Picosecond Phenomena ΠΙ Proceedings of the Third International Conference on Picosecond Phenomena Garmisch-Partenkirchen, Fed. Rep. of Germany June 16-18,1982

Editors K.B.Eisenthal R.M.Hochstrasser W.Kaiser A. Laubereau

With 288 Figures

Springer-Verlag Berlin Heidelberg New York 1982

Contents

Part I A d v a n c e s in t h e G e n e r a t i o n o f U l t r a s h o r t L i g h t P u l s e s

Moving from the Picosecond t o t h e Femtosecond Time Regime By C.V. Shank, R.L. Fork, and R.T. Yen 2

Femtosecond O p t i c a l Pulses: Towards T u n a b i l i t y a t t h e Gigawatt Level By A. Migus, J.L. M a r t i n , R. A s t i e r , A. A n t o n e t t i , and A. Orszag .. 6

Femtosecond Continuum G e n e r a t i o n . By R.L. Fork, C.V. Shank, R.T. Yen, C. H i r l i m a n n , and W.J. Tomlinson 10

New Picosecond Sources and Techniques By A.E. Siegman and H. Vanherzeele 14

Generation o f Coherent Tunable Picosecond Pulses i n the XUV By T. S r i n i v a s a n , K. Boyer, H. Egger, T.S. Luk, D.F. Müller, Η. Pummer, and C.K. Rhodes 19

New I n f r a r e d Dyes f o r Synchronously Pumped Picosecond Lasers By A. S e i l m e i e r , B. Kopainsky, W. K r a n i t z k y , W. K a i s e r , and K.H. Drexhage 23

Acousto-Optic S t a b i l i z a t i o n o f Mode-Locked Pulsed Nd:YAG Laser By H.P. Kortz 27

A c t i v e Mode S t a b i l i z a t i o n o f Synchronously Pumped Dye Lasers By A . I . Ferguson and R.A. T a y l o r 31

Spectral Hole Burning i n the S a t u r a t i o n Region o f Mode-Locked Nd-Glass Lasers. By A. Penzkofer and N. Weinhardt 36

Sin g l e and Double Mode-Locked Ring Dye Lasers; Theory and Experiment By K.K. L i , G. A r j a v a l i n g a m , A. Dienes, and J.R. Whinnery 40

T h e o r e t i c a l and Experimental I n v e s t i g a t i o n s o f C o l l i d i n g Pulse Mode-Locking (CPM). By W. D i e t e l , D. Kühlke, W. Rudolph, and B. Wilhelmi 45

Picosecond C a r r i e r Dynamics and Laser A c t i o n i n O p t i c a l l y Pumped Buried H e t e r o s t r u c t u r e Lasers By T.L. Koch, L.C. Chiu, Ch. Harder, and A. Y a r i v 49

O p t i c a l l y Pumped Semiconductor P l a t e l e t Lasers i n E x t e r n a l C a v i t i e s By M.M. Salour 53

V I I

Two Photon Pumped Bulk Semiconductor Laser f o r t h e Generation o f Picosecond Pulses. By Wei-Lou Cao, Fei-Ming Tong, De-Sen Shao, S.A. S t r o b e l , V.K. Mathur, and Chi H. Lee 57

The Pulse D u r a t i o n o f a D i s t r i b u t e d Feedback Dye Laser Under S i n g l e Pulse C o n d i t i o n s . By Z. Bor, Β. Racz, G. Szabo, and A. Müller 62

Picosecond D i s t r i b u t e d Feedback Dye Laser Tunable i n a Broad Sp e c t r a l Range. By A.N. Rubinov, I . Chesnulyavichus, and T.Sh. Efendiev .... 66

Modelocking o f a Wavelength Tunable High-Pressure C02~Laser by Synchronous M o d u l a t i o n o f a Broadband I n t r a c a v i t y S a t u r a b l e Absorber. By J.K. A j o , Y. H e f e t z , and A.V. Nurmikko 68

The Non-Mode-Locked Picosecond Laser By F. Armani, F. D e M a r t i n i , and P. Ma t a l o n i 71

A Novel Method f o r Generating Sub-Transform L i m i t e d Picosecond Nd:YAG Laser Pulses. By S.C. Hsu and H.S. Kwok 74

O p t i c a l Dephasing i n I n o r g a n i c Glasses By R.M. Shelby and R.M. MacFarlane 78

Part 11 U l t r a s h o r t M e a s u r i n g T e c h n i q u e s

Picosecond Holographic G r a t i n g Experiments i n Molecular Condensed Phases. By M.D. Fayer 82

S e l f - D i f f r a c t i o n from Laser-Induced O r i e n t a t i o n a l G r a t i n g s i n Semiconductors. By A.L. S m i r l , T.F. Boggess, B.S. Whe r r e t t , G.P. Perryman, and A. M i l l e r 87

