JEAN H. FUTRELL AND THOMAS 0. TIERNAN
158
Acknowledgment. Part of this work was supported by a grant from the Research Board, University of Illinois. The authors also wish to express apprecia-
tion to Professor A. H. Beavers, Agronomy Department, University of Illinois, for assistance with the density-gradient column.
Ionic Reactions of Unsaturated Compounds.
I.
Polymerization of Acetylene by Jean H. Futrell and Thomas 0. Tiernan Aerospace Research Laboratories, Chemistry Research Laboratory, Wright-Patterson Air Force Base, Ohio 64633 (Received J u n e 19, 1967)
Ion-molecule reactions of acetylene were investigated in conventional, high pressure, and tandem mass spectrometers. Evidence was obtained from ionization efficiency curves and from charge-exchange experiments for the existence of an excited molecule ion, C2H2+*, with an appearance potential of about 15.9 ev, which reacts differently from the ground vibronic state ion, C2H2+. Reactions of the individual primary ions and selected secondary, tertiary, and subsequent ions were investigated, and CzDz was examined in some experiments to clarify mechanistic details and to evaluate isotope effects. A highly branched chain reaction for the ionic polymerization of acetylene is deduced from these results.
Introduction >lass spectrometric investigations of ionic reactions in acetylene have been reported by several laboratories, using a variety of techniques‘-l1 for deducing the principal reactions involved. I n two of these studies,’~~ a fairly complete kinetic analysis for this system over the pressure range 0.001-0.3 torr was attempted. In addition, a novel experimental approach using a 3-Mev proton beam from a Van de Graaff accelerator as an ionizing medium for source pressures t o 1.3 torr was reported.ll One of the striking features of these studies is the complexity of the reaction scheme of this relatively simple molecule. Moreover, it is apparent from these studies that the kinetic order, and in some cases the parent-daughter relationship, in the chain sequence of reactions is often different from that deduced from stoichiometry. We have recently developed a high-pressure mass spectrometer system,12 and the considerable extant body of information on ion-molecule reactions of acetylene prompted its selection as a system for evaluating the performance of the spectrometer. A tandem mass ~pectrometerl~ was also used to evaluate elementary reaction steps suggested by the high-pressure results in order to define various steps in the reaction sequence. Since some of the data and deductions in The Journal of Physical Chemistry
the literature are contradictory, it seems appropriate to summarize our findings as the first report of a systematic study of ion-molecule reactions of unsaturates.
Experimental Section The apparatus and experimental procedures used in the pressure study have been described in detail else(1) F. H. Field, J. L. Franklin, and F. W. Lampe, J . Am. Chem. SOC.,79, 2665 (1957). (2) R. Barker, W.H. Hamill, and R. R. Williams, J . P h y s . Chem., 63, 825 (1959). (3) P. 9. Rudolph and C. E. Melton, ibid., 63, 916 (1959). (4) R. Fuchs, 2. Naturforsch., 16a, 1026 (1961). (5) A. Bloch in “Advances in Mass Spectrometry 11,” R. M.Elliot, Ed., Pergamon Press, New York, N. Y.,1963,p 48. (6) E. Lindholm, I. Szabo, and P. Wilmenius, Arkiv Fysik, 25, 417 (1963). (7) M. S. B. Munson, J . Phys. Chem., 69, 572 (1965). (8) J. H.Futrell and L. W. Sieck, ibid., 69, 892 (1965). (9) G. A. W. Derwish, A. Galli, A. Giardini-Guidoni, and G. G. Volpi, J . Am. Chem. SOC.,87, 1159 (1965). (10) C. E. Melton and W. H. Hamill, J . Chem. Phys., 41, 1469 (1964). (11) S, Wexler, A. Lifshita, and A. Quattrochi, Advances in Chemistry Series, No. 58,American Chemical Society, Washington, D. C., 1966,p 200. (12) J. H. Futrell, T. 0.Tiernan, F. P. Abramson, and C. D. Miller, unpublished data. (13) J. H. Futrell and C. D. Miller, Rev. Sci. Znstr., 37, 1521 (1966).
