DETERMINATION OF HYDROGEN ATOMSIN BURNTGAS
June, 1958
693
TABLE IV SUMMARY OF CRYSTALLOQRAPHIC DATAOF Compound
Cell tY w
Space group
Cubic Cubic Hexagonal
Ini3vn F23 P321
LiaPb LisPba
Cubic Monoclinic
Fm3m C2/m
4 2
p-LiPb b'-LiPb
Cubic Rhombohedral
Pm 3m R3m
1 1
Pb a
LITHIUM-LEAD INTERMETALLIC COMPOUNDS' Cell constants
z 2 16
Li LizzPbs Li7Pb2
THE
a = 3.508A. a = 20.08 A. a = 4.751 c = 8.589A. a = 6.687A. a = 8.24A: b = 4.757A. c = 11.03A. b = 104.5" a = 3.563A. (220') a = 3.542-k. (Y = 89.5" a = 4.950A. .
h.
1
Cubic Fm3m 4 All values a t room temperature except for @-LiPb.
formly the Pb atoms amid the Li atoms. Figure 3 shows a two-dimensional representation of the ideal structures pictured in the layer corresponding t o the (110) plane of the body-centered sub-cell. I n LizzPbsthere are two types of layers which differ only by the number of Pb atoms per layer. These layers stack upon each other in such a way as to distribute the Pb atoms uniformly. Small deviations from the model positions exist in most of the structures. Only in Li6Pb3 do the P b atoms actually touch each other; however, given the 8/3 ratio, this aPpears t o be the most efficient way of distributing the Pb atoms. The pairing of Pb atoms is a common feature in the Na-Pb system, more so than in the
X-Ray density, g./cc.
Mole
Wt.
% Li
Yo Li
Ref.
0.53 3.86 4.59
100.0 81.5 77.8
100.0 12.8 10.5
13
5.06 5.37
75.0 72.7
9.1 8.2
5 4
7.86 8.00
50.0 50.0
3.2 3.2
3 3
11.35
0.0
0.0
14
.. 5
Li-Pb system.16 No evidence has been found for the compound LiloPbereported by Rollier and Arreghini.I6 I n the powder patterns there exist similarities in the spacings between the various compounds; probably a mixture of phases (LiaPb and LilPbz, possibly) was misinterpreted as being a single phase. Ac~owledgments.-we would like to thank Mr. vernonsilveira for much of the photography, Mr. LeRoy Green for preparing a pure sample, Mr. Robert Lim for the chemical analysis, and Dr. D. HaTempleton for his interest and his discussions On false symmetry. (15) N.E.Weston, D. P. Shoemaker, Abstracts of the Communications, 4th International Congress, Internatirnal Union of Crystallography, Montreal 10-19, July, 1957. (16) M. A. Rollier and E. Arreghini, 2. Krisl., 101, 470 (1939).
(13) H. Perlitz and E. Aruja, Phil. Mag., 80,55 (1940). (14) H.P. Klug, J . Am. Chem. Soc., 68, 1493 (1946).
DETERMINATION OF HYDROGEN ATOMS IN RICH, FLAT, PREMIXED FLAMES BY REACTION WITH HEAVY WATER BY C. P. FENIMORE AND G. W. JONES Research Laboratory, General Electric Co., Schenectady, N . Y . Received January dq9 1968
The concentration of hydrogen atoms in the burnt gas from flames burning on a cooled porous burner is determined by adding D 2 0 to the reactants and measuring the rate of formation of H D in the products. [HI can be inferred if the rate kz D20 +HD OD is known. kz is taken from Avromenko and Lorentso with a small change, constant of the reaction H and the consistency of [HI by this method with [HI as measured by Bulewicz, James and Sugden in a quite different manner is evidence that both methods are correct. In a 1300°K. hydrogen flame, or hydrogen plus carbon monoxide flame, [HI is about 2500 times the equilibrium concentration of H atoms in the burnt gas, [HI,,,. The ratio [H]/[H].,, decreases with rising temperature; it is about 140 in the burnt gas from a 1500°K. flame. The average rate of consumption of oxygen
+
+
+ e.+ k4
in such flames is equal to the rate of the reaction H OZ OH 0 if k d has a steric factor of order unity and if E, = 20 f 2 kcal. The great excess of hydrogen atoms is a peculiarity of hydrogen and hydrogen plus carbon monoxide flames. I n the burnt gas from rich hydrocarbon flames [HI = [HI,,,. Furthermore, the burnt gas from mixed fuels of hydrogen plus a little hydrocarbon possess much smaller ratios of [HI/ [Hle,, than the burnt gas from hydrogen flames at the same temperature.