A Picosecond Raman Technique w i t h R e s o l u t i o n Four Times B e t t e r than Obtained by Spontaneous Raman Spectroscopy By W. Z i n t h , M.C. Nuss, and W. Kais e r 91

Broadband CARS Probe Using t h e Picosecond Continuum By L.S. Goldberg 94

J i t t e r - F r e e Streak Camera System By W. Knox, T.M. Nordlund, and G. Mourou 98

E l e c t r i c a l T r a n s i e n t Sampling System w i t h Two Picosecond R e s o l u t i o n By J.A. Valdmanis, G. Mourou, and C.W. Gabel 101

H i g h - R e s o l u t i o n Picosecond M o d u l a t i o n Spectroscopy o f Near I n t e r b a n d Resonances i n Semiconductors By S. Sugai, J.H. H a r r i s , and A.V. Nurmikko 103

E l e c t r o n D i f f r a c t i o n i n the Picosecond Domain Steven W i l l i a m s o n and Gerhard Mourou and Synchronous A m p l i f i c a t i o n o f 70 fsec Pulses Using a Frequency-Doubled Nd:YAG Pumping Source. By J.D. Kafka, T. S i z e r I I , I.N. D u l i n g , C.W. Gabel, and G. Mourou 107

V I I I

Picosecond Time-Resolved P h o t o a c o u s t i c Spectroscopy By M. B e r n s t e i n , L.J. Rothberg, and K.S. Peters 112

Subpicosecond Pulse Shape Measurement and Modeling o f P a s s i v e l y Mode-Locked Dye Lasers I n c l u d i n g S a t u r a t i o n and S p a t i a l Hole Burning By J.-C. D i e l s , I.C. McMichael, J.J. F o n t a i n e , and C.Y. Wang 116

E x p e r i m e n t a l Demonstration o f a New Technique t o Measure U l t r a s h o r t Dephasing Times By J.C. D i e l s , W.C. Wang, P. Kumar, and R.K. J a i n 120

O p t i c a l Pulse Compression w i t h Reduced Wings By D. Grischkowsky and A.C. B a l a n t 123

P o l a r i t i o n - I n d u c e d Compensation o f Picosecond Pulse Broadening i n O p t i c a l F i b e r s . By G.W. Fehrenbach and M.M. Salour 126

Port III A d v a n c e s i n O p t o e l e c t r o n i c s

Generation and P u l s e w i d t h Measurement o f A m p l i f i e d U l t r a s h o r t U l t r a v i o l e t Laser Pulses i n Krypton F l u o r i d e . By P.H. Bucksbaum, J. Bokor, R.H. S t o r z , J.W. White, and D.H. Auston 130

Addressing and C o n t r o l o f High-Speed GaAs FET Logic C i r c u i t s w i t h Picosecond L i g h t Pulses By R.K. J a i n , J.E. Brown, and D.E. Snyder 134

Surface Metal-Oxide-Si 1icon-Oxide-Metal Picosecond P h o t o d e t e c t o r By S. Thaniyavarn and T.K. Gustafson 137

S o l i d - S t a t e D e t e c t o r f o r Single-Photon Measurements o f Fluorescence Decays w i t h 100 Picosecond FWHM R e s o l u t i o n By A. Andreoni, S. Cova, R. Cubeddu, and A. Longoni 141

Picosecond O p t o e l e c t r i c M o d u lation o f Millimeter-Waves i n GaAs Waveguide By M.G. L i , V.K. Mathur, Wei-Lou Cao, and Chi H. Lee 145

Synchroscan Streak Camera Measurements o f Mode-Propagation i n O p t i c a l F i b e r s . By J.P. W i l l s o n , W. S i b b e t t , and P.G. May 149

Part IV R e l a x a t i o n P h e n o m e n a in M o l e c u l a r P h y s i c s

Picosecond L i f e t i m e s and E f f i c i e n t Decay Channels o f V i b r a t i o n a l Models of Polyatomic Molecules i n L i q u i d s By C. Kolmeder, W. Z i n t h , and W. K a i s e r 154

V i b r a t i o n a l P o p u l a t i o n Decay and Dephasing o f Small and Large Polyatomic Molecules i n L i q u i d s By H. Graener, D. R e i s e r , H.R. T e l l e , and A. Laubereau 159

Mechanisms f o r U l t r a f a s t V i b r a t i o n a l Energy R e l a x a t i o n o f Polyatomic Kolecules. By S.F. F i s c h e r 164

I X

S t u d i e s o f the Generation and Energy R e l a x a t i o n i n Chemical I n t e r m e d i a t e s - D i v a l e n t Carbon Molecules and S i n g l e t Oxygen By E.V. Sitzmann, C. Dupuy, Y. Wang, and K.B. E i s e n t h a l 168

New Developments i n Picosecond Time-Resolved Fluorescence Spectroscopy: V i b r a t i o n a l R e l a x a t i o n Phenomena By B.P. Boczar and M.R. Topp 174

