Two Studies in Gas-Phase Ion Spectroscopy: Vacuum-Ultraviolet Negative Photoion Spectroscopy and Ion-Molecule Reaction Kinetics

168 Pages·2012·4.587 MB·English

by  Matthew J. Simpson (auth.)

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Matthew J. Simpson
Two Studies in Gas-Phase
Ion Spectroscopy
Vacuum-Ultraviolet Negative Photoion
Spectroscopy and Ion-Molecule Reaction
Kinetics
Doctoral Thesis accepted by
University of Birmingham, UK
123
Author Supervisor
Dr. Matthew J.Simpson Prof.Dr. Richard P.Tuckett
Science Department School ofChemistry
KingEdward’s HighSchoolforGirls Universityof Birmingham
Birmingham Edgbaston, Birmingham
B152UB B152TT
UK UK
e-mail: [email protected] e-mail: [email protected]
ISSN 2190-5053 e-ISSN 2190-5061
ISBN 978-3-642-23128-5 e-ISBN978-3-642-23129-2
DOI 10.1007/978-3-642-23129-2
SpringerHeidelbergDordrechtLondonNewYork
LibraryofCongressControlNumber:2011937631
(cid:2)Springer-VerlagBerlinHeidelberg2012
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Parts of this thesis have been published in the following journal articles
[1] M.J. Simpson and R.P. Tuckett, Vacuum-UV negative photoion spectroscopy
of polyatomic molecules, International Reviews of Physical Chemistry 30,
197–273 (2011). *Reproduced with permission.
[2] M.J. Simpson and R.P. Tuckett, Vacuum-UV negative photoion spectroscopy
of SF Cl, Journal of Physical Chemistry A 114, 8043–8048 (2010). *Repro-
5
duced with permission.
[3] M.J. Simpson, R.P. Tuckett, K.F. Dunn, C.A. Hunniford, and C.J. Latimer,
Vacuum-UV negative photoion spectroscopy of CF Cl, CF Br and CF I,
3 3 3
Journal of Chemical Physics 130, 194302,1–194302,11 (2009). *Reproduced
with permission.
[4] M.J. Simpson, R.P. Tuckett, K.F. Dunn, C.A. Hunniford, C.J. Latimer, and
S.W.J. Scully, Vacuum-UV negative photoion spectroscopy of SF CF , Jour-
5 3
nal of Chemical Physics 128, 124315,1–124315,10 (2008). *Reproduced with
permission.
[5] N.J. Rogers, M.J. Simpson, R.P. Tuckett, K.F. Dunn, and C.J. Latimer,
Vacuum-UV negative photoion spectroscopy of CH , Molecular Physics 108,
4
895–904 (2010). *Reproduced with permission.
[6] N.J. Rogers, M.J. Simpson, R.P. Tuckett, K.F. Dunn, and C.J. Latimer,
Vacuum-UV negative photoion spectroscopy of CH F, CH Cl and CH Br,
3 3 3
Physical Chemistry Chemical Physics 12, 10971–10980 (2010). *Reproduced
with permission.
[7] M.A. Parkes, S. Ali, M.J. Simpson, R.P. Tuckett, and A.E.R. Malins,
Thresholdphotoelectronphotoioncoincidencespectroscopyoftrichloroethene
and tetrachloroethene: the effect of Cl substitution in the series C H Cl ,
2 x 4-x
Molecular Physics 106, 1739–1749 (2008). *Reproduced with permission.
[8] V.A.Mikhailov,M.A.Parkes,M.J.Simpson,R.P.Tuckett,andC.A.Mayhew,
Selected ion flow tube ion-molecule reactions of monochloroethene, tri-
chloroetheneandtetrachloroethene:comparisonwithTPEPICOdata,Journal
ofPhysicalChemistryA112,9012–9022(2008).*Reproducedwithpermission.
Iwasthe principalauthorof[2–4],mademajor contributions to[1,5]and [6],
and minor contributions to [7] and [8]. The data of Chaps. 7–9 of this Springer
Thesis have yet to be published.
SincemythesiswasexaminedandsubmittedtotheUniversityofBirmingham
in November 2010, the review article, reference [1], was submitted and subse-
quently published in the International Reviews of Physical Chemistry in June
2011. Parts of chapter 1.A of this Springer Thesis have therefore been modified,
andinadditionTable4.2andAppendixIIIaregreatlyexpandedfromtheirversion
in my original Ph.D. thesis. I am grateful to my supervisor, Professor Richard
Tuckett, for his major contribution to these modifications.
v
Supervisor’s Foreword
The research described in Matthew Simpson’s Ph.D. Thesis involves two aspects
of the spectroscopy and reaction kinetics of gas-phase ions. First, the observation
and analysis of negative ions following vacuum-ultraviolet excitation of poly-
atomic molecules using tunable radiation from a synchrotron source. Second, the
determination of rate coefficients and branching ratios of either cations or anions
reacting with polyatomic molecules in a Selected Ion Flow Tube at 298 K. This
thesiswillleadtoca.tenpapersplusonereviewintheinternationalpeer-reviewed
literature.
Using tunable vacuum-ultraviolet radiation from a synchrotron, negative ions
have been detected following photoexcitation of 24 gaseous molecules. The
molecules studied were CF , SF and CH ; the CF X series where X = Cl, Br, I;
4 6 4 3
theCH YserieswhereY = F, Cl, Br;andSF ZwhereZ = CF ,Cl.Spectraand
3 5 3
raw data only are reported for other members of the CH F , CH Cl including
x y x y
CCl ,andCF Cl serieswhere(x+y) = 4;andsaturatedandunsaturatedmembers
4 x y
of the C H and C F series up to m = 3. Product anions resulting from uni-
m n m n
molecular ion-pair dissociation reactions were detected, and their ion yields
recorded in the range 8–35 eV at a resolution down to 0.02 eV. Absolute cross
sectionsforion-pairformationandresultingquantumyieldswerecalculated.This
vast collection of data is summarised and ion-pair formation from polyatomic
molecules is reviewed.
SelectedIonFlowTubemassspectrometryhasbeenusedtostudythereactions
of cations and anions with ethene, monofluoroethene, 1,1-difluoroethene, triflu-
oroethene and tetrafluoroethene. Calculated collisional reaction rate coefficients
are compared to those measured by the experiment. The product ions from these
reactions have been detected and their branching ratios measured. Many of these