Introduction This report describes measurement of the concentration of hydrogen atoms in the burnt gas from rich flames. A flame of known burning velocity and temperature is established on a water cooled,
porous metal burner. A little DzO is added to the reactants and the concentration of hydrogen atoms is inferred from the rate of appearance of HD. With rich hydrogen flames, our results prove to be consistent with those of Bulewicz, James and
C. P. FENIMORE AND G. W. JONES
694
.-----
vessel to prevent condensation at any point in the system. 50 cc./sec. of carrier nitrogen is sufficient when 10 cc./sec. or less of deuterium is oxidized. The mixed reactants are burnt in a flat flame on a porous metal burner which is cooled with warm water. Samples of the burnt gas are withdrawn through fine quartz probes into a sample bottle maintained at about 1 mm. pressure by pumping. The samples are analyzed mass spectrometrically. Temperatures are measured with fine quartz coated thermocouples. The burner and thermocouples are constructed according to Kaskan.*
128YK, 28 cms/sec
0.04 0.12 r
0'08
Calculation of the Concentration of Hydrogen Atoms Figure 1 shows the results for four typical runs with added DZand four with DzO. When a little Dz is added to the reactants of hydrogen air flames, d[HD]/dt is zero everywhere in the burnt gas. The ratio [HD]/[Hz] is equal t o the expected equilibrium ratio, that is, approximately equal to ~ [ D z ] o / [ Hadded ~ ] o in the unburnt reactants. It can be concluded that Hz, H D and Dz are always in equilibrium among themselves in the burnt gas. When an equal amount of DzO is added to the reactants instead of Dz, the [HD]/[Hz] ratio is smaller just downstream of the flame, and increases to the equilibrium value only after one to five milliseconds. Evidently the attack of H atoms on DzO is much slower than on Dz. It is assumed that H D is formed and destroyed in the burnt gas by the reactions
c t 7-
T - 0
1500°, 4 9 cms/sec
0.06
0.04 0
0.5
PROBE DISTANCE FROM BURNER SURFACE
Fig. 1.-Formation of H D in burnt gas from rich Hz, air flames. Burnt gas temperature and velocity of cold reactants noted on each plot. Solid symbols, DS added; open symbols, equal amount of DzO added instead.
Sugdenl who deduced the concentration of hydrogen atoms in sodium or lithium colored flames from the assumption that equilibrium is established in the burnt gas between alkali metal atoms and the hydroxide
+ H2O
MOH
+H
They measured alkali metal concentrations by the emitted intensity of the resonance lines, took MOH by difference, and used estimated equilibrium constants to obtain [HI. We have examined other fuels as well as hydrogen. It will be seen that the large excess, relative to equilibrium, of hydrogen atoms observed in fairly cool hydrogen or hydrogen plus carbon monoxide flames is not found in the burnt gas from hydrocarbon flames. Experimental Arrangement Nitrogen, fuel and air are metered through critical flow orifices and mixed. The nitrogen is passed through a column of hot copper oxide before mixing with the other reactants. Deuterium is added to the nitrogen stream either upstream of the copper oxide, and oxidized to heavy water, or if desired i t is added downstream of the copper oxide. Thus nitrogen, traces of oxygen and either deuterium oxide or deuterium, as desired, are supplied to the fuel air mixture. The copper oxide is a 2.5 cm. diameter by 20 cm. long column of oxidized wire clippings in a quartz tube heated to redness. The downstream end of this tube is joined to a brass mixing vessel through a uartz to metal seal, and the other reactants are warmed Before entering the mixing (1) E. M. Bulewicz, C. G. James and T. M. Sugden, Proc. Roy. Boc. (London), 8236, 89 (1956).
