15
Structure and Dynamics of Weakly Bound Molecular Complexes
Structure and Dynamics of Weakly BoundMolecular Complexes
NATO ASI SeriesAdvanced Science Institutes Series
A series presenting the results of activities sponsored by the NATO Science Committee,which aims at the dissemination of advanced scientific and technological knowledge,with a view to strengthening links between scientific communities.
The series is published by an international board of publishers in conjunction with theNATO Scientific Affairs Division
A Life Sciences Plenum Publishing CorporationB Physics London and New York
C Mathematical D. Reidel Publishing Companyand Physical Sciences Dordrecht, Boston, Lancaster and Tokyo
D Behavioural and Social Sciences Martinus Nijhoff PublishersE Applied Sciences Dordrecht, Boston, Lancaster
F Computer and Systems Sciences Springer VerlagG Ecological Sciences Berlin, Heidelberg, New York, London,H Cell Biology Paris, and Tokyo
Series C: Mathematical and Physical Sciences Vol. 212
Structure and Dynamics ofWeakly BoundMolecular Complexesedited by
Alfons WeberMolecular Spectroscopy Division,National Bureau of Standards,Gaithersburg, Maryland, U.S.A.
D. Reidel Publishing Company
Dordrecht / Boston / Lancaster / Tokyo
Published in cooperation with NATO Scientific Affairs Division
87-18793CIP
Proceedings of the NATO Advanced Research Workshop onStructure and Dynamics of Weakly Bound Molecular ComplexesAcquafredda di Maratea, ItalySeptember 21-26, 1986
Library of Congress Cataloging in Publication Data
NATO Advanced Research Workshop on Structure and Dynamics of Weakly Bound MolecularComplexes (1986: Acquafredda di Maratea, Italy)
Structure and dynamics of weakly bound molecular complexes / edited by Alfons Weber.p. cm.- (NATO ASI series. series C, Mathematical and physical sciences; vol. 212)"Proceedings of the NATO Advanced Research Workshop on Structure and Dynamics of
Weakly Bound Molecular Complexes, Acquafredda di Maratea, Italy, September 21-26,1986"-eIP t.p. verso.
"Published in cooperation with NATO Scientific Affairs Division."Bibliography: p.
Includes index.ISBN 90-277-2584-51. Molecular association-Gongresses. 2. Complex compounds-Gongresses.
I. Weber, Alfons, 1927- . II. Title. III. Series: NATO ASI series. Series C,Mathematical and physical sciences; no. 212.
QD461.N335 1986541.2'24-dc 19
Published by D. Reidel Publishing CompanyPO. Box 17,3300 AA Dordrecht, Holland
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All Rights Reserved© 1987 by D. Reidel Publishing Company, Dordrecht, Holland.No part of the material protected by this copyright notice may be reproduced or utilizedin any form or by any means, electronic or mechanical, including photocopying, recordingor by any information storage and retrieval system, without written permission from thecopyright owner.
TABLE OF CONTENTS
International Organizing Committee
Acknowledgments
Preface
PART I. SPECTROSCOPY, STRUCTURE, POTENTIALS
A. Rotational Spectra
Rotational Spectroscopy of Weakly Bound Complexes:Capabilities and Limitations
John S. Muenter
Pulsed-Nozzle, Fourier-Transform MicrowaveSpectroscopy of Hydrogen-Bonded Dimers
A. C. Legon
Structure Determination of Weakly Bound ComplexesT. R. Dyke
;·1icrowave Spectra and l-leak Intramolecular HydrogenBonding in 3-Butene-l-Thiol and N-Hethylallylamine
K.-}1. Harstokk and Harald ;1e\llendal
B. Rotation-Vibrational Spectra
High Resolution Infrared Spectroscopy ofvan der Waals Molecules
Brian J. Howard
Vibration-Rotation Spectroscopy of ArHClby Far-Infrared Laser and Microwave/Far-InfraredLaser Double Resonance Spectroscopy
Ruth L. Robinson, Douglas Ray,Dz.-Hung Gwo, and Richard J. Saykally
Vibrational Anomalies and Dynamic Couplingin Hydrogen-Bonded van der Waals Molecules
A. S. Pine
Xl.
