Surface Interactions lsetweeri Water and Plutonium Dioxide
581
ours in the temperature dependence, their value of E , tained a Fowler-Guggenheim expression with n = 8 and E = 128.7 kcal/mol. It is now evident that there was no being anomalously low (69.0 kcal/mol). The discrepancy is not likely to be eliminated by the nonequilibrium corphysical ground for doing this. In fact, n = 8 requires that rections of their k ~ values. ’ It appears that their rate data all the vibrational degrees of freedom for C2N2 be ininvolve some technical errors which tend to lower the k ~ ’ volved in the activation process, a situation which is highvalues at high teniperatures. ly unlikely to occur. Further, n = 8 gives the steric factor In this connection, it should be noted that emission exX = 0.017, which is somewhat too small for reactions of periments appear to necessitate far greater technical prethe type studied here. Their interpretation of the kinetic cautions than absorption studies. In preliminary studies, data is thus hardly justifiable. we observed( that both peak intensities and initial slopes of emission strongly depended on the cleanliness of the Acknowledgments. The authors wish to express grativacuum system. Only after most stringent precautions to tude to Professor G. Kamimoto and Dr. H. Matsui of avoid contamination could reliable values of hD’ be obKyoto University for helpful advices on the experimental tained. work. They are also indebted to Mr. K. Murakami, presSlack, et u!., combined their high-temperature data ently at the Dainippon Ink Co. Ltd., for assistance in the with the low-temperature results of Tsang, et ul., and obconstruction of the apparatus.
A Thermal Desorption Study of the Surface Interactions between Water and Plutonium Dioxide’ J. L. Stakebake Dow Chemical U . S. A., Rocky Fiats Division, Golden, Colorado 80401 (Received September 18, 1972) Publication costs assisted by The Dow Chemical Company
The interactions between water vapor and plutonium dioxide have been investigated using a mass spectrometric thermal desorption technique. Chemisorbed water vapor was found to be desorbed in two temperature ranges: one between 100 and 150” and the second between 300 and 350”. In terms of adsorption, these results are attributed to the hydroxylation of the oxide followed by the double hydrogen bonding of water molecules to the hydroxyl groups. The heat of adsorption was caculated to be 68 kcal/mol for hydroxylation and 20 kcal/mol for the hydrogen bonding.
Introductioin Following exposure to the atmosphere the surfaces of metal oxides are usually covered with adsorbed water. This contamination can significantly affect oxide sintering characteristics and other surface properties such as catalytic activity and selective adsorbability. A knowledge of the mechanism of water adsorption including adsorbed species, bond strengths, and the temperature required for desorption could provide valuable criteria for powder conditioning. The interaction between water and several metal oxides has been studied fairly extensively by a number of workers.2-6 It is generally agreed that oxide surfaces become hydroxylated upon exposure to water vapor. The exact conditions under which this occurs, however, have not been agreed upon and may in fact depend on the nature of the oxide. hi addition to the dissociative adsorption forming a hydroxylated surface, water may also be adsorbed in two molecular forms. Little has been done to investigate the plutonium dioxide-water system because of the toxic nature of plutonium. An earlier study showed water vapor to be irreversibly adsorbed on plutonium d i ~ x i d e Thermogravimetric .~ desorption measurements further revealed that this irre-
versibly adsorbed water consisted of two different adsorbed phases or species. To provide additional information on the characteristics of these two species the desorption of water from plutonium dioxide was investigated by a “thermal desorption” technique. Thermal desorption is the removal of adsorbed species by heating the sample under vacuum. During the linear heating cycle different species are desorbed at different temperatures depending upon their binding energy. This technique provides information on several adsorption parameters including (a) the number of adsorbed phases or species, (b) the adsorbed population in each phase, (c) the activation energy of desorption reactions, and (e) the (a) Work performed under the auspices of the U. S. Atomic Energy Commission, Contract No. AT(29-1)-1106. (b) Presented, in part, at the 163rd National Meeting of The American Chemical Society, Boston, Mass., April 9-14, 1972. P. J. Anderson, R. F. Horlock, and J. F. Oliver, Trans. Faraday Soc., 61, 2754 (1965). (a) P. T. Dawson, J. Phys. Chem., 71, 838 (1967); (b) A. Zecchina, S. Coluccia, E. Guglielminotti, and G. Ghiotti, ibid., 75, 2774 (1971). R. C. Day and G. D. Parfitt, Trans. FaradaySoc., 69, 708 (1967). J. E. Peri and R. B. Hannan, J. Phys. Chem., 64, 1526 (1960). J. H. deBoer, J. M. H. Fortuin, 9. C . Lippens, and W. H. Meijs, J. Catal., 2, 1 (1963). J. L. Stakebake and L. M. Steward, J. CoNo/d lnferface Sci., in press. The Journal of Physical Chemislry, Val. 77, No. 5, 1973