Picosecond Photon Echo and Coherent Raman S c a t t e r i n g Studies of Dephasing i n Mixed M o l e c u l a r C r y s t a l s By K. Duppen, D.P. Weitekamp, and D.A. Wiersma 179

Picosecond Laser Spectroscopy o f Molecules i n Supersonic J e t s : V i b r a t i o n a l Energy R e d i s t r i b u t i o n and Quantum Beats By A.H. Zewail 184

Picosecond S t u d i e s o f I n t r a m o l e c u l a r V i b r a t i o n a l R e d i s t r i b u t i o n i n S p r D i f l u o r o b e n z e n e Vapor. By R.A. C o v e l e s k i e , D.A. Dolson, S.C. Muchak , CS. Parmenter, and B.M. Stone 190

D i r e c t Picosecond Resolving o f Hot Luminescence Spectrum By J. Aaviksoo, A. A n i j a l g , A. F r e i b e r g , M. Le p i k , P. S a a r i , T. Tamm, and K. Timpmann 192

The Temperature Dependence o f Homogeneous and Inhomogeneous V i b r a t i o n a l L i n e w i d t h Broadening S t u d i e s Using Coherent Picosecond Stokes S c a t t e r i n g . By S.M. George, A.L. H a r r i s , M. Berg, and C.B. H a r r i s 196

A Picosecond CARS-Spectrometer Using Two Synchronously Mode-Locked CW Dye Lasers. By J. Kuhl and D. von der Linde 201

Picosecond S t u d i e s o f I n t r a m o l e c u l a r Charge T r a n s f e r Processes i n E x c i t e d Α-D Molecules By H. Sta e r k , R. M i t z k u s , W. Kühnle, and A. W e i l e r 205

Femtosecond T r a n s i e n t B i r e f r i n g e n c e i n CS2 By B . I . Greene and R.C. Farrow 209

Time-Resolved Observation o f M o l e c u l a r Dynamics i n L i q u i d s by Femtosecond I n t e r f e r o m e t r y . By C.L. Tang and J.M. Halbout 212

Time-Resolved Measurement o f N o n - l i n e a r S u s c e p t i b i l i t i e s by O p t i c a l Kerr E f f e c t . By J. Etchepare, G. G r i l l o n , R. A s t i e r , J.L. M a r t i n , C. Bruneau, and A. A n t o n e t t i 217

Subpicosecond Laser Spectroscopy: Pulse D i a g n o s t i c s and Molecular Dynamics i n L i q u i d s . By C. Kalpouzos, G.A. Kenney-Wal 1 ace, P.M. Kroger, E. Q u i t e v i s , and S.C. Wallace 221

Viscosity-Dependent I n t e r n a l R o t a t i o n i n Polymethine Dyes Measured by Picosecond Fluorescence Spectroscopy By A.C. Winkworth, A.D. Osborne, and G. P o r t e r 228

R o t a t i o n a l D i f f u s i o n i n Mixed S o l v e n t s Measured by Picosecond Fluorescence A n i s o t r o p y . By T. Doust and G.S. Beddard 232

X

I n v e s t i g a t i o n o f Level K i n e t i c s and R e o r i e n t a t i o n by Means o f Double Pulse E x c i t e d Fluorescence By D. Schubert, J. Schwarz, Η. Wabnitz, and Β. W i l h e l m i 235

Dynamics o f P h o t o i s o m e r i z a t i o n 3y G.R. Fleming, S.P. Velsko, and D.H. Waldeck 238

Evidence f o r the E x i s t e n c e o f a S h o r t - L i v e d Twisted E l e c t r o n i c S t a t e i n T r i phenyl methane Dyes 3y V. Sundström, Τ. G i l l b r o , and H. Bergström 242

K i n e t i c s o f S t i m u l a t e d and Spontaneous Emission o f Dye S o l u t i o n s Under Picosecond E x c i t a t i o n . By B.A. Bushuk, A.N. Rubinov, A.A. Murav'ov, and A.P. Stupak 246

Picosecond R e s o l u t i o n S t u d i e s o f Ground S t a t e Quantum Beats and Rapid C o l l i s i o n a l R e l a x a t i o n Processes i n Sodium Vapor By R.K. J a i n , H.W.K. Tom, and J.C. D i e l s 250

Part V P i c o s e c o n d C h e m i c a l P r o c e s s e s

U n i m o l e c u l a r Processes and V i b r a t i o n a l Energy Randomization By R.A. Marcus 254

Picosecond Dynamics o f l£ P h o t o d i s s o c i a t i o n . By P. Bado, P.Η. Berens, J.P. Bergsma, S.B. W i l s o n , K.R. W i l s o n , and E.J. H e l l e r 260

V i b r a t i o n a l P r e d i s s o c i a t i o n o f S-Tetrazine-Ar van der Waals-Molecules By J.J.F. Ramaekers, J. Langelaar, and R.P.H. R e t t s c h n i c k 264