Xl.l.l.
xv
3
23
43
57
69
85
93
vi
Slit Jet IR Absorption Spectroscopy ofMolecular Complexes
David J. Nesbitt
Sub-Doppler Resolution Infrared Spectroscopyof Binary Molecular Complexes
R. E. Miller
The Infrared Spectrum of H2-Ar: New Observationsin the v=1-0 and 2-0 Bands of H2
A. R. W. McKellar
Dynamical Properties of SimpleHydrogen-Bonded Clusters
J. W. Bevan
Infrared Spectroscopy of Hydrogen-Bonded andvan der Waals Complexes
James M. Lisy, Kirk D. Ko1enbrander, andDaniel W. Michael
TABLE OF CONTENTS
107
131
141
149
171
Ab Initio Calculations of Vibrational Frequenciesand Infrared Intensities for the Hydrogen-Bonded Complex HCN---HF
P. Botschwina 181
The Role of Tunneling Models in Analyzing HighResolution Spectra of Weakly Bound Molecular Complexes
Jon T. Hougen 191
Bibliography of Rotational Spectra of WeaklyBound Complexes
Stewart E. Novick 201
C. Electronic Spectra
Structure and Dynamics of Mercury van der WaalsComplexes
W. H. Breckenridge, M. C. Duval,C. Jouvet, and B. Soep
The Structure of van der Waals Moleculesof s-Tetrazine
Donald H. Levy
Spectra of Mixed DimersE. W. Schlag, H. L. Selzleand K. U. Boernsen
213
231
251
TABLE OF CONTENTS
Solvent Shifts, Spectroscopy and Structurein van der Waals Complexes of Perylene
A. T. Amos, S. M. Cohen, J. C. Kettley,T. F. Palmer, and J. P. Simons
Spectroscopy in the Visible and Near UltravioletRegion of Some Organic Molecules and theirvan der Waals Complexes
W. M. van Herpen, W. A. Majewski,D. W. Pratt, and W. L. Meerts
263
279
vii
Supersonic Jet Spectroscopy of Complexes of Carbazoleand N-Ethyl Carbazole with Alkyl Cyanides
Anita C. Jones, Alan G. Taylor,Elizabeth H. Gibson, and David Phillips 291
Photo ionization of Hydrogen-Bonded MolecularAggregates
P. Bisling, E. Rlihl, B. Brutschy, andH. Baumgartel
D. Potential Functions
The Unavoidable Importance of Electrostatic Effectsin the Structures of Weakly Bonded Complexes
Clifford E. Dykstra and Shi-yi Liu
Intermolecular Potentials, Internal Motions and theSpectra of van der Waals Molecules
G. Brocks and A. van der Avoird
Non-Bonding Atom-Diatom Potentials via a DoubleMany-Body Expansion Method
A. J. C. Varandas
The Determination of, Intermolecular Forcesby Data Inversion Methods
E. Brian Smith
Transport Properties of van der Waals MoleculesComputed from Accurate Interactions
F. A. Gianturco and M. Venanzi
Determination of Anisotropic Interaction Potentialsfrom Rotational State Resolved Scattering Data
M. Faubel
303
319
337
357
373
389
405
viii
van der Waals Interactions from Glory andDiffraction Scattering
V. Aquilanti, F. Pirani, andF. Vecchiocattivi
High Resolution Crossed Molecular Beam Studiesof van der Waals Forces
Laura Beneventi, Piergiorgio Casavecchia,and Gian Gualberto Volpi
E. Summary: Part I
TABLE OF CONTENTS
423
441
Where Are We in Weak Intermolecular Interactions?Willia~ Klemperer
PART II. DYNAMICS
455
Interpretation of Linewidths in the InfraredPhotodissociation Spectra of van der WaalsMolecules
W. Ronald Gentry 467
Infrared Photodissociation of van der Waals ComplexesSelectively Prepared by Molecular Beam Scattering
U. Buck, F. Huisken, Ch. Lauenstein,T. Pertsch and R. Sroka 477
IR Dissociation of Weakly Bound van der WaalsComplexes: (SF6)n, (SiF4)n, (SiH4)n. (C2H4)n,(n=2,3) in the 9-11 ~m Range
M. Snels, R. Fantoni, and J. Reuss 489
Infrared (9-11~m) Dissociation of the HydrogenBonded Clusters (NH3)n (~2) Detected byBolometric Technique
M. Snels, R. Fantoni, and W. Leo Meerts 495