.
kl
0.8 cms
H +
M
Vol. 62
H
+ D2O
D
-= +
z H D~ + D 'lzki
kZ
HD
1/&3
1/2k3
OD
HDO '/zkz
+D
'lZkZ DP
+ OH
k3
and also by the similar set of reactions obtained by exchanging H and D in the formulas above for every species. In view of the high temperature, the rate constant for each type of reaction is assumed the same for different isotopic species. According to the literature, k , has a value in the neighborhood of 1011e-7,000/fi* (mole/l.) sec.-1.314 IC3 has been measured15 though not hitherto confirmed by independent work; and since kz and ks are related^ through a known equilibrium constant, the in literature suggests that kz = 6 X 1011e-25~500/RT our temperature range. The present work confirms Avromenko and Lorentso within a factor of two. Since reasons will appear for thinking to be somewhat larger than the literature value, we use a temperature independent factor of 10l2 for kz rather than 6 X lo1'. Anticipating a little, it can be said that the measurements with hydrocarbon fuels suggest that [HI in the burnt gas from hydrocarbon flames is the equilibrium concentration. Then an independent estimate of k2 can be obtained and this is the source (2) W. E. Kaskan, "Sixth Symposium on Combustion," Reinhold Publ. Corp., New York, N. Y., 1957, p. 134. (3) A. Farkas and L. Barkas, Proc. R o y . SOC.(London), A l l , 124 (1935). (4) M. van Meersshe, BUZZ. ~ O C .chim. belg., 60, 99 (1951). (5) L. Avromenko and R. Lorentso, Zhur. Fix. Khim., 24, 207 (1950).
c
DETERMINATION OF HYDROGEN ATOMSIN
June, 1958
BURNT
695
GAS
of the increase we give the Russian value.6 From the assumed mechanism, it follows that
+
Jc2
{1HI[DzOl
+ [DI[HzOl + [HDOl([Hl 2
- k3
[HDI (IOHI
c
+ PI)
f [OD11
but this expression can be simplified. The differences observed between the addition of D2and DzO lead to the conclusions that Icl>>kz, in agreement with the literature, but that the term in k , is zero since Hz, D2 and HD are in equilibrium among themselves everywhere in the burnt gas. Then for the case of heavy water addition, the expression for d [HD]/dt can be rewritten as expression I
by omitting the term in kl; by neglecting [D] in the sum ([D] [HI) and [OD] in ([OD] [OH]); by writing [DzOIo= [DzO] ([HD] [HD0])/2, [Hzlo = [Hzl [HzOl, [Dl = [HDl[Hl/2 IHzl; and by assuming that kz [HI [HzO] = k8 [OH][Hzl. The approximations are all fairly obvious except the last one which cannot be proven to be correct until [HD ]/ [Hz] has attained its equilibrium value; then the last assumption is also obvious. Since our measurements are made when [HD]/[Hz] is 70% or more of the equilibrium value, even the last approximation could not introduce a grave error. Furthermore, it might be mentioned that the last approximation is claimed as an experimental fact by Bulewicz, James and Sugden.' I n Fig. 2, the upstream points obtained by adding DzO are replotted from Fig. 1 so that expression I can be applied. The time scale is made on the assumption that the gas velocity is the final burnt gas velocity everywhere downstream of the burner. The curvature of the lines in Fig. 2 shows that [HI decays a little with time, but the decay is small during intervals of a millisecond. Knowing [Hz] and [H2IO,one can obtain kz[H] at one millisecond time or less and, by substituting for kz, get [HI. The value of kz from the literature must be trusted through a 1000° extrapolation to the flame temperature, of course. k z is trustworthy because it can be checked approximately by the curvature of the graphs of Fig. 2. (Other checks will be evident later.) Bulewicz, James and Sugden' found that hydrogen atoms recombine in the burnt gas a t one atmosphere at a rate d (l/[H])/dt = 1.2 X 107 (mole/l.)-l sec.-l, a rate smaller than but reasonably close to that found at lower temperatures.7 If l/kz[H] from the
+
+
+
++
(6) Avromenko and Lorentso expressed their constant in the form ATL/28-EIRT,and this is the form extrapolated with subsequent absorption of T L h into a new frequency factor. One of the refereea pointed out that if the form A'Te-EIRT had been extrapolated instead, the absolute reaction rate form, the values obtained would have been about twice as large and so the upward revision of bz would have been automatic. (7) W. Steiner, Trans. Faraday Soc., 31, 623 (1936).
