n,耵’)state)andthe second(S2(耵,耵’)state)excitedstateofpyridineisat 287.6and260.7nn]1,21,respectively.Extensive researchonthedecaydynamicsresearchofpyridinehas beenstudiedE.一]atdifferentexcitedenergywithdifferent methods.In1983,Yamazakieta1.measul’edlifetimesof S1varyingfrom20to60ps,dependingonexcitation wavelengthusingthedirectpicosecondfluorescencedecay measurements[引 .Usingthefemtosecondtimeresolved mass—spectrometrictechnique,theZewailgroupfound threedecaycomponents,400fs,3.5and15pswiththe pumpenergyat277nm.Similarbehaviorwasobserved whenthewavelengthwaschangeto282nm.Thedecay timedecreasedto130fswhenthepumpenergychanged to307nmtwo—photonexcitation.Withtheultrafast electrondiffraction(UED)method,theyobserveda l7psdecaytimewiththepumpenergyat267nm. Femtosecondphotoelectronimagingmethod..yielded thelifetimeattheS1origintobe(32?5)ps. Recently,usingahome—madefemtosecondlaser ProjectsupportedbytheNationalNaturalScienceFoundationofChina(1037 4012). 籼 Correspondingauthor,Email:zhangjy@dicp.ac.cn.Received19September2 005;infinalform20October200t 860化学物理第18卷 systemcombinedwithatime-of-flight(TOF)mass spectrometer,weinvestigatethedecaydynamicsatthe S1excitedstateofpyridine. Asthedetailsforthissystemhavebeendescribed extensivelyelsewhere,weprovideonlyabrief descriptionhere.Thesecondharmonicpulse(398nlT1) andthethirdharmonicpulse(265nlT1)wereusedinthis experiment.OnepulseexcitedthesampletotheS1state. Thesecondpulsethenionizedthem.TheionsignalCall bemeasuredbythechangeindelaytimebetweenpump andprobelaserpulses.Figure1showesthepump—probe signalat265nlT1.Basedonagenerallysimplifiedmodel inwhichtheobservedsignalistheconvolutionofthe exponentialdecayfunctionandtheautocorrelationone, thedecaytimeofpyridineat265nlTlpulsepumpCallbe determinedtobe=(3.3?0.1)ps. Delaytime/ps Fig.1Pump—probesignalforpdine(C5H5N)at265nm When benzeneE.] givenenough exhibita vibrational sudden energyin decrease fluorescencequantumyieldandintersystem S1state, inits crossing rate.Thereasonwasconsideredtoarapidly nonradiativerelaxationprocess,termedasthe “ channelthree”process.Thisphenomenaalsooccur insomearomaticmolecules[12].suchaspyridine. Threeexplanationshasbeenproposedforthis phenomena:?directinternalconvemionfromS1to So,?aphotochemicalreaction[3.1..,?ahidden intermediateelectronicstate….Forpyridine.this thresholdenergyisabout1600cm,abovetheS1 origin’t. Nearthisthresholdof”channelthree” Yamazakiet1.[]foundthatthefluorescencelifetime isreducedsharplyfrom30psto20pswiththe dissociationenergyincreasedfrom276.5nmto 274.5nm.Theythinkthatthisnewdecaychannelmay berelatedtophoto-isomerizationprocess.Zewailet a1.L4JbelievedthatRingopeningprocessisdominantin the”channelthree”dynamicsofpyridineexcitedby 267nm.Theirresultyieldedthatthering—opened structurewasformedin17ps.Inourexperiment,the decaylifetime,7_=(3.3?0.1)ps,ismuchshorter thantheUEDresultandYamazakieta1.,sresults.We canseethatthedecaylifetimeofpyridinedecreased withtheexcitedenergybeyondthe”channelthree” threshold,especiallyfrom17psat267nmto3.3psat 265nm.Nootherfragmentbuttheparentmolecularion signalcanbefoundonly.Theexperimentatdifferent excitedwavelengthcan’tbedoneherebecauseourlaser systemisnottunable.Combinedwithotherspeople’s results,averyfastnon-radiativerelaxationprocess whichshouldbelongto”channelthree”processis dominantwhenthepumpenergyat265nm.Thereasons of”channelthree”needmorethoroughexperimental andtheoreticalinvestigation. 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