Highly Excited SystemsJ. Reuss 501
Vibrational Predissociation Dynamics of theNitric Oxide Dimer
Michael P. Casassa, John C. Stephenson andDavid S. King
Complex Forming Reactions in Noble Gas ClustersD. Levandier, R. Pursel, and G. Scoles
513
525
TABLE OF CONTENTS ix
Structure and Dynamics of the Rare Gas-Halogen van derWaals Molecules: Product State Distributions forVibrational Predissociation of NeBr2
Joseph I. Cline, Dwight D. Evard, Brian P. Reid,N. Sivakumar, Fritz Thommen, and Kenneth C. Janda 533
Dynamics of Energy Transfer in van der WaalsMolecules of s-Tetrazine and Argon
Marc Heppener and Rudolf P. H. Rettschnick ~53
Theory of van der Waals Photofragmentation DynamicsJ. Alberto Beswick 563
Dissociation Dynamics of the He-I2-Nevan der Waals Complex
G. Delgado-Barrio, P. Villarreal,A. Varad~, N. Martin, and A. Garcia 573
Dynamics of the Ar---H2 van der Waals Complex:A Diabatic Distorted Wave Approach IncludingDiscrete-Discrete Couplings
P. Villarreal, G. Delgado-Barrio,O. Roncero, E. de Pablo, and S. ~iret-Artes 583
Vibrational Predissociation Dynamics of WeaklyBonded Dimers: A Summary
David S. King 593
List of Participants 599
List of Contributors 605
List of Poster Papers 607
List of Names 613
Subject Index 617
INTERNATIONAL ORGANIZING COMMITTEE
A. Weber (Chairman)Molecular Spectroscopy DivisionNational Bureau of StandardsGaithersburg, MD 20899, USA
F. A. GianturcoDipartimento di ChimicaUniversita degli Studi di Roma00100 Roma ADItaly
B. J. HowardPhysical Chemistry LaboratoryOxford UniversityOxford, OX1 3QZGreat Britain
A. R. W. McKellarHerzberg Institute of AstrophysicsNational Research Council of CanadaOttawa, Onto K1A OR6Canada
A. van der AvoirdTheoretical Chemistry InstituteFaculty of Mathematical andPhysical Sciences
Katholieke Universiteit Nijrnegen6525 ED NijmegenThe Netherlands
xi
ACKNOWLEDGMENTS
The conduct of the NATO-Advanced Research Workshop on the "Structureand Dynamics of Weakly Bound Molecular Complexes" was made possible bythe primary sponsorship and support of the NATO Scientific AffairsDivision in Brussels, Belgium and special thanks are due to the lateDr. Mario DiLullo and to Dr. Craig Sinclair of this division. TheWorkshop was assisted by the generous support provided by the NationalBureau of Standards, the Coblentz Society, the Laser Analytics Divisionof Spectra Physics, BOMEM, Inc., and the Standard Oil Research andDevelopment Company.
The search for a suitable locale for the conduct of the Workshop wasably assisted by Dr. and Mrs. Tilo Kester of ITST v.z.w., inOverij se, Belgium. Their mediation in making the formal arrangementswith the management of the Hotel Villa del Mare in Acquafredda diMaratea, Italy was of great help in getting the meeting off to a goodstart. Special thanks and commendations are also due to Mr. A.Guzzardi and Mrs. Susi Travisano and their staff of the Hotel Villa delMare. Their solicitous attention to detail and the comfort of theparticipants made the Workshop an enjoyable event.
The planning of the scientific program was done in consultation withthe members of the international organ~z~ng committee as well asfriends and colleagues active in the field. To all of them as well asthe reviewers of the manuscripts I express my gratitude for theirthoughtful comments and suggestions.
Special thanks are due to Ms. R. A. Flynt for her excellentsecretarial assistance throughout the preparative and follow-up stagesof the Workshop and the preparation of this book.
