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ferometry, 110 elaborate, vibration-damping optical mounts were necessary in the experimental setup. A conventional, lathe-type optical bench was used on a heavy laboratory bench. There are several advantages which holographic interferometry has to offer over classical methods of interferometry. I n the first place, alignment and preparatory procedures are far less critical than for many conventional forms of interferometry. The common path nature of the holographic interferometer provides significant flexibility. It permits the use of imperfect optical elements. Irregularly shaped electrochemical cells of ordinary laboratory glass may be used in the scene without in any way degrading the fringes produced. Furthermore, it is possible to place a ground glass diffuser behind the scene so that the light is caused to traverse the scene in many directions, thereby permitting three-dimensional information to be recorded. During reconstruction, the image can be examined from diff ererit directions and the interference pattern corresponding to each of these directions analyzed. Thus, it is possible to investigate such matters as the localization of regions of electrochemical activity, the nature of flows which do not have rotational symmetry, and the performance of asymmetric electrodes. Holographic interferometry enables one to observe changes which occur in a subject as a function of time, thus producing a differential interferogram. Because those aspects of the subject which do not change do not affect the interference pattern, one has a technique for measuring subtle changes in very complex subjects incapable of being explored with any of the classical methods of interferometry.
COAIRIG~ICATIONSTO THE
EDITOR
ing the variation of trans-2-butene yield from the sensitization of cis-2-butene (or cis-%butene from trans2-butene) in the absence and in the presence of varying amounts of other olefinic quencher molecules. The result of our experiment indicates that triplet benzene is an electrophilic donor and furthermore it provides new data of current interest in benzene photochemistry. The gaseous samples were handled in a vacuum line free of mercury and grease. A Hanovia mercury resonance lamp provided 2,537-A radiation, and a Corning 68-7-54 filter was used to filter out radiations with wavelengths shorter than -2400 A. The photolysis was carried out in a cylindrical quartz cell with two flat end windows. The pressure of benzene was 2.50 mm and that of cis-2-butene was 1.00 mm, while the quencher molecules were in varying amounts for the sets of runs presented here. The conversion of cis-2butene was typically less than 5%, and the product analysis was carried out with a gas chromatograph equipped with a thermistor detector. The separation of 2-butene isomers was complete with either a GO-ft or 22-ft, 0.25-in. o.d., dimethylsulfolane column at room temperature. The notation used by Cundall, et ~ l . , ~inb kinetic expressions of sensitization and isomerization will be adopted here for convenience. Only two competing reactions of interest are shown below
TI
+ C.B. -% G + &To T~ + Q G + Q'
(1)
(11)
where TI is the triplet benzene, C.B. is cis-2-butene, cis-To the cis-butene triplet intermediate, G the ground state benzene, Q the olefinic quencher, Q' the quencher PHYSIC 4~ RESEARCH CESTER C. K N O X TRW SYSTEMS GROVP R. R. S A Y ~ N O triplet intermediate, and k3c and k,, the bimolecular TRW Isc. E. T. SEO rate constants for reactions I and 11,respectively. The REDONDO BEICH,CALIFORNII90278 H. P. SILVERMAN yield of fmns-2-butene is used as a measure of the &-To RECEIVED 11 i~ 15, 1967 yield or the extent of reaction 1, since cis-To mill either give cis-Zbutene back or eventually isomerize to trans2-butene. Two more reactions involving the triplet benzene should be considered in the kinetic treatment, Benzene Photosensitized cis-trans Isomerization (1) H . Ishikawa and W. -1.Nojes, J r , J . Chem Phys , 37, 583 of 2-Butenes: Competitive Quenching Study
Siy: The excited singlet benzene (lBqu)produced in the gas phase is known to undergo fluorescence and intersystem crossover to a triplet ~ t a t e , l -and ~ a triplet energy transfer process is responsible for the cis-trans isomerization of 2-butenes by benzene photosensitizaWe have been studying the tion in the gas competitive efficiencies of various olefinic molecules for quenching triplet benzene in the gas phase by measurThe Journal o j Physical Chemistry
(1962). (2) G. B. Kistiakowsky and C. S Pnrmenter, ibzd, 42, 2942 (1965). (3) W.A. Noyes, Jr., IY.A . 31ulnc, and D A Harter, ibid , 44, 2100 (1966). (4) (a) R. B. Cundall and T. F. Palmer, Trans. Faraday SOC, 5 6 , 1211 (1960), (b) R B Cundall, F. J. Fletcher, and D G. llilne, J . Chem. Phys., 39, 3536 (1963); Trans. Faraday S O C ,60, 1146 (1964); (r) R. B Cundall and A. S Davies, i h z d , 62, 1151 (1966). (5) (a) S. Sato, K . Kikuchi, and 31 Tanak:i, J . C'hem. Phys , 39, 239 (1963); (b) A1. Tanaka, T. Terumi, and S Snto. R d l . Chem. SOC. Japan, 38, 1645 (1965). (6) P. Sigal, J . Chem. Phys , 42, 1953 (1965), 46, 1043 (1967) (7)
W A. Koyes, J r , and D A . Harter, % b i d ,46,
674 (1967)
COMMUNICATIONS TO THE EDITOR
3105
Table I : Relative Rates of Reactions with Various Olefins
Olefin
I
0
I
I
1
2
I
I
3
4
[QI
I
5
I
6
I
7
I
8
I
9
I
0 atom! Cvetanovics temp, 25'
0.16 f 0.02 0.51 f 0.04 0.50 f 0.04 0.51 f 0.04
0.042 0.24 0.24
...