J. i.Stakebake
582
preexponenlia! kinetic factor for the desorption of each phase. The desorption process was followed with a time-offlight mass spectrometer.8 This instrument provided a simultaneous measurement of desorption rates and an identification of the desorbed species. This paper is a discussion of the results obtained from the thermal desorption of water from plutonium dioxide and proposes a mechanism for water adsorption. Theory When plutonium dioxide is heated at a linear rate under vacuum, the amount of surface coverage by water molecules varies as a function of time ( t ) and temperature (T). The rate of desorption of a chemisorbed gas has been found to be governed by the Arrhenius equation exp(-Ed/RT)
do/& =. -v$
(1)
where u is the surface coverage at temperature, T; u the preexponential kinetic factor; E d the activation energy of desorption; and x the order of the reaction. During the thermal desorption process the sample temperature is increased at a linear rate, /!?; hence, T = TO P t where TO is the initial temperature and T is the temperature at time t . A t some temperature T , in the desorption process the rate of desorption from the sample will reach a maximum value and rPcr/dt2 = 0. Imposing this condition on eq 1 the foilowing reluLions between Ed and ! ! , ' have been derived.9-12 PEJR'Pm2v, = exp(-E,/RT,) (for x = 1) (2)
+
(for x = 2) B E d / R T z ~ u o v=: 2exp(-E,/RT,) where LTO is the initial surface coverage. When the desorption reaction is first order with a fi activation energy of desorption, the peak which appears at Tm in the desorption spectrum is not altered by a change in the surface coverage. For a first-order reaction, eq 2 can be further simplified to 2 In Tm -
1rU
p
=
E,/RT,,,
+ 1l,!
Ed/&
(4)
which i s the equation used by several workers.lOJ1 A plot of the left side of eq 4 us. l/Tm will yield a straight line from which E d and Y may be calculated. If a value for the preexponential factor is assumed, an estimate of the activation energy of desorption can be obtained from eq 2. The theoretical value of the preexponential factor u , at some absolute temperature T , can be calculated from transition state theory by v = kT/h
(5) where k is the Boltzmann constant and h is Planck's constant. For ithe desorption of water u is approximately equal to 1013 see-l edhead has numerically evaluated E d as a function of using various values of P9 and u . I 3 This relationship was very nearly linear. A change in u of IO3 was found to produce a change of only 20% in E d calculated from measured T,.
Experiment,d ! ~ e c ~ ~ o ~ Sample Preparution. Plutonium dioxide used for this study was prepared by the air oxidation of plutonium This oxide was conditioned by exposure to oxygen for 2 hr. The physical properties of the plutonium prepared in this manner are shown in Table I. O
The Journal of Physical Chemistry, Vo/. 77, No. 5, 1973
TABLE I: Physical Properties of Plutonium Dioxide
Composition Surface area, m2/g Crystallite size, A Particle size, p Lattice parameter, A
f"uOa.0 I .3 260 i-5 5.394 a 0,001
In preparation for thermal desorption, samples of oxide were placed in the adsorption system shown in Figure 1. This system contains an electromagnetic recording microbalance for measuring adsorption. The samples were outgassed to a constant weight at 1000".Water was then introduced into the system from sulfuric acid solutions. The water was adsorbed on the oxide and partly removed by evacuation at 30". The water remaining after evacuation was irreversibly adsorbed and was of primary interest. Samples containing approximately three monolayers of irreversibly adsorbed water were used for the thermal desorption studies. The amount of water adsorbed on the individual samples was determined by measuring the total water desorbed during the thermal desorption cycle.
PUO, SAMPL
THERMOCOUPLE Figure 1. Gravimetric adsorption system.
