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Vacuum Ultraviolet Photochemistry of CyclobutanoneAlfred A. Scala and Daniel G. Ballan Citation: The Journal of Chemical Physics 57, 2162 (1972); doi: 10.1063/1.1678546 View online: http://dx.doi.org/10.1063/1.1678546 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/57/5?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Vacuum ultraviolet surface photochemistry of water adsorbed on graphite J. Chem. Phys. 117, 6667 (2002); 10.1063/1.1506143 Electric dichroism spectroscopy in the vacuum ultraviolet. I. Cyclobutanone, cyclopentanone,cyclohexanone, and cycloheptanone J. Chem. Phys. 72, 2623 (1980); 10.1063/1.439407 Argon Resonance Line Lamp for Vacuum Ultraviolet Photochemistry Rev. Sci. Instrum. 39, 126 (1968); 10.1063/1.1683089 Vacuum Ultraviolet Photochemistry. Part IV. NO at 1236 A J. Chem. Phys. 25, 674 (1956); 10.1063/1.1743026 Vacuum Ultraviolet Photochemistry. Part III. Acetylene at 1849 A J. Chem. Phys. 24, 1034 (1956); 10.1063/1.1742673
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2162 R. F. CODE AND J. D. NOBLE
6 H. Gliittli, A. Sentz, and M. Eisenkremer, Phys. Rev. Letters 28, 871 (1972).
6 A. R. Sharp, S. Vrscaj, and M. M. Pintar, Solid State Commun. 8,1317 (1970).
7 Z. T. Lalowicz and J. W. Hennel, Acta Phys. Polon. A40, 547 (1971).
8 E. P. Jones and L. P. Montgomery, Phys. Letters A35, 229 (1971).
9 J. H. Colwell, J. Chern. Phys. 51, 3820 (1969) (this paper contains references to previous calorimetric studies by J. H. Colwell, E. K. Gill and J. A. Morrison).
10 J. A. Morrison and P. R. Norton, J. Chern. Phys. 56, 1457 (1972) .
11 A. Abragam, The Principles of Nuclear Magnetism (Clarendon, Oxford, 1962).
12 F. N. H. Robinson, J. Sci. lnstr. 36, 481 (1959). 13 M. Goldman, Spin Temperature and Nuclear Magnetic
Resonance in Solids (Clarendon, Oxford, 1970). 14 H. Betsuyaku, J. Phys. Soc. Japan 30, 641 (1971). 16 G. A. de Wit and M. Bloom, Can. J. Phys. 47, 1195 (1969).
16 T. Yamamoto and Y. Kataoka, Phys. Rev. Letters 20, 1 (1968) .
17 T. Yamamoto, J. Chern. Phys. 48, 3193 (1968). 18 T. Yamamoto and Y. Kataoka, J. Chern. Phys. 48, 3199
(1968) . 19 Y. Kataoka and T. Yamamoto, Progr. Theoret. Phys.
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(1959) .
THE JOURNAL OF CHEMICAL PHYSICS VOLUME 57, NUMBER 5 I SEPTEMBER 1972
Vacuum Ultraviolet Photochemistry of Cyclobutanone* ALFRED A. SCALA AND DANIEL G. BALLAN
Department of Chemistry, Worcester Polytechnic Institute, Worcester, Massachusetts 01609
(Received 3 April 1972)
The photodecomposition of cyclobutanone in the vacuum ultraviolet is characterized by
(1)
(2)
At 147.0 nm and high pressure the quantum yields of Reactions (1) and (2) are approximately 0.7 and 0.25 respectively. At 123.6 and 106.7-4.8 nm the ratio of the quantum yield of Reaction (2) relative to Reaction (1) is 0.28. The quantum yield of carbon monoxide is unity at 147.0 and 123.6 nm and 0.81 at 106.7-4.8. Although Reaction (2) is best interpreted in terms of a trimethylene diradical intermediate, at 147.0 nm Reaction (2) produces propylene in a primary process with a quantum yield of 0.09. There is no evidence for the production of primary propylene at 123.6 or 106.7-4.8 nm. Pressure studies at 106.7-4.8 nm indicate that the cyclopropane produced in Reaction (2) contains only about 90 kca!.mole of excess vibrational energy. This result requires that carbon monoxide is produced either with 175 kcai/mole of excess vibrational energy or more likely in an electronically excited state.
