Atom, Molecule, and Cluster Beams I: Basic Theory, Production and Detection of Thermal Energy Beams

361 Pages·2000·12.324 MB·English

by  Professor Dr. Hans Pauly (auth.)

Springer Series on
ATOMIC, OPTICAL, AND PLASMA PHYSICS 28
Springer-Verlag Berlin Heidelberg GmbH
9:J ...........
PhysicsandAstronomy
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Springer Series on
ATOMIC, OPTICAL, AND PLASMA PHYSICS
The Spnnger Senes on AtomlC, Ophcal, and Plasma Physics covers m a compre
henslve manner theory and experiment in the entue fteld of atoms and molecules
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vanced optlCS, aeronomy, and engmeenng. Laser phYSICS is a partIcular connectmg
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in the fleld. The purpose of the se ries IS to cover the gap between standard und er
graduate textbooks and the research literature Wlth emphasls on the fundamental
ideas, methods, techmques, and results in the fleld.
'1.7 Quantum Squeezmg
By P.D Drumond and Z. Splcek
28 Atom, Molecule, and Cluster Beams I
BasIc Theory, ProductlOn and Detectlon of Thermal Energy Beams
ByH Pauly
29 Polar1Z8hon, Ahgnment and Orientation in Atomic Collislons
By N Andersen and K Bartschat
30 PhYSICS of Sohd-State Laser PhySics
ByR C Powell
(Pubhshed In the former Senes on Atomlc, Molecular, and Optlcal Physlcs)
31 Plasma KmetIcs m Atmosphenc Gases
Editors M Capltelh, C M Ferrelra, B F Gordlets, A I OSIPOV
3'1. Atom, Moleeule, and Cluster Beams 11
Cluster Beams, Fast and Slow Beams, Accessory Equlpment and ApphcatlOns
ByH Pauly
Series homepage - http://www.sprmger.de/phys/books/ssaop/
Vols 1-26 of the former Springer Senes on Atoms and Plasmas are hsted at the end of the book
Hans Pauly
Atom, Moleeule,
and Cluster Beams I
Basic Theory, Production and Detection
of Thermal Energy Beams
With 124 Figures
, Springer
Professor Dr. Hans Pauly
MPI ftir Stromungsforschung
Bunsenstrasse 10, 37073 Giittingen, Germany
ISSN 1615-5653
ISBN 97B-3-6.j.2-0862.3-6
Library of Congress Cataloging-in-Publication Data applied for.
Die Deutsche Bibliothek -CIP-Einheitsaufnahme.
Paul)', Ham: Atom, molecule, and cluster beams 1 : basi<: theory, production and
detection of thermal energy beams /
Hans Pauly. -Berlin; Heidelberg; New York; Barcelona ; Hong Kong: Landon ;
Milan ; Paris; Singapore; Tokyo: Springer. 2000
(Springer series on atomic, optical, and plasma physics ; 28)
(Physics and astronomy online library)
ISBN 978-3-642-08623-6 ISBN 978-3-662-04213-7 (eBook)
DOI 10.1007/978-3-662-04213-7
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Preface
HanDy any other expenmental method has resulted 10 so much depth of knowl
edge and fundamental mslghts 10 the phYSICS and chemlstry of the 20th century as
has the molecular beam method Its successful apphcatlOns can be traced 10 many
and even diStant branches of these SClences
Although many reVIew artlcles about the experlffiental techmques and therr
deployment to solve problems in various fields have been written, the number of
"textbooks" has stayed low After the first, small monograph by Ronald Fraser
(1931, 1937) ("Molecular Rays"), outl101Og the baslcs of the then current tech
nologles and the results of early 1Ovestlgahons, WhlCh was revlsed and updated 10
the 1950s by Kenneth F. Srruth (1955) ("Molecular Beams"), the book by Norman
F. Ramsey (1956) ("Molecular Beams") appeared It comprehenslVely descnbed
the then current status of the techmques and gave an excellent survey of the
molecular beam resonance method, lts foundatlOns, and the results obtamed so far
ThlS book, repnnted unrevlsed after almost thlrty years, lS wtthout doubt counted
as one ofthe great standard works ofmodem phYSICS
When Ramsey's book appeared, the area was already 10 astate of change
Whlle molecular beam work had concentrated for twenty years on the resonance
method, other shll open problems were now belOg plcked up, especlally questlOns
fundamental to cherrustry, where It became posslble for the first time to study ele
mentary reachons 10 lsolated, s10gle colhsl0ns In 1973, Fluendy and Lawley
summanzed thlS partlcular aspect and the then current progress 10 expenmental
techmques 10 therr book "Chemlcal ApphcatlOns of Molecular Beam Scattenng".
More recent aspects of cherrucal apphcatlOns of molecular beams are addressed 10
Bemste1O's book on "Chemlcal Dynarrucs VIa Molecular Beam and Laser Tech
mques", WhlCh appeared 10 1982.
