Fourier transform ion cyclotron resonance mass spectrometry investigation of the photolysis of polycyclic aromatic hydrocarbons

161 Pages·2001·6.4 MB·English

by  Dibben, Mark J., 1963-

FOURIERTRANSFORMIONCYCLOTRONRESONANCEMASS
SPECTROMETRYINVESTIGATIONOFTHEPHOTOLYSISOFPOLYCYCLIC
AROMATICHYDROCARBONS
By
,
MARKJ.DIBBEN
ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL
OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT
OFTHEREQUIREMENTSFORTHEDEGREEOF
DOCTOROFPHILOSOPHY
UNIVERSITYOFFLORIDA
2001
Thisdissertationisdedicatedtomywife,Lynn.
ACKNOWLEDGMENTS
TherearemanyindividualsIwouldliketothankwhohavegivenmethe
opportunitytobewhere1amtoday. Myparentstaughtmeresponsibilityand
determinationatanearlyage. Twoofmyhighschoolteacherswereveryinspirationalto
me:B.R.WellsinmathematicsandJaySchweitzerinchemistryandphysics.
Dr.Valahasbeenphenomenal. Notonlyhashehelpedmewritepapersandthis
dissertation,hehasalsobeenveryavailabletodiscusstheprojectsIhaveworkedon. It
hasbeengreattoworkwithsomeonethatissodedicated.
Dr.Eylerhasbeenwonderfulaswell. Iusedhisinstrumentsforthisentire
projectandwouldneverhavebeenabletooperatethelaserwithouthiselectronicsskills.
Themembersofmygrouphavealwaysbeenhelpful,bothinDr.Vala’sgroup
andDr.Eyler’s. ThetopofthislistisDr.JanSzczepanskiwhoalwayshadananswerfor
whateverquestionIcameupwith. Hewasespeciallypatientinteachingme
instrumentationmyfirstyearhere.
Mychildren,Jason,LuisandAmanda,havealwaysbeenaninspirationtome. 1
hopetheycanbehalfasproudofmeas1amofthem. AnnetteandAngelahavebeen
verypatientwithmethelastthreeyears,andunderstandingwhenIhavenotalwaysbeen
theretohelpthemwiththeirmathandsciencehomework. 1reallyappreciatetheir
tolerance.
iii
ThanksalsogotoColonelMuchandtheAirForceAcademyforsponsoringmy
Ph.D. Nowhereelsecould1havegottenanopportunityliketheonetheyhavegivenme.
1amgoingtoenjoyteachingthereforthenextfiveyears(orlonger!).
IwouldalsoliketothanktheemployeesattheGateconveniencestore,especially
ClaraandLinda. Isawthemeverymorningwhen1gotmy44ounceDietCokeandthey
alwayshadafriendlywordformeandhelpedmetonottakethingssoseriously.
Mostespecially,1thankmywife,Lynn. Shehastakencareofallthoselittle
thingstomakemylifeeasierwhile1havebeeninschool. Shehasbeenunderstanding,
sympatheticand,aboveall,verysupportiveandproudofthework1haveaccomplished.