159
IONIC REACTIONS OF UNSATURATED COMPOUNDS where12 and will be described only briefly. The ion source has a dual leak dual reservoir sampling system, but in the present experiments only one inlet was used. Acetylene, obtained from the Matheson Co. and purified as described previously,s was introduced into the reservoir connecting to the ion source via a GranvillePhillips Series 213 automatic pressure controller. A static pressure tap from the ion source to an MKS Baratron Model 77H1 pressure transducer provided the reference signal to the controller, which, when energized, maintained ion-source pressure within about 1% of the selected value or =kO.OOOl torr, whichever is greater. The pressure differential from the source to pumping chamber was approximately 1000: 1 and the differentially pumped analyzer pressure did not torr a t 1 torr source pressure. rise above 2 ;< The distance from the collimated electron beam to the source exit aperture is 0.28 cm and a field strength of 10.6 v/cm was used in these experiments. With ionizing voltage set at 100 v and no gas in the chamber, the ionizing electron current was adjusted to amp in order to minimize approximately 5 X space charge effects. The pressure transducer (MKS Baratron) was then zeroed on its most sensitive range. The pressure desired for a particular run was then set to four-digit precision on the pressure meter, an appropriate control range mas selected, and the controller was switched on. After allowing a few minutes for source stabilization, the mass range of interest was scanned and recorded. Because of the procedure used to achieve space focus, as required for time-of-flight mass analysis, data reduction required correction for mass discrimination as described previously.12 Experiments with the tandem mass spectrometer followed the same format as previous studies.13J4 Since mass analysis of the impacting ion is an inherent characteristic of 1hese experiments, no precautions were taken to purify gases which were used as the source of impacting ions in this instrument. Except as otherwise stated, impacting ions of kinetic energy 0-0.4 ev were used in this research. Pulse-counting techniques were used for measuring the intensities of secondary ions. Appearance potential measurements were made on a modified Consolidated 21-103C mass spectrorneter.'6 Ionization efficiency curves were recorded directly by means of a Varian model F-80 X-Y recorder.
Results Pressure Dependence of I o n Currents. The principal results of the pressure study are presented in Figures 1-3 and Tables I and 11. Figure 1 illustrates the apparent chain-polymerization sequence for the major ions in the acetylene spectrum. A logarithmic pressure scale is used to emphasize both the apparently simple parent-daughter relationships and the fact that these ions constitute a gradually decreasing fraction of total
I
t
0.5
I
I
I
A
too SOURCE
loo0 PRESSURE IN MICRONS
Figure 1. Mass spectrum of acetylene as a function of ion-source pressure.
I
I
I
I
I
I
I
t
i
0.07 0.061
1
0.01
1
-1 0.7 0.8
I
40
I
I
I
,
I
60 80 SOURCE PRESSURE IN MICRONS
Figure 2. Semilogarithmic plots of the fractional intensities of C2H2+and C % H +as a function of acetylene pressure.
ionization with increasing pressure. The data reproduce very well up to a pressure of about 0.4 torr all the qualitative features of the analogous Figure 3 of Derwish, et al.' An attempt a t a more quantitative comparison, using ion-path length as a scale factor was only moderately successful. However, an error in pressure measurement or ion path length of ea. 25% (14) F. P. Abramson and J. H. Futrell, J. Chem. Phys., 45, 1925 (1966). (15) K. R. Ryan, L. W. Sieok, and J. H. Futrell, ibid., 41, 111 (1964). .
Volume 7.9, Number 1 January 1068
160
JEAN H. FUTRELL AND THOMAS 0. TIERNAN
Table I1 : Cross Sections for Reaction of Some Abundant Ions with Acetylene
0.3 u)
.
Reactant ion
z
e
-I 0.2
-
cz
t 4
+
CzH +
0 I-
CzHz CaHz C4H3
+
+
+
-Cross section for 10 v/cm field strengthThis researcha Lit. values X lOIB om=/ X 1010 cm2/ molecule molecule
113 77 46 18 14
7Zb 70b 62b 33b 18b
75. 12gd 72c 153d 48< 91d 46d 50d
a Distance between electron beam and ion-exit aperture, 0.28 cm. bReference 9, distance between electron beam and ion-exit aperture, 0.34 cm. data frofn ref 7 obtained by averaging electrometer and multiplier results, which differed by a factor of 1.6. Distance between electron beam and ionexit aperture, 0.2 cm. d Reference 11, distance between electron beam and ion-exit aperture, 1.0 cm.
0 01
IO0
200
300
400
500
SOURCE PRESSURE IN MICRONS
Figure 3. Semilogarithmic plots of the fractional intensities of C4H2 + and C4H3 + as a function of acetylene pressure.
