The Journal of Physical Chemistry, Vol. 83,No. 10, 1979
Reaction of O("P) Atoms with Fluoroethenes
R. G. Sauer and S. W. Benson for helpful discussions. References and Notes (1) J. H. Boer, "Reactivity of Solids", Elsevier, Amsterdam, 1961, p 381. (2) B. M. Arghiropoulos and S. J. Teichner, J. Catal., 3, 477 (1964). (3) F. A. Kroger, "Chemistry of Imperfect Crystals", North Holland Publishing Co., Amsterdam, 1964, p 692. (4) H. 2. Chon and C. D. Prater, Discuss. faraday Soc., 41, 380 (1966). (5) H. Krebs, "Fundamentals of Inorganic Crystal Chemistry", McGraw-Hill, London, 1968, p 162. (6) P. Amigues and S. .I. Teichner, Discuss. Faraday Soc.,41,362 (1966). (7) J. S. Choi and B. W l . Kim, Bull. Chem. SOC.Jpn., 46, 21 (1973). (8) J. S.Choi, K. H. Kim, and S. R. Choi, Int. J . Chem. Kine!., 9, 489 (1977). (9) J. S. Choi and K. H. Kim, J . Phys. Chem., 80, 666 (1976).
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W. Balz, Badische Anilin and Soda Fabrik., Fr. 1, 357, 866 (1964). J. S. Choi and K. H. Yoon, J. Phys. Chem., 74, 1095 (1970). J. S. Choi, H. Y. Lee, and K. H. Kim, J. Phys. Chem.,77, 2430 (1973). J. S. Choi, Y. H. Kang, and K. H. Kim, J. Phys. Chem., 81, 2208 ( 1977). J. S. Choi and K. H. Kim, J. Kor. Chem. SOC., 13, 241 (1969). I. Matsuura, T. Kubokawa, and 0. Toyama, Nippon Kagaku Zasshi, 81, 997 (1960). K. Otsuka, K. Tanaka, and K. Tamaru, Nippon Kagaku Zasshi, 88, 830 (1967). G. I. Chizhikova, Kine!. Katal., 7, 660 (1966). A. J. Pignocco and G. E Pellissier, J . Electrochem. Soc., 112, 1188 ( 1965). A. J. Pignocco and G. E. Pellissier, Surface Sci., 7, 261 (1967). S. H. Chang and W. H. Wade, J. Phys. Chem., 74, 2484 (1970).
Mechanism of HF Production and Stimulated Emission from the Reaction of OpP) Atoms with Fluoroethenest M. E. Umstead, F. J. Woods, and M. C. L h " Chemistry Division, Naval Research Laboratory, Washington, 0.C. 20375 (Received November 29, 1978) Publication costs asslsted by the Naval Research Laboratory
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HF laser emission was observed in the reaction of CzH3Fwith O(3P)produced by the flash photolysis of NO2 (A >*300nm). Several P(J) lines were present in the 1 0 band. The laser intensity was found to increase
linearly with flash energy. Analyses were made of the stable products of the reaction in both the flash photolysis system and in a discharge-flow system where O(3P)was produced by the N + NO reaction. The observed HF laser emission is believed to result from the following reactions: NOz + hu NO + O(3P);O(3P)+ CzH3F C,H3FOt HFt CHzCO, AH = -106 kcal/mol, where CzH3FOtmay be vibrationally excited fluoroethylene oxide, CH2FCH0, or CH3CF0. On the basis of appearance time measurements for the laser lines in a grating-tuned cavity, the HF population ratio between u = 1and v = 0 was determined to be N l / N o = 0.52 f 0.02, which is significantly higher than the value expected statistically. This is interpreted as resulting from the occurrence of a direct three-centered HF elimination from the initial adduct, OCHFCHz, taking place concertedly with the attack by the 0 atom. The mechanisms of the reaction of 0 atoms with other fluorinated ethenes are also discussed.