Picosecond Laser Induced Fluorescence Probing o f NO2 Photofragments By P.E. Schoen, M.J. Marrone, and L.S. Goldberg 269

E x c i t e d S t a t e Proton T r a n s f e r i n 2-(2-'Hydroxyphenyl)-Benzoxazole By G.J. Woolfe, M. M e l z i g , S. Schneider, and F. Dörr 273

Picosecond Dynamics o f Unimolecular Ion P a i r Formation By K.G. Spears, T.H. Gray, and D. Huang 278

E f f e c t o f P o l y m e r i z a t i o n on the Fluorescence L i f e t i m e o f Eosin i n Water By Wei-Zhu L i n , Yong-Lian Zhang, and Xin-Dong Fang 282

Part VI U l t r a s h o r t P r o c e s s e s i n B i o l o g y

Picosecond Processes I n v o l v i n g CO, O2, and NO D e r i v a t i v e s o f Hemeproteins. By P.A. C o r n e l i u s and R.M. Hochstrasser 288

Femtosecond and Picosecond T r a n s i e n t Processes A f t e r P h o t o l y s i s o f Liganded Hemeproteins. By J.L. M a r t i n , C. P o y a r t , A. Migus, Y. L e c a r p e n t i e r , R. A s t i e r , and J.P. Chambaret 294

Picosecond Fluorescence Spectroscopy o f Hematoporphyrin D e r i v a t i v e and Related Porphyrins By M. Yamashita, T. Sato, K. Aizawa, and H. Kato 298

X I

Resonance Raman Spectra o f Picosecond T r a n s i e n t s : A p p l i c a t i o n t o B a c t e r i o r h o d o p s i n . By M.A. El-Sayed, Chung-Lu Hsieh, and M. N i c o l 302

Picosecond S t u d i e s o f B a c t e r i o r h o d o p s i n I n t e r m e d i a t e s from 11-cis Rhodopsin and 9 - c i s Rhodopsin. By J.-D. Spa!ink, M.L. Applebury, W. S p e r l i n g , A.H. Reynolds, and P.M. Rentzepis 307

M u l t i p l e Photon Processes i n Molecules Induced by Picosecond UV Laser Pulses. By V.S. Antonov, E.V. Khoroshi1 ova, N.P. Kuzmina, V.S. Letokhov, Yu.A. Matveetz, A.N. Shibanov, and S.E. Yegorov 310

P-BR and I t s Role i n the Photocycle o f B a c t e r i o r h o d o p s i n By T. G i l l b r o and V. Sundström 315

Picosecond L i n e a r Dichroism Spectroscopy o f R e t i n a l . By M.E. L i p p i t s c h , M. R i e g l e r , F.R. Aussenegg, L. M a r g u l i e s , and Y. Mazur 319

Picosecond A b s o r p t i o n Spectroscopy o f B i l i v e r d i n By M.E. L i p p i t s c h , M. R i e g l e r , A. L e i t n e r , and F.R. Aussenegg 323

Picosecond Time-Resolved Resonance Raman Spectroscopy o f t h e P h o t o l y s i s Product o f Oxy-Hemoglobin

By J. Terner, T.G. S p i r o , D.F. Voss, C. Paddock, and R.B. M i l e s ... 327

Part VII A p p l i c a t i o n s in S o l i d - S t a t e P h y s i c s

Picosecond Time-Resolved D e t e c t i o n o f Plasma Formation and Phase T r a n s i t i o n i n S i l i c o n By J.M. L i u , H. Kurz, and N. Bloembergen 332

Spectroscopy o f Picosecond R e l a x a t i o n Processes i n Semiconductors By D. von der Linde, Ν. F a b r i c i u s , J. Kühl, and Ε. Rosengart 336

Picosecond Spectroscopy o f E x c i t o n i c Molecules and High D e n s i t y E l e c t r o n - H o l e Plasma i n Direct-Gap Semiconductors. By S. Shionoya 341

Picosecond Time-Resolved Study o f H i g h l y E x c i t e d CuCl. By D. H u l i n , A. A n t o n e t t i , L.L. Chase, G. Hamoniaux, A. Migus, and A. Mysyrowicz 345

Picosecond Dynamics o f E x c i t o n i c P o l a r i t o n i n CuCl By Y. Aoyagi, Y. Segawa, and S. Namba 349

Picosecond Spectroscopy o f H i g h l y E x c i t e d GaAs and CdS By H. S a i t o , W. Graudszus, and E.O. Gobel 353

Non-Linear A t t e n u a t i o n o f E x c i t o n i c P o l a r i t o n Pulses i n CdSe By P. L a v a l l a r d and P.H. Duong 357