Table I : High-pressure Mass Spectra of Acetylene m/e
24 25 26 27 37 38 39 50 51 52 53 61 62 74 75 76 77 86 87 88 100 101 102 103 104
--Relative 70 P
0.3 1.2 19.9 5.6 0.9 0.9 1.4 21.3 39.8 2.7 1.0 0.6 1.2 1.0 1.4 0.8
intensity, 70350 p
2.0 1.3
2.8 2.2 10.6 3.4 5.6 2.4 1.2 25.1 26.7 0.6 1.6 0.7 1.4 0.8 3.9 4.9 1.0
in either experiment would bring the results into excellent agreement. It is of interest to note that the ion CeHe+ (m/e 78) appears as a relatively important ion above 0.6 torr. The Journal of Physical Chemistry
Munson7 has commented on the significance of the nonobservation of this ion in acetylene a t elevated pressure. It is now apparent, however, that this ion does become prominent at higher pressures than those employed in the earlier work. This ion is kinetically of higher order than the other C6 ions observed (m/e 76, 77), which are already disappearing by reaction before C6H6+appears. Table I reports the mass spectrum at pressures of 0.07 and 0.35 torr. The extensive branching noted previously by Wexler, et al.," is quite apparent. In addition to the even-carbon-number chains already noted there is an odd-carbon chain of much lower intensity. Another low intensity sequence is apparently initiated by the vinyl ion CzH3+(mle 27), which leads to C4Hs+ (m/e 53) at 350 g source pressure. At 1 mm, ions of m / e 140 f 2 and 180 f 3 of several percent relative abundance appear in addition to the ones cited in Table I as well as very low intensities of intermediate mass ions. These should probably be identified with the ions designated as CllHl0+ (m/e 142) and CI4Hl4+(m/e 182) by Wexler, et al.," or ClrH12+ ( m / e 180) reported by M u n ~ o n . ~ In Figures 2 and 3 are presented semilogarithmic plots of the normalized intensity of the principal primary ions and first generation secondary ions, respectively. Cross sections deduced from the slopes of the straight-line portions of these curves are given in Table 11,,which compares our results with earlier work. Although there is considerable variation in the reported values, the results are considered to be in reasonable accord for such measurements. Reactions of CJ12+. That the principal primary ion in acetylene, C2H2+,is a precursor of the principal secondary ions, C4H2+and C4H3+,has been known for quite some time.1-5J-11 Its possible importance as a precursor of several minor ions has been a matter of conjecture, Table I11 reports the results of an experi-
161
IONIC REACTIOKS OF UNSATURATED COMPOUNDS ment using the tandem spectrometer in which lowenergy C2H2+ions are impacted on acetylene molecules at two different collision-chamber pressures. Although several fragments ions are observed from this interaction, the C4H2+and C4H3+ions together account for some of the total products. Rforeover, the results at 50 p show clearly that the ionic polymerization of acetylene does not proceed by a simple sequence of reactions, as the C6Hs+:C6H4+:C6H3+ ratio is greatly different from the C4H3+:C4H2+:C4H+ratio.
Table I11 : Reaction of C2H2+ with CzH2 -Relative
Product ion, m/e
Species
50 P
(CzHz)
(CzHz)
0.016 0,0002 0.0006 0.0003 0.001 0.28 0.70
27 37 38 39 49 50 51 74 75 76 77
intensity-
5 P
the presence of isolated states of the acetylene molecule ion. These states also are manifested in photoionization studies,16 although they are not clearly resolved by electron impact.lO Implications of this property of acetylene have been discussed previously.* In the present work, we have bombarded acetylene with ions of different recombination energies at sufficiently high pressures that secondary reactions of the ions initially produced by charge exchange may 0 c ~ u r . l ~The results of this experiment are reported in Table V. The ions Xe+ (RE of 2Ps/,state = 12.13 ev) and Br+ (RE = 11.8 ev) produce C2H2+in the ground state, while Ar+ (RE = 15.76 and 15.94 ev) produce C2H2+in an excited state. The data show that the reactions of CeH2+ in the two states, as noted earlier by Lindholm, et U Z . , ~ are substantially different.
0.015 0.0006 0.0003 0.28 0.69 0.001 0.005 0.007 0.004
a Because secondary ions of mass 26 could not be detected in this experiment no correction of m/e 27 for (21.3could be made. All other data in these tables have been corrected assuming an abundance of 1.170(213.