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Introduction Several chemical. laser systems have recently been reported arising from reactions of O(3P).1-6 Chemical HF laser emission has now been observed in the reaction of O(3P), produced lby the flash photolysis of NO2 at wavelengths longer than 300 nm, with vinyl fluoride (C2H3F)and some other fluorinated ethenes (cis- and trans-1,2-C2HzF2,X,,1-C2H2F2, and C2HF3). The reaction of 0(3P)with C2H3Fand other fluoroethenes has recently been investigated by Gutman and co-workers using crossed molecular beams in conjunction with photoionization mass s p e ~ t r o m e t r y .They ~ ~ ~ found that the reaction wnth C2H3Fproceeds by the following three major routes: 0(3P)-I- C2H3F HF + CH&O (1)
-
+
CHzF + CHO
(2)
CH3 + CFO (3) Ketene was identified as a product. The branching ratio for route 1 was found to be 0.11; route 3, 0.82. Route 1and its analogous paths +
Preliminary work of this paper was presented inthe 169th National Meeting of the American Chemical Society, Philadelphia, PA, April, 1975.
with the other fluorinated ethenes are believed to be responsible for the observed HF stimulated emission from these reactions. The present work is a detailed study of the C2H3Freaction which includes a frequency analysis of the vibrational-rotational lines comprising the stimulated emission, a study of the pressure effects of the reactant gases as well as inert gases, and the flash energy dependence of the stimulated emission. A detailed analysis has been made of the stable products of the photolysis reaction and also of the reaction carried out in a fast-flow reactor in order to help elucidate the reaction mechanism, particularly with respect to the principal laser pumping reaction.
Experimental Section The laser apparatus consisted of a 135-cm X 12-mm i.d. Pyrex tube fitted with a total reflecting gold mirror (3 m radius of curvature, 2.54 cm diameter used internally) and a replaceable high-transmission BaF2window mounted at the Brewster angle. A quartz flash lamp was concentrically sealed around the Pyrex laser tube. Twenty torr of 1% Xe in Ar was used as the flash gas. The optical cavity was formed by the gold mirror and either a gold-coated grating (300 lines/mm blazed at 2.75 pm with an efficiency of -90% between 2.6 and 3.2 pm) or another similar gold mirror for total laser emission measurements. The gap
This article not subject to U.S. Copyright. Publlshed 1979 by the American Chemical Society
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The Journal of Physical Chemistry, Vol. 83, No. 10, 1979
M. E. Umstead, F. J. Woods, and M. C. Lin
3
2
I 1
0
20
40
60
00
100
P/torr
0
I
I
I
I
1
1
2
3
4
5
N02/C2H3F Figure 1. Relative total laser emission as a function of the NO2/CZH3F ratio. Varying pressures of NOz added to 2.5 torr of a 1:4 C,H,F:He mixture. The flash energy was 1.6 kJ.
between the BaF2window and the grating (or mirror) was flushed with dry Nz continually to avoid atmospheric water absorption. The laser emission, coupled out of the Brewster window, was detected by means of a gold-doped germanium detector maintained at 77 K, in conjunction with a Tektronix Model 7633 storage oscilloscope. For spectral analysis, the beam was passed through a 50-cm Minuteman Model 305-M13 monochromator. The stable products of the reaction were measured by means of a Beckman GC-4 gas chromatograph equipped with a low-pressure sampling system.s A 5A Molecular Sieve column (183 X 0.635 cm 0.d.) and a thermal conductivity detector were used to measure CO, and a 183 X 0.476-cm 0.d. column of Porapak S in series with a similar column of Porapak T in conjunction with a flame ionization detector was used for the organic products. CO could be measured a t partial pressures as low as torr, and organic compounds, below torr. For measurement of products under conditions similar to the laser experiments, a Pyrex tube which was sealed at one end and connected at the other to the chromatographic sampling system via a greaseless stopcock was placed in the center of a Suprasil flash lamp. The appropriate gas mixtures was added to the evacuated tube, flash photolyzed, and then introduced immediately into the chromatograph. For the flow experiments, a conventional fast-flow reactor was used. The O(3P)atoms were produced by the N NO reaction, employing a 100-W 2450-MHz Raytheon microwave generator and a McCarroll version of an Evenson cavity (Opthos Instrument Co.) to dissociate the Nz. Typical reaction conditions were as follows: 0 atoms, 5 X 1014atoms/cm3; C2H3F,5-40 X 1014molecules/cm3; N2, 8 X 10l6molecules/cm3; total pressure, 4 torr; linear flow velocity, 1 m/s; and reaction temperature, 300 K. The products of the reaction were analyzed with the chromatograph, which was connected directly downstream of the flow reactor by a method previously described.8 The C2H3F(99.9% min), NO (99% min), NOp (99.5% rnin), SF6(99.8% rnin), and He and Ar (both gold-labeled products) were all obtained from the Matheson Co. CFzCHF and cis- and trans-C2H2F2were obtained from PCR, Inc. Condensable chemicals were purified by trap-to-trap distillation, while the others were used without further purification. No major impurities were detected in the C2H3Fby gas chromatographic analysis.
