Fundamentals of Gas Phase Ion Chemistry

438 Pages·1991·19.011 MB·English

by  R. J. Donovan (auth.), Keith R. Jennings (eds.)

Fundamentals of Gas Phase Ion Chemistry
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Series C: Mathematical and Physical Sciences -Vol. 347
Fundamentals of
Gas Phase Ion Chemistry
edited by
Keith R. Jennings
Department of Chemistry,
University of Warwick,
Coventry, U.K.
Springer Science+Business Media, B.V.
Proceedings of the NATO Advanced Study Institute on
Fundamentals of Gas Phase Ion Chemistry
Mont Ste. Odile, France
June 25 - July 6, 1990
Library of Congress Cataloglng-in-Publication Data
NATD Advanced Study Institute on Fundamentals of Gas Phase Ion
Chemistry (1990 : Sainte-Ddile, France)
Fundamentals of gas phase ion chemistry : proceedings of the NATD
Advanced Study Institute an Fundamentals of Gas Phase Ion Chemlstry,
Mont Ste. Ddile, France, 25th June-6th July, 1990 / edited by Keith
R. Jennings.
p. cm. -- (NATD ASI series. Series C, Mathematlcal and
physical SClences ; val. 347)
Includes lndex.
ISBN 978-94-010-5556-7 ISBN 978-94-011-3518-4 (eBook)
DOI 10.1007/978-94-011-3518-4
1. Chemical reactlons, Condltions and laws of--Congresses.
2. Gases. Ionized--Congresses. 1. Jennings, Keith R., 1932-
II. Title. III. Ser ies: NATO ASI series. Series C, Mathematical
and physical sciences ; no. 347.
00501.N365 1990
541.3·9--dc20 91-26411
ISBN 978-94-010-5556-7
Printed on acid-tree paper
AII Rights Reserved
© 1991 Springer Science+Business Media Dordrecht
Originally published by Kluwer Academic Publishers in 1991
Softcover reprint of the hardcover 1s t edition 1991
No part of the material protected by this copyright notice may be reproduced or
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CONTENTS
PREFACE ix
MULTIPHOTON IONISATION: PART 1 FUNDAMENTAL
PRINCIPLES
Robert J.Donovan 1
MULTIPHOTON IONISATION: PART 2 APPLICATIONS
Robert J.Donovan 9
ION DISSOCIATION AND ION-MOLECULE REACTIONS
STUDIED WITH STATE-SELECTED IONS
Odile Dutuit 21
GENERATION AND REACTIVITY OF STATE SELECTED
ATOMIC AND SIZE SELECTED TRANSITION METAL
CLUSTER IONS
Michael T. Bowers, Paul R.Kemper, Gert von HeIden and
Ming-Teh Hsu 55
TECHNIQUES FOR PREPARING AND STUDYING THE
PROPERTIES OF LARGE CLUSTER IONS BY HIGH
RESOLUTION MASS SPECTROMETRY
Anthony J. Stace 87
CHEMICAL REACTIONS IN AND ON CLUSTER IONS
Anthony J. Stace 105
SEMICONDUCTOR CLUSTER ION REACTIONS AND
ENERGETICS
Scott L. Anderson 117
GAS-PHASE METAL ION CHEMISTRY: SUMMARY OF THE
PANEL DISCUSSION
Robert R. Squires 131
CLUSTER ION CHEMISTRY: SUMMARY OF THE
WORKSHOP
Peter B. Armentrout 147
vi
CHARACTERIZATION OF IONS VIA THEIR ELECTRONIC
TRANSmONS
John P. Maier 155
VIBRATIONAL MODE EFFECTS IN POLYATOMIC ION
REACTIONS
Scott L. Anderson 183
WORKSHOP: THE ROLE OF ENERGY IN ION-MOLECULE
PROCESSES
Denise C. Parent 197
RADIATIVE ASSOCIATION: SUMMARY OF THE
WORKSHOP PRESENTATIONS
Robert C. Dunbar 209
WORKSHOP: SPECTROSCOPY OF IONS
Christoph Ottinger 219
THE SEARCH FOR ELUSIVE POTENTIALLY
INTERSTELLAR NEUTRALS BY NEUTRALIZATION
REIONIZATION MASS SPECTROMETRY: POLYCARBON
CHALCOGENIDES X(Cn)Y (X,Y:O,S).