Time-Resolved Photo!uminescence Study o f η Type CdS and CdSe Ph o t o e l e c t r o d e By D. Huppert, Ζ. H a r z i o n , Ν. C r o i t o r u , and S. G o t t e s f e l d 360

Time-Resolved S p a t i a l Expansion o f the E l e c t r o n - H o l e Plasma i n P o l a r Semiconductors By A. Cornet, T. Amand, M. Pugnet, and M. Brousseau 364

X I I

Weak-Wave R e t a r d a t i o n and Phase-Conjugate S e l f - D e f o c u s i n g i n Si By E.W. Van S t r y l a n d , A.L. S m i r l , T.F. Boggess, and F.A. Hopf 368

U l t r a f a s t R e l a x a t i o n s o f Photoinduced C a r r i e r s i n Amorphous Semiconductors. By Z. Vardeny, J. S t r a i t , and J. Taue 372

P e r i o d i c R i p p l e S t r u c t u r e s on Semiconductors Under Picosecond Pulse I l l u m i n a t i o n . By P.M. Fauchet, Zhou Guosheng, and A.E. Siegman 376

T r a n s m i s s i o n o f Picosecond L a s e r - E x c i t e d Germanium a t Various Wavelengths. By C.Y. Leung and T.W. Nee 380

N o n l i n e a r I n t e r a c t i o n s i n Indium Antimonide By M. Hasselbeck and H.S. Kwok 384

Picosecond R e l a x a t i o n K i n e t i c s o f H i g h l y Photogenerated C a r r i e r s i n Semiconductors By S.S. Yao, M.R. Junnarkar, and R.R. A l f a n o 389

Picosecond R a d i a t i v e and N o n r a d i a t i v e Recombination i n Amorphous AS2S3 By T.E. O r l o w s k i , B.A. W e i n s t e i n , W.H. Knox, T.M. Nordlung, and G. Mourou 395

Index of Contributors 399

X I I I

Picosecond Lifetimes and Efficient Decay Channels of Vibrational Models of Polyatomic Molecules in Liquids

C. Kolmeder, W. Z i n t h , and W. Kais e r

Physik Department der Technischen Universität München, D-8000 München, Fed. Rep. o f Germany

C o n v i n c i n g e v i d e n c e i s p r e s e n t e d t h a t a n h a r m o n i c c o u p l i n g b e t w e e n f u n d a m e n t a l v i b r a t i o n a l modes and o v e r t o n e s o r c o m b i n a t i o n modes i s o f m a j o r i m p o r t a n c e f o r t h e l i f e t i m e o f v i b r a t i o n a l s t a t e s . The s e l e c t i o n r u l e s known t o h o l d f o r F e r m i r e s o n a n c e d e t e r m i n e t h e d e c a y c h a n n e l s . I n a number o f e x a m p l e s t h e d e c a y p a t h w a y s o f v i b r a t i o n a l e n e r g y w e r e o b s e r v e d e x p e r i m e n t a l l y by m e a s u r i n g t h e p o p u l a t i o n and d e p o p u l a t i o n o f s u b s e q u e n t v i b r a t i o n s . D r a s t i c v a r i a t i o n s o f v i b r a t i o n a l l i f e t i m e s w e r e f o u n d f o r d i f f e r e n t v i b r a t i o n s o f t h e same m o l e c u l e .

M o l e c u l e s a r e f i r s t e x c i t e d by an u l t r a s h o r t r e s o n a n t i n f r a r e d p u l s e and t h e i n s t a n t a n e o u s d e g r e e o f e x c i t a t i o n i s m o n i t o r e d by o b s e r v i n g t h e a n t i - S t o k e s Raman s i g n a l o f a d e l a y e d p r o b e p u l s e . D i f f e r e n t v i b r a t i o n a l modes a r e d i s t i n g u i s h e d by t h e i r c h a r a c t e r ­i s t i c a n t i - S t o k e s f r e q u e n c y .

We h a v e i n v e s t i g a t e d numerous m o l e c u l e s and f o u n d w i d e l y v a r y ­i n g v a l u e s o f t h e p o p u l a t i o n l i f e - t i m e s b e t w e e n 1 p s and 240 p s i n p o l y a t o m i c m o l e c u l e s a t room t e m p e r a t u r e / 1 , 2 / . S p e c i a l a t t e n t i o n was p a i d t o t h e C H - s t r e t c h i n g modes i n t h e f r e q u e n c y r a n g e o f 3 0 0 0 ± 1 0 0 cm" 1.