~~
0
Fig. 2.-Data
2
4
TIME, MILLISECONDS. of Fig. 1 for DzO addition replotted,
1285" curve of Fig. 2 is plotted against time, a line of slope 0.6 is obtained; whence, assuming the rate constant for hydrogen atom recombination to be that quoted, one finds kz = 2 X lo7. But k2 as derived from Avromenko and Lorentso is 4.5 X lo7 with the increase we give their value, or 2.7 X lo7 if the original temperature independent factor of 6 X lo1' is used, and the good agreement argues for the correctness of the extrapolated value. It may be noted that the agreement is better with the original temperature independent factor. Because of the approximate nature of the test, however, we do not think it can discrininate between values differing by a factor of only about two. A similar check can be obtained at 1324", but this is less persuasive because the curve in Fig. 2 for 1324" is so nearly straight. Results for Hydrogen and Hydrogen-Carbon Monoxide Flames These findings are summarized in Table I. It might be mentioned that the water gas equilibrium is always fairly well attained in the burnt gas from carbon monoxide flames. Perhaps this should be anticipated from measurements made long ago.8 The seventh column of Table I shows thst [HI is many times its equilibrium concentration in the burnt gas, [ H l e p , . The ratio of these quantities decreases with rising temperature. At constant burning velocity, [HI decreases moderately with rising temperature, but [HI,,, increases strongly of course; so, roughly, the logarithm of average [H]/[HIequ varies linearly with the reciprocal of temperature. This crude relation allows a comparison of our data with the results of Bulewicz, James and Sugden' obtained at higher temperatures by a different method. Figures 1 and 4 of their paper show that they too found log { [H]/[HIequ\ t o be roughly linear in 1/T below 2000°K. For them, the logarithm to the base ten is 1 at 104/T = 5.3 to 5.6, and 1.5 at 5.8 to 6.1. For us, the logarithm is 2 at 104/T = 6 . 5 , 2 . 5 at 6.9, and 3.0 at 7.3. Obviously the two sets of results are mutually consistent. We are interested in the question whether the great excess of hydrogen atoms would be expected, say by a comparison of the rate of reaction 4 (8) F. Haber and F. Richardt, Z . anarg. Chem., 38, 5 (1904).
