J. Phys. Chem. 1982, 86, 3177-3184
tions and rate constants being the following: e,- + Trp, k = 3.6 X lo8 M-' s-l (ref 38), 1.2 X lo8 M-' s-l (ref 39); e,, - e, 5 X log M-' s-l (ref 38). should also be emphasized that the absence of a notable decay of e, in the picosecond-nanosecond time range does not characterize specifically IH, and Trp, photoionization. A similar situation has been encountered in particular for aqueous phenol and phenolate photoionization.15J8 We have also shown that the 440-nm absorbance is negligible at 1.6 ns. This fact confirms that the triplet state arises from the relaxed fluorescent state and not from a nonrelaxed excited complex state or an excited FranckCondon state. This conclusion agrees with that of Klein et based on quenching experiments. The N-H bond dissociation yield is known to be negligible for IH in water?p4 However, we have noticed a high 530-nm absorbance at 1.6 ns, attributable to the neutral I. radical. This assumption is based on the relatively weak absorption of the radical cation IH+. at 530 nm.' If this is correct, N-H bond dissociation of IH could arise from a consecutive biphotonic process.
It
So
+ hv
+
Conclusion The picosecond laser-induced photoionization of aqueous indole and tryptophan at 265 nm can be satisfactorily represented by the following reaction scheme: (37)M.T.Pailthorpe, J. P. Bonjour, and C. H. Nicolls, Photochem. Photobiol., 17, 209 (1973). (38)M.Anbar, M.Bambenek, and A. B. Roes, Natl. Stand. Ref. Data Ser. (U.S., Natl. Bur. Stand.), 43 (1973). (39)H. Templer and P. J. Thietlethwaite,Photochem. Photobiol., 23, 79 (1976).
3177
265 nm
S1*nr
--- + + -
Si*nr (nonrelaxed excited state) Si*nr R+ + e,,;
SI* (relaxed fluorescent state)
(1) (2)
(3)
SI*
So (internal conversion)
(4)
S1*
T (intersystem crossing)
(5)
S1*
So
Si*nr or S1*
hv' (fluorescence) hu
(6)
R+ + e,,;
(7)
We have shown, at least in the case of indole, that the monophotonic e,,; generation takes place from an unrelaxed excited singlet state, and we believe that this conclusion can be extended to tryptophan. The sequential biphotonic process described by reactions 1 7 or 1 3 + 7 depends on the laser intensity and is more efficient in tryptophan. Intersystem crossing to the triplet state involves the fluorescent state, and a possible N-H bond dissociation can be due to a consecutive biphotonic process. It must be emphasized that the extent of the recombination of e,,< and IH+- or Trp+. produced by either a monophotonic or a consecutive biphotonic process is relatively small, or zero, in the picosecond time range.
+
+
Acknowledgment. We thank Professor L. I. Grossweiner (Illinois Institute of Technology, Chicago), Professor G. R. Fleming (The University of Chicago),Professor H. Lami (UniversiW Louis Pasteur, Strasbourg), and Dr. R. Lopez Delgado (UniversiW de Paris-Sud, Orsay) for sending us copies of their work before publication and for several fruitful discussions.
Laser-Photolysls Study of the External Magnetic Field Effect upon the Photochemical Processes of Carbonyl Compounds in Micelles Yoshlo Sakaguchi, Hlsaharu Hayashi, and Saburo Nagakura' The Institute of phvslcel end Chemical Research, Weko, Saitema 351, Japan (Re~slved:December 16, 198 1; I n Final F m : March 24, 1982)
The external magnetic field effects upon the primary photochemical processes of benzophenone and dibenzyl ketone in sodium dodecyl sulfate (SDS) and other micelles have been studied by nanosecond laser photolysis. The decay rate constants of the ketyl and benzyl radicals in the micelles were found to decrease in the presence of weak external magnetic fields and were determined for the ketyl radical in the SDS micelle as (2.82 f 0.05) X loe s-l at zero field and (1.89 f 0.05) X los s-l at 700 G. On the other hand, the amount of the escaping ketyl and benzyl radicals was found to increase in the presence of magnetic fields. Magnetic isotope effects were studied and the decay rate constants in SDS micelles at 700 G were determined as (2.16 f 0.05) X lo6 s-l for (C6H5)z13COH and (1.86 f 0.05) X lo6 s-l for (C6D5),COH.The observed magnetic field and magnetic isotope effects were interpreted in terms of reductions in the triplet-singlet conversion rates of intermediate radical pairs in the presence of magnetic fields.