Apparatus. The thermal desorption process was followed with a Bendix Model 12-107 time-of-flight mass spectrometer. This instrument provided simultaneous qualitative analyses of the desorption products and a quantitative measure of the desorption rates. The m l e range of 1 to 100 may be scanned at approximately 5-sec intervals or any given peak can be monitored continously. For this study the water peak ( m / e 18) was monitored continuously and recorded at 30-sec intervals. Prior to beginning a run the sample desorption cell was connected to a short inlet tube leading directly into the ionizing region of the spectrometer (Figure 2). During desorption the sample was pumped on continuously with all of the desorbed gases being pumped through the spectrometer source and detected. The temperature of the sample was continuously recorded using the thermocouple a t the bottom of the sample tube. This thermocouple had previously been calibrated with a second thermocouple buried in the sample. ( 8 ) J. L. Stakebake, R . W . Loser, and C. A. Chambers, Appi. Spectrosc., 25, 70 (1971). (9) P. A. Redhead, Trans. FaradaySoc., 57, 641 (1961). (IO) Y. Amenomiya and R. J. Cvetanovic, J. Phys. Chem., 67, 144
(1963). (11) I, V. Krylova, A. P. Filonenko, and Yu. P. Sitonite, Zh. Fiz. Khim., 41,2839 (1967). (12) P. A. Redhead, Vacuum, 12, 203 (1962). (13) P. A. Redhead, Amer. Vacuum Soc. Symp., 12, (1959).
Surface Interactions beiween Water and Plutonium Dioxide FILIOYENT
,--lONlZlNG
--j
583
REGION
I
30t
ACCELERATINO GRIDS SEPARATINO REOIDN
ELECTRON TRAP
201
1 VALVES \L
' L -
} PHYSICAL ADSORPTION
QUARTZ LINED S / 9 SAMPLE TUBE
RESiSTLNCE HSATER
SAU1I)LE
Figure 2. Inlet section of the mass spectrometer as used for thermal desorption
Procedurt.. For each run a sample weighing approximately 50 mg was loaded into the sample tube which was in turn attached to the mass spectrometer. It was found that when samples larger than 50 mg were used the amount of water desorbed during a run would overload the instrument. The sample tube was evacuated a t room temperature until the pressure in the ionization region of the spectrometer reached the Torr range. Actual pressures in the sample chamber were slightly higher due to the location of the ionization gauge tube. During each run a temperature programmer was used to increase the temperature of the sample at a linear rate from 25 to 900". The inertia of the system required the use of fairly slow heating rates. For this study approximate heating rates of 5, 18, 20, ,ind 30"/min were chosen. The exact heating rate was measured for each individual run. The temperature of that portion of the desorption cell above the furnace was maintained at about 135" to minimize readsorption of the gases before they reached the mass spectrometer source. The spectra obtained from the spectrometer during a desorption run were processed via a time-sharing Fortran computer program .I4 This program converted measured peak height into outgassing rates in standard cm3 per sec. The program also provided a summation of the water desorbed during a run.
'\
I
I
200
Figure 3.
ide.
400
I
600 TEMP, OC
800
1000
Gravimetric desorption of water from plutonium diox-
The first chemisorbed phase to be desorbed is believed to consist of water molecules hydrogen bonded to the surface. Molecules in this phase were removed by heating under vacuum to 500". The second chemisorbed phase encountered during desorption was the result of what is believed to be a dehydroxylation process. As mentioned earlier the initial adsorbed layer of water is believed to consist of hydroxyl groups. When these hydroxyl groups are desorbed from metal oxides, they reassociat,e to form water molecules. Temperatures of 1000" were required to remove this second chemisorbed phase. Thermal Desorption. Results from the thermal desorption of water vapor are presented as thermal desorption spectra which indicate a two-phase chemisorption of water on plutonium dioxide (Figure 4). Samples used for Resul1,sand Discussion these spectra contained from 0.72 to 1.1 mg of chemiGrauimetric Desorption. The initial water desorption sorbed water per gram of oxide. Similar spectra were obstudies had previously been carried out gra~imetrically.~ tained from samples containing various amounts of chemWater was first adsorbed on a sample of plutonium dioxisorbed water. ide at 27". Following adsorption the surface was saturated Table I1 summarizes the results of this study and shows with adsorbed water. While the sample was still in the the location of the water desorption peaks. All of the demicrobalance, the water was desorbed by heating the sorption results show one species to be desorbed in the sample under vacuum at successively higher temperatemperature range from 100 to 150" while a second species tures. The results of this study are summarized in Figure was removed between 300 and 350". 3. The desorption curve contains two discontinuities inThe total chemisorbed water removed from these samdicating three different modes of adsorption. The first ples varied from about 0.72 to 1.15 mg/g and was associtype of desorption results from the physical adsorption of ated with both adsorbed species. Since the peak height of water. Approximately 67% of the water was adsorbed in this each species is proportional to the total water removed manner and could be removed under vacuum without the (14) R. W. Loser, C. A. Chambers, and E. D. Ruby, RFP-1400, "Ttmeapplication of heat. 'The remaining 33% of the water was Sharing Fortran Program for the Dynamic Analysis of Gases by present as two chemisorbed phases which could only be reTOF Mass Spectrometry," The Dow Chemical Go., Rncky Flats Division, Golden, Colorado, 1969. moved by heating up to 1000". The Journal of Physical Chemistry, Val. 77,No. 5, 1973
J. L. Stakebake
584 TABLE II: Analysis of Thermal
Desorption Spectra for H20 Adsorbed on PuOg
_ I _ -
Maximum desorption Species I Run
FD-A
0.72
0.073
FD-5
1.15 0.99
0.161
FD-G FD-D
0.363 0.498
0.72
Species iI
-
Tm, "K
Rate, cm3/sec
Tm. "K
371 378 393 398
1.5 x 10-3 4.5 x 10-3 8.0 x 10-3 7.5 x 10-3
598 601 613 618
--
Rats, cm3/sec
1.2 x 3.5 x 6.9 x 7.4 x
10-3 10-3 10-3 10-3
8400
7600
j3 = 0.073°C/sec * /3 = 0161°C/sec
j
ma x
6800
\
p p
q,
= =
0.363OC/sec 0.498°C/sec
A
3000
o
2800
.
