Matrix isolation and AB initio theoretical investigations of carbon-based molecules of astrophysical interest / by Scott P. Ekern

183 Pages·1996·5.8 MB·English

by  Ekern, Scott P

MATRIXISOLATIONANDABINITIOTHEORETICALINVESTIGATIONSOF
CARBON-BASEDMOLECULESOFASTROPHYSICALINTEREST
By
SCOTTP.EKERN
ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL
OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT
OFTHEREQUIREMENTSFORTHEDEGREEOF
DOCTOROFPHILOSOPHY
UNIVERSITYOFFLORIDA
1996
TABLEOFCONTENTS
LISTOFTABLES v
LISTOFFIGURES viii
ABSTRACT »v
CHAPTERS
1 INTRODUCTION 1
Background 1
Experimental ^
Overview ^^
2 SPECTROSCOPYANDPHOTOCHEMISTRYOFTHE
Cj-HjOCOMPLEX 12
Introduction 12
Theoretical 14
Results 1'7
TheCj'HjOComplex 17
Thetrans-HPDIsomer 30
Thecis-HPDIsomer 37
HPDIsomerInterconversion 42
Discussion 49
Summary 51
3 THEC3H2OPOTENTL\LSURFACE 53
Introduction 53
Theoretical 56
Results 57
Discussion 69
Summary 76
u
APHOTOCHEMICALMECHANISMFORC3OFORMATION 81
Introduction 81
Theoretical 83
Results 84
TheC3H2OPotentialSurface 89
BimolecularReactionsFormingC3O 97
Summary ^^
EXPERIMENTALOBSERVATIONOFLONGCHAIN
CARBONANIONS 101
Introduction 101
Experimental 102
Results 104
Electronic 104
Vibrational 118
Summary 120
THEORETICALSTUDIESOFCARBONANIONS 122
Introduction 122
Theoretical 123
ResultsandDiscussion 124
LinearAnions 124
CyclicAnions 133
Summary 138
THEORETICALSTUDIESOFC3PERTURBEDBYAN
ARGONMATRIX 139
Introduction 139
Theoretical 140
Results 140
Discussion 147
FUTUREWORK 148
m
LISTOFREFERENCES 154
BIOGRAPHICALSKETCH 165
IV
)
LISTOFTABLES
Table page
2-L Experimentalfrequenciesandvibrationalassignmentsforsmallcarbon
clustersintheirgroundstates 16
2-2. Comparisonofexperimental(Armatrix)andcalculated(HF/6-31G*)
IRfrequenciesandintensitiesfortheCj'HjOcomplex. Frequencies
incm''andintensitiesinkm/mol 20
2-3. Theexperimental(Armatrix)andcalculated(HF/6-3IG*)IR
fcroemqpuleenxc.iesFrfeoqrutehneciC•eCsCm• acsmym-1metricstretchingmodeof' Cj'HjO 0^0^
2-4. Theexperimental(Armatrix)andcalculatedIRfrequencies(cm")and
intensities(km/mol)fortrans-3-hydroxypropadienylidene(trans-HPD)
initsgroundelectronicstate 31
2-5. Experimentalandcalculated(HF/6-3IG*)IRfrequencies(cm'')for
aalslyimsmoettorpiocmesrtrsetocfh,ciCsCanHd+tHrCanOs-bHePnDdf(otrrtahnes-mHoPsDt)ianntednHseCCOCCbend
+COstretch(cis-HPD)modes 35
2-6. Theexperimental(Armatrix)andcalculatedIRfrequencies(cm"
andintensities(km/mol)forcis-3-hydroxypropadienylidene(cis-HPD)
initsgroundelectronicstate 40