Introduction The magnetic field effect upon chemical reactions in solutions has been studied extensively and successfully during the past decade by measuring the product yields of photochemica1172or thermochemical3reactions and also *Address correspondence to this author at the Institute for Molecular Science, Myodaiji, Okazaki, Aichi 444 Japan. 0022-3654/82/2088-3177$01.25/0
by detecting directly reaction intermediates by pulse radiolysis4or laser photolysis." Concerning the interme(1)Y.Tanimoto, H. Hayashi, S. Nagakura, N. Sakuragi, and K. Tokumaru, Chem. Phy5. Lett., 41,267 (1976). (2)Y.Sakaguchi, H.Hayashi, and S. Nagakura, Bull. Chem. Soc. Jpn., 53, 39 (1980). (3)R.Z.Sagdeev, Yu. N. Molin,K. M.Salikhov, T. V. Leshina, M. A. Kamha, and S. M.Shein, o g . Magn. Reaon., 5 , 603 (1973).
@ 1982 American Chemical Society
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diates, one expects the magnetic field to affect not only their yields but also their dynamical behavior. The magnetic field effect on the dynamical behavior, however, has been studied only by pulse r a d i ~ l y s i s .Under ~ ~ these circumstances, we have extended laser-photolysis studies to the magnetic field effect on the dynamical behavior of some transient intermediate^.^"^ The magnetic field effect upon chemical reactions in solutions was proved to occur through the singlet-triplet conversion of the intermediate radical pairs8ye promoted by the electronic Zeeman and electron-nuclear hyperfine coupling (abbreviated hereafter to hfc) interactions of the component radicals.'O The magnetic isotope effect was also shown to occur through the hfc mechanism." These effects were found to be enhanced by the confinement of the radical pairs in micelles.12 We have investigated the magnetic field7hband magnetic isotope13effects on the primary photochemical processes of some carbonyl compounds in some micelles with nanosecond laser photolysis and have succeeded in observing directly the effects not only on the yield but also on the dynamical behavior of the reaction intermediates. Experimental Section Benzophenone (BP), dibenzyl ketone (DBK), sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium chloride and bromide (CTAC and CTAB), and Brij 35 were purified by repeated recrystallization from ethanol, methanol, methanol-ethanol mixture, tetrahydrofuran, methanol-tetrahydrofuran mixture, and bemenen-hexane mixture, respectively. Benzophenone-dlo (99 atom % D, Merck Sharp and Dohme, BP-dlo), benzophenone-carbonyl-13C (90 atom % 13C,Merck Sharp and Dohme, BP13C),and copper(I1) chloride (CuC12.2H20,Koso Chemical) were used without further purification. Spectrograde 2propanol, cyclohexane, and n-hexane were used as solvents without further purification. Water was deionized and distilled. The micellar solutions were made by sonication. Laser photolysis experiments were performed on degassed solutions at room temperature by using the fourth harmonic (266 nm) of a Quanta-Ray DCR-1 Nd:YAG laser as an exciting light source. The laser pulse width was 5 (4)(a) B. Brocklehurst, R. S. Dixon, E. M. Gardy, V. J. Lopata, M. J. Quinn, A. Singh, and F. P. Sargent, Chem. Phys. Lett., 28,361 (1974); (b) F.P.Sargent, B. Brocklehurst, R. S. Dixon, E. M. Gardy, V. J. Lopata, and A. Singh, J. Phys. Chem., 81,815 (1977). (5)(a) K. Schulten, H. Staerk, A. Weller, H. J. Werner, and B. Nickel, 2.Phys. Chem. (Frankfurt am Main), 101,371(1976);(b) H. J. Werner, Z. Schulten, and K. Schulten, J. Chem. Phys., 67,646 (1977);(c) H. J. Werner, H. Staerk, and A. Weller, ibid., 68,2419(1978);(d) K. Schulten and P. G. Wolynes, ibid., 68,3292 (1978). (6)M. E.Michel-Beyerle, R. Haberkorn, W. Bube, E. Steffens, H. Schrder, H. J. Neusser, E. W. Schlag, and H. Seidlitz, Chem. Phys., 17, 139 (1976). (7)The preliminary results have been published (a) Y. Sakaguchi, S. Nagakura, and H. Hayashi, Chem. Phys. Lett., 72,420(1980);(b) H. Hayashi, Y. Sakaguchi, and S. Nagakura, Chem. Lett., 1149 (1980).Turro et al. also studied the magnetic field effect upon the dynamical behavior of photochemical reaction intermediates by laser photolysis: (c) N. J. Turro, M. F. Chow, C. J. Chung, Y. Tanimoto, and G. C. Weed, J. Am. Chem. Soc., 103,4575(1981);(d) J. C. Scaiano and E. B. Abuin, Chem. Phys. Lett., 81,209 (1981). (8)R. Kaptain, J. Am. Chem. SOC.,94,6251 (1972). (9)H. Hayashi and S. Nagakura, Bull. Chem. SOC.Jpn., 51, 2862 (1978). (10)H. Hayashi, K. Itoh, and S. Nagakura, Bull. Chem. SOC.Jpn., 39, 199 (1966);K. Itoh, H. Hayashi, and S. Nagakura, Mol. Phys., 17,561 (1969). (11)A. L.Buchachenco, E. M. Galimov, V. V. Ershov, G. A. Nikiforov, and A. D. Pershin, Dokl. Akad. Nauk SSSR, 228, 379 (1976). (12)(a) N. J. Turro, B. Kraeutler, and D. R. Anderson, J . Am. Chem. Soc., 101,7435(1979);(b) N. J. Turro and W. R. Cherry, ibid., 100,7431 (1978);(c) N. J. Turro and B. Kraeutler, ibid., 100,7432 (1978). (13)Preliminary results: (a) Y.Sakaguchi, Ph.D. Thesis, The University of Tokyo, 1980; (b) Y.Sakaguchi, S. Nagakura, A. Minoh, and H. Hayashi, Chem. Phys. Lett., 82,213 (1981).
Sakaguchi et al.
l
a
0
300
50 0 h /nm
GOO
600
Flgure 1. Transient absorptlon spectra of a micellar SDS (8 X lo-* mol dm3) solution of BP (1 X lo3 mol dm3) observed (a) immediately, (b) 150 ns, (c) 500 ns, and (d) 1.5 ps after excitation.
a
/2\ 400
A/nm
500
600
s
Flgure 2. Transient absorption s ectra of a micellar CTAC (3 X lo-* mol dm3) solution of BP (1 X 10 mol dm3) observed (a) immediately, (b) 200 ns, (c) 500 ns, and (d) 1 pus after excitation.
ns. The details of the laser photolysis apparatus were published e1~ewhere.l~ For the usual observation of transient behavior, a Tektronix 485 oscilloscope was used. For more accurate measurements, an Iwatsu DM-901 digital memory (10 ns/point, 8 bit) controlled by an LSI-11 micro~omputerl~ was used. The output of the digital memory was treated by a YHP 9825A desktop computer. A magnetic field was applied to the sample cell by a Helmholtz coil and was stabilized by a current-regulated dc power supply (fluctuation less than 0.1%). The strength of the magnetic field was measured by a YEW 3251 gaussmeter. The highest available magnetic field was 700 G (1G = T). The residual magnetic field of the coil itself is negligible compared with terrestrial magnetism. Hereafeter we denote the experiments under the terrestrial magnetic field as the experiments under "zero magnetic field". Results and Discussion Time-Resolved Absorption Spectra of BP. Time-resolved absorption spectra after laser pulse irradiation have been measured for aqueous solutions containing BP (1X loT3mol dm-3) and a detergent (SDS; 8 X mol dm-3, CTAC; 3 x mol dm-3, or Brij 35; 5 X mol dm-3). The time-resolved absorption spectra of the micellar SDS and CTAC solutions are shown in Figures 1 and 2, respectively. The transient absorption spectra of the micellar (14)H. Hayashi and S. Nagakura, Bull. Chem. SOC.Jpn., 53, 1519 (1980). (15)M. Nakano, K.Namba, and A. Minoh, Laser Science Progress Report of IPCR, 2, 23 (1980).
The Journal of phvsical Chemistty, Vol. 86, No. 16, 1982 3179
Magnetic Field Effects on Photochemical Processes
a
%
901.1 0
I
1
I
2
I
4
0
TIME/ps Flgure 3. The I ( f ) curve observed at 325 nm for a micellar SDS solution of B P (a) in the absence of a magnetlc field: (b) in the presence of a magnetic field of 700 G.