Table V : Ion-Molecule Reaction Products in Acetylene Initiated by Charge Exchange
Ar+
Xe
C4HZ+ C4Ha
0.65 0.35
0.23 0.77
+
Table IV:
Products from the Reaction of C ~ H Zwith + CZDZ
Product ion, m/e
Species
Relative intensity
27 28 29 50 51 52 53
CzHD + CzDz CZDzH + CiHz CiHD + CdDz +, C4HzD + CaDzH +
0.036 0.076 0.014 0.02 0.14 0.31 0.42
+
+
Br +
+
0.24 0.76
Table VI : Reaction of C J I + with CzH.2 --Relative
Product ion, Species
m/e
The ambiguity in the ion product of m/e 27 is easily resolved through the use of isotopically labeled reactants. Results from the reaction of C2H2+with CZDZ are given in Table IV. The ions, which would appear as m / e 27 for nondeuterated compounds, are now resolved into three products: C2D2+from simple charge exchange, C2HD+ from charge exchange with isotopic exchange, and. the proton-transfer product, C2D2H+. It is also noted that considerable isotopic mixing of the C4product ions occurs. Lindholm and co-workers16in a study of charge exchange of a number of ions with acetylene, detected
Charge exchange agent
r-
Product
intensity-
5 P
50 P
(CzHz)
(CzHz)
0.08 0.005 0.0005 0.0006 0.0013 0.013 0.90 0.002
26 27 37 38 39 49 50 51 74 75 76
0.92 0.016 0.007 0.03 0.02
Table VII: Isotopic Distribution of C4 Ions from C4HzDz+Complex
Speoies
C4H2' CaHD C4Dz+, C4HzD + CaDzH+ -+
V C a l c d distributionxz -X
-
0.02 0.14
0.04
0.29 0.42
Obsd
0.02 0.14 0.33 0.42
0.02 0.14 0.31 0.42
(16) R. Botter, V. H. Dibeler, J. A. Walker, and H. M. Rosenstock, J . Chem. Phys., 44, 1271 (1966). (17) This technique was introduced explicitly in Lindholm, Advances in Chemistry Series, No. 58,American Chemical Society, Washington, D. C., 1966, p 14.
Volume 78, Number 1 January 1Q68
162
JEAN H. FUTRELL AND THOMAS 0. TIERNAN
Table VIII: Reaction of CZH+with CZDZ Product ion, m/e
27 28 29 50 51 52
Species
CzHD + CzDz CzDiH CaD + CiHD + CaDz +
+
+
Table IX : Products from the Reaction of C4H4+ with CZHZ‘ Relative intensity
0.005 0.08 0.007 0.006 0.60 0.31
Reactions of C2H+. Experiments using mass- and energy-resolved beams of C2H+ analogous to those described for C2Hz+ were carried out. The results are summarized in Tables VI-VIII. The pattern is quite similar to that from C2Hz+impact, except that essentially only C4HZ+ is formed as an ion-molecule reaction product. Somewhat surprisingly, charge transfer is about as important a reaction mode for C2H+ as for CzHz+. The complexity of the seemingly simple ionic polymerization chain for acetylene is clearly demonstrated by the higher-pressure experiment. The CdH2+ ions do not produce C6H4+ in an elementary reaction, as hydrogen elimination apparently occurs as the usual reaction mode. It is also noteworthy that, a t the higher pressure, some C4H3+is also observed as a product, suggesting that stabilization of the ion-molecule complex is possible. Reaction of Other Ions. The minor ions Cz+ and CH+ were also reacted with acetylene in a tandem experiment. For C2+, small amounts of charge exchange (ca. 14%) and the formation of CdH+ ( m / e 49) constitute the reaction products. For na/e 13 (ca. 60% CH+ and 40% C2Hz2+,according to Munson’), the principal reactions are the formation of C3H1+and C3H+ plus significant amounts of charge transfer and proton transfer. With increasing pressure the C3H2’ product is favored. The observation of CsH6+as a product ion at high pressure and nonobservation as a product a t the intermediate pressures where other c6 ions predominate suggested that the reactions of C4H4+ ions with acetylene should be studied. Table IX presents the results of bombarding acetylene with C4H4+ ions derived from benzene. It is of interest to note that even at a pressure too low for collisional stabilization, C&,+ is observed as a product and the relative intensity of C&b+ increases with pressure. In addition, the distribution of ions bears little resemblance to that noted in the pressure experiments. Ionization Eficiency Curves for C4H2+ and C4Ha+. The peculiar shape of the C4Hz+ionization efficiency curve compared with “normal” shapes for other acetylene primary and secondary ions was noted by Derwish, Galli, Giardini-Guidoni, and Volpi.9 These The Journal of Physical Chemistry
Product ion
---Relative sl.4
0.096 0.819 0.085
C6H4’ CP&+ CaHa+
intensity---25 l.4
0.125 0.737 0.138
04 The CaHa+ ions were derived from electron-impact ionization of benzene. Product ions corrected for 18C-isotope contribution assuming 1.1% 1% in reactant molecule.
