Acid solvation versus dissociation at “stardust conditions” Reaction sequence matters Devendra Mani.pdf

该【Acid solvation versus dissociation at “stardust conditions” Reaction sequence matters Devendra Mani 】是由【探春文档】上传分享，文档一共【8】页，该文档可以免费在线阅读，需要了解更多关于【Acid solvation versus dissociation at “stardust conditions” Reaction sequence matters Devendra Mani 】的内容，可以使用淘豆网的站内搜索功能，选择自己适合的文档，以下文字是截取该文章内的部分文字，如需要获得完整电子版，请下载此文档到您的设备，方便您编辑和打印。SCIENCEADVANCES|RESEARCHARTICLECHEMISTRYCopyright?2019The?Authors,somerightsreserved;Acidsolvationversusdissociationat“stardustexclusivelicenseeAmericanAssociationconditions”:ReactionsequencemattersfortheAdvancementDevendra?Mani1,RicardoPérez?deTudela2,Raffael?Schwan1,Nitish?Pal1,Saskia?K?rning2,.?GovernmentHarald?Forbert,Britta?Redlich,A.?.?vanderMeer,Gerhard?Schwaab,?Marx*,Martina?Havenith*-NC).show,studyingreactionsinastepwisemannerinultracoldheliumnanodropletsbymass-selectiveinfrared(IR)spectroscopyprovidesanavenuetomimicthese“stardustconditions”/?1theoreticalstudy,essivelyaddH2OmoleculestoHCl,wediscloseauniqueIRfingerprintat1337cm+thatheraldshydronium(H3O)formationand,thus,,noreactionisobservedwhenreversingthesequencebyallowingHCltointeractwithpreformedsmallembryonicice-%evenattemperaturesof20K.?eedingAciddissociation,protonsolvation,andchargedefectmigrationinstudy(31),92%ionizationofHClwasreportedat50K.?Theseioniza-aqueousenvironmentsallplayafundamentalroleinaplethoraoftionrateswerefoundtobeindependentoftemperature,astheyhttp://advances./processesrangingfromchemistryandphysicstobiologyand,therefore,weresimilarfor50and90K,supportingthetheoreticalpredictionhavebeenanalyzedinutmostmoleculardetailusinginfrared(IR)thatHCldissociationonicesurfacesisabarrierlessprocess(19).spectroscopyinboththegasandcondensedphases(1–15).WhileTheseresultsgaverisetoacontroversialdiscussionontherateofthermalfluctuationsandvividH-bonddynamicsarepivotalatHClionizationonicesurfaces(32,?33).ambientconditions(16),distinctlydifferentmechanismstakeoveratHere,wereporttheresultsofajointexperimental/theoreticalstudylowertemperatures,forinstance,enablingHCl-inducedacid/baseofthegenericHCl-watersysteminsuperfluidheliumnanodroplets,chemistryonicegrainsinEarth’louds(2,?17–19).whichareknowntoenablethecontrolledformationofH-(34).Usinginterstellarspace(20–22),andtheyareprobablecandidatesforthethehigh-intensitypulsedfree-electronlasers(FELs)atFELIXinsincludingEarth(23,?24).Nijmegen,ourmeasurementswereperformedintheIRfingerprintIndenseinterstellarclouds,muchlowertemperaturesoftheorderregion(about1000to1700cm?1)basedontherecentlydevelopedonJune9,******@FELIXendstation(35).(22,?25).Afundamentalquestioniswhetheracid/basechemistry,suchInoureffortsofestablishingananolabformolecularlycontrolledlouds,couldalreadybetriggeredatcryochemicalsynthesis,******@FELIXhoststheseultracold“stardustconditions”bydissociationofacids,.,twodistinctpickupcells—denotedascell1andcell2inthefollowing—HCl,-mmorifice(wherecross-contaminationfromonehighlyrelevanttoearlychemicalevolution,,20cm;).Thisendstationenableslouds(PSCs)ustocontrolthesequenceandthepressureforeachdopantinde-catalyzestheformationofmolecularchlorine(Cl2)(26,?27).Mostofthependently,.,wecannowchoosewhetherweseedthenanodropletsexperimentalstudiesconfirmthatatPSCtemperatures(about190K),withHClinthefirstcellfollowedbysubsequentpickupofwaterintheionizedformofHClprevailsonicesurfaces(2,?28–31).However,(?al.