Brij 35 solution are similar to those of the CTAC one. The spectra observed for the micellar SDS and CTAC solutions immediately after irradiation (curve a in Figures 1 and 2) have two peaks a t 325 and 525 nm. They are assigned to the triplet state of BP (3BP*)from comparison with the spectrum of 3BP* in the literature.16 The spectra of both solutions observed several hundred nanoseconds after excitation (curves b and c in Figures 1 and 2) also have two peaks at nearly the same wavelengths but with slight shifts toward longer wavelengths when compared with the spectrum of 3BP*. Similar phenomena have already been observed for BP solutions in usual solvents and have been ascribed to formation of the benzophenone ketyl radical (K-).lB-18 Since BP is dissolved in the micelleslg and is surrounded by detergent molecules (RH), K. is considered to be formed by hydrogen atom abstraction of 3BP* from RH. The formation of K. in some micelles has also been described by other authors.20-21 In the time-resolved absorption spectra observed for SDS and CTAC solutions in the microsecond region (curve d in Figures 1and 2), the peak in the 500-600-nm region becomes very weak or disappears completely, while in the 300-400-nm region a peak still remains. This long-lived peak is assigned to a reaction product because the same spectrum was obtained after irradiating the solutions for several minutes.22 The lifetimes of this long-lived com(16) T. S. Godfrey, J. W. Hilpem,and G. Porter, Chem. Phys. Lett., 1, 490 (1967).
(17) 0. Brede, H. Helmstreit, and R. Mehnert, Z . Phys. Chem. (Leipzig), 256,513 (1975). In Figure 2 of this paper, there are some misprints. The absorption spectrum of the BP ketyl radical should correspond to that denoted by ( 0 )and the spectrum of B P to that denoted by (0). (18) For example, N. J. T w o , "Modern Molecular Photochemistry", W. A. Benjamin, Menlo Park, CA, 1978, pp 362-413. (19) J. H.Fendler, E. J. Fendler, G. A. Infante, P. Shih, and L. K. Patterson, J.Am. Chem. SOC.,97, 89 (1975). (20) R. Brealow, S. Kitabatake, and J. Rothbard, J. Am. Chem. Soc., 100,8156 (1978). (21) A, M. Braun, M. Krieg, N. J. Turro, M. Aikawa, and G. A. Graf, 'Abstract of VI11 IUPAC Symposium on Photochemistry", Seefeld, Austria, July 1980, p 88. (22) The assignment of the reaction product to
may be moet probable, because the absorption spectrum of the long-lived component is similar to that" of
4
2 TIME/ps
Li
0
Z
3 CK
0 ln
m
a0 t : 0
ju
2
L
TIME/ys L
3
I .!
I
w
0
Z
a
m CK 0
ln
9 0
0
0
2 TIMEIPS
4
Flgure 4. The I ( t ) curve observed at 525 nm for a micellar SDS solution of (A) BP, (8) BP-d,,, and (C) BP-I3C: (a) In the absence of a magnetlc field; in the presence of a magnetic field of (b) 100 0,(c) 200 0,(d) 400 G, and (e) 700 0.