C. P. FENIMORE AND G. W. JONES
696
Vol. 62
region hugs the burner surface closely and is about TABLEI HYDROGEN ATOMSIN THE BURNTGAS FROM RICH, FLAT 0.05 em. thick with no systematic variation due to temperature or flow rate. Furthermope, the temHYDROGEN-CARBON MONOXIDE FLAMES
perature, as measured by fine quartz coated thermocouples, attains its final value, within 4%, 0.05 em. from the burner surfase. T, OK. Solving U = 2k4[02][H]for k4, one expects to 1285 1.19 1.92 0 28 1 . 7 4400 2.9 0.05 obtain k4 = 10~2e-(17,000to 22,ooo)/RT. k4 is listed in 1324 0.98 2.70 0 41 2 . 2 2600 3 . 4 .05 the eighth column of Table I. The values are cor1.29 1.75 0 28 1.3 1700 3 . 8 .05 related by k4 = 8 X 10iie-20~000~~r. Thus the 0 18 0.8 2000 4.1 .05 notion is supported that hydrogen atoms partici1.93 1.27 1340 0.94 2.67 66 22 0.7 1300 4 . 8 .06 pate in the combustion in the way anticipated. 0.87 2.67 34 30 1 . 4 1700 3 . 9 .05 The expression found for le4 is not a very good de0.97 2.67 80 19 0 . 5 1300 4 . 6 .08 termination because of the approximations made, 1420 1.19 1.82 0 39 1.0 390 7 . 5 .05 but the partly compensating errors should not be 0.96 2.22 0 48 1.5 500 6 0 .05 serious enough to alter the conclusion that the great 1.05 2.22 67 26 0 . 6 .490 7 . 5 .06 excess of hydrogen atoms observed is required to maintain the flame. 1500 1.52 1.27 0 33 0.6 130 11 .05 Hydrocarbon Flames.-In the burnt gas from 1.11 1.89 0 49 1.1 160 9 .05 hydrocarbon flames, [HI can be determined almost 1.01 2.22 67 33 0.7 130 10 .06 in the same way as for hydrogen flamqs. Again ( [Nz + A] in air + carrier [NS])/[fuel in reactants]. IJ Fuel in reactants/stoichiometric fuel. Derived from the addition of D2 to the reactants gives a constant kz[H] at one millisecond or less with kz = lO12e+5300O’RT. [HD]/[H2]ratio everywhere in the burnt gas, but (moles fuel burnt/unit area, sec.) D20 addition gives smaller ratios which increase where [02]= d2k4 = [HI [02] X flame thickness with time to the equilibrium value. Afew per cent. O2fed, measured at the h a 1 flame 2‘. of the fuel appears in the burnt gas as acetylene or methane where it decomposes slowly. Therefore k4 H+Oz+OH+O the approximation made to form expression I, (4) [ H ~ ]= o [Hz] .[HzO], is replaced by CY = [Hz] with the average reaction velocity in the flame [H20]where a increases a little with time in the U = (moles fuel burntjunit area, sec.)/flame thickness burnt gas. Also in expression I, the fraction I n hydrogen flames, or hydrogen plus carbon mon- [H2]/[H210is replaced by [Hz]/a but this is very oxide flames, oxygen molecules are consumed only nearly constant in a single run. These changes by reaction 4 according t o current views;-and there- cause no difficulty since a complete analysis of the fore the rate of reaction 4 should be ‘/2 U since 2H2 gas is made at each sample point. or 2CO are consumed for every 0 2 . . Hydrocarbon flames cannot be burnt very rich The comparison is possible under some crude ap- without soot forming; for example, acetylene flames proximations: that [HI in the flame is the same as richer than about 1.6 X stoichiometric fuel form [HI in the burnt gas just beyond the flame, an soot under our conditions. We avoid sooty flames. approximation partly supported by the slow decay Also to obtain low temperature, low burning velocof [HI in the burnt gas; that all reaction occurs at ity flames of propane and methane, it is convenient the final flame temperature, not an unreasonable TABLP) I1 approximation in view of the work of Kaskan2; that the average molecular oxygen in the flame HYDROGEN ATOMSIN THE BURNTGASFROM RICH HYDRO[02], is l / 2 , or some such known fraction, of the CARBON FLAMES‘ oxygen fed when measured at the flame temperaRescN L A “;zi,”,flow, tant mole/l. [HI, AH]/ ture. Then the rate of reaction 4 is kq[HI [ 0 2 ] ; where OT, K. -Fuelfuel strength cm./sec. X lo’ [ lequ [HI is taken from Table I, and k4 has an activation 1700 1.7 1.0 9.4 C2H2 9.4 1.59 energy of 17-22 kcal., and a probable steric factor 1775 1.0 3.5 CzHz 12.7 1.59 12.7 of unity. Lewis and Von Elbee base a suggested 1850 CzH2 15.2 1.59 15.2 5 0.7 steric factor of 10-3 partly on the work of Farkas 1600 1.4 3.7 1.1 C3Hs 8.8 1.24 and Sachsselo but three more recent 1.0 5.0 1.7 CaH8 5 . 