+
Figure 2. Total laser emission as a function of total pressure for a 1:3:50 C,H,F:NOZ:He and a 1320 C,H,F:NO,:SF, mixture, both at a flash energy of 1.6 kJ. 1.4
c
01 10
20
30
1
I
40
50
P/torr
Figure 3. Total laser emission as a function of inert gas pressure. He and SF, added to 4 torr of 3:1 NOz:SF6. The flash energy was 1.6 kJ.
Results and Discussion H F laser emissions were observed from mixtures of 1,l-CzH2F2, and CzHF3 CzH3F,cis- and trans-l,2-CzHzF2, with NO2 and He in the ratio of 1:3:50, respectively, all flashed at 1.6 kJ of energy. The flash had a rise time of about 3 ps and a 7 fis half-width. The laser emission began at 5-15 ps and continued until about 20-30 ps, the time depending upon the individual fluorocarbon. The strongest emission was obtained from cis- and trans1,2-C2H2F2,whose traces were identical, and the weakest from 1,1-C2H2F2.No laser emission was obtained from C2H3Clunder similar experimental conditions. C2H3Fis the only member of this series that has been studied in detail. Effect of Reactant Gas Pressures. Figure 1 shows the dependence of the total laser emission intensity (obtained by using two total reflecting gold mirrors) on the NO2/ C2H3Fratio. The maximum laser output was obtained at a ratio of about 3:l. No laser emission was obtained in the absence of NOz. Figure 2 shows the dependence of the intensity of total laser emission on total pressure for a 1:3:50 C2H3F:N02:He and a 1:3:20 CzH3F:No2:SF6mixture, using the NO2/ C2H3Fratio that produced the maximum output. It can be seen that the maximum occurs at a total pressure of about 40-80 torr for the He mixture and about 20 torr for the SF6mixture. Since SF6does not relax HFt effi~iently,~ the much lower output from the SF6diluted mixture can be attributed to the reduction in 0(3P)-atomconcentration caused by the more effective quenching of electronically excited NOz by SF,. The product yield from the photolysis of 50 torr of 1:3:50 CzH3F:NOz:SF6was about 80% lower
The Journal Of Physical Chemistry, Vol. 83, NO. 10, 1979
Reaction of O('P) Atoms with Fluoroethenes
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87-
9
*
Ly
4-
Y
5-
Id
0 -_I 1.0
1.2
I
I
I
I
1.4
1.6
1.8
2.0
'1 * 3
E & (KJ)
Figure 4. Total laser einission as a function of flash energy for 4 torr of a 1:3:4 C,H3F:NO2:Ho mixture.
than that obtained from a similar mixture containing He. This quenching effect is further demonstrated by the results shown in Figure 3, which were obtained by adding varying amounts of He and SF6separately to 4 torr of 3:l N02:C2H3Fmixtures flashed at an energy of 1.6 kJ. The maximum laser output was obtained with zero or very little added gas (in the case of He); at higher pressures, the emission was strongly quenched. SF6was a more efficient quenching agent than He, consistent with the results shown in Figures 2. Flash Energy Dependence. Figure 4 illustrates the linear dependence of peak laser intensity of the flash energy used for photolysis. The linear dependence is consistent with a mechanism in which only one of the reactive species is generated photolytically. Laser Transitions and Inversion Ratios. From 50 torr of 1:3:50 C2H3F:NOp:Ar(or He) mixtures photolyzed at an energy of 1.6 k J in the grating-tuned cavity, four lines in the u = 1 u = 0 P-branch transition were observed in the following order of appearance: P(5), P(6), P(4), and P(7). P(6) and P(4) appeared closely together. On the basis of the results of a gain calculation (with appropriate corrections for pressure broadening), the above sequence of appearance times corresponds to an inversion ratio of N,/No = 0.5%i 0.02. Similar measurements for cis- and trans-1,2-C&F2 and C2HF3gave rise to N,/N,, = 0.61 i 0.04 (all from 50 torr of Ar-diluted 1:3:50 mixtures as given above). In these three systems, emissions were stronger and more lines were observed. The sequence of their appearance times wm P(5), P(4), P(6), P(3), P(7), P(2), and P(8),all in the 1 0 manifold. No 2 1 emission was detected. Neither was any emission detected in the 0 + 1,1-C2H2F2 reaction in the grating-tuned cavity, apparently due to its lower gain, In these experiments, the observed appearance times could be reproduced to i0.2 ps. In cases where two lines appeared closely together, repeated measurements were made to resolve them unambiguously. Although 110 laser emission was detected in the 0 1,1-C2HzFz reaction in the grating-tuned cavity, laser action was detected in the cavity consisting of two total reflecting gold mirrors. Analysis of the total emission from 50 torr of a 1:3:50 1,J-C2H2F2:N02:Ar(flashed at 1.6 kJ) showed that two lines, P(6) and P(7), of the 1 0 transition were present, with P(6) appearing first. This observation in-
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+
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Figure 5. Products of the CzH3F-0(3P)reaction as a function of the CzH3F/0 ratio. Fast-flow reactor, for conditions see text.
