NOTES
2696
the membrane relative to the other ion, whether chloride was i he faster moving or slower moving ion at 1 atm. The changes in bip with pressure were found to be additive between various pairs of anions; i.e., the bip’s are algebraically additive between pairs of ions a t 600 atm pressure, as they have been shown to be at atmospheric pressure by Dray and Sollner.6 The mechanism of the change in bip with pressure is not understood. Pressure is known to influence both the activity and the mobility of ions in solution.7Ss However, the magnitude of the change in bip is too large to be accounted for by changes in activity of the ions in solution when subjected to pressure. The equation of Dray and Sollnerg for bi-ionic potentials
can be used to calculate the expected change of bip per 100 atm by substituting for the activities of the two ions, CXJand UK, the ratio of the activity of each ion at 100 atm, to that at 1 atm, obtained from Harned and Owena7 T J ~and T K O are the standard transference numbers of the ions in the membrane and are assumed to remain unchanged for the purposes of this calculation; and R, T , and F have their usual Table IV shows that this can account for only a small fraction of the observed potential change. I n the case of NaC1-NaNOs, where pressure has the same effect on .~- the activities of the two ions, there would be no change in bip as a result of this effect. A similar calculation can be made for the effect of pressure on the transference numbers of the ions in the membrane, with the assumption that the ratio of the transference numbers in the membrane is related to the ratio of the ionic mobilities in the solutions.
that a change in the interaction between the counterion and the membrane (or in the membrane itself) is involved rather than a change limited to the properties of the ions in the solutions. Such interaction might lead to a decrease in volume, which would be promoted by elevated pressure. Further clarification might be obtained by measurement of the quantity of counterion absorbed a t various pressures by ion-exchange materials. I n summary, the pressure dependence of the bip across permselective membranes between solutions with different counterions was studied up to pressures of 600 atm. The magnitude and sign of the change was independent of the magnitude and sign of the bip at atmospheric pressure, and the change was additive between various pairs of ions.
Acknowledgment. The author wishes to thank Dr. R. J. Podolsky, who suggested the experiments and in whose laboratory a t the Naval Medical Research Institute the pressure measurements were made. He and Dr. K. Sollner contributed helpful discussion of the results. The author is indebted to Mr. C. E. Hubert for assistance with the experimental work. (6) S. Dray and K. Sollner, Biochim. Biophys. Acta, 22, 220 (1956). (7) H. 9. Harned and B. B. Owen, “The Physical Chemistry of Electrolytic Solutions,” 3rd ed, Reinhold Publishing Corp., New York, N. Y., 1958, p 507. (8) 5.D. Hamann, “Physico-Chemical Effects of Pressure,” Butterworth and Co. Ltd., London, 1957, p 119. (9) 5.Dray and K. Sollner, Biochim. Bwphys. Acta, 21, 126 (1956).
An Apparently Anomalous Effect on Hydrogen Peroxide Yields in the Radiolysis of Aerated 0.8 N Sulfuric Acid Solutions of Potassium
Bromide with -15-Mev Electrons Table IV: Calculated Change of Bi-ionic Potential Due to Effect of Pressure on the Activities of Chloride and of a Paired Anion (A-) Soln paired with 0 . 1 M NaCl
0.1 M 0.1M 0.1 M 0.1 M
NaCl NaBr NaI NsNOa
ap-soq ap-i
_ .
1.0021 1.0017 1.0013 1.0021
aCl-im/aCl-i aA-lw/aA-l
... 1.0004 1.0008 1.0000
-Abip/lOO Calcd, mv
0.010 0.101 0.021
0.000
atmObsd, mv
... 0.09 0.24 0.30
by Farhataziz’ Radiation Laboratory,2 University of Notre Dame, Notre Dame, Indiana 46666 (Received March 17, 1966)
The suppression of molecular-product yields by scavengers in water radiolysis has been treated theoretically by Magee and co-worker~.~The model em(1) On leave from Pakistan Atomic Energy Commission.
The fact that the observed change is influenced by the nature of the counterion which penetrates the membrane and not by the nonpenetrating ion suggests The Journal of Physical Chemistry
(2) The Radiation Laboratory of the University of Notre Dame is operated under contract with the U. S. Atomic Energy Commission. This is A.E.C. Document No. COO-38-464. (3) The paper of A. K. Ganguly and J. L. Magee, J. Chem. Phys., 2 5 , 129 (1956), Includes references t o the earlier papers on this subject.