t
2600
(1
a
J
* 2400
?
4400
I
3600
2a 1800
2800
a 1600 0
z
2000
P
1400 4
E 1200
I200
3 0 1
IO0 203 300 400 500 600 700 800 900 TEMP., 'C
Flgure 4. Thermal desorption spectra of water chemisorbed on Dlutonium dioxide.
1000
800 600
400
during the run, the approximate amount of water adsorbed in each phase can be calculated. Table 111 shows the approximate amounts of water adsorbed as species I and II and the relative surface coverage for each species. The ratio of the water adsorbed as species I to that adsorbed as species 11 varied from I to 1.3. The fact that the relative surface coverages were greater than 1.0 for each species is attributed to two probable causes: (1) some of the water was being adsorbed in the next molecular layer, and (2) variations in the surface area of the individual samples due to the surface area being measured on the bulk sample. Another illustration of the two-phase adsorption of water is shown in Figure 5. These spectra were obtained by thermally desorbing water from a sample over the temperature range from 100 to 900" and then cooling the sample to rooin temperature while stili under vacuum. The desorption process was then repeated a second time over the same temperature range. Both adsorbed species appear t o be desorbed ad a higher temperature than the comparable ones shown in Figure 4. This is the result of a 1-pparticulate filter which was used to contain the radioactive contamination. This filter retarded the flow into the mass spectrometer thus producing Tm values which were abnormally high and decreasing the spectral resolution. Nevertheless, these data still provide qualitative comparisons. The Journal of Physical Chemistry, Vol. 77, No. 5 , 1973
200 L
1
I
I
I
1
I
1
B
I
100 200 300 400 500 600 700 800 900 T,'C
I
Figure 5. Run 1, thermal desorption spectrum of water chemisorbed on plutonium dioxide. R u n 2, thermal desorption spectrum of water readsorbed on plutonium dioxide which had been heated under vacuum to 900'. All of the water adsorbed as species I was re-moved during the first desorption run. The strongly bound water adsorbed as species I1 also appeared to be completely removed during the first run. However, when the second run was made, desorption spectrum 2 shown in Figure 5 was obtained indicating some readsorption of species II. This is indicative of a very reactive plutonium dioxide surface being formed during the high-temperature evacuation. When the sample was cooled traces of water in the residual gas were readsorbed as species II. Such adsorption under vacuum has also been observed in the case of thorium oxide.l5 The activation energy of desorption for each of the two themisorbed species shown in Figure 4 was calculated (15) E. L. Fuller, Jr., H. F. Holmes, and C. H. Secoy, J. Phys. Chem., 70, 1633 (1 966).
Surface lnteracfions oetween Water and Plutonium Dioxide
585
TABLE II I: Surface Coverage of Chemisorbed Species
Species I
Run
FD-A FD-5 FD-C FD-D
Total chemisorbed water, mg/g
Adsorbed water, mg/g
Relative surface coverage
Adsorbed water, mg/g
0.72 1.15 0.99
0.41 0.66
1.3 2.1 1.? 1.2
0.31 0:49
0.53 0.36
0.72
STEP
14.8
1
I 4.4
2 14.0 g 13.6
SPEC1 E§
Ed = 68 kcal/mole
"
N
131.2
"
0.46 0.36
-
I: A H 9 6 8 kcal/mols_
/
fi
J
i
"
t: _I
--
Relative surface coverage
I
E:
P
1
Species I I
-
SPECIES
I:
Ed = 2 0 kcal/mole
STEPll: A H = 20 kcal/mok
t+ _* *_ r~
12.8
"
OH OH
12.4 .