(28),80-mJenergyper5-to8-?sdurationpulse)allowustorecordmass--usingCs+reactiveionscatteringandsecondaryionmassspectrome-selectiveIRspectrawithagoodsignal-to-noise(S/N),?al.(2),esstotheimportantIRfingerprintregionforacidforma-techniques,proposedthatnoionizationtakesplacebelow50K,tion,,therateofionizationwasfoundUponsequentialmicrosolvationofHClbyH2Omolecules,wetoincrease:from~15%pleteionizationtakingearlierdiscoveredapeculiarreactionmechanism—aggregation--placeat90to95K.?Incontrast,ParentandLaffon(29)reportedaninduceddissociation—(9,?10,?36).Accordingtothismechanism,thedissociationreaction+1LehrstuhlfürPhysikalischeChemieII,Ruhr-Universit?tBochum,44801Bochum,producinghydronium,H3O,ürTheoretischeChemie,Ruhr-Universit?tBochum,44780energyminima,whichwouldbeimpossibletosurmountatultracold3Bochum,,InstituteforMoleculesandMaterials,Radboudconditions(34).Addingthefourthwatermoleculeyieldsthesolvent--University,herlands.+?*:martina.******@(.);dominik.******@sharedionpair(SIP),H3O(H2O)3Cl[(.)Fig.?1?(B?and?C)],asdepictedintheleftreactionchannelofFig.?.,;5:eaav81797June20191of7SCIENCEADVANCES|RESEARCHARTICLEacidcandissociateandtransferitsprotontothesepreexistingem-bryonicice-,weusedisotopicallypureH2O.?Whereas+35+16H(HCl)nandH(H2O)2nionizationfragmentsaredetectedatthesame[mass/chargeratio(m/z)]channelinthemassspectrometer,+35thesefragmentscanbeseparatedinthecaseofH(HCl)nand+18H(H2O)2n[seealso(10)].WerecordedtheIRspectrumofpure1818H2Oclusters(cell2,)atm/z?=?41[whichcorre-+18spondstotheH(H2O)2fragment].BecausemolecularpickupbyheliumdropletsfollowsPoissonstatistics(37),atthispartialpressureofwater,therelativesizedistributionofwaterclusterscouldbeestimatedtobetetramer(~55%),pentamer(~30%),andhexamer(~15%).Thewell-knownfingerprintofthewaterbendwasobservedaround?1181620cm,whicharisespredominantlyfrom(H2O)4(seeFig.?1A)Downloadedfrom18(38).WhenaddingHClinthefirstcellandH2Ointhesecondcell18inourcryo-nanolab(cell1,;cell2,),weobservedabroadabsorptionbandcenteredat~1337cm?1(seeFig.?1B),inagreementwiththetheoreticalpredictionsfortheuniquespectroscopicfingerprintofthe(hindered)umbrellamotion+?1ofH3Oat1357cm(39).ThisischaracteristicoftheSIPconformerhttp://advances./ofthe“smallestdropletofdissociatedHClacid”(9,?10,?36).Attheseexperimentalconditions,,yieldingapreferenceforclustersdopedwithasingleHClandadistributionofwaterclustersizesrangingfromn?=?-selectivedepletionpickupcurves()revealthatthespectroscopicsignalat1320cm?1(seeFig.?1B)isdominatedbyaclusterwithoneHClandfourwatermolecules,,asreportedhere,hastheadvantagethatthehydroniumumbrellamotion(39)ofthesmallestdropletofacidisuncongested,incontrasttothehigherfrequencyrange(2100to2900cm?1)wherethemodesareonJune9,2019stronglycoupledandthespectroscopicsignaturesfordissociationoverlapwiththebandsfromundissociated(HCl)m(H2O)nclusters,which,inthepast,ledtoacontroversialdiscussionabouttheexperi-mentalverificationofHCldissociationforaclusterwithoneHClandfourwatermolecules(9,?10,?40).