Detlev Siilzle and Helmut Schwarz 237
THE MEASUREMENT AND INTERPRETATION OF ONSET
ENERGIES
Tomas Baer 249
THERMODYNAMIC INFORMATION FROM DRIFT-TUBE
EXPERIMENTS? SUMMARY OF THE PANEL DISCUSSION
Michael Henchman 267
ION THERMOCHEMISTRY: SUMMARY OF THE PANEL
DISCUSSION
John E. Bartmess 281
COLLISIONAL STUDIES OF GASEOUS NEGATIVE IONS
Alex G. Harrison 289
FUNDAMENTALS OF COLLISIONALACTIVA TION:
SUMMARY OF THE PANEL DISCUSSION
Alex G. Harrison 315
TIME-RESOLVED STUDIES OF UNIMOLECULAR GAS
PHASE ION DECOMPOSITIONS BY FIELD IONIZATION
KINETICS
Nico M.M.Nibbering 333
vii
ION-MOLECULE REACTIONS AND STEREOCHEMISTRY IN
TANDEM MASS SPECTROMETRY
Jean-Claude Tabet 351
E2/SN2AND OTHER ORGANIC ION MOLECULE
REACTIONS: SUMMARY OF THE PANEL DISCUSSION
Charles H. DePuy and Hans Griitzmacher 373
ISOMERS AND ISOMERIZATION OF MOLECULAR IONS:
THE FORMATION OF STABLE ION-NEUTRAL COMPLEXES
DURING UNIMOLECULAR DISSOCIATION
Steen Hammerum 379
INDUSTRIAL APPLICATIONS OF GAS PHASE ION
CHEMISTRY
James H. Scrivens and Keith Rollins 391
APPLICATIONS OF MASS SPECTROMETRY IN AN
INDUSTRIAL RESEARCH LABORATORY
Jan C. Kleingeld, Fred J. Fels and Wim J.L. Genuit 417
INDEX 437
PREFACE
This volume presents the proceedings of the 1990 Advanced Study Institute entitled "Fundamentals of
Gas Phase Ion Chemistry" held at Mont Ste. Odile , Alsace, France, 25th June -6th July, 1990. The
Institute brought together over 100 physicists, physical and organic chemists working on a wide variety
of topics with gas-phase ion chemistry as the common theme. Many different viewpoints, making use
of very different experimental and theoretical approaches, were brought to bear on the subject and
provided a stimulating and up-to-date account of the subject. Although the Institute was built around
the invited lectures, many specific points were addressed in workshops which consisted of informal
discussion groups which were organised by participants during the Institute. This volume therefore
contains not only chapters based on the lectures but summaries of many of the workshops which adds
considerably to the diversity of information presented.
This Advanced Study Institute was the fifth in a series of NATO-sponsored institutes devoted to various
aspects of the physics and chemistry of gas phase ions. These meetings have been held every four
years since the first, held in Biarritz in 1974, considered "Interactions between Ions and Molecules".
The five volumes which comprise the proceedings of these meetings illustrate very clearly the many
advances in theory and experiment which have taken place over the last 20 years. As this volume
indicates, the increasing use of lasers has allowed the study of state-selected species, cluster ion
chemistry is now a very active field and the processes involved in the unimolecular and bimolecular
reactions of organic ions are becoming clearer. The increased understanding of gas phase ion
chemistry has led to mass spectrometry being used in increasingly diverse ways in industry as described
in two chapters in this volume.
Much of the local planning of the meeting at Mont Ste Odile fell upon Rose Marx whose invaluable
help I should like to acknowledge. The meeting also benefited considerably from the experience of
Pierre Ausloos and Sharon Lias and from the assistance in planning the meeting given by Alzira
Almoster-Ferreira and Nico Nibbering.
The Organising Committee would like to acknowledge the assistance given by the staff at Mont Ste.
Odile and the support of Dr. Luis V da Cunha, Director of the ASI Programme of the Scientific Affairs
Division of NATO.
Keith R. Jennings
University of Warwick,
Coventry,
United Kingdom.
June, 1991
ix
K. R. Jennings (ed.), Fundamentals olGas Phase Ion Chemistry. ix.
© 1991 Kluwer Academic Publishers.
MULTIPHOTON IONISATION: PART I FUNDAMENTAL PRINCIPLES
R J DONOVAN
Department of Chemistry
University of Edinburgh
West Mains Road
Edinburgh EH9 3JJ
Scotland
ABSTRACT: The fundamental processes involved in resonant and
non-resonant mul t iphoton ionisat ion of atoms and molecules in the gas
phase, using pulsed lasers, are described. The mechanisms for ion
fragmentation are considered and the change from ladder switching to
ladder climbing, with decreasing laser pulse duration (10-9 - 10-13 s),
is discussed. Multiple ionisation and above threshold ionisation
processes are also briefly discussed.