The latest survey of the expenmental techmques, as weB as a detaded presen
tahon of the many areas WhlCh now make use of them, IS finaBy found 10 the two
volume work "Atorruc and Molecular Beam Methods" edtted by G Scoles (1988,
1992), wmch has grown to be an 10dlspensable reference for everyone who works
Wlth molecular beams.
Agam, when the book by G Scoles appeared, new research dlrectlons began
to take shape, uhhz10g molecular beam techmques They led to new areas of work
now grow1Og Wlth enormous Impetus. One example IS the area of cluster research,
where the translhon from atoms and molecules to sohd-state bulk matenalls belOg
VI Preface
mvesngated. Here, the expenmental techmques have made slgmficant progress,
especially m the areas of umversal cluster sources and of beam dlagnosnc tools
Another example IS the producnon of slow, cold atoms, therr mampulatlOn by laser
hght, and therr storage m traps, a fascmatmg development WhlCh only began m the
IDld-1980s and has already led to great sClentlfic successes. Atom optlcs and atom
mterferometry, areas of great potentlal for the future, are further examples But
also m the more conventlonal areas, new techmques, experunental only a decade
ago, have grown mto standard methods and have found wldespread use Such ex
amples are the productlon of molecular and cluster beams by laser ablatIOn, or the
productlon of clusters and nanopamcles by laser-mduced pyrOlYSlS.
Fast moleeular beams of hyperthermal energles have also found many sClen
tlfie apphcanons, reaehmg from eoaxlal laser spectroscopy and photo fragment
translatlon speetroscopy to preclslon measurements of hfebmes Beyond that,
these beams have found numerous apphcabons as dlagnosbc tools m plasma
physlcs On a large and techmcal sc ale, fast molecular beams are ubhzed for the
heatmg offuslon plasmas.
The book at hand presents a conslstent, up-to-date descnpbon of the extremely
vaned expenmental teehmques WhlCh nowadays enables work Wlth neutral partl
eIes m an energy range spannmg elghteen orders of magmtude. As far as the scope
of thlS book pefIDlts, special effort lS made to lay the physlcal foundatlOns for an
understandmg of the vanous experunental methods. Towards thlS goal, Chaps. 2
and 3 present a collectlon of the most relevant results of gas kmebcs and dynam
ICS Thus, thlS book IS not only auned at the expenenced sClenbst applymg mo
lecular beam methods as a reference standard, but also at the begmner, m order to
enable htm or her to gam a solid background and mtroduction to the field and Its
techmques In thts context, one has to conslder that this expenmental techmque
ubhzes methods from across the whole of physlcs, Just as ItS apphcatlons reach
many dtfferent areas ofphyslcs and chemlstry. The expenmental methods are ex
plamed and demonstrated by a multltude of sClentlfic apphcatIOns m the most
vaned areas of sClentlfie research, paymg special attenbon to recent developments.
Numerous references allow readers mterested m further detaIls easy access to other
bterature. However, the selecbon of references out of a vast abundance IS dlfficult
It IS eharactenzed by the alm not to Omlt older work where Important steps of
progress m expenmentanon ongmated, but also to name recent work whlch allows
modem expenmental methods to be recogmzed and WhlCh would make lt posslble
to completely trace baek the hterature concemmg a glven problem
The matenal was spht mto two volumes m such a way that the first volume
starts Wlth a general mtroductlon to the vanous areas where molecular beams have
Ylelded unportant results (Chap. 1), demonstratmg the broad scope and wlde ap
phcablhty of molecular beams m phYSICS and chemlstry. In the next two chapters 2
and 3 the fundamentals of the kmetlc theory of gases, statlstlcal mechamcs, and
gas dynarmcs have been assembled, smce they are drawn upon m many parts of
both volumes. Then follow the vanous methods for the produchon and detechon
of thermal energy atomic and molecular beams (Chaps. 4 and 5), WhlCh are the
Preface VII
general basIs of convenbonal molecular beam work The second volume - refer
ences to chapters of volume 2 are marked by the Roman numeral II m front of the
chapter number - completes these methods wlth a descnption of the production
and detecbon offast molecular beams (Chap II 1), WhlCh reqUlre rather dIfferent
experllllental techruques compared to thermal energy beams Chapter II 2 de
scnbes the producbon and analysIs of cluster beams, WhlCh allow the mvestlgatlOn
of the llllpOrtant "transltlonal state" between a smgle atom or molecule and the
sohd state. The subsequent chapters 1I.3 and II 4 glve a survey on the numerous
methods of selecbon and analysIs of molecular beams by velocIty and quantum
state. The ftnal chapter 11.5 IS meant to mtroduce the reader to the new and exclt
mg field of slow and cold atoms, covermg the full range of atom mampulatlon by
opbcal means (deceleratlon, coolmg, and storage of atoms m traps) and of atom
optics Numerous new apphcatlons are 100mmg, the most fascmatmg one bemg
the atom laser, WhlCh wIll provlde atom sources that are as dIfferent from conven
bonal atoIDlc beams as lasers are from hght bulbs. A number of apphcatlOns de
nved from the molecular beam methods or worked on at thlS tlme are also de
scnbed m the second volume May thlS summary of the 20th century develop
ments and results be a gUlde to the new mtllenmum.