3-1. T(koctaall/meonle)r,giaensd(hzaerrtor-epeosi),ntzeerneor-gpioeisnt(kccoarlr/emcotle)dorfelaaltlimveineinemragies
calculatedattheHF/6-3IG*level. Totalenergy(hartrees)
calculatedattheQCISD(T)/6-3lGV/HF/6-3IG*level. HF/6-3IG*
calculatedzero-pointcorrectionsscaledby0.90 59
)
3-2. Totalenergies(hartrees),zero-pointcorrectedrelativeenergies(kcal/mol),
andzero-pointenergies(kcal/mol)ofeachtransitionstateattheHF/6-31G*
level. Totalenergy(hartrees)calculatedattheQCISD(T)/6-3IG*//
HF/6-31G*level. HF/6-31G*calculatedzero-pointcorrections
scaledby0.90 60
3-3. Totalenergies(hartrees),zero-pointcorrectedrelativeenergies(kcal/mol),
andzero-pointenergies(kcal/mol)ofminimacalculatedatthe
MP2/6-31G*level. MP2/6-31G*calculatedzero-pointcorrections
scaledby0.95 61
3-4. Totalenergies(hartrees),zero-pointcorrectedrelativeenergies(kcal/mol),
andzero-pointenergies(kcal/mol)foralltransitionstatesfoundatthe
MP2/6-31G*level. MP2/6-31G*calculatedzero-pointcorrections
scaledby0.95 62
3-5. Rotationalconstants(GHz)ofminimafoundattheMP2/6-3IG*level.
Experimentalvaluesinparenthesis 78
3-6. Vibrationalfrequencies(cm"'),intensities(km/mol),andsymmetries
ofeachCjHjOisomerfoundattheMP2/6-31G*level 79
4-1. Totalenergies(hartrees),zero-pointcorrectedrelativeenergies(kcal/mol),
spinsquaredeigenvalues,andzero-pointenergies(kcal/mol)ofminima
foundattheMP2/6-3IG*leveloftheory 85
4-2. Totalenergies(hartrees),zero-pointcorrectedrelativeenergies(kcal/mol),
spinsquaredeigenvalues,andzero-pointenergies(kcal/mol)of
transitionstatesfoundattheMP2/6-31G*leveloftheory 85
5-1. Eaxnpdearbismoernbtaanlceelsecftorroannicioanbiscocraptriboonnbcalunsdteprossiitsioolnatse(dkininnnemo,nvanidnacrmg'on
matricies. Bandwidths(FWHM,incm'')inparenthesis. All0-0
transitionenergiesareplottedinFigure5-6 110
6-1. Linearcarbonaniontotalenergies(hartrees),zero-pointenergies
(kcal/mol),rotationalconstants(GHz),spinsquaredvalues,intheir
groundelectronicstatescalculatedattheB3LYP/6-31G*leveloftheory.... 126
6-2. Vibrationalfrequencies(cm''),IRintensities(km/mol),andsymmetries
forlinearcarbonanionsC„'(n=2-9)calculatedattheB3LYP/6-3IG*
leveloftheory 127
VI
6-3. Acomparisonofexperimentalandselectcalculatedlinearcarbon
anionbands. Frequenciesincm'\intensitiesinkm/mol 128
6-4. Energiesofreaction(kcal/mol)betweenneutrallinearcarbonchains
(np^<.9atoms)calculatedattheB3LYP/6-3IG*leveloftheory.
Notzero-pointcorrected 130
6-5. Energiesofreaction(kcal/mol)betweenlinearcarbonneutrals
(abscissa)andlinearcarbonanions(ordinate)yieldingalongerlinear
carbonanion. CalculatedattheB3LYP/6-3IG*leveloftheory.