V i b r a t i o n a l e n e r g y i s t r a n s f e r r e d f r o m t h e C H - s t r e t c h i n g modes (^3000 cm"1) v i a o v e r t o n e s and c o m b i n a t i o n modes t o l o w e r e n e r g y s t a t e s . I n t r a m o l e c u l a r a n h a r m o n i c c o u p l i n g , t h e F e r m i r e s o n a n c e , m a n i f e s t s i t s e l f i n t h e i n f r a r e d and Raman s p e c t r a . O v e r t o n e s and h i g h e r o r d e r c o m b i n a t i o n modes b o r r o w i n t e n s i t y f r o m CH-s t r e t c h i n g modes. We d e f i n e a s a m e a s u r e o f F e r m i - r e s o n a n c e m i x i n g t h e i n t e n s i t y r a t i o , R, b e t w e e n t h e f i n a l a nd i n i t i a l s t a t e t a k e n f r o m t h e i n f r a r e d o r Raman s p e c t r u m . I n a r e c e n t p u b l i c a t i o n a f o r m u l a was d e r i v e d w h i c h a l l o w s t o e s t i m a t e t h e l i f e t i m e T«| o f v i b r a t i o n a l s t a t e s :

T 1 = N ( 1 ~ R ) 2 R " 1 e x p ( o ) / f i ) 2 / 3 T 2 ( f ) ( 1 )

Ν c o r r e s p o n d s t o t h e number o f s t a t e s i n i t i a l l y e x c i t e d , R i s a m e a s u r e o f t h e F e r m i r e s o n a n c e , and T 2 ( f ) s t a n d s f o r t h e d e -p h a s i n g t i m e o f t h e f i n a l s t a t e . T 2 ( f ) may be e s t i m a t e d f r o m t h e Raman l i n e - w i d t h Δν a s T 2 ( f ) = (2πσΔν)"' ι ( T 2 ( f ) i s e q u a l t o T 2 / 2 m e a s u r e d i n c o h e r e n t Raman e x p e r i m e n t s ) . The f r e q u e n c y ω r e p r e s e n t s t h e e n e r g y d i f f e r e n c e b e t w e e n t h e i n i t i a l a n d f i n a l s t a t e . Ω h a s a v a l u e c l o s e t o 100 cm~^ .

As an e x a m p l e f o r t h e i m p o r t a n c e o f F e r m i r e s o n a n c e we p r e s e n t d a t a o f t h e two m o l e c u l e s 1 , 1 - d i c h l o r o e t h e n e and t r a n s 1 , 2 -

154

d i c h l o r o e t h e n e w h i c h a r e made up o f t h e same atoms; o n l y two a t o m s h a v e e x c h a n g e d t h e i r p o s i t i o n s . The i n f r a r e d a nd Raman s p - e c t r a b e t w e e n 2950 cm""1 and 3250 cm"*1 o f b o t h m o l e c u l e s a r e d e p i c t e d i n F i g . 1 . T h e r e a r e d r a s t i c d i f f e r e n c e s i n t h e a n h a r -mo:nic c o u p l i n g o f t h e C H - s t r e t c h i n g modes. I n F i g . 1 a we s e e s t r o n g F e r m i r e s o n a n c e o f CH2=CCl2 b e t w e e n t h e f u n d a m e n t a l v-j a n d V 2 + V 3 ,

b o t h o f A<| symmetry and b e t w e e n t h e f u n d a m e n t a l V7 and v2+vg+vi 1 , b o t h o f B-j symmetry / 3 / . T h i s o b s e r v a t i o n s u g g e s t s t h a t we h a v e t o c o n s i d e r a t l e a s t two d e c a y c h a n n e l s f o r t h e C ^ - s t r e t c h i n g modes. F o r t h e d e c a y v^ -+ v2+\>3 we e s t i m a t e t h e i n t e n s i t y r a t i o R = 0 . 2 ± 0 . 0 5 and c a l c u l a t e T 2 ( f ) = 0.3 p s f r o m t h e Raman l i n e -w i d t h o f Δν = 17 cm""1. W i t h N=1 and ω = 45 cm""1 we c a l c u l a t e f r o m ( 1 ) a v a l u e o f T<| = 4±2 p s . F o r t h e s e c o n d d e c a y c h a n n e l \>7 -> v2+vg + v<ii we h a v e t o t a k e a s h o r t d e p h a s i n g t i m e T 2 ( f ) o f t h e c o m b i n a t i o n mode. We e s t i m a t e T 2 ( v 2 + v 6 + v 1 -j) ~ 0.2 ps fr o m t h e o b s e r v e d l i n e w i d t h . W i t h R = 0 . 6 ± 0 . 1 , N=1 and ω = 45 cm""1 we c a l c u l a t e T>| = 1.5 p s .

A c c o r d i n g t o F i g s . 1a and 1b t h e s y m m e t r i c ( v j ) and a s y m m e t r i c (v-7) C l ^ - s t r e t c h i n g v i b r a t i o n s a r e s e p a r a t e d by 100 cm" 1. We e s t i m a t e an e n e r g y - t r a n s f e r t i m e b e t w e e n t h e C H 2 " - s t r e t c h i n g modes o f T>|(v-| -> V 7 ) - 3.3 p s u s i n g t h e f o r m u l a T^ (ω-j = T2 (ω-j ) e x p (ω/Ω) 2 / 3 , w h e r e Τ 2 ( ω ι ) was t a k e n from t h e Raman s p e c t r u m .