It lS a pleasure to express my profound thanks to my long-standmg colleague
and fnend Prof R K B Helbmg from the Umverstty of Wmdsor, for his substan
baI contnbubon He not only read the whole manuscnpt, translated several chap
ters from the ongmal German verSIon, and corrected the others. but also made
many construcbve cntlclsms, suggesttons, and Improvements
Furthermore, Irecord my thanks to many sClentlsts and co-workers of the
Max-Planck Instttute for Flow Research and a number of colleagues from other
mstltlltes, who have helped me In many ways whlle prepanng thlS book In par
tlCUlar, I acknowledge the help of Prof U Buck, Prof R Ouren, Or R Feltgen,
Prof. L Huwel, Prof. F HUlsken, Or. M Lewerenz, Prof. H -G. Rubahn, and Prof
R. Schmke, who read parts of the manuscnpt, gave valuable comments for 1m
provements, or kmdly granted permissIon to use thelr matena1 The dlScusslons
Wlth and the encouragement glven by Prof. I.P. Toenmes, a long standmg-col
league and sClentlftc compamon for more than forty years, have also been very
helpful
Last but not least, I wlsh to express my appreclatIon for the valuable secretar
tal help from Mrs Ch SchneIder and to Mr W. Kelderhng, who has prepared the
drawmgs Wlth unfallmg patIence and care.
The fuendly and dynamtc atrnosphere of the Max-Planck InstItute for Flow
Research and the support of the Max-Planck Soclety are also gratefully acknowl
edged.
Of course, my pnnclpal acknowledgment IS to my wlfe, Chnsta, for her un
derstandmg and moral support provlded over many years
GottIngen H Pauly
January 2000
Contents
1. The Role of Molecular Beams in the 20th Century
1 1 Histoncal Development ., . 5
lUThe Work ofthe School ofOtto Stern 5
1 1 2 Molecular Beam Magnetlc Resonance 6
1 1 3 Early Work wlth Fast Molecular Beams 7
1.1 4 Developments m the Second Half of the 20th Century 8
1.2 Mam ApphcatIOns of Molecular Beams . 9
1.2.1 Elastlc Scattenng .. 10
1 2.2 Ine1astlc Scattenng . 11
1 2.3 Reactlve Scattenng 14
1 2.4 Investlgatlon of Gas-Surface InteractIOns 14
1.2 5 DetermmatIOn of Electncal Polanzabllltles 16
1.2.6 Cluster Research . ..... " . 17
1.2 7 Slow Atom Beams and Cold Atoms 19
1 3 Thermal Energy Molecular Beam ApphcatIOns m other Flelds 20
1 3 1 Photon Expenments 20
1 3 2 Low Energy Electron and Ion Scattenng . 22
1 3 3 Plasma Dlagnoshcs . 22
1 3 4 Cluster and Nozzle Beams as Targets m HIgh Energy PhYSICS . 22
1.3 5 Molecular Beam EpItaxy and Llthography 22
1 4 Fast Beam Apphcahons 23
1.4 1 Plasma Dlagnoshcs wlth Fast Beams 24
1 4.2 Iomzahon of Rydberg Atoms m Electrlc and Magnetlc Flelds 24
1 4 3 Merged Beams 24
1 5 Examples of Molecular Beam Machmes . 25
1 5 1 A Umversal Scattenng Apparatus .. 26
15.2 Reqmrements for a Scattenng Expenment 26
1 5 3 Techmcal Reahzatlon . 28
1 5.4 A Molecular Beam Apparatus for Surface Investlgatlons 30
2. Fundamentals of Kinetic Gas Theory . 35
2 1 Ideal Gases m Thermodynamlc Eqmhbnum 35
2 1 1 The Maxwelhan Veloclty DIstrIbutIOn 36
X Contents
2.1.2 Number ofWall Colhslons, Pressure, and EquatIOn ofState 38
2.1.3 Mean Free Path, Colhslon Rates, and Colhston Frequencles 40
2 1.4 RotatIonal State Dtstnbutton of Molecules 46
2 1.5 VIbratIonal State DlstnbutIon ofMolecules . . 49
2 1.6 Total DIstnbutIon and PartItton FunctIon 50
21.7 FractIon ofDlmers and Degree ofDlssoclatIon at EqUlhbnum 51