IV
TABLEOFCONTENTS
e^e
ACKNOWLEDGMENTS
iii
LISTOFTABLES viii
LISTOFFIGURES ix
ABSTRACT xvii
CHAPTERS
1 POLYCYCLICAROMATICHYDROCARBONSINSPACE
Introduction .1
ChemistryofPAHsinSpace .4
UnidentifiedInfraredBands .7
DiffuseInterstellarBands .9
RelatedEfforts 10
2 FUNDAMENTALSOFFOURIERTRANSFORMIONCYCLOTRON
RESONANCEMASSSPECTROMETRY .14
HistoricalPerspective 14
MotionofTrappedIons 16
InstrumentOverview 21
Magnet 21
VacuumSystem 22
AnalyzerCell 22
DataAcquisition 23
ExperimentalProcedures 23
ExperimentalParametersUsedinthisStudy 29
3 PHOTODISSOCIATIONOFFLUORENECATION .33
Introduction 33
HydrogenLoss 33
Fragmentation 39
m/z166 40
m/z165: 42
V
1
m/z164: 42
m/z163: 42
m/z162: 42
m/z161: 45
Kinetics 51
FragmentationPathways 53
ComputationalProcedures 54
SequentialHydrogenLoss 54
Lossoffirsthydrogen 57
Lossofsecondhydrogen 58
Lossofthethirdhydrogen 58
Lossoffourthhydrogen 59
Lossoffifthhydrogen 60
Lossofsixthhydrogen 60
StructuralIntegrityvsRingOpening 60
FurtherFragmentation 62
Photoproductsfromthem/z165ion 63
Photoproductsfromthem/z163ion 63
Photoproductsfromthem/z161ion 64
4 ABSORPTIONSPECTRAOFFLUORENECATION 70
ActionSpectrumofFluoreneCation 71
LaserInducedActionSpectrum 73
5 ION-MOLECULEREACTIONPRODUCTSOFFLUORENE 78
AggregateFormation 78
SourceOfPhotoaggregates 80
CC57HH,1//I(omn/sz(8m4/-z926)2-68) 8824
C9H,/(m/z108-115) 87
C,|H,/(m/z132-141) 89
CnH,/(m/z161-166) 89
6 PHOTOLYSISOFNAPHTHALENEAND1,2-BENZANTHRACENE 96
Naphthalene 97
CioHn^(m/z126-129) 99
CgHft^(m/z102) 104
C(,H/(m/z76) 104
C20H,/(m/z250-255) 107
C19H,/(m/z231-243) 107
C,8H„^(m/z224-228) 109
C,6H,/(m/z198-204) 110
NaphthaleneSummary 11
1,2-Benzanthracene 113
VI
HydrogenLoss 113
C,gH„^(m/z226-228) 119
CiyH,/(m/z209-218) 119
C,6H/(m/z197-204) 119
C,5H„^(m/z184-191) 123
Ion-moleculereactions 123
1,2-BenzanthraceneSummary 125
7 CONCLUSIONS 127
REFERENCES 131
BIOGRAPHICALSKETCH 140
vii
LISTOFTABLES
Table Page
1. AssignmentsofIRemissioncomponentswithinthePAHhypothesis 8
2. Fragmentionyieldsandrateconstantsforphotodissociationofthefluorenecationand
itsdehydrogenatedpartners 47
3. C-Hbondenergies(inkcal/mol(eV))andenergiesofprecursors(inHartrees)
calculatedatB3LYP/4-31Gleveloftheoryforsequentialhydrogenlossin
photodissociationreactionsoffluorenecation(C^Hio^,m/z166). Energiesare
ZPEX0.957corrected. HydrogennumberingisdefinedinFig.37. Energetically
favorablereactionsaregiveninboldtype. Reactionsproceedsequentiallybasedon
thepreviousreactiongiveninparentheses 56
4. Laserdyesandtheirusefulranges 75
5. Summaryoftheaggregatesformedduringafourseconddelaytime(column3)with
theirformulas. Thelastcolumnliststhephotolysisproductsoftheisolated
aggregatesafterfoursecondsofirradiation 95
viii
LISTOFFIGURES
Figure Page
1. TheUnidentifiedInfraredbandsinBD+30°3639. Prominentbandsarepresentat
3.29,6.2,7.7,8.6,and11.2pm. AdaptedfromAllamandolaetal 2
2. TheDiffuseInterstellarBandspectrum. Thegraphisacompositeofgaussianprofiles
fittedtoallcertainandprobableDIBs. Thisspectrumisthoughttobecharacteristic
ofdiffusemediummatter 3
3. SchematicoftheOmegatroninwhichionsareacceleratedcontinuouslytolarger
cyclotronradiusuntiltheystrikeacollectorelectrode. AdaptedfromMashall 15
4. Powerabsorptionmeasurement(withamarginaloscillator)duringsimultaneous