I
L.L--.-L&-&/ 1
4
I
8
1,
,
J
-Pu-
I
Pu-
4-
He0
--.)
-Pu
1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 1000/Tm Figure 6. Activation energies for the desorption of chemisorbed water from plutonium dioxide.
using eq 4 for a first-order reaction and eq 3 for a secondorder reaction. The best fit of the data was obtained from the first-order equation. A plot of eq 4 for the two species is shown in Figure 6, For the first desorbed species the activation energy of desorption was calculated from a leastsquares fit of the data and found to be 20 kcal/mol and the preexponential kinetic factor was equal to 4 x lo9 sec-l. This observed value is somewhat less than that calculated from transition state theory. However, it is probably more realistic since it was determined from experimental data. This also tends to suggest that this species is not chemisorbed in the strictest sense of the word. In the cast3 of the second desorbed species the activation energy of desorption was calculated to be 68 kcal/mol. The preexponeatial kinetic factor was equal to 4 X 1012 sec-l. Both of these values are typical of a chemisorbed species. Mechanisrn of Water Adsorption. Results from the gravimetric and thermal desorption studies have shown water to be (desorbed from plutonium dioxide in three different steps. This is interpreted as being indicative of three adsorbed species involving two or three different types of bonds. Adsorption of these species is the result of a combination of physical and chemical adsorption processes. Positive identification of each species has not been made. However, on the basis of this investigation and the conclusions ireached by other workers7JeJ7 the three-step adsorption mechanism shown in Figure 7 can be proposed. Step I. Chemisorptton. The intitial step (in terms of desorption this is species n) involves the adsorption and dissociation of the water molecule to form two adsorbed hydroxyl groups. This process occurs very rapidly on a clean plutonium dioxide surface which is typical of nonactivated chemisorption. The heat of adsorption can be assumed
STEP III:
H' 8 I
A H = IO kcaI/mob
"H
O I
-
Pu-
H
H
H I
Proposed mechanism for the adsorption of water on plutonium dioxide. Figure 7.
to be equal to the activation energy of desorption for species IT. For this hydroxylation step this is 68 kcal/mol. This value is comparable to the 60 kcal/mol observed by Ustinov and Ionovl8 for their 0 2 adsorbed phase of water on tungsten. Step 11. Quasi-Chemisorption. The second step in the chemisorption process involves a species which is not too strongly bound. The most likely candidate for this type of adsorption is a water molecule held by a hydrogen bond between the oxygen of the water molecule and the hydrogen atoms of the surface hydroxyl groups. Water adsorbed in this manner may either be singly or doubly hydrogen bonded to underlying surface hydroxyls. If the molecules are doubly bonded, the maximum number which could be adsorbed in this manner would equal the number of molecules actually chemisorbed. Single hydrogen bonds would allow twice as many water molecules to be quasi-chemisorbed. A rough comparison of the amount of water adsorbed as species I and 11 indicates that thg ratio of chemisorbed water molecules to hydrogen bonded molecules is I: 1 as (16) T. Morimoto, M. Nagao. and
F. Tokuda, J. Phys. Chem., 73, 243
(1W39). (17) H. F. Holmes, E. L. Fuller, Jr., and C . H. Secoy, J. Phys. Chem., 72, 2095 (1968). (18) Yu. K. Ustinov and N. I . lonov, Phenomena loniz. Gases, Int. Conf., Contrib. Pap., 8th, 1967, 2, E, 4 (1967). The Journal of Physicai Chemistry, Vol. 77,
No. 5 , 7973
Y.
586
required for double hydrogen bonding. The heat of adsorption for this step can be approximated by the activation energy of desorption of species I1 of about 20 kcal/ mol. This value is the same as that reported by Ustinov water species adsorbed on tungand Ionovls for their sten. It is also similar to the 19 kcal/mol reported by Holmes, et al.,I7 for the heat of adsorption encountered in the hydroxylation of thorium dioxide. Step III. Physisorption. The final step in the adsorption of water vapor is the actual physisorption of water molecules on a water covered plutonium dioxide surface. Interactions in this step are primarily between water molecules. The heat of adsorption for this step was not determined, however, it should approximate the heat of liquefaction of water.