2 2 Quantum StattstIcs . . . . . .. .. .... 54
22 1 Bose StattstIcs .. .,. . ... . 55
2 2.2 Bose-Emstem Condensatton 58
2.3 Molecular Flow Through an Ideal Aperture 60
2 3 1 Parttcle Flux . 61
2.3.2 Parttcle Number Denslty. ..... 63
2 4 Molecular Flow Through Channels ., 66
2.4 1 Channels of Crrcular Cross SectIon . 66
2.4 2 Channels ofNoncrrcular Cross Sectton . 75
2.4 3 MultIchannel Arrays 76
3. Fundamental Principles of Gas Dynamics . 77
3 1 Some Fundamentals ofTbermodynamtcs . 78
3 2 Govemmg EquatIons of Steady Flow 80
3 3 One-DtmenslonaI Flow .. . 81
3.3.1 Speed ofSound and Mach Number. 81
33.2 Flow Through Passages wlth Changing Cross-Sectlonal Area 83
33.3 Flow Through a Convergmg-Dlvergmg (Laval) Nozzle 85
33.4 Flow Through Convergmg Nozzles 89
3.3.5 Unsteady Flow, Normal Shock Waves 90
3 4 Two-Dtmenslonal Flow . 93
341 Oblique Shock Waves. 93
342 Planar Supersomc Flow over a Symmetncal Wedge 96
3 4 3 AXlsymmetnc SupersoDlc Flow over a Cone 97
3 4.4 Prandtl-Meyer Expansion. . 99
3.4 5 Mach Waves . . . . . . . . . . 102
3 4 6 Numencal Techmques and Results 103
3 5 Free-Jet ExpanSIOn. .. .. 105
36 Tbe Transitton to NoneqUllIbnum ConditIOns 111
3.6 1 Colhsion Cross SectIons .... ., ., 111
3.6 2 ColbsIOn Rates. ... . . 113
3.6.3 Terrnmal Temperature and Speed RatIO 117
36.4 VelocIty DIstnbutIon m Nozzle Beams. 120
3 65 IntensIty ofNozzle Beams 125
37 Internal Energy Relaxation. ., . 129
37 1 RotatIonal Energy RelaxatIOn. . 129
3.8 Bmary Gas Mixtures . 136
38.1 VelocIty and Temperature SlIp 136
Contents XI
382 Veloclty Shp due to Molecular Onentanon 138
3.83 Gas Separanon . . . . .. .. .. 138
3.9 Condensanon and Cluster Formation. . 139
39.1 Survey and Concepts ofModels . 140
3.92 Scalmg Laws for Cluster Formation. 143
39.3 Cluster Temperature .. ...... . .. 146
4. Thermal Energy Molecular Beam Sources 147
4.1 Experunental Requrrements . . . . . . .. . 149
41.1 Producnon ofNozzles, Apertures, and Sklmmers 149
4.12 Pumpmg Requrrements. 154
413 Beam Guldance and Beam Absorption 158
4.2 Gas Sources (4-600 K). .. ..... .. . 160
4.3 Ovens for Gases and Sohds " .. . . . . . 162
4.31 Temperature Range up to 1200 K. 162
4.3 2 Temperatures up to 2800 K. .. . 165
4.3 3 Sources for HIghly Refractory Matenals . 167
4 4 Laser Ablanon . 169
4 5 Sputtenng Sources . .. .. .. .. ..... 171
4 6 Recrrculanng Sources and Sources for SpecIal Apphcatlons 171
4.6.1 Sources Wlth Internal Shutter 174
4 6 2 Internal ColhmatlOn . 175
4.7 Sources for Beams ofRadlcals. . . . 176
4 7.1 PyrOlYSlS .. ... .... .. . 177
4.7.2 Gas DIscharges . . .. .. .. .... 181
4 7 3 Hollow-Anode DIscharges ... 181
4.74 Radlofrequency and Mlcrowave DIscharges . 182
4 7.5 Corona DIscharges . 186
4.7.6 Flow Tube Sources .. ....... 187
4.7.7 PhotolyslS.. . 189
4.8 Producbon ofMetastable Partlcles 190
4.8 1 Electron Impact Excltation . . 190
4 8 2 Gas DlScharges 192
4.8 3 Flow Tubes . 196
4 8.4 Opncal Excltation 197
49 Rydberg Atoms.. .. . .... '" ......... 198
49.1 Electron Impact Excltanon '" . " 200
4.9 2 Opbcal ExcltatlOn . .. .. .... . .. . . 200
410 Pulsed Beam Sources " " 201
4.101 Companson between Pulsed and Contmuous Beam Sources 202
4.10.2 Producnon ofPulsed Beams . 204
410.3 Propemes ofPulsed Beams. " 211
4 11 Sources of Slow and Cold Atoms . 213