0.27 (1.00) 1.19 1.25 3.3 4.3
(1.00) 1.08 f 0 . 0 8 1.06 f 0 . 0 8 1.7 1 0 . 2 3.0 1 0 . 3
...
10
1 IC.81
Figure 1.
and they are the unimolecular decay to the ground state benzene with a rate constant k2 and the bimolecular self-quenching by benzene with a rate constant kz'. If a. is the quantum yield of trans-2-butene at a given pressure of benzene and of cis-2-butene, and is the quantum yield of trans-2-butene in the presence of a competing olefinic molecule but a t the same pressures of benzene and cis-Zbutene, then it can be shown that
Equation 1 can be simplified for our experimental condition to
+
Ethylene Propylene 1-Butene 1-Pentene 1-Hexene cis-2-Butene trans-2-Butene Cyclopentene Trimethylethylene Tetramethylethylene
Triplet
Triplet benzene, this w o r i temp, 23
since our ratio of kz k2'(4H) to k34C.B.) at 2.5 mm benzene pressure and 1.0 mm cis-2-butene pressure has been determined to be 0.06. The experimental results are shown in Figure 1 and are presented to test the fit of eq 2. Therefore, the relative quenching efficiencies (k3q/k30) can now be evaluated in a straightforward manner. The efficiency of the quenching of triplet benzene definitely increases with the increase in degrees of alkyl-group substitution a t ethylenic x-bond, in contrast to the earlier report that ethylene and cis-2-butene have the same quenching effi~iency.~ Furthermore, ~ our data indicate that Oz is only 0.3 times as efficient a quencher as cis-Zbutene, if the appropriate correction is made for the singlet quenching by 0 2 . 1 The variation in reactivity of olefins toward triplet benzene parallels that observed in the rate of triplet oxygen atom addition to olefins.* The rates relative to cis-2-butene are compared in Table I . It has been suggested that the triplet 0 atom
is an electrophilic reagent for olefins,s and the same can be said of the triplet benzene. Our additional observations of importance are the following. (1) The relative quenching rates listed in Table I are in good agreement with the rates measured in our laboratory from an independent set of experiments in which quenching of the benzene photosensitized biacetyl phosphorescence emission1 is studied by an addition of olefins. (2) The photostationary state ratio of trans/cis for the benzene-butene system, k3ck~ck~t/k&tk5c, is 0.92 f 0.01 in agreement with the one value6 in the literature but in disagreement with branching ratio, the other ~ a l u e . ~(3)~The , ~ t~ans/cis ~ k40k5t/k4tli5c,is 1.02 =t 0.02 as compared to the previously reported value of 1.37.4b$9 (4) The ratio of quenching cross sections of trans-2-butene to cis-2butene, k3t/k3c,is 1.08 i= 0.08 as it was measured from a set of parallel competition experiments in which trans-2-butene and 1-butene were used. The result of (2) and (3) yields a value of 1.11 f 0.03 for the ratio in (4),and the internal consistency between this value and the above independently measured value is remarkable. It should now be mentioned that our data in (3) cast some doubt on the validity of the previously measured value of 0.63 as the triplet benzene quantum yield,4 and that further work is necessary to obtain more reliable quantum yield data. The lifetime of the 3 B ~benzene u has been measured recently, and it is -26 psec at 20 mm benzene pressure.1° I n the absence of a directly measured value of the triplet benzene lifetime at 2.5 mm pressure of benzene, the absolute value of quenching cross sections for (8) (a) R. J. Cvetanovic, Can. J . Chem., 38, 1678 (1960). (b) For a review of 0-atom reactions with olefins, see R. J. Cvetanovic, Adean. Photochem., 1, 115 (1963). (9) R. B. Cundall, private communication. . 4 new measurement of this ratio is found t o be 1.08 i 0.05. (10) C. S. Parmenter and B. L. Ring, J . Chem. Phus., 46, 1998 (1967).