Alfons WeberNational Bureau of StandardsGaithersburg, MD 20899, USA
xiii
PREFACE
The study of weakly bound molecular complexes has in recent yearsbrought this field of investigation to the forefront of physical andchemical research. The scope of the subject is wide and differentterminology and nomenclature is current among the varioussubspecial ties. Thus, the term "metal cluster" often connotes to theorganic chemist a metal-organic compound, while the physicist will morelikely think of groups of metal atoms held together by weak interatomicforces. Aggregates, clusters, complexes, van der Waals molecules,hydrogen-bonded molecules, etc. are terms currently in use, sometimesinterchangeably while other times with well defined and mutuallyexclusive meanings. The subjects of this volume are the free, isolatedvim der Waals and hydrogen-bonded molecules. Owing to the presentstate of experimental knowledge these are mostly dimers, i.e., entitiesformed by two strongly bound molecules, an atom and a molecule, or twoatoms held together by the weak hydrogen-bonding, or the still weakervan der Waals forces. Weakly bound complexes formed of more than twostrongly bound sub-units, i.e., trimers, tetramers, etc., are nowcoming wi thin reach of experimental observation and several papers inthis book deal with them.
The study of van der Waals and hydrogen-bonded interactions has beenpursued for several decades. Most of these ,investigations have,however, dealt with systems in the condensed phase in which bulkeffects are commingled with and therefore mask the weak binaryinteractions. However, significant advances in both theoretical andexperimental studies of isolated van der W'aals and hydrogen-bondedmolecules have taken place in recent years and the Pimentel (1) andBrinkman (2) reports recently issued by the U. S. National Academy ofSciences indicate that this field of research will retain a prominentposition in the future. It was therefore deemed to be appropriate toconvene a meeting of experts to discuss the status of the field and toassess the directions along which future advances would most likelyoccur.
The present book represents the proceedings of the NATO AdvancedResearch Workshop on the "Structure and Dynamics of Weakly BoundMolecular Complexes" held in Acquafredda di Maratea, Italy, September21 through 26, 1986. The purpose of this Workshop was to bringtogether researchers from a variety of disciplines and with differentbackgrounds who are working on various aspects of the structures anddynamics of van der Waals and hydrogen-bonded complexes in the gaseousphase. Different experimental and thepretical, approaches are used forthe determination of the structures, potential functions, dynamics, andpredissociation effects that characterize weakly bound complexes.Several key questions were prominent among the various problemsaddressed.
xvi PREFACE
The structures of over 100 molecules have now been determined bymicrowave and molecular beam electric resonance (MBER) spectroscopy(see, for example, the bibliography provided by S. Novick, pp 201-212).While some of these are predicted by accepted theory andphenomenological models, many complexes have quite unexpectedstructures. These findings therefore raise the question as to what arethe underlying principles that determine how molecules stick together.This obviously has important implications for condensed phase work andthe understanding of condensation phenomena. Here the interactionbetween the experimental spectroscopists and the quantum theoreticiansis beneficial to answer the question "can structures be predicted fromsome fundamental principles or is each unique, requiring a separatespectroscopic study or ab initio calculation?"
The interaction between molecules is described by an intermolecularpotential energy function - this interaction is most readily probed inweakly bound dimers. There are both theoretical and empiricalapproaches to this topic, each of which has its own problem areas. Forexample, how reliable are current ab initio calculations and how maythey be improved to determine accurately that very small part of thetotal system energy that describes the intermolecular interactions?Further, how reliable are the current semi-empirical methods to map outthe energy surfaces for small dimer complexes and, by extension, forlarger complexes leading ultimately to clusters? On the other hand,can spectroscopy, perhaps in conjunction with other experimental data,be used to obtain unique anisotropic intermolecular potential surfaces?
Weakly bound complexes with internal energy less than their bindingenergy possess large amplitude internal degrees of freedom and executetunneling motions between different equivalent conformations. Thesebehaviors motivate the search for the best methods, analytical andgroup theoretical, to study the dynamics of these motions on thepotential surface and to determine the most likely pathways out of themany possible for a conformation change to occur.