TABLE I: Reaction Product Distribution in the Flash Photolysis of 1 6 torr 1:3:20 C,H,F:NO,:He Mixtures
product
co
l,l-C,H,F, CH,F
cz H,
vield. %
72 2.3 0.23 0.12
product
yield, %
0.11 0.022
ProPYne
propadiene cis-1,2-C,H,Fz
0.10
dicates that the inversion ratio lies in the vicinity of 0.40-0.44, which is noticeably lower than the values es-
timated for the other fluorinated ethenes. The implication of these observations will be discussed later. Product Analysis. Figure 5 shows the yields of some of the stable products of the reaction carried out in the fast-flow reactor as a function of the C2H3F/0 ratio. Product yields were based upon the disappearance of C2H3F. As can be seen from the figure, the major organic products found were C2H, and 1,1-C2H2F2.Other major products expected, such as CHzO and CH2C0, could not be detected under the conditions used. Minor products included CH3F,CzHz,propyne, propadiene, cis-1,2-CzHzF2, and higher molecular weight compounds that were not identified. trans-1,2-C2H2Fzwas also present, but could not be measured quantitatively because of interference from the tail of the CzH3F peak. Its concentration, however, was comparable to that of cis-1,2-C2H2Fz. Table I lists the products found in the photolysis of 16 torr of a 1:3:20 C2H3FNOa:Hemixture flashed at an energy of 1.8 kJ. Again, the yields are based upon the disappearance of C2H3F. The most striking difference between the products found in the flow and in the photolytic systems is the complete absence of ethylene in the latter. Mechanism of Chemical Pumping. The observed HF stimulated emissions from this series of reactions are believed to result from the direct elimination of HP from vibrationally excited adducts. Since the 0 CH2=CHF reaction was examined more closely than the others in this work, we shall consider this reaction first.
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M. E. Umstead, F. J. Woods, and M. C. Lin
The Journal of Physical Chemistry, Vol. 83,No. 10, 1979
40
1'-
20
0.
0.
0 -
-20
CH3+ CFO
(< 7%)
-
-40-
-
-60
-80
-
-100 -100
-
Y CbCFO
Figure 6. Schematic diagram of possible reaction paths for the C2H3F-0(3P) reaction. Energy (E) in kcal/mol.
Scheme I 0. CHzi-CHF]
-
CH2FCHOt
+
CHzF
+ +
[HzC-kHF]
-
CHO
(W
\
f
-
CH3CFOt
-
CH2CO
CH3 t CFO
There are several routes by which HFt can be formed, they are shown in Scheme I.697 The schematic diagram of these reaction paths are shown in Figure 6. The diagram was constructed on the basis of the known mechanism of the 0 CzH4 reaction.l0J The energetics of various intermediates were estimated from kinetic data for the 0 + CH2=CHFlZ and the ethylene oxide thermal decomposition reactions,13from estimated values of AHof for CHzF14and CF0,16and from the approximation that D(CH,-CHO) N D(CH3-CFO) N 85 kcal/mol. Activation energies for the four-centered HF elimination from fluoroethylene oxide and CHzFCHO were placed in the range of 65-70 kcal/mol, similar to those observed for the elimination of H F from f l u ~ r o e t h a n e s . ~ ~ , ~ ~ In addition to the four-centered elimination paths labeled by (a), (b), and (c) in scheme I, a direct threecentered elimination via the OCHFCH2 intermediate, as indicated by the dotted arrow (d), may also occur. Since there is no atom migration involved in this path, HF elimination may take place concertedly with the attack by the 0 atom. H F formed by this path is expected to be vibrationally hotter than that formed by four-centered elimination which should have a greater extent of energy reshuffling (due to bond rearrangement). In order to identify the mechanism of HF production from the aforementioned several possibilities, we have computed the statistically expected HF vibrational energy distribution based on a simple statistical model which has previously been shown to be applicable to reactions occurring via long-lived i n t e r m e d i a t e ~ . ~The ~ J ~computed distribution, No:N,:Nz:N3= 1:0.31:0.091:0.025,predicts a
+