resonantexcitation. Amassspectrumisobtainedbyslowlyvaryingthemagnetic
fieldatfixedexcitation/detectionfrequency. AdaptedfromMarshall 16
5. Originofioncyclotronmotion. Thepathofanionmovingintheplaneofthepaperis
bentintoacirclebytheinward-directedLorentzmagneticforceproducedbya
magneticfielddirectedperpendiculartotheplaneofthepaper. Adaptedfrom
MarshallandVerdun 17
6. ICRorbitalfrequency,Vc=k>J2ti,inHz,asafunctionofionicmass-to-chargeratio,
m/z,inDaltonspermultiple(z)oftheelementaryelectroncharge,ateachoffive
magneticfieldstrengths: 1.0,3.0,4.7,7.0,and11.5tesla. NotethatICRfrequencies
forionsintheusual“chemical”mass-to-chargeratio(~15<m/z<10,000)typically
liebetweenafewkHzandafewMHz. AdaptedfromMarshalletal 18
7. ICRorbitalradius,r,vs.ionicmass-to-chargeratios,m/z,(inupermultipleof
elementaryelectroniccharge)ateachoffiverepresentativemagneticfieldstrengths;
1.0,3.0,4.7,7.0,and11.5teslaat298K. Notethatevenrelativelyheavyionsare
confinedtoconvenientlysmall-radiusorbitsbysuchmagneticfields. Adaptedfrom
Marshalletal 19
8. Iontranslational(kinetic)energy(Eq.7)asafunctionofICRorbitalradius,atfive
differentmagneticfieldstrengths: 1.0,3.0,4.7,7.0,and11.5tesla,foranionof
m/z=100. Ionsmaybeacceleratedtorelativelyhighenergywhilestillconfinedto
relativelysmallorbitalradii. AdaptedfromLegeretal 20
IX
9. Acubicanalyzercellandacylindrical,open-endedcell. Thearrowshowsthe
orientationofthemagneticfieldlines 20
10. ThebasicstepsinanexperimentalsequenceusingFTMS 24
11. Excitationcorrespondingtoselectedmassranges(m/z112-116and165-168)inthe
lowerpanelisconvertedintoaSWIFTexcitationwaveform(upperpanel)byinverse
Fouriertransform 27
12. Transformationofthetimedomainspectrum(upperpanel)tothefrequencydomain
spectrum(lowerpanel). Sincefrequencyisinverselyrelatedtothemass,themasses
appearinreverseorder 28
13. Schematicofthe2teslaFT-ICRinstrument. Vaporfromliquidorhighvolatility
solidscanbeinletthroughthesampletubesandcontrolledwiththeleakvalves. The
solidsprobeisusedforlowvolatilitysolids. Theelectronicallycontrolledshutter
allowsthelamptoilluminatethecellthroughawindow. AdaptedfromKage 29
14. SehematicoftheMIDAShardware. AdaptedfromSenkoetal 31
15. Typicalpulsesequence. ThisincludesSWIFTisolationoftheparention,irradiation
bytheXearclamp,isolationofoneormoreofthephotofragments,further
irradiationandfinallychirpexcitationanddetection 32
16. FluoreneMolecule,C13H10,mass166 33
17. FTICRmassspectrumofphotolysisproductsafterafoursecondirradiationperiodof
them/z166ion 34
18. Relativeabundanceofphotolysisproductsandfluorenecationparentasafunctionof
irradiationtime 35
19. FTICRmassspectrumofphotolysisproductsafteraonesecondirradiationofthe
m/z166ionwhilesimultaneouslyejecting m/z165 36
20. FTICRmassspectrumofphotolysisproductsafterthreesecondsofirradiationofthe
m/z166ionwhilesimultaneouslyejectingm/z163 36
21. FTICRmassspectrumofthephotolysisproductsafterthreesecondsofirradiationof
them/z166ionwhilesimultaneouslyejectingm/z164 38
22. FTICRmassspectrumofthephotolysisproductsaftersevensecondsofirradiationof
them/z166ionwhilesimultaneouslyejectingm/z162 38
23. FTICRmassspectrumofthephotolysisproductsafterfoursecondsofirradiationof
them/z166ionshowingfullfragmentationoftheparentfluoreneion 40
X