ponent was more than 20 min under degassed conditions. Reaction Mechanism for BP in Micelles. From the above-mentioned time-resolved absorption spectra, the primary photochemical reactions of BP in micellar solutions are considered to occur through the following processes which are similar to those in usual organic solvents.18 BP -!!L 'BP*
(1)
lBP* 3BP* 3BP* + RH -* 3(K.-R)
(2)
3(K*.R)--* '(K**R)
(4)
-
+
(3)
3J(K*.R) K. R(5) '(K*.R) K-R, BP + RH (6) By irradiation with the laser, BP is excited to ita excited singlet state, lBP* (reaction 1). 'BP* becomes %P* within -+
3180
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The Journal of Physical Chemlstfy, Vol. 86, No. 16, 1982
tens of picoseconds (reaction 2).24 3BP* abstracts a hydrogen atom from a detergent molecule, RH, forming a triplet radical pair of a benzophenone ketyl, K., and an alkyl, R., within a micelle (reaction 3). The electron spin state of the radical pair changes between the triplet and singlet states through the radical pair theory (reaction 4)?p0 The magnetic field is expected to influence the rate of triplet-singlet (T-S) conversion through the hfc and/or electronic Zeeman (Ag) mechanisms.'O The radicals in the triplet and singlet radical pairs separate from each other to form so-called escaping radicals (reaction 5). Furthermore, the radicals in the singlet radical pair react with each other and give some products (reaction 6). The radicals disappear through this reaction, the rate of which can be considered to be much faster than that of reactions 4 or 5. The yield of the escaping radicals from the singlet radical pair is considered to be much lower than that from the triplet one because reaction 6 occurs in parallel with reaction 5 for the singlet pair. Time Dependence of the Transient Absorption Zntensity of BP. The time dependence of the transient absorption intensities, Z(t), was measured with the digital memory at 325 and 525 nm for the SDS micellar solution of BP in the absence and presence of magnetic fields and the results are shown in Figures 3 and 4A. Similar measurements were also carried out for the SDS solutions of BP-dlo and BP-W, and the results observed at 525 nm are shown in parts B and C of Figure 4, respectively. The concentration effect upon the transient behavior was investigated with solutions containing various concentrations of BP and SDS (BP/SDS = 1 X mol mol dm-3 which is the normal condition of dm9/8 X our experiments, 5 X 1049/8 X 2 X 10-4/8 X and 5 X 10-4/5 X The critical micelle concentration of SDS is reported as 8.4 X mol dm-3 at 20 0C,25and its aggregation number is reported as 60 f 2.% The number of BP molecules per one micelle under our experimental conditions was less than 12' and the interaction between the BP molecules within one micelle can be disregarded. In the concentration range of the present experiment the magnetic field effects were found to be independent of the concentrations. The Z(t) curves of BP have also been measured for other micellar solutions. The concentrations of BP, CTAC, CTAB, and Brij 35 were 1 X 5X 3X and 5X mol dmM3,respectively. The decay rate of the absorption in the 500-600-nm region was found to increase in the following order: SDS < CTAC N Brij 35 ancvfrom the hfc mechanism ogserved for the SDS solition" of BP. Acknowledgment. The authors thank Dr. Arimichi Minoh, the Intsitute of Physic. and Chemical Research, for his kindness in allowing them to have the digital memory system at their disposal. is also indebted to Professor Nicholas J. Turro, Columbia University, for his valuable comments. (41)Yu. N. Molin, R. Z. Sagdeev, and K. M. Salikhov, Sou. Sci. Reu. Sec. B, Chem. Rev., 1, 1 (1979).
Picosecond Fluorescence Lifetimes of Anthraquinone Derivatives. Radiationless Deactivation via Intra- and Intermolecular Hydrogen Bonds Haruo Inoue; " Mltsuhlko Hlda," Nobuakl Nakashlma,lband Keitaro Yoshiharalb Department of Industrial Chemlsby, FacuHy of Technolosv. Tokyo Metropolitan Unlverslty, Setsgaya-ku, Fukazawa, Tokyo, 158 Japan, and Institute for Molecular Science, Myodayl, okezakl, 444 Japan (Received: January 5, 1982; In Final Form: April 12, 1982)
Radiationless deactivations from the S1('CT) states of seven 1-and 2-substituted aminoanthraquinoneswere investigated by measuring picosecond fluorescence lifetimes and fluorescence quantum yields in benzene, acetonitrile,and ethanol. The Sl('CT) states of all derivatives were largely deactivated in ethanol. Deuterium isotope effects of the solvents on the nonradiative rate constants k,(in EtOH)/k,(in EtOD) = 9.0 (1-NH2(2)), 2.1 (2-NH2(5)), and 1.7 (2-piperidino (7)) were observed. The fluorescence quantum yield in ethanol was not affected by temperature (278-343 K). In benzene the excited 1-aminoanthraquinoneswere deactivated faster than 2-aminoanthraquinones. These observations were interpreted in terms of the radiationless deactivations of S1('CT) through the intra- and intermolecular hydrogen bonds.