much lower inversion ratio (N,/No = 0.31) than the observed value, Nl/No = 0.52, for the 0 CH2CHFreaction (taking AH", = -106 kcal/mol). This finding, although indirect, suggests the possibility of the occurrence of both three- and four-centered eliminations, as was postulated by Gutman and co-workers7to take place in the reactions of 0 atoms with the fluoroethenes. This also is consistent with the observed larger inversion ratio, Nl/No = 0.61 for the 0 + C2HF3and the cis- and trans-1,2-C2H2F2reactions in which the formation of the OCHF-C< intermediate is favored or the only possibility. On the other hand, in the case of the 0 1,1-CzH2F2reaction, the formation of the OCHzCF2intermediate is favored.7 In this case, rapid three-centered 1,l-elimination of HF cannot occur and thus the observed HF emission probably results mainly from four-centered elimination via the epoxide or aldehyde intermediates. The observed inversion ratio N l / N o N 0.42 is, interestingly, closer to the statistical limit, 0.31. In their crossed jets experiments, Gutman and co-workers observed comparable ion signals for CzHFO from both the 1,l-and 1,2-CzH2F2reactions and concluded that 1,l-and 1,2-HF elimination occurred with comparable probability. Before concluding the discussion, we should briefly consider the possibility of other laser pumping reactions and the results of end product analysis in both flash photolysis and discharge flow experiments. It should be noted that HF laser emission has been observed previously in the vacuum-UV flash photolysis of C2H3Fq20In the present study the photolysis was carried out in Pyrex (A >300 nm). In the absence of NOz, no laser emission was observed, and no dissociation of CzHBFcould be detected by gas chromatography which indicates that the direct photodissociation of C2H3Fis not important under these conditions. Secondary reactions which may involve radicals, such as CH2F and CH3,are believed to be unimportant to laser action, since these alkyl radicals appear to be efficiently scavenged by excess NO2 or by NO produced by the photodissociation of NO2. In the fast-flow reactor studies, CzH4 was a major product (-11%),and its most likely source is CHzF CH3 CzH4I- HF. However, in the photolysis experiments, C2H4 was absent, undoubtedly due to the removal of CHzFand CH, by NO and/or NOz. The linear dependence of laser intensity on flash energy (Figure
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Current Efficiency Studies of Electrogenerated Chemiluminescence
The Journal of Physical Chemistty, Vol. 83, No. 10, 1979
4) supports a mechanism in which only one of the contributing reactive species is formed photolytically. Additionally, the observed appearance time sequence was found to remain the same when a lasing mixture of C2H3F was diluted from 1350 to 1:3:100 (C2H3F:NO:Ar), indicating that the secondary reactions shown above are probably not important. The presence of products containing two or more fluorine atoms, such as the difluoroethenes in the flow experiment, indicates that F atoms were formed in the 0 + C2H3Freaction, undoubtedly by secondary processes. The reaction of F with hydrocarbons is well known as a pumping process for H F laser emission. In the flash system, the unimportance of F atoms to the laser emission was shown by the absence of DF laser emission upon the addition of I)2 to the reaction mixture. The presence of small amounts of allene and methylacetylene in the low pressure flow experiments may result from the reaction of CH2with C2H3F followed by HF elimination. The CHz radical may be produced by the decomposition of excited CH,CO, which is expected to carry a large fraction of the 106 kcal/mol reaction energy in view of the low HF inversion ratio observed experimentally.
1293
elimination processes taking place simultaneously. Molecules in which the three-centered process is favored give rise to vibrationally hotter HF. Secondary radical reactions are not considered important to the laser emission because of the efficient scavenging of radicals by NO and NOz present in the system.