1. Introduction
Multiphoton ionisation techniques have been used extensively for
fundamental spectroscopic and photophysical (dynamic) studies of atoms
and molecules [1]. Applications to mass spectrometry have until
recently been rather slow to materialise but the pace is increasing [2]
and commercial instruments are becoming more generally available.
Powerful new techniques which combine laser desorption of involatile and
fragile (biological) molecules, combined with laser multiphoton
ionisation and mass spectrometry, are also being developed [3].
In this chapter we briefly review the fundamental principles which
underpin the multiphoton ionisation (MPI) technique and discuss the
various ways in which both resonant and non-resonant ionisation
processes can be used to their best advantage. In the following chapter
a number of applications of the MPI technique will be outlined. As we
shall see, two of the principle advantages of MPI in mass spectrometry
are the ability to selectively ionise one component in a mixture and to
bring about either soft or hard ionisat ion, simply by changing the
intensity or the frequency of the laser radiation.
The main attract ion of the MPI technique for analyt ical appl icat ions
is the high sensitivity achievable (single atom detection is possible)
[4,5]. We note that multiphoton excitation is operationally very much
more convenient than the use of vacuum ultraviolet radiat ion (i .e.
single photon ionisation) as it avoids the problems associated with
evacuating the optical path and the use of LiF or MgF2 optics. The
1
K. R. Jennings (ed.), Fundamentals o/Gas Phase Ion Chemistry, 1-7.
© 1991 Kluwer Academic Publishers.
2
selection rules for MPI are also more generous than those for single
photon excitation and this allows a wider range of excited states to be
accessed [1].
2. Resonant multiphoton ionisation
Multiphoton ionisation involves the absorption of two or more photons by
the same molecule, the combined energy being sufficient to cause
ionisation (i.e. nhv;;;. IE; n ;;;. 2). The efficiency of the process is
greatly enchanced if a real intermediate state is resonant with a simple
mUltiple of the laser frequency and the highest efficiencies are
observed when a single photon is sufficient ly energet ic to reach the
intermediate state and a second photon sufficient to bring about
ionisat ion from the intermediate state (see figure la). The important
point here is that in many cases the intermediate state wi 11 have a
relatively long lifetime (;;;. 10-8 s), unless predissociation is
important, and thus the absorpt ion of a second photon during the same
laser pulse, by the excited molecule, has a relatively high probability.
In this 1+1 resonance enhanced mul t iphoton ionisat ion (REMPI) process
the photons are absorbed sequentially, i.e. incoherently. The
intensities available with pulsed laser systems are generally high
enough to saturate most electronic transitions (i.e. produce a number
density in the upper state that is comparable to that in the lower
state). The only disadvantage of this 1+1 REMPI scheme is that tunable
far ultra-violet radiation (A200 300nm) is required in order to
provide sufficient energy to ionise most molecules. This requires
frequency doubl ing and auto-tracking the output of a tunable dye laser
which adds another level of sophistication and expense to the techniques
involved. Commercial systems for frequency doubl ing and auto-tracking
are now widely available but their optimisation and routine application
is still significantly more difficult than the direct use of the
fundamental output from a pulsed dye laser.
An alternative approach is to use the non-linear properties of the
molecules themselves to bring about simultaneous two-photon absorpt ion
(see figure Ib). In this process a virtual intermediate state of the
molecule is involved. This virtual state can be thought of as a state
in which the molecule is "dressed" or perturbed by the photon field (NB
a virtual state is not an eigen state of the molecule). Thus, if a
second photon is incident on the molecule, within a sufficiently short
period of time (ca 10-15 s), both photons are absorbed simultaneously
(i.e. coherently). Clearly excitation only occurs when the resonance
condition, 2hv = .1E, is met. The selection rules for this type of
process are similar to the Raman selection rules, as Raman scattering is
itself a two photon process. Higher order processes involving 3, 4 and
more photons have been observed but the cross- sections for such
processes fall rapidly [1] and the laser intensities required for such
high order processes can cause broadening of spectra and molecular
fragmentation. Non-radiative processes (e.g. predissociation) which
deplete the intermediate state wi 11 lead to a reduct ion in ionisat ion
efficiency. However, the up-pumping rate even with nanosecond pulses