results have been explained with arrow-pushing mechanisms which are used by
organic chemists. Perhaps more than many papers and reviews on ion-molecule
reactions,thisworktriestoexplainwhycertainproductsareformedpreferentially
over other products at a microscopic level of understanding.
TheworkreportedinthisThesiswillbeofprimaryrelevancetothoseinvolved
in experimental studies of the spectroscopy and kinetics of gas-phase ions,
vii
viii Supervisor’sForeword
especially those working in the under-studied area of negative anions. The data
reported in Chap. 6 forms the most comprehensive set of vacuum-ultraviolet
excitation spectra forming anions in the scientific literature to date.
Birmingham, September 2011 Prof. Richard P. Tuckett
Acknowledgments
TheGardenat21KingEdward
Thank you for all your help to: Sahangir Ali, Liam Cox, Ken Dunn, Jonelle Harvey, David
Holland, Adam Hunniford, Colin Latimer, Chris Mayhew, Victor Mikhailov, Mike Parkes,
NicolaRogers,DavidShawandRichardTuckett.
ix
Contents
1 Introduction and Background Information . . . . . . . . . . . . . . . . . . 1
1.1 Ion-Pair Formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Direct and Indirect Ion-Pair Formation,
Rydberg States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1.2 Thermochemical Aspects of Ion-Pair Formation. . . . . . . 7
1.2 Ion–Molecule Reactions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.2.1 Cation-Molecule Reactions. . . . . . . . . . . . . . . . . . . . . . 10
1.2.2 Anion-Molecule Reactions. . . . . . . . . . . . . . . . . . . . . . 11
1.2.3 Collisional Rate Coefficients . . . . . . . . . . . . . . . . . . . . 11
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2 The Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1 Negative Photoion Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . 15
2.1.1 The Synchrotron Radiation Source . . . . . . . . . . . . . . . . 15
2.1.2 The Experimental Endstation . . . . . . . . . . . . . . . . . . . . 17
2.1.3 The Determination of Absolute Ion-Pair
Cross Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.1.4 The Determination of Quantum Yields . . . . . . . . . . . . . 18
2.1.5 Considerations When Detecting Ions with the QMS . . . . 19
2.2 Ion–Molecule Reactions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2.1 The Selected Ion Flow Tube . . . . . . . . . . . . . . . . . . . . 19
2.2.2 The Determination of the Reaction Rate Coefficient. . . . 23
2.2.3 The Determination of the Product Branching Ratios . . . . 25
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3 Vacuum Ultraviolet Negative Photoion Spectroscopy
of SF , CF and SF CF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6 4 5 3
3.1 Background Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.2 Sulphur Hexafluoride (SF ). . . . . . . . . . . . . . . . . . . . . . . . . . . 29
6
3.3 Tetrafluoromethane (CF ). . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4
xi
xii Contents
3.4 Trifluoromethyl Sulphur Pentafluoride (SF CF ). . . . . . . . . . . . 36
5 3
3.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4 Vacuum Ultraviolet Negative Photoion Spectroscopy
of CF Cl, CF Br and CF I. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3 3 3
4.1 Background Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.2 The Anions Observed from CF Cl, CF Br and CF I . . . . . . . . . 46
3 3 3
4.3 F- from CF Cl, CF Br and CF I. . . . . . . . . . . . . . . . . . . . . . . 46
3 3 3
4.4 Cl- from CF Cl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3
4.5 Br- from CF Br and I- from CF I . . . . . . . . . . . . . . . . . . . . . 53
3 3
4.6 F - and FX- (X = Cl, Br) from CF Cl, CF Br and CF I . . . . . 55
2 3 3 3
4.7 CF - (n = 1–3) from CF Cl, CF Br and CF I. . . . . . . . . . . . . . 56
n 3 3 3
4.8 Bond Dissociation Energies . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.9 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
5 Vacuum Ultraviolet Negative Photoion Spectroscopy of SF Cl. . . . 65
5
5.1 Background Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5.2 F- from SF Cl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
5
5.3 Cl- from SF Cl. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5
5.4 SF - from SF Cl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5 5
5.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
6 Vacuum Ultraviolet Negative Photoion Spectroscopy
of Small Polyatomic Molecules. . . . . . . . . . . . . . . . . . . . . . . . . . . 75
6.1 Summary of Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
6.2 Ion-pair Appearance Energies and Thermochemical
Thresholds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
6.3 Ion-pair Formation Below the Ionisation Energy. . . . . . . . . . . . 81
6.4 Quantum Yields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
6.5 Competing ion-pair Reactions. . . . . . . . . . . . . . . . . . . . . . . . . 84
6.6 Electron Attachment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.7 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
7 The Reactions of CF + (n 5 1–3) with C H , C H F, C H F
n 2 4 2 3 2 2 2
and C HF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
2 3
7.1 Background Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.2 The Reactions of CF? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
7.3 The Reactions of CF ?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
2
7.4 The Reactions of CF ?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
3
7.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100