One very important dynamical process when complexes are excited by aphoton of energy greater than that of the intermolecular bond ispredissociation. This phenomenon manifests itself in broad spectrallines in a rotation-vibration band or in the break-off of therotational branches at a particular J-value (rotationalpredissociation). Different rotation-vibration bands of a complex mayshow different line broadenings or branch break-off at different Jvalues. Among the questions that have been debated are the following:are the broad lines observed in some rotation-vibration bands a measureof vibrational predissociation or are they due to some internal energyredistribution effect?, as well as what are the underlying requirementsfor rapid predissociation? Much photodissociation work has been donewith line tunable lasers with results that sometimes disagree withthose obtained with high resolution continuously tunable lasers. Suchdiscrepancies pose the question regarding the relative merits of these
PREFACE xvii
two techniques for studying the dissociation processes. Picosecondtechniques for measuring the vibrational predissociation lifetimes ofexcited states have only recently been developed. It remains to beseen whether these lifetimes are consistent with those determined byhigh resolution, frequency domain spectroscopic methods.
This book is the result of the deliberations on these and otherquestions. The papers are contributions based on the invited talks.Also included are selected contributions based on poster paperspres&nted at the Workshop. For convenience the papers are grouped intwo sections, the first dealing with spectroscopy, and thedetermination of structures and potential functions while the secondsection deals with dynamical phenomena. This division is somewhatarbitrary since a fair number of papers in the first section deal withdynamical effects and a substantial spectroscopic content is inevidence in the second section.
The first four papers deal with the methods of microwavespectroscopy to deduce the structures of complexes held together byintermolecular forces or the conformations determined by intramolecularhydrogen-bonding. This section is followed by papers dealing withrotation-vibration spectra. The latter field has experiencedremarkable progress during the last few years owing to the advances inexperimental techniques by means of which it is now possible to fullyresolve the rotation-vibration bands of, albeit simple, van der Waalsand hydrogen-bonded molecules. Papers dealing with the high resolutionvisible and near ultraviolet spectra complete the spectroscopy section.
Information about the intermolecular potential is an important byproduct of the spectroscopic studies, but other methods play veryimportant roles as well. This is especially so for regions of thepotential surface not accessible to spectroscopic study; here the beamscattering experiments provide a wealth of information. Theinterpretation of various models, the contributions of the differentclassical and quantum mechanical couplings that comprise the overallintermolecular potential, the relationships between bulk physicalproperties and the potential and how it can be determined by inversiontechniques from macroscopic data, these and other questions are takenup in the last section of part I.
While dynamical effects are discernible in the spectra throughlinewidths and the break-off of the rotational branches, it is theinterpretation of photodissociation experiments that has given causefor much discussion. The second part of the book deals with these andother aspects of the dynamics of predissociation, energy transfer, andhighly excited vibrational states.
The program of the Workshop was designed to include all aspects ofthe study of free van der Waals and hydrogen-bonded molecularcomplexes, unperturbed by effects ~ttributable to a surrounding medium,
xviii PREFACE
and the papers contained in this book reflect the spirit of thisattempt. It is fair to point out however, that some of the topicstaken up in this book are also presented in other publications, ofwhich only a few of the most recent ones will be cited here [3-5].Research in the field of weakly bound molecular complexes is movingalong very rapidly and many new results have been reported in theliterature since the conclusion of the Workshop. It is hoped that thepresent book will nevertheless be useful to researchers in the fieldfor several years to come.
REFERENCES
1. Opportunities in Chemistry, (National Academy Press, Washington,D.C., 1985).
2. Physics Throu~h the 1990's. Atomic. Molecular. and OpticalPhysics, (National Academy Press, Washington, D.C., 1986).
3. Van der Waals Systems, Topics in Current Chemistry, Vol. 93(Springer-Verlag, Berlin-Heidelberg-New York, 1980).
4. Van der Waals Molecules, Faraday Disc. Chern. Soc., No. 73 (1982).
5. Hydro~en-Bonds, Topics in Current Chemistry, Vol. 120, P.Schuster, Editor (Springer-Verlag, Berlin-Heidelberg-New York,1984).
A. WeberMolecular Spectroscopy DivisionNational Bureau of StandardsGaithersburg, MD 20899, USA