-waterclusters,resultingHavingshownthatfourwatermoleculesaresufficienttodisso-frompickupsequencecell1(HCl)andcell2(water),measuredatdifferentciateHCl,weinvestigatedwhetherlargerdissociatedclusters18masschannels.(A)IRspectraofpureH2Oclusters,measuredatm/z?=?41.()SpectrainthepresenceofasmallamountofHClgas,measuredatm/z?=?41,61,+18+18+18m/z?=?61[H(H2O)3fragment]andm/z?=?81[H(H2O)4fragment]and81,(H2O)2(m/z?=?41),aredepictedinFig.?1,?C?and?D,+18mz+18mzH(H2O)3(/?=?61),andH(H2O)4(/?=?81)?=?61isdominatedtothebendingvibrationofthepurewater(HO)n(n?=?4and5)clustersarehigh-2byclusterscontainingfourwatermolecules,?1+m/z?=?-containingfive(ormore)watermolecules(Table?1;seethe“.,:Parentclustersizedetermination”sectionintheSupplementaryMaterialsformoredetails).ThehydroniumThealternativesynthesispathwayinvolvesaggregationofaspecificbandisred-shiftedwhenrecordedatm/z?=?paredtothebandnumberofH2Omoleculesasthefirststep,followedbyapickupofrecordedatm/z?=?-Inanefforttocharacterizetheformedionpairspeciescontainingdroplets,watermoleculesaggregateintocyclicH-bondedstructures,fivewatermolecules(Fig.?1D),abinitioaggregationsimulations(36)leadingeventuallytothe“smallestpieceofice”(34).Butwhatisthewereperformedtodisclosewhathappensifthefifthwatermoleculefateofanacidmoleculeifattachedtotheseice-plexes?reactswithSIP(seethe“AbinitioaggregationsimulationsofSIPKnowingthatfourH2OmoleculessufficetodissociateHClinheliumwiththefifthH2Omolecule”sectionintheSupplementaryMaterials).nanodroplets(9,?10),theinterestingquestionishow,orevenif,theTheyunveilthatonlytwospecificionpairstructuresoutofmanyManietal.,;5:eaav81797June20192of7SCIENCEADVANCES|(H2O)4clustersinheliumdroplets,depictingthatacidformationatultracoldtemperaturesfollowsauniquepathway.(Left)ThefirstHCland,subsequently,fourwatermoleculesarepickedup,yieldingaggregation-induceddissociationofHClandtheformationofthe+?smallestdropletofacid,H3O(H2O)3Cl.(Right)Thefirstfourwatermoleculesaggregatetoformacyclicwatertetramer,anduponsubsequentadditionofoneHClmol-ecule,://advances./(n)contributingtotheobservedbands,determinedfromthefitofthepressure--“IonizationmechanismofpurewaterandmixedHCl-wateraggregates”and“Theumbrellamotionofhydronium:Parentclustersizedetermination”(cm?1)(atomicmassunits)n1320414onJune9,2019132061414006141250815candidates(seethe“StructuresearchandharmonicanalysisofHCl(H2O)nspecies”sectionintheSupplementaryMaterials)areexclusivelyformed,namely,then?=?5solvent-sharedandcontact+,whoseH3Oumbrellamotionfrequencies(unscaledharmonicMP2)arered-shiftedby51and128cm?1withreferencetothen?=?4SIPspecies,respectively(seetableS1).Giventhatanharmonicityeffectsand,thus,redshiftsintheumbrellafrequencyofSIPhavebeenshowntobesmall(39),18whereasenormousanharmonicitiesareexpectedforthecorrespond--H2Oclusters,measuredat/?=?41,(41,?42),weperformedabinitiopathintegralmz()HClpickupprecedesthepickupofwatermolecules.(B)(seethe“Nuclearquantumeffectsonn=5CIPversusSIPspecies”sectionintheSupplementary?1Materials).InstarkcontrasttoSIP5,inwhichthethreeO─Hbondswhichisred-shiftedby~32cm,canbeassignedtotheumbrella+withinH3Oaresimilarandwelllocalized,theonepointingtowardmodeofspeciesSIP5,asdepictedinthemolecularmodelinFig.?1D.?ClinCIP5isextremelyanharmonicbecauseofpronouncedaniso-WhathappensifthepickuporderofHClandH2Oisreversed18tropicquantumdelocalization().Th