5466
J . Phys. Chem. 1988, 92. 5466-5469
(HF)* which are present in appreciable concentrations under equilibrium conditions86may profit from the simplification of their IR spectra in supersonic jets. The possibility of simplification of infrared spectra is probably the most interesting potential of the jet-FTIR technique. Even for small polyatomic molecules ordinary IR spectra are often extremly complex and cannot be assigned and analyzed by traditional techniques. CHF3 presented in this paper provides a striking example of what kind of simplification can be expected in such spectra. However, in this particular case part of the spectrum could be assigned before, putting up with exceptional difficulties. For two other freons, CCIF3 and CBrF3, we have shown that spectra which could not be analyzed before became almost textbook examples for analysis after observation in our jet-FTIR spectrometer ~ y s t e m . ' ~There , ~ ~ are numerous longstanding similar problems in the analysis of IR spectra of moderately complex polyatomics where there is now great hope of an easy solution. Several aspects of simplifying IR spectra by jet cooling have been discussed recently by Davies and MortonJones.65 Even more intriguing is the investigation of large polyatomic molecules which under ordinary conditions show broad unstruc-
tured, continuous spectra because of thermal congestion. Jet-FTIR spectroscopy offers the potential to answer the fundamental question of what these spectra will look like in the low-temperature limit when the thermal congestion is removed. The vibrational structure of such spectra would provide essential information on the intramolecular vibrational dynamics and statistical mechanics of large polyatomic m01ecuIes.~~
(83) Baldacchini, G.; Marchetti, S.; Montelatici, V. Chem. Phys. Lett. 1982, 91, 423. (84) Chakraborti, P. K.; Kartha, V. B.; Talukdar, R. K.; Bajaj, P. N.; Joshi, A. Chem. Phys. Lett. 1983, 101, 397. (85) Matsumoto, Y.; Takami, M. J . Chem. Phys. 1986, 85, 3785. (86) Puttkamer, K. v.; Quack, M. Mol. Phys. 1987, 62, 1047.
SOC.1983. 75. 197.
Acknowledgment. This article is dedicated to the memory of E. K. C. Lee, whose loss is greatly felt by us. He was among the first visitors of our group in Zurich in 1983, with whom we discussed our earliest efforts in jet-FTIR spectroscopy. The early experiments profited from the help of H.-R. Dubal and discussions with M. Faubel and H. van den Bergh. The expert help of E. Peyer in the construction of the jet apparatus is acknowledged, as well as help from and discussions and correspondence with H. Burger, G. Graner, H. Hollenstein, P. Locher, and J. Reuss. Our work is supported financially by the Schweizerischer Schulrat and the Schweizerischer Nationalfonds. Registry No. CO, 630-08-0; NO, 10102-43-9; CH4, 74-82-8; CzH2, 74-86-2; CH,CCH, 74-99-7; CHF3, 75-46-7. (87) httkamer, K. v.; Dubal, H.-R.; Quack, M. Faraday Discuss. Chem. (88) Michelot, F.; Moret-Bailly, J.; Fox, K. J . Chem. Phys. 1974, 60, 2606; Ibid. 1974, 60, 2610. (89) (a) Oldani, M.; Andrist, M.; Bauder, A,; Robiette, A. G. J. Mol. Spectrosc. 1985, 110, 93. (b) Hilico, J. C.;Loete. M.; Champion. P.; Destombes, J. C.; Bogey, M. J Mol. Spectrosc. 1987, 122, 381..
Pressure Dependence on Excited-State Intramolecular Electron-Transfer Dynamics in Polar Solvents D. H u p p e d and P. M. Rentzepis* Department of Chemistry, University of California, Irvine, California 9271 7 (Received: February 25, 1988)
The effect of pressure on intramolecular electron transfer of p-(9-anthryl)-N,N-dimethylaniline(ADMA) has been studied by means of picosecond time-resolved fluorescence It is shown that the intramolecular electron-transfer rate is related to the longitudinal dielectric relaxation time.