Electronicstatesinparenthesis 131
6-6. Symmetries,totalenergies(hartrees),spinsquaredvalues,zero-point
energies(kcal/mol),andthenumberofimaginaryfrequencies(/v)
foundforeachofthecycHccarbonanionspecies 135
6-7. Vibrationalfrequenciesofthecycliccarbonanionscalculatedatthe
B3LYP/6-3IG*level. Frequenciesareincm"'andintensitiesarein
km/mol 136
7-1. Totalenergies(hartrees),relativeenergies(kcal/mol),geometric
parameters(inangstromsanddegrees),andMullikenchargesforthe
centralcarbon-argonorientationasafunctionofC3-Ardistance 141
7-2. Totalenergies(hartrees),relativeenergies(kcal/mol),goemetric
parameters(inangstromsanddegrees),andMullikenchargesforthe
bridgingcarbon—argonorientationasaftinctionofC3-Ardistance 142
7-3. Totalenergies(hartrees),relativeenergies(kcal/mol),goemetric
parameters(inangstromsanddegrees),andMullikenchargesforthe
terminalcarbon-argonorientationasafunctionofCj-Ardistance 143
vu
LISTOFFIGURES
Figure page
1-1. Experimentalset-upformatrixisolationofcarbonanionsproduced
byelectronimpactionization 5
1-2. Expandermoduleandmatrixwindow 6
1-3. Ebxypdeurailmelnastearlvsaepto-ruipzaftoiromnaotfrigxraipshoiltateiaonndofytctarribuomnmaentiaolnsproduced 7
1-4. TheexperimentalreactionschemerelevanttoChapters2,3,and4 11
2-1. Structuresoftheintermediateshydroxyethynlcarbene(HEC,1),cis-3-
Hydroxypropadienylidene(cis-HPD,2),trans-3-hydroxypropadienylidene
(trans-HPD,3),theCj'HjOcomplex(4),andthetransitionstate
betweenthecomplexandtheHPDisomers(5) 15
2-2. PortionsofthelOKmatrixinfraredspectrumof19C/Ar+HjO
(0.1%)intheasymmetricstretchregion(ca.2000cm'')andinthe
OHasymmetric(V3)andsymmetric(vi)region(ca.3700cm').
Monomer(M)anddimer(D)bandsaremarked;Cj'HjOcomplex
bandsarestarred. InsetshowstheVj+V3combinationbandofHjO 18
2-3. P([o'r^tCi]o:n['o^fC]th=ea1n:1n)ea(lteodp)(3an2dK)ofma't^rCix(1i2nKfr)ar(ebdotstpoemct)rianotfhe'^aCs/y'm^mCe/tArric
CCstretchingregion. TheC3isotopomersaremarkedbytriangles,while
theC3»H20complexisotopomersaremarkedwithdots. Themarked
bandsinthelowerspectrumareduetoC9(1998cm''),C3(2039cm''),
andtheC3«H20complex(2052cm'') 21
2-4. Portionofthe12Kmatrixinfraredspectraof'^Cn/Ar+HjO(0.2%)
intheOHstretchregionbeforephotolysis(b)andafterphotolysis(a).
Themonomer(M),dimer(D),andtrimer(T)bandsofwateraremarked
accordingly. ThestarredbandsaretheOHstretchesintheC3«H20
complex 24
vm
2-5. Portionofthe12Kmatrixinfraredspectraof'^Cn/Ar+HjO(0.2%)
beforephotolysisandafterphotolysis(k>390nm). Bandswhichhave
grownuponphotolysisareduetoC3O,propynal,andtrans-HPD.
NotethattheCj'HjOcomplexbandhasdecreaseduponphotolysis.
C3»(H20)n(n=2and3)bandsaremarkedbystars 25
2-6. Portionofthe12Kmatrixinfi-aredspectraof'^Cn/Ar+HjO(0.2%)
beforephotolysis(b)andafterphotolysis(a)(A.>390nm). Allbands
inthedifferencespectrumareduetotrans-HPD 26
2-7. Electronicspectrafor'^Cjand'^Cj'HjOcomplexbeforephotolysis
(upper)andafter(lower). Bandat405.4nmisassignedtothe
'^Cj'HjOcomplex 28
2-8. Comparisonoftheexperimental(upper)andtheoretical(lower)spectra
oftrans-HPD. Bandswithonestar,twostars,anddotsareduetothe
Cj'HjOcomplex,propynal,andtrans-HPD,respectively 32
2-9. Portionofthe12Kmatrixinfi-aredspectraof'^C/'^C/Ar+H2O(0.15%)
([*^C]:['^C]=1:2)beforephotolysisandafter30minofphotolysis
(X>390nm). Thenegativepeaksinthedifferencespectrum(triangles)are
theasymmetricCCCstretchesofthe'^'^^Cj'HjOcomplexisotopomers.