The e s t i m a t e s g i v e n h e r e i n d i c a t e t h a t v i b r a t i o n a l e n e r g y f l o w s f a s t e r o u t o f t h e ν η mode t h a n i t i s s u p p l i e d by t h e t r a n s ­f e r ν 1 -> V7. F o r t h e e x c i t e d and i n t e r r o g a t e d mode v<j we s i m p l y a d d t h e two d e c a y r a t e s f o r t h e two d e c a y c h a n n e l s v-j -> V7 and v 1 v 2 + v 3 a n c ^ a r r i v e a t a l i f e t i m e T-|(v<|) - 2 p s .

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Frequency ν Ccm'j Frequency vCcrrf 1!

F i g . 1 I n f r a r e d a b s o r p t i o n ( a ) and Raman (b) s p e c t r a o f CH2CCI2 between 2950 and 3250 cm" 1. Two c o m b i n a t i o n t o n e s a r e i n s t r o n g Ferrr.i r e s o n a n c e w i t h t h e two C H - s t r e t c h i n g modes v-| and V7. I n f r a r e d a b s o r p t i o n ( c ) and Raman (d) s p e c t r a o f t r a n s CHC1CHC1. T h e r e i s l e s s F e r m i - r e s o n a n c e m i x i n g t h a n i n C H 2 C C l 2 .

155

Ο 10 20 30

J I I L 0 10 20 30

D e l a y T i m e t 0 C p s J

F i g . 2 A n t i - S t o k e s s c a t t e r i n g s i g n a l v e r s u s d e l a y t i m e o f t h e p r o b i n g p u l s e . ( a ) C H 2 C C 1 2 i n C C 1 4 ( c = 0.35 m . f . ) . The d e c a y o f t h e C H 2 ~ s t r e t c h i n g mode a t 3036 cnv*"1 i s shown. (b) t r a n s CHC1CHC1 i n C C 1 4 ( c = 0.35 m . f . ) . The C H - s t r e t c h i n g mode a t 3084 cm" 1 i s e x c i t e d and t h e mode a t 3073 cm" 1 i s m o n i t o r e d . The b r o k e n c u r v e s a r e t h e c r o s s - c o r r e l a t i o n f u n c t i o n s o f t h e I R e x ­c i t i n g and g r e e n p r o b i n g p u l s e s .

I n F i g . 2 a we p r e s e n t e x p e r i m e n t a l d a t a o f t h e d i r e c t d e t e r ­m i n a t i o n o f t h e T-j v a l u e . The s c a t t e r e d Raman s i g n a l o f t h e v-j mode r i s e s t o a s l i g h t l y d e l a y e d maximum d u r i n g t h e e x c i t a t i o n p r o c e s s and d e c a y s w i t h a r e l a x a t i o n t i m e o f T-j d i s c u s s e d i n t h e p r e c e d i n g p a r a g r a p h . The b r o k e n c u r v e s i n F i g . 2 a r e c r o s s -c o r r e l a t i o n c u r v e s o f t h e e x c i t a t i o n and p r o b i n g p u l s e ; t h e y d e t e r m i n e t h e z e r o p o i n t on t h e t i m e a x i s and g i v e a good i n d i ­c a t i o n o f t h e t i m e r e s o l u t i o n o f t h e e x p e r i m e n t .

I n F i g . 1 c we s e e t h e i n f r a r e d a c t i v e C H - s t r e t c h i n g mode V9 and i n F i g . l d t h e Raman a c t i v e s y m m e t r i c v-j mode o f t r a n s CHC1CHC1 H e r e we f i n d a c o n s i d e r a b l y s m a l l e r F e r m i r e s o n a n c e . The Raman s p e c t r u m o f F i g . l d s u g g e s t s some a n h a r m o n i c c o u p l i n g b e t w e e n v-j and 2 v 2 , b o t h o f A symmetry / 3 / . W i t h t h e v a l u e s R = 0 . 1 5 ± 0 . 0 2 , T 2 = 0.3 p s , N=2 and ω = 80 cm" 1 we c a l c u l a t e T 1 = 13 p s . I t s h o u l d be n o t e d t h a t t h e r e m i g h t be a d d i t i o n a l weak F e r m i r e s o n a n c e b e t w e e n t h e ν 9 mode and h i g h e r c o m b i n a t i o n modes ( e . g . ν 2 + ν 5 + ν 1 θ ) b u r r i e d u n d e r t h e h i g h f r e q u e n c y t a i l o f t h e V9 f u n d a ­m e n t a l . T h e s e a d d i t i o n a l d e c a y c h a n n e l s may r e d u c e somewhat t h e e s t i m a t e d T-| v a l u e .