Volume 7 1 , Sumber 9
August 1967
COMMUNICATIONS TO THE EDITOR
3106
various olefins cannot presently be calculated with confidence, since values of IC2 and k2' are not so accurately known to warrant an infallible answer. The variation of the observed quenching efficiencies reflects the variation in the energy level separation between the triplet and the ground state of olefinic molecules through systematic structural changes (an alkyl-group substitution for a hydrogen atom bonded to an sp2 carbon Detailed discussions of this work and other related work will appear soon.
Z
0
VI
2
I
VI
Z
Acknowledgment. E. K. C . Lee wishes to express his sincere appreciation for valuable comments and suggestions made by Professor W. Albert Noyes, Jr.
a M
i
(11) S. Sat0 and R. J. Cvetanovic, J . Am. Chem. Soc., 81, 3223 (1959). (12) N. L. Allinger and J. C. Tai, ibid.,87,2081 (1965).
DEPARTMENT OF CHEXISTRY UNIVERSITY O F CALIFORNIA
G. A. HANINGER, JR. EDW.4RD K. c. LEE
IRVINE, CALIFORNIA92664 RECEIVED MAY17, 1967
I 0
I 3800
I
I
I
3600
FREQUENCY
The Location of Hydroxyl Groups in Hydrogen Y Zeolite
Sir: Spectroscopic studies of hydrogen Y zeolite have shown the existence of at least three types of structural hydroxyl groups with infrared frequencies near 3740, 3635, and 3540 ~ m - ' . ' - ~ Recent studies3v4have suggested that the 3540-cm-' band represents hydroxyl groups located in the SI or bridge positions in the structure. This conclusion was based on observations that olefins do not interact with the 3540-cm-' band whereas they did with the 3635-~rn-~ band, and that the 3635cm-l band, but not the 3540-cm-' band, was perturbed by the adsorption of molecules such as Nz, 02, CH4, Ar, and Kr. We have observed the infrared spectra of pyridine and water adsorbed on hydrogen Y zeolites which have been preheated to 450". Spectra for pyridine are shown in Figure 1. These spectra show that the 3635cm-l band is removed and the 3540-cm-' band is greatly diminished by interaction with pyridine a t 10 mm pressure. Heating to 200" with evacuation restores the 354O-cm-' band, showing that it interacts least strongly with the adsorbed molecules. Similar results have been reported by Liengme and Ammonia and deuterium oxide have also been found to interact with the 3540-cm-' band. It appears, then, that the 3540-cm-' band interacts with polar molecules but not with nonpolar molecules. The crystal structure of Y zeolite5 is such that if The Journal o j Physical Chemistry
I
I
3400
I
I
3200
(em-')
Figure 1. Spectra of hydroxyl groups on hydrogen Y zeolite: a, zeolite calcined and evacuated at 450'; b, zeolite exposed to pyridine at 10 mm and 25' for 2 hr; c, evacuation for 2 hr a t 200'.
hydroxyl groups were located in the SI positions, they would be unassessable to adsorbate molecules. Hence, the hydroxyl groups represented by the 3540-cm-I band must be in other locations. The suggestions of Eberly3 and White, et d l 4 that the two strong absorption bands at 3635 and 3540 cm-' represent different types of hydroxyl groups is supported by the pyridine adsorption data of Figure 1, which shows that these bands act independently. The exact location of the hydroxyl groups is not known a t this time, but it is probable that they represent different locations in the truncated octahedra sections of the structure. Further work is in progress to clarify the locations of these hydroxyl groups. (1) C.L.Angel1 and P. C. Schaffer, J . Phys. Chem , 69,3463 (1965). (2) B. V. Liengme and W. K. Hall, Trans. Faraday SOC.,62, 3229
(1966). (3) P. E. Eberly, presented before the Division of Petroleum Chemistry, 153rd National Meeting of the American Chemical Society, Miami Beach, Fla., April 1967. (4) J. L. White, A. N. Jelli, J. M. Andre, and J. J. Fripiat, Trans. Faraday Soe., 63, 461 (1967). (5) D. W.Breck, J . Chem. Educ., 41, 678 (1964).
UNIONOILCOMPANY OF CALIFORNIA UNIONRESEARCH CENTER BRE.4, C.4LIFORNI.4 92621 RECEIVED May 19, 1067
JOHN W. WARD