Hatano, K. Takeuchi, and S. Takao
Summary and Conclusions Gravimetric and thermal desorption studies have illustrated the complexity of the water adsorption process. Thermal desorption spectra showed water to be chemisorbed as two different species with different binding energies. Hydroxylation of the oxide surface took place with a heat of adsorption of 68 kctil/mol while chemisorption on the hydroxylated surface took place with a heat of adsorption of 20 kcal/mol. A single physisorption process accompanied the two chemisorption processes. Acknowledgment. The author gratefully acknowledges the assistance of T. L. McFetters and D. I. Hunter in making some of the experimental measurements and processing the data.
xygen-Containing Products in the Radiolysis Solutions of Nitrous Oxide Yoshihiko Hatarto,” Ken-ichi Takeuchi, and Satoshi Takao laboratory of Physical Chemistry, Tokyo lnstitute of Technology, Meguro-ku, Tokyo, Japan (Received July 13, 1972)
0xygen-containing products in the radiolysis of cyclohexane solutions of NzO have been quantitatively measured and found to be HzO and c-C~HIIOH,denoted by ROH. The yield of ROW, most of which is HzO, is in good agreedent with that of Nz. This finding shows that the decomposition of NzO in liquid cyclohexane finally leads to Nz and ROH with the ratio of one to one. A further study of the correlation of the nitrogen yield with the decrement in the hydrogen yield has been made in order to estimate the nitrogen yield per electron captured by NzO. Possible processes on the decomposition mechanism of NzO in the radiolysis of cyclohexane solutions are discussed.
Introduction Further, an attempt has been made on the correlation of the nitrogen yield with the decrement of the hydrogen Nitrous oxide has received more attention than any yield upon the addition of NzO in the radiolysis of liquid other solute among electron scavengers, particularly becyclohexane. Assuming that electron scavengers depress cause of the comparative ease with which the nitrogen the hydrogen yield from liquid cyclohexane by an amount formed can be measured. The formation of Nz from cycloapproximately equivalent to the yield of scavenged elechexane solutions of NzO has been studied by many trons,I1 one can estimate the nitrogen yield per electron gr0ups.l The results, however, cannot always be interpretcaptured by NzO. ed solely in terms of electron capture. The difficulty in interpreting the results arises from the fact that the ob(1) J. M. Warman, K . 4 . Asmus, and R. H. Schuler, Advan. Chem. served yield of Nz is much greater than the expected yield Ser., No. 82, 52 (1968), and the references cited therein. of electron in the radiolysis of liquid cyclohexane and also (2) R. Blackburn and A. Charlesby, Nature (London), 210, 1036 (1966). from the fact Chat the overall study on the formation of (3) N. H. Sagert and A. S.Blair, Can. J. Chem., 45, 1351 (1967). oxygen-containing products after the decomposition of (4) R. A. Holroyd, Advan. Chem. Ser., No. 82,488 (1968). (5) S. Sato, R. Yugeta, K. Shinsaka, and T. Terao, Bull. Chtrm. SOC. NzO has not been established yet. Jap., 39, 156 (1966). As the oxygen-containing products, thus far, the forma(6) In hydrocarbon-N20 systems other than cyclohexane7q8the formations of C - C , $ H ~ ~ Qand H ~Hz05 - ~ were reported in the cytion of H20 and alcohols was also detected. (7) A. Menger and T. Gaumann, Helv. Chim. Acta, 52, 2477 (1969). clohexane-NzO system.6-8 The yield of c - C ~ H ~ ~ Owhich H, (8) R. C. Koch, J. P. Houtman, and W. A. Cramer, J. Amer. Chem. occupied only a few per cent of the expected yield of oxySOC.,90, 3326 (1968). gen-containing products, was measured q~antitatively.~ (9) Recently in our laboratory the quantitative analysis of H20 in the gas-phase radiolysis of NZO-hydrocarbon mixtures has also been The yield of HzO, however, has scarcely been known. In carried out gas chromatographically.10 (10) S. Takao, Y. Hatano, and S. Shida. Bull. Chem. SOC.Jan. 44, 873 the present study, the measurements of H20 and other (1971). oxygen-containing products in the radiolysis of cyclohex(11) K.-D. Asmus, J. M. Warman, and R. H. Schuler, J. Phys Chem., 74, 246 (1970). ane solutions of NzO have been accurately carried The Journalof Phyticrrl Chemistry, Vol, 77, No. 5, 1973