workers suggested that the structure in the curve might well be related to reaction of excited acetylene ions CzHz+* and to the parallel production of CdH2+ from CZH+primary ions. Since the branching ratios for producing C4HZ+ and C4H3+do appear quite different for C2H2+and C2H2+*,it seemed worthwhile to attempt to resolve the structure of the C4H2+ ionization efficiency curve. A possible rationalization of the experimental curves is given in Figure 4. Solid curve A is a tracing of the experimental X-Y recorder plot of the ionization efficiency curve for C4Hz+. The ratio of C4H2+:C4H3+ was determined in this research to be 0.45 f 0.01 below 15-ev electron energy, in good agreement with !\funson’s 0.04.’ Hence the branching ratio is value of 0.44 constant below this energy. Solid curve B is an exnorperimental ionization efficiency curve for c4I&+, malized instrumentally, te the intensity of the previously traced C4Hz+ion at 15 ev. It is noted that curves A arid B superpose quite accurately, as anticipated, from threshold to 15 ev. The ionization potential for C2H2+ is indicated on the figure to match the vanishing point for both secondary ions; i e . , there is no evidence for chemi-ionization by electron impact analogous to the photochemically produced chemi-ionizing states a t 10.4 ev, reported by Kovano, Tanaka, and Omura. l8 Curve C is a calculated ionization efficiency curve for estimating the intensity of C4&+ to be attributed to CZH+. The relative intensities of the primary ions C2H+:C2H2+ was determined to be 0.196 for 25-ev electron impact. From the total reaction cross sections of Table IV and the partial cross sections for C4H2’ production of Tables I1 and V, the relative contribution to the total C4Hz+curve a t 25 ev derived from CZH+ was deduced. This value was then used in conjunction with the concurrently measured ionization efficiency curve of C2H+to construct curve C of Figure 4. Curve D is obtained by a point-by-point substraction of curve C from curve A. It therefore represents a “corrected” ionization-efficiency curve, which is assumed to include C4H2+ions, produced from CZHZ+
*
(18) I. Koyano, I. Tanaka, and I. Omura, J . Chem. Phys., 40, 2734 (1964).
163
IONIC REACTIONS OF UNSATURATED COMPOUNDS
a d
cumulatibn of error, or it may indicate that the asumption of a constant branching ratio above 15 ev is in error. Although the circuitous procedure used here precludes a high level of confidence in the detailed resolution of these curves, it does provide a plausible deconvolution of the observed structure. Moreover, the appearance potential of C2H2+*deduced here is a rather more reliable result than the actual ionization efficiency curve, and the general features of the treatment would seem to be correct.
3 >
Discussion
v)
t 2 5)
t K 4
a
t m
t v)
5I-
z
-x
The fairly complex reaction sequence required to rationalize the ionic polymerization of acetylene has been discussed in some detail by M ~ n s o nby , ~ Derwish, et al.,S and by Wexler, et al." Neglecting minor products the chain initiated by the most abundant primary
Figure 4. Ionieittion efficiency curves for CIHI+ and ClHa + product ions in acetylene.