The t i m e d e p e n d e n c e o f t h e C H - s t r e t c h i n g modes o f t r a n s CHC1CHC i s d e p i c t e d i n F i g . 2 b . The m o l e c u l e i s e x c i t e d v i a t h e V9 mode a t 3084 cm" 1 and t h e p o p u l a t i o n o f t h e mode a t 3073 cm" 1 i s m o n i t o r e d by a n t i - S t o k e s Raman s c a t t e r i n g . The r a p i d r i s e o f t h e Raman s i g n a l , i . e . t h e f a s t p o p u l a t i o n o f t h e ν Ί mode, g i v e s

156

c l e a r e v i d e n c e o f t h e q u i c k e n e r g y e x c h a n g e b e t w e e n t h e two CH f u n d a m e n t a l s ν^ and V Q . The d e c a y o f t h e s i g n a l c u r v e s u g g e s t s a l o n g l i f e t i m e o f t h e two C H - s t r e t c h i n g modes o f T 1 = 10±2 p s . T h i s number i s i n good a g r e e m e n t w i t h t h e v a l u e e s t i m a t e d a b o v e . The s m a l l i n t r a m o l e c u l a r c o u p l i n g g i v e s r i s e t o t h e l o n g e r v i b r a ­t i o n a l l i f e t i m e .

T h e v i b r a t i o n a l s t a t e s o f a c e t y l e n e a r e w e l l documented i n t h e l i t e r a t u r e / 4 / . I n s p e c t i o n o f t h e e n e r g y - l e v e l s y s t e m ( s e e F i g . 3 ) s u g g e s t s t h e f o l l o w i n g i n t e r e s t i n g s i t u a t i o n s : ( i ) E n e r g y i n t h e h i g h l y i n g C H - s t r e t c h i n g modes a r o u n d 3200 cm" 1 r e a d i l y f l o w s i n t o s e v e r a l c o m b i n a t i o n modes, a l l o f w h i c h c o m p r i s e t h e symme­t r i c C E C - s t r e t c h i n g mode a t v 2 = 1968 cm" 1. ( i i ) The e n e r g y t r a n s ­f e r f r o m t h e v 2 mode t o n e i g h b o r i n g c o m b i n a t i o n modes i s f o r b i d d e n by s y m m e t r y s e l e c t i o n r u l e s . T h u s we e x p e c t a l o n g p o p u l a t i o n l i f e - t i m e o f t h e v 2 mode.

E x p e r i m e n t a l l y we i n v e s t i g a t e d a s o l u t i o n o f C 2 H 2 i n C C I 4 . A c e t y l e n e m o l e c u l e s f i r s t a r e v i b r a t i o n a l l y e x c i t e d v i a t h e i n f r a ­r e d a c t i v e C H - s t r e t c h i n g mode V3 = 3287 cm" 1 and t h e p o p u l a t i o n and d e p o p u l a t i o n o f t h e v 2 mode a t 19 68 cm" 1 i s m o n i t o r e d . I n F i g . 4 we i n d e e d s e e a r a p i d p o p u l a t i o n o f t h e v 2 mode w i t h i n < 3 p s and a v e r y s l o w d e p o p u l a t i o n w i t h a t i m e c o n s t a n t o f 240 p s . The -j2 mode i n a c e t y l e n e r e p r e s e n t s a b o t t l e - n e c k s t a t e . I t e x ­h i b i t s t h e l o n g e s t r e l a x a t i o n t i m e o b s e r v e d s o f a r i n a p o l y a t o m i c m o l e c u l e i n t h e l i q u i d s t a t e a t room t e m p e r a t u r e .

3000

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157

v e x c = 3265 cm

ν Λ , Λ κ . - 1968 cm '

100 Delay Time t D C p s 3

200

F i g . 4 A n t i - S t o k e s s c a t t e r i n g s i g n a l o f C 2 H 2 i n C C 1 4 v e r s u s de­l a y t i m e . E x c i t a t i o n f r e q u e n c y i s 3265 cm" 1. The d e c a y o f t h e C E C mode a t 1968 cm" 1 i s m o n i t o r e d .

R e f e r e n c e s

1 A. F e n d t , S . F . F i s c h e r , and W. K a i s e r , Chem. P h y s . _57, 55 (1981; 2 A. F e n d t , S . F . F i s c h e r , and W. K a i s e r , Chem. P h y s . L e t t . -82,

350 ( 1 9 8 1 ) 3 L.M. S v e r d l o v , M.A. K o v n e r , E.P. K r a i n o v , V i b r a t i o n a l S p e c t r a

o f P o l y a t o m i c M o l e c u l e s , W i l e y , New Y o r k , N.Y. 1974, and r e ­f e r e n c e s t h e r e i n

4 G. H e r z b e r g , I n f r a r e d and Raman s p e c t r a o f P o l y a t o m i c M o l e c u l e s von N o s t r a n d , P r i n c e t o n , N.J. 1945

158