2 1.24 1700 indicate a value near unity. 1.8 0.8 3.8 1700 CsHs 7 . 0 1.57 For flames conU is calculable from Table I. 0.5 0.6 4.0 4.0 1.18 CHI taining carbon monoxide, the flame thickness tabu- 1650 1700 CHI 2.7 1.18 4 . 8 1 . 0 0.7 lated is the thickness of the strongly luminous zone. 150 Hydrogen flames are invisible but they must be 1455 7.9%czHz 2 . 7 1.26 18.3 31 65 about 0.05 cm. thick. If a trace of acetylene is 1455 19.0%CzHz 4.7 1.21 12.6 10 added to hydrogen flames, the resulting emission 1345 91 1600 2 . 0 1.27 18 Hz (Nz
+
Q MixC8 in tureb strength fuel
Reackr tants X 1O-sd Flame flow [HIC mole/-1 thickH] 1. ness, om.) mol&. I om. sec. X 106 [Hlequ. sec.-l
.
0
+
(9) B. Lewis and G. Von Elbe, “Combustion. Flames, and ExpIosions in Gases,” Academic Press, New York, N. Y., 1951, p. 59. (10) L. Farkasand H. Sachsse, 2.physik. Chem., [I312 1 , 111 (1934). (11) N. Semenoff, Acta Physicochim., 20, 291 (1845). (12) R. R. Baldwin, N. 8. Corney and R. F. Simmons, “Fifth Combustion Symposium,” Reinhold Publ. Corp., New York, N. Y., 1955, p.
602.
(13)
R. R. Baldwin, Trans. Faraday Soc., 62,
1344 (1956).
+
970 48 1 . 9 1.34 18 1.2% C2Hz 1345 36 560 1.6% C ~ H Z 1 . 9 1.40 18 1345 1345 1.1%CHI 1 . 9 1.36 16.5 44 720 0 The last 6 rows in the table refer to predomjnantly Hz, air flames containing small hydrocarbon additlon. Thus at 1345O, an H2 flame was burnt, a mixed G H z , Ht flame follows with 1.2% CgHz in the fuel, etc.
b
June, 1958
OXIDATIVEDEGRADATION OF DEUTERATED STYRENE POLYMERS
to use oxygen as the oxidant. Acetylene flames are burnt with air. The results are listed in Table 11. For purposes of comparison, we estimate that [HI would be about 50 times the equilibrium concentration of hydrogen atoms in hydrogen flames a t 1600°K., and perhaps 10 times at 1850". It is remarkable that no such excess of hydrogen atoms is observed in hydrocarbon flames. With the chosen value of k2, [HI works out to be essentially the equilibrium concentration in each run. That [HI is 'the equilibrium concentration in the burnt gas from hydrocarbon flames is partly an imposed result. The value of kz derived from Avromenko and Lorentso was increased by a factor of 1.7, as explained earlier, in order to achieve it. Even with a smaller value of k2, [HI works out to be very close to the equilibrium concentration. Since [HI increases markedly with temperature in hydrocarbon flames, but does not do so in hydrogen flames where it is present in great excess, we infer that there is no excess in the gas from hydrocarbon flames; and k2 is adjusted slightly to make the excess zero. The last six entries in Table I1 show that hydrocarbons are effective in decreasing excess [HI in hydrogen flames. At 1445"K., a pure hydrogen air flame has [H]/(H]e,, = 300 approximately. But if the fuel is 7.9% acetylene plus hydrogen, [HI/ [HI,,, is only 150; and for 19% acetylene it is only 65. At 1345"K., the poisoning action of acetylene is even more marked, and methane is similar in its action. In these runs with mixed fuels, a little acetylene and methane always sur-
697