XOTES
ployed is based on diffusion-controlled reactions of reactive species formed in energy-deposition spurs whose distribution along the radiation particle track is determined by the linear energy transfer (LET) of the radiation particle. Such a treatment indicates that for radiations of less than a certain LET, interspur distances should be so great as to preclude molecularproduct formation in interspur reactions; ie., each spur develops independently. For both 'j0Co y rays and 1.3-1lev electrons, the LET lies well below the limit for spur interaction; consequently, the spur model suggests that no difference in effect of scavengers on molecular-product yields should be observed on comparison of either 6oCoy radiation or 1.3-h4ev electron radiation with electromagnetic or electron radiations of higher energy (provided the energies are low enough to preclude nuvlear reactions). However, Burton and K ~ r i e nin, ~a comparison of 6oCoy radiation and 24-Mev X-radiation from a Betatron, have reported a difference in effect of KBr and KC1 on HzOz yields in aerated, aqueous 0.8 N H2S04solutions. Because the Betatron X-radiation was pulsed and also included a continuous distribution of radiation energies up to 24 hlev, some uncertainty arises in attribution of the reported difference in molecular-product behavior to a difference in radiation energy. The theoretical significance of such an energy-dependent difference in behavior of molecular-product yields prompted a reexamination of this problem. I n the present investigation, 15.2-hlev pulsed electrons from the Linac a t Argonne Xational Laboratory, 1.S-Mev pulsed electrons from a Van de Graaff generator, and 6oCoy rays have been used to study the suppression of HzOz yields by KBr in aerated 0.8 N H2S04solutions.
2697
plate uniformly. Six sample tubes and three dosimeter tubes were irradiated simultaneously. The mean of the three dosimeter readings was taken as the dose for each sample. Triangular pulses were used of 15.2hlev electrons at 20 ma for 0.4 psec wit.h 30 pulses/sec and a total of 30,000-45,000 pulses. These conditions give the initial yield of HzOz. Van de Graaff irradiations were performed in a Pyrex cell (cf. Figure 1) similar to that used by Saldick and Allen;6 15.4 ml of solution was used. Two cells were fixed adjacent to each other in a Bakelite block that was placed in a reproducible position in the center of the electron beam at 63 ern from the van de Graaff window. The beam diameter was large enough to cover both cells. One cell contained the sample solution and the other the Fricke solution. I n a separate experiment, both cells were irradiated containing Fricke solution for calibration with respect to each other. Solutions were stirred a t 900 rpm during irradiation. Rectangular pulses were used of 1.5-Mev electrons at 29 ma for 0.5 psec with 30 pulses/sec and a total of 45,000-54,000 pulses. Initial yields of HzOz are obtained.
Platinum wire for charge leakage
Experimental Section The analytical methods, cleaning of glassware, preparation of solutions, and the syringe technique for 6oCo y irradiation have been de~cribed.~Linac irradiations were performed in Pyrex test tubes (1.3 cm 0.d. X 13 cm) fitted with l0/3o -f joints. The test tubes were completely filled with solution and sealed with ground-glass stoppers so that no vapor was present. The average volume of solution was 10.9 ml. A small piece of glass rod in the test tube functioned as a stirrer. The irradiation vessels were clamped with spring clips on a circular Bakelite plate, which could accommodate ten such vessels. The whole assembly was rotated at 2 rpm in a plane perpendicular to the plane of the electron beam. Care was taken to align the centers of the Bakelite plate and the electron beam. At 300 cm from the Linac window, the beam was broad enough to irradiate the whole Bakelite
f
All glass magnetic
~
0.2 m
rn thick glass
/
4
3 111 I Illy
....-. -3Y3lGlll
L1.5cm-
window
Figure 1. Van de Graaff cell.
(4) M.Burton and K. C. Kurien, J. Phys. Chem., 63, 899 (1959). (5) Farhatasis and P. J. Dyne, CRC-1205 or AECL-2113, 12 (1964). (6) J. Saldick and A. 0. Allen, J. Chem. Phys., 2 2 , 438 (1954).