and C2Hz+*. It may be compared now with curve B, which represents C4H3+ions formed from the same precursor ions. The point where they diverge a t ca. 16.3 ev is the point where the branching ratio changes; i e . , the appearance potential of CzHZ+*. The value deduced, 16.3 ev, is in reasonable agreement with literature values: (possibly autoionization level) 15.5 ev,16 14.8 ev,le 16.27 ev," and 16.5 ev18 obtained from charge exchange, photoionization, photoelectron spectroscopy, and Penning ionization studies, respectively. Since ionization of acetylene is observed in these experiments using Ar+ ions retarded to less than 0.3 ev, there must be a t least a small probability of ionization down to about 15.94 ev (2P/l,zAr+). If we now assume that the branching ratio for the Ar+ charge-exchange initiated reaction of Table V is typical of C2H2+*,we may construct curve E using this ratio and a point-by-point substraction of curve B from curve D. The resulting curve E now represents C4H3+ and/or C4HZ+ derived from the ground-state acetylene ion C2H2+; except for the branching ratio normalization factor, these curves should be identical. Curve F is then obtained by substracting curve E from curve D. It represents the ionization efficiency curve for C4HZf derived from C2H2+*. Similarly, curve G is obtained by subtracting curve E from curve B and represents the ionization efficiency curve for C4H3+ ions produced from C2H2+*. Except for a normalization factor, curves F and G should both be a measure of the ionization efficiency curve of C2H2+*. The slight difference in their shapes may be the result of an acVolume 7g3Number 1 January 1968
164
KOICHITAKAKURA AND BENGTRANBY
The second most abundant primary ion in acetylene is C2H+, which initiates an analogous chain
C2H+
+ C2Hz
+ [G&+]
+H C4H3+ + CzH2
[GH3+] +C4H2+ [C4Hs+]
+ C2H2
(16) (17) (18)
The brackets denote a collision complex which will dissociate unless stabilized by collision. Each step of the proposed reaction sequence has been demonstrated or can be inferred from the data presented here. In addition, other products from ionmolecule interaction of all primary ions have been reported, and a plausible reaction sequence for the oddcarbon chain and for other minor products could be written using the above scheme as a guide. We have included in our mechanism reactions (5c and 8c), since Derwish, et U Z . , ~ observed metastable ions corresponding to these dissociations. These workers searched for and failed to observe any metastables corresponding to C4H$+ dissociation, and the question arises whether dissociation of this ion is so rapid that the concept of a C4H4+ complex has any validity for this system. We believe that it does, for
the following reasons. One argument is that C4H4+is observed as a product ion a t moderate pressures. In addition, the increasing importance of CeH6+ a t 1 torr pressure requires an abundant C4H4+ precursor, which is difficult to account for on the basis of back reactions such as l l a . Additional evidence for C4H4+ is obtained in the isotopic experiment of Table IV. Both the existence of an isotopically mixed product from the back reaction and the isotopic mixing of the C4 product ions suggest an intermediate of finite lifetime. Since both m/e 51 and m/e 53 peaks are unambiguously identified, they may be used as base points for calculating the distribution of isotopically labeled products. The results of such a calculation are summarized in Table VII. We have applied here the infinite-temperature isotope as discussed previously, in effect factors of connection with an analogous cal~ulation.'~The agreement is quite satisfactory, and we conclude that the concept of a stabilizable complex C4H4+ is probably correct. The mechanism deduced seems adequate to describe the experimental results and, with minor changes, can probably be generalized to other reactive systems.
aj
Studies of Free-Radical Species from the Reactions of Titanium(II1) Ions with Hydrogen Peroxide by Koichi Takakura and Bengt Rinby Department of Polyner Technology, The Royal Institute of Technology, Stockholm, Sweden Accepted and Transmitted by The Faraday Society
(June 14, 1967)
Electron spin resonance studies of reaction products from titanium(II1) ions with hydrogen peroxide in aqueous solutions using a flow system have shown spectra with two well-resolved peaks which are interpreted as due to HO and HOz. radicals, respectively. Both radicals are coordinated with Ti(1V) ions and, possibly, also with other molecular species.
-
Since Dixon and Norman' observed the esr signal ascribed to hydroxyl radicals during the reaction of Hz02 and TiCL in aqueous solution using a flow system, several detailed studies have been made of this reaction. have shown that the intensity ratio of Piette, et the two esr signals obtained was rather sensitive to the experimental conditions for the reaction. They attributed the principal low-field peak (g value, 2.0132) to HOz. radicals, and the minor high-field peak (g value, The Journal of Physical Chemistry
2.0119) to KO. radicals. As reported earlier,a we have also obtained the two esr signals and varied their in(1) W.T. Dixon and R. 0. C. Norman, Nature, 196, 891 (1962); J . Chem. SOC.,3119 (1963). ( 2 ) L. H. Piette, G. Bulow, and K. Loeffler, Preprint, Division of
Petroleum Chemistry, American Chemical Society, Washington, D. C., April 1964. (3) H. Yoshida and B. Rinby, paper presented at the IUPAC Symposium on Macromolecular Chemistry, Prague, 1965; J . Polymer Sci., C16, 1333 (1987).