vives into the burnt gas. There is no evidence that acetylene actually exchanges hydrogen atoms with the substrate, however. Acetylene recovered from a rich flame of a 90% acetylene, 10% deuterium mixture gives a pattern on the mass spectrometer which does not differ significantly from that of the acetylene fed in the reactants. A steady rich hydrogen, acetylene, air flame cannot be burnt a t 1345°K. if the hydrocarbon is increased much beyond the percentages shown in Table 11. The flame burns with a pulsating noise if the hydrocarbon is increased. At the same time, the temperature jumps rapidly with increasing hydrocarbon. Dr. W. E. Kaskan of our group explains this as follows: the flame is quenched and locally extinguished at some point on the burner surface. When the gas reignites above this point, .piloted by the surroundings, the igniting volume being farther from the burner possesses a burnt gas temperature nearer the adiabatic flame temperature. To this explanation we would add that hydrocarbon additions possibly quench the flames because they destroy hydrogen atoms or other radicals. It might be more nearly correct to suppose that fragments derived from hydrocarbons rather than the hydrocarbon itself catalyze the recombination of hydrogen atoms or of other radicals. Otherwise, acetylene might be partly deuterated after passage through an acetylene deuterium flame. If hydrocarbon fragments are the active catalysts, then one wonders whether C2 and CH emission may not derive its excitation energy partly from this catnlytic process. The suggestion is not original, but the decrease of excess [HI found by hydrocarbon addition has not been observed previously in flames.
OXIDATIVE DEGRADATION OF A SERIES OF DEUTERATED STYRENE POLYMERS1 BY MAXTRYON AND LEOA. WALL Rubber Section, National Bureau of Standards, Washington $6,D. C. Received January 86, 1968
The oxidation of polystyrene and a series of polymers prepared from specifically deuterated styrene monomers has been investigated in the presence of ultraviolet radiation and air a t 60". A ronounced isotope effect was obseryed when olymers contained deuterium in place of hydrogen in the a-position. All porymers in which the a-position was occupieaby deuthe post-effect terium or a methyl group showed a slower rate of increase in absorbance a t 340 mp wave length and about as compared with those with a hydrogen atom in the a-position. Values for the rate constants and apparent activation energies for both the fast and slow components of the, post-irradiation effect for each of the polymers are given. The results of a study of the photo-isomerization of trans-benzalacetophenone to the cis-isomer and thermal cis-trans isomerization of this material in a polystyrene matrix show that such an isomerization reaction is possible and may account for part of the post-irradiation effect.
Introduction Previous work in this Laboratory on the oxidation of styrene and or-deuterostyrene polymers2 indicated a pronounced isotope effect on the initial rate of increase in absorption at 340 mp due to oxidation in the presence of ultraviolet radiation and air at 60". The post-irradiation effect previously (1) Presented in part a t the 129th Meeting of the Amerioan Chemical Society in Dallas, Texas, April 9-13, 1956. (2) L. A. Wall, Mary R. Harvey and Max Tryon, THIBJOURNAL, 60, 1306 (1956).
observeda for polystyrene also was observed for the deuteropolymer. Studies of the reaction occurring during post-irradiation of polystyrene indicated two first-order reactions with activation energies of the order of 16 and 20-24 kcal. per m ~ l e . ~It. ~was suggested that these reactions were a hydroperoxide decomposition and a cis-trans isomerization. I n the present work the oxidation behavior of a (3) M. J. Reiney, M. Tryon and B. G . Achhammer, J . Raseorch Notl. BUT.Slonderds, 61, 155 (1953). (4) Leo A. Wall and Max Tryon, Nature, 1'78, 101 (1956).