Volume 7 0 , Number 8 August 1966
NOTES
2698
Dose rates used in this study were as follows: 15.2Mev electrons, 1.22 X loz3 ev 1.-l sec-l; 1.3-Mev electrons, (1.63-2.57) X loz3ev I.-' sec-'; 6oCo y rays, 3 X lo1*ev 1.-l sec-l. G(Fe3+) was taken as 15.6 for the Fricke dosimeter solution with [Fez+] = 2 mM. For pulse radiolyses, dose rates were calculated by division of the total number of pulses and the pulse duration into the total dose and multiplication by the ratio of total solution volume to irradiation volume. Because 15.2-Mev electrons have a range of 7.2 cm in water' at 25", the solution volume and irradiation volume are identical. Under the experimental conditions for the 1.5-Mev Van de Graaff irradiations, the electrons enter the solution with an average energy of about 1.3 MeV for which the range in water at 25" is 0.6 cm.' Thus, the irradiation volume is estimated to be 5.4 ml (0.35 of the total volume). It has been establisheds-10 that G(Fe3+) of the Fricke dosimeter is independent of dose rate up to ev 1. -l sec-'.
Results and Conclusions G(HzOZ) as a function of log [KBr] is shown in Figure 2. The curves for 1.3-Mev electrons and MCo y rays have identical shapes, whik that for 15.2-AIev electrons is very different. The difference between the curves for 1.3-hfev electrons and "Co y rays may not be real, because both sets of results agree with one another within *4%. However, the important observation is that the curves for 1.3-Mev electrons and MCo y rays both have a shape similar to that of the general curve obtained by Schwarz" for dependence of molecular G values on the logarithm of scavenger concentration. Furthermore, the data for 1.3-hfev electrons and 6oCoy rays both obey an empirical cube root 1aw,12 while results for 15.2-Mev electrons do not (cf. Figure 3). Treatment of the data by the methcd of Burton and Kurien4 has not been attempted bccause of difficulty in the determination of G(H20&, for zero concentration of KBr, by extrapolation of the 15.2-Mev data. However, the results clearly demonstrate that the behavior of HzOz yields is not significantly affected by the pulse conditions used and that a real difference does exist between the effect of 15.2-Mev electrons and that of 1.3-Mev electrons or 6OCo y rays 011the behavior of H ~ Oyields. Z It is important to note that in the Linac irradiations, the effect observed is determined by the energy-deposition pattern produced by a primary electron as it loses energy from -15 to -13 MeV; in the Van de Graaff irradiations, the energy-deposition pattern is that produced by a primary electron as it loses energy from 1.3 ME'V to 0. Mozumder and Magee13 have The Journal of Physical Chemistry
1.31
1
0.8
10
100 [KBrl, r M .
10,000
1000
Figure 2. G(H202) as a function of log [KBr] for aerated solutions in 0.8 N H2S04: 0, 15.2-Mev electrons; A, "Co y rays; 0, 1.3-Mev electrons.
1.3
I
h
Q
1.1
z G 0.9
2
6
10 [KBr]'/a, pM'/a.
16
20
Figure 3. G(H202) as a function of cube root of KBr concentration in aerated 0.8 N H2S04 solutions: 0, 15.2-Mev electrons; A, W o y rays; 0 , 1.3-Mev electrons.
theoretically calculated distribution of deposited energy among three entities (cf. Table I). The spur corresponds to a deposition of -6-100 ev, the blob to -100500 ev, and short tracks (which represent roughly finite cylindrical regions of high LET) to -500-5000 ev . It is difficult to judge whether such differences in track character are sufficient to account for the differences observed on the basis of a diffusion-kinetics (7) M. J. Berger and S. M; Seltzer, "Studies in Penetration of Charged Particles in Matter, Publication 1133, National Academy of Sciences, National Research Council, 1964. (8) J. Rotblat and H. C. Sutton, Proc. Roy. Sac. (London), A255, 490 (1960). (9) A. R. Anderson, J . Phys. Chem., 66, 181 (1962). (10) J. K. Thomas and E. J. Hart, Radiation Res., 17, 408 (1962). (11) H. A. Schwarz, J . Am. Chem. Sac., 77, 5852 (1955). (12) T. J. Sworski, ibid., 76, 4687 (1954). (13) A. Mozumder and J. L. Magee, Radiation Res., 28, 203 (1966).