Introduction Fluorescence quenching by proton transfer or hydrogen-bonding interactions has received special attention as one of the fundamental processes of radiationless deactivatiOn.2-13v18-20 (1)(a) Tokyo Metropolitan University; (b) Institute for Molecular Science. (2)(a) N. Mataga and T. Kubota, 'Molecular Interactions and Electronic Spectra", Marcel Dekker, New York, 1970,pp 346-51, and references therein; (b) E. C. Lim, 'Vibronic Interactions and Luminescence in Nitrogen-Heterocyclicand Aromatic Carbonyl Compounds in Excited States", Vol. 3,Academic Press, New York, 1977,and references therein. (3)A. Weller, 2.Electrochem., 60,1144 (1956);K. K. Smith and K. J. Kaufmann, J.Phys. Chem., 82,2286 (1978). (4)H. Shizuka, K. Matsui, T. Okamura, and I. Tanaka, J. Phys. Chem., 79,2731(1975);H. Shizuka,K. Matsui, Y. Hirata, and I. Tanaka, ibid., 80,2070 (1976). (5)S. Y. Hou, W. M. Hetherington, G. M. Korenowski, and K. B. Eisental, Chem. Phys. Lett., 68,282 (1979). (6)K. P. Sengupta and M. Kasha, Chem. Phys. Lett., 68,382(1979). (7)P. F. Barbara, P. M. Rentzepis, and L. E. Brus, J. Am. Chem. SOC., 102,2786 (1980). (8)P. F.Barbara, L. E. Brus, and P. M. Rentzepis, J. Am. Chem. Soc., 102,5631(1980). (9)N. Mataga and S. Tsuno, Naturwissenschaften, 10, 305 (1956); Bull. Chem. SOC. Jpn., 30,711 (1957);N. Mataga, ibid., 31,481 (1958); N.Mataga, Y. Torihashi, and Y. Kaifu, 2.Phys. Chem. (Frankfurt am Main), 34,379(1962): N. Mateaa, F. Tanaka, and M. Kato, Acta. Phvs. Pol. 34, 733 (1968). (10)K. Kikuchi. H. Watarai. and M. Koizumi. Bull. Chem. SOC.JDn.. . . 46,749 (1973). (11)K. C. Ingham and M. A. El-Bayoumi, J. Am. Chem. Soc., 96,1674 (1974);M. A. El-Bayoumi, P. Avouris, and W. R. Ware, J . Chem. Phys., 62, 2499 (1975);W. M. Hetherington, 111, R. H. Micheels, and K. B. Eisenthal, Chem. Phys. Lett., 66, 230 (1979). (12)M. M. Martin and W. R. Ware, J. Phys. Chem., 82,2770(1978). 0022-3654/82/2086-3184$01.25/0
Chart I
Such quenching is explained either by (1)the intramolecular interaction^,^-^ most of which involve rapid deactivation through a keto-enol tautomeric reaction, or by (2) intermolecular interactions (a) between two ?r-conjugated systems*1g and (b) between one conjugated molecule and (13)H. Masuhara, Y. Tohgo, and N. Mataga, Chem. Lett., 59 (1975);
N.Ikeda, T. Okada, and N. Mataga, Chem. Phys. Lett., 69,251 (1980). (14)N.Mataga, Y. Kaifu, and M. Koizumi, Bull. Chem. Soc. Jpn., 29,
373 (1956);30,368,711 (1957). (15)J. W. Sidman, Chem. Rev., 58,689(1958);M. A.El-Sayed and M. Kasha, Spectrochim. Acta, 15,758 (1968);E. C. Lim and J. M. H. Yu, J. Chem. Phys., 45,4742(1966);Y.H. Li and E. C. Lim, Chem. Phys. Lett., 9,279(1971);R. Li and E. C. Lim, J. Chem. Phys., 57,605(1972). (16)L. J. Noe, E. 0. Degenkolb, and P. M. Rentzepis, J. Chem. Phys., 68,4435 (1978). (17)M. M. Martin, Chem. Phys. Lett., 35,105 (1975);43,332 (1976). (18)N. Mataga and K. Ezumi, Bull. Chem. Soc. Jpn., 40,1350(1967). (19)T. Forster, Chem.Phys. Lett., 17,309(1972);S.G.Schulman and P. Liedke, 2. Phys. Chem. (Frankfurt am Main), 84, 317 (1973);H. Shizuka, Y. Ishii, and T. Morita, Chem. Phys. Lett., 51, 40 (1977);K. Tsutaumi and H. Shizuka,ibid., 52,485(1977);H.Shizuka, K. Tsutsumi, H. Takeuchi, and I. Tanaka, ibid, 62,408 (1979). (20)L. A. Hallidy and M. R. Topp, Chem. Phys. Lett., 48,40(1977); J . Phys. Chem., 82,2273,2415 (1978).
0 1982 American Chemical Society