References and Notes (1) M. C. Lin, Int. J. Chem. Kinet., 6, 173 (1973). (2) M. C. Lin, "Chemiluminescence and Bioluminescence", M. J. Cornier, D. M. Hercules, and J. Lee, Ed., Plenum Press, New York, N.Y., 1973, p 61. (3) M. C. Lin, Int. J. Chem. Kinet., 6, 1 (1974). (4) R. G. Shortridge and M. C. Lin, J. Phys. Chem., 78, 1451 (1974). (5) D. S. Y. Hsu and M. C. Lin, Int. J. Chem. Kinet., 10, 839 (1978). (6) 1. R. Slagle, D. Gutman, and J. R. Gilbert, Symp. (Int.) Combust., [Proc.], 15th, 785 (1975). ( 7 ) J. R. Gilbert, I. R. Slagle, R. E. Graham, and D. Gutman, J . Phys. Chem., 80, 14 (1976). (8) M. E. Umstead, J. Chromatogr. Sci., 12, 106 (1974). (9) J. K. Hancock and W. H. Green, J . Chem. Phys., 59, 6350 (1973). (10) R. J. Cvetanovic. Adv. Photochem.. 1. 115 11963). (11) J. R. Kanofsky, D. Lucas, and D. Gutman, Syhp. (h.) Combust., [Proc.], 285 (1973). (12) D. S. Jones and S. J. Moss, Int. J. Chem. Kinet., 6, 443 (1974). (13) K. H. Mueller and W. D. Walters, J. Am. Chem. Soc., 73, 1458 (1951); 76, 330 (1954). (14) H. W. Chang and D. W. Setser, J. Am. Chem. Soc., 91, 7648 (1969). (15) H. J. Gangloff, D. Milks, K. L. Maloney, T. N. Adams, and R. A. Matula, J. Chem. Phys., 63, 4915 (1975). (16) P. Cadman, M. Day, and A. F. Trotman-Dickenson, J. Chem. SOC. A , 2498 (1970): 248 (1971). (17) E. TschuIkow-ROux and'W. J. Quiring, J. phys. Chem.,75, 295 (1971); 74. 2449 f197Ol -, (18) M.'C Lin, R. G. Shortridge, and M. E. Umstead, Chem. Phys. Lett., 37, 279 (1976). (19) M. C. Lin. J. Chem. Phvs.. 68. 2004 (1978). (20) M. J. Berry and G. C. Pimentel,'J. Cheh. Phys., 51, 2274 (1969).
Concluding Remarks The HF laser emission observed in the reaction of O(3P) with C2H3F and the other fluoroethenes is believed to result from the direct elimination of vibrationally excited HF from CzH,E,O. The vibrational excitation of the HF is significantly greater than that expected statistically, which is attributed to both three- and four-center H F
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\
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Current Efficiency Studies of Electrogenerated Chemiluminescence using an Alternating Symmetrical Square Wave Current Program James A. Seckel and J. T. Maloy" Department of Chemistry, West Virghia University, Morgantown, West Virginia 26506 Publication costs assisted by the Petroleum Research Fund
A method has been developed for measuring the current efficiency of electrogenerated chemiluminescence (ECL) in solution by using an alternating, symmetrical square wave current program; this results in a long time (3140 h) constant integrated amplitude ECL signal with an integrated intensity that is directly proportional to the current level. The slope of ECL intensity-current level plot is a measure of the relative current efficiency of the EEL process. This technique allows for direct actinometry to be performed to obtain absolute current efficiencies for energy sufficient or deficient systems in pure or mixed solvents. Analysis of oscilloscope traces of the light spikes produced by this method yields ECL current efficiencies by a somewhat different method; these results are consistent with those of the slope measurement technique. Absolute results that are obtained by either method agree with previously published ECL efficiencies. The generation frequency variation of both the dope (efficiency)and the current intercept of ECL intensity-current plots has also been investigated.
Introduction Electrogenorated chemiluminescence (ECL) occurs when electrogenerated radical anions and cations undergo an electron transfer reaction resulting in the production of light. The radical cation and radical anion can be formed from the same parent compound, as in the case of 9,lO*To whom correspondence should be addressed at the Department of Chemistry, Seton HiaXl University, South Orange, N J 07079. 0022-3654/79/2083-1,293$01 .OO/O
diphenylanthracene (DPA), or from different parent molecules as in the mixed system of thianthrene (TH) or N,N,N',N'-tetramethyl-p-phenylenediamine(TMPD) and DPA. After undergoing the electron transfer reaction, or other subsequent reactions, a first excited singlet state of one of the compounds is formed which can return to its ground electronic state by emitting light of characteristic frequency, depending on the compound and solvent used.' The spectrum obtained is, in most cases, not unlike the 0 1979 American Chemical Society