NOTES
2699
Table I : Energy Distribution among Spurs, Blobs, and Short Tracks for Monoenergetic Electrons18 % of energy in different geometrical entities Short Spurs Blobs tracks
Energy of electrons, mev
54 64 67 71 78 79
0.1 0.5 1.0 2.0 10.0
15.0
14 12 11 10 7
7
32 24 22 19 15 14
model. However, it is evident that the cube-root relationship is a fortuitous consequence of the over-all energy-deposition pattern characteristic of an electron with initial energy of the order of 1 MeV, as predicted by Magee3 and demonstrated by Burton and Kuriena4
Acknowledgments. The author is grateful to Professor M. Burton for suggesting this problem. The author is indebted to Drs. E. J. Hart and J. K. Thomas of Argonne National Laboratory and Dr. M. Dillon for their help with the Linac experiments. It is a pleasure to acknowledge the encouragement received from Dr. R. R. Hentz.
Flash Photolysis of Cyclic Ethers.
I. Ethylene Oxide' by B. C. Roquitte Radiation Research LUbOTatOTies, Mellon Institute, Pittsburgh, Pennsyltania (Received March 7, 1966)
Due to the complexity of the mechanism of the direct photolysis of ethylene oxide2 at conventional low light intensity, the primary process CH2-CH2
\/
2CHs + CHO (CO + H) (a)
0
is still somewhat uncertain. I n view of this, a study of the flash photolysis of ethylene oxide, where secondary reactions should be less important, was thought to be desirable.
Experimental Section A ~ ~ad~procedure. , . ~h~ ~ flash ~ ~reactor ~ consisted of a cylindrical Pyrex reaction vessel (1275 ml) containing a coaxial flash tube. The flash tube was
made of fused quartz provided with a tungsten electrode at each end, separated by 8 in. Argon at a pressure of 72 mm was used as a discharge medium. Since the lamp was made of fused quartz and ethylene oxide absorbs below 2000 A, the effective wavelength was thought to be -1900 A. Energies up to 2160 joules could be obtained by discharging capacitors of 120 pf charged at voltages up to 6 kv. The reactor was permanently attached to a conventional high-vacuum system through mercury cutoffs. The lifetime of a single light pulse, measured by means of a 935 RCA phototube connected to an oscilloscope, was 44 psec a t half width. The analytical side of the high-vacuum system consisted of a solid nitrogen trap, two LeRoy stills, and a Toepler pump-gas buret. After an experiment, the reaction mixture was transferred from the reaction zone into the first LeRoy still kept at - 196". H2,CO, and CH4 were removed by pumping with a mercury diffusion pump and a Toepler pump through another LeRoy trap a t -196b, and a solid nitrogen trap (-210") until the residual pressure in the reaction vessel was less than 10-5 mm. After measuring the total volume and pressure in the gas buret, they were transferred into a sample tube for mass spectrometric analysis. Hydrogen, carbon monoxide, and methane were quantitatively analyzed on a Consolidated 21-103C mass spectrometer. The next fraction consisting of C2H4, C2H6, and C 0 2 was removed at -145' and measured in a gas buret. This fraction was analyzed by gas chromatography, using a 2-m silica gel column at 50". The remaining portion of the reaction mixture was transferred to a sample tube for gas chromatographic analysis. Two different columns were used for the analysis of this fraction, a 2.5-m polyepichlorohydrin on firebrick (23% by wt) and a 2.5-m dinonylphthalnte on firebrick (30% by wt). On analysis, it was revealed that this fraction did not contain any measurable amount of high-boiling products. In order to be sure that the condensable fraction did not contain any carbonyl compounds, this fraction was collected from several runs and dissolved in spectrograde hexane. The absorption spectra of this solution on a Cary Model 14 indicated very small or no carbonyl absorption. I n addition, the condensable fraction was tested for f~rmaldehyde,~ which was found to be absent. Therefore, the condensable fraction was discarded in most of the runs reported here.
u.
(1) Supported in Part by the 8. Atomic Energy Commission. (2) R. Gomer and W. A. Noyes, Jr., J . Am. Chem. SOC.,72, 101 (1950). (3) D. Matsukawa, J. Biochem. (Tokyo), 30, 386 (1939).
Volume 70, n'umber 8 August 1966