Thepositivepeaks(dots)aretheasymmetricCCCstretchesofthe'^^^Cj
sustitutedtrans-HPDisotopomers 34
2-10. Portionofthe12Kmatrixinfraredspectrumof'^C/'^C/Ar+HjO
(0.15%)([^^C]:['^C]=1:2)after30minphotolysis(k>390nm).
Isotopomericbandsareduetotrans-HPD 36
2-11. Portionofthe12Kmatrixinfraredspectraof'^C„/Ar+HjO(0.2%)
beforeandafter30minofphotolysis(A,>390nm),butrecordedduring
photolysis. The3245.2and3258.9cm"'bandsaretheVj+V3
combinationbandsinC3andtheCj'HjOcomplex 38
2-12. Portionofthe12Kmatrixinfraredspectraof'^C/"C/Ar+HjO(0.15%)
(['^C]:['^C]=1:2)beforephotolysisandafter30minphotolysis
(X>390nm),butrecordedduringphotolysis. The1254.3cm"'bandis
theCOHbend+COstretchofcis-HPD 39
IX
2-13. Portionofthe12Kmatrixinfraredspectraof'^C/"C/Ar+HjO(0,15%)
([^^C]:['^C]=1:2)after30minofphotolysis(k>390nm)andrecorded
withthephotolysislampon(bottom)andoff(middle). Inthedifference
spectra(top)areshowntheCCCasymmetricstretchingmodesofthe
Isotopomersofcis-HPD(positivepeaks)andtrans-HPD(negativepeaks). ... 41
2-14. Timedependenceofthedifferencespectrum(A^-A„). Thet= and
andsubsequentplotswerescannedafterthephotolysislampwasturned
off. Eachspectrumwasrecordedforca.10sec,withA„scannedafter
2hrs. The1992.5cm"'(trans-HPD)bandisatamaximumabsorbance
att=2hr,atwhichtimethe1999.6cm'*(cis-HPDbandisatits
maximumabsorbance 43
2-15. Dependenceofln|A^-A„|vs.timeafter30minofphotolysis(X>390nm)
ofthe^^CJAt+HjO(0.15%)matrixforT=11and20K. TheA,and
A„absorbancesareidenticaltotheonesshowninFigure2-14 45
2-16. PotentialenergysurfacefortherotationoftheHatomabouttheC-0
bondofHPDinitsgroundelectronicstate. SeetextforAEandAG°
values ^°
3-1. UnoptimizedstructuresofCjHjOisomersstudied 58
3-2. TheHF/6-3IG*calculatedpotentialsurface. Onlylowestenergy
isomersareshown. Zero-pointcorrectedenergies(kcal/mol)
relativetoAinparenthesis 63
3-3. TheQClSD(T)/6-3lG*//HF/6-310*calculatedpotentialsurface.
Onlylowestenergyisomersareshown. Zero-pointcorrectedenergies
(kcal/mol)relativetoAinparenthesis 64
3-4. TheMP2/6-3IG*calculatedpotentialsurface. Onlylowestenergy
isomersareshown. Zero-pointcorrectedenergies(kcal/mol)
relativetoAinparenthesis 65
3-5. OptimizedstructuresofallminimafoundattheMP2/6-3IG*level
oftheory 66
3-6. Optimizedstructuresofalltransitionstructuresfoundatthe
MP2/6-3IG*leveloftheory 68
3-7. Portionofthe12Kmatrixinfraredspectrumof^^C^/Arbeforeand
afterphotolysis(k>390nm)withawaterfilterpresent 74