Introduction Attention has been focused recently on the role of the solvent in fast electron-transfer (ET) reactions. Experimental results indicate that the relaxation of the initially excited state to a charge-transfer state is governed by the longitudinal relaxation time, TL,'-' which is related to the dielectric relaxation time, T D , of t h e solvent by the expression 71 = (t-/%)TD (1) In addition, theoretical work6'* supports the experimental findings that the relaxations of initial events in molecular electron-transfer reactions are dominated by the longitudinal relaxation times. In previous published work on p(dimethy1amino) benzonitrile (DMABN),13*14we reported that the fluorescence decay of the initial excited nonpolar electronic state to the final charge-transfer state was nonexponential. Time-dependent fluorescence studies on coumarin 153, in alcohols and other solvents, have shown that3 the decay from the initial excited state to the (final) solvated charge-transfer state is nonexponential. Grabowski et allSaand 'Permanent address: Department of Chemistry, University of Tel-Aviv, Tel-Aviv, Israel.
0022-3654/88/2092-5466$01.50/0
Heisel and Miehel5" focus attention on the viscosity dependence of internal motion to form the twisted intramolecular charge(1) Kosower, E. M.; Huppert, D. Chem. Phys. Lett. 1983, 96, 433. (2) (a) Su,S. G.; Simon, J. D. Chem. Phys. Lett. 1986,132, 345. (b) Su, S . G.; Simon, J. D. J . Chem. Phys. 1986,90,6475. (c) Su, S. G.; Simon, J. D.J . Phys. Chem. 1987, 91, 2693. (3) Maroncelli, M.; Fleming, G. R. J . Chem. Phys. 1987, 86, 6221. (4) McGuire, M.; McLendon, G. J . Phys. Chem. 1986, 90, 2549. (5) (a) McManis, G. E.; Golovin, M. N.; Weaver, M. J. J . Phys. Chem. 1986, 90, 6563. (b) McManis, G. E.; Mishra, A. K.; Weaver, M. J. J. Chem. Phys. 1987,86, 5550. (6) Mozumder, S. J. Chem. Phys. 1%9,50,3153. See. especially Appendix I in: Electron-Soluent and Anion-Solvent Interactionr; Kevan, L., Webster, B. C., Eds.; Elsever: Amsterdam, 1976; pp 139-173. (7) Hubbard, J.; Onsayer, L. J . Chem. Phys. 1977, 67, 4850. (8) Zusman, L. D. Chem. Phys. 1980, 49, 295. (9) Sumi, H.; Marcus, R. A. J . Chem. Phys. 1986, 84, 4894. (10) (a) Rips, I.; Jortner, J. Chem. Phys. Lett. 1987, 133, 411. (b) Rips, 1.; Jortner, J. j . Chem. Phys., in press. (11) Calef, D. F.; Wolynes, P. G. J . Chem. Phys. 1983, 87, 3387. (12) (a) Van der Zwan, G.; Hynes, J. T. Chem. Phys. 1984, 90, 21. (b) Van der Zwan, G.; Hynes, J. T. Chem. Phys. 1982, 76, 2993. (13) Huppert, D.; Rand, S. D.; Rentzepis, P. M.; Barbara, P. F.; Struve, W. S.; Grabowski, Z. R. J. Chem. Phys. 1981 75, 5714.
0 1988 American Chemical Society
Electron-Transfer Dynamics in Polar Solvents
The Journal of Physical Chemistry, Vol. 92, No. 19, 1988 5467
TABLE I: Lifetime of the Decay and Rise of ADMA Nonpolar and Charge-Transfer States Trip, PS
solvent ethanol 1-propanol 1-butanol 1-pentanol 1 -hexanol 1-heptanol 1-octanol 1-decanol 1,2-ethanedioI 1,3-propanediol 1,4-butanediol
viscosity (20 " C ) 1.2 2.26 3.0 3.1 5.32 7.0 9.15 14.3 20.0 50.0 65.0
71:
PS 430 661 927 1210 1465 1780 2019
ADMA (20 "C) shortc longd
-
-10 20 35 50 70 90 150
70 100 180 250 350 500 900