INTRODUCTION
The gas phase near ultraviolet photochemistry of cyclobutanone has been investigated by a number of researchers.l Ethylene, ketene, carbon monoxide, propylene, and cyclopropane have been reported as products and their formation has been attributed to
(1)
(2)
Lee and Lee2 have established that in the direct photolysis of cyclobutanone Reaction (1) occurs from a highly vibrationally excited ground state produced from the first excited singlet by internal conversion, while Reaction (2) results from the decomposi-
tion of the triplet state. Lee and Denschlaga have also shown that in the benzene photosensitized decomposition of cyclobutane, Reaction (1) is the result of IB2u
benzene sensitization, and Reaction (2) is the result of triplet energy transfer from the 3B1u state of benzene. There is some disagreement in the literature concerning the CaR6 produced in Reaction (2). It has not been established whether propylene is produced only as a result of cyclopropane isomerization or is also produced as a primary product.u ,6
Although the near ultraviolet photochemistry of cyclobutanone has been rather thoroughly investigated, there has been only a preliminary investigation of the vacuum ultraviolet photolysis of cyclobutanone.6
Because of our continuing interest in the photochemistry of highly excited molecules, we have undertaken a thorough study of the vacuum ultraviolet photolysis of cyclobutanone in order to determine the primary modes
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PHOTOCHEMISTRY OF CYCLOBUTANONE 2163
FIG. 1. The dependence of the ratio Ca/C2 upon the reciprocal of the cyclobutanone pressure.
~ C2
0.35 ,
0.30 0
----.:.:::: 0.25
0.20
of decomposition and compare them with the primary processes which occur from the lower excited states produced in the near ultraviolet.
EXPERIMENTAL
The experimental procedures were essentially the same as those used in our previous study of the vacuum ultraviolet photolysis of cyclohexanone.7 Cyclobutanone (Aldrich) was distilled on a thirty theoretical plate spinning band column. The middle 1/3 was thoroughly degassed by several trap to trap distillations at -78°C and stored on the vacuum line in a darkened vessel. Gas chromatographic analysis showed that the cyclobutanone contained no detectable hydrocarbon impurities and only 0.3% of a material which, based upon retention time, was 2-butanone.
TABLE I. Photolysis of cyclol;lUtanone."
Wavelength
Products 147.0 123.6 106.7
CO 100 (1.0)b 100 (0.97)b 100 (0.81) b H2 20.0 21. 7 33.0 CH. 3.16 5.6 7.2
C2H2 2.66 3.5 11.5 (0.09) C2H. 80.6 (0.81) 86.9 (0.84) 76.9 (0.62) C2H6 3.31 4.13 3.94
CaH6 15.24 8.45 4.73 CaHs 1.37 3.26 0.56 CaH. 1.55 6.64 9.43 C-CaH6 2.61 7.17 6.52
l-C.Hs 5.42 1. 78 2.00
" Pressure = 10 torr. b Quantum yield.
CJ = 106.1- 4.8 NM !J. = 123.6 NM o • 141.0 NM
0.1 0.2 0.3
PcVCLOBUTANONE
RESULTS
The product distributions observed when 10 torr of cyclobutanone was photolyzed at 147.0, 123.6, and 106.7-4.8 nm are presented in Table I. The conversion in these experiments was <0.1%. Conversions as high as 1.0% had little effect on the relative product yields reported in Table I. The yields of methane as well as the Ca products, propylene, cyclopropane, and allene, relative to carbon monoxide, are given in Table II, as a function of cyclobutanone pressure for the xenon, krypton, and argon photolyses. The effects of pressure on the ratios of certain product yields are conveniently displayed in Figs. 1-4. In Fig. 1 is plotted the ratio (total Ca) / (total C2) as a function of the reciprocal
TABLE II. Pressure dependence of the methane, propylene, allene, and cyclopropane yields from the photolysis of cyclobutanone.
Yield ReI. to CO = 100
Wavelength Pressure" CH. CaH6 CaH. C-CaH6
147.0 3.0 4.3 15.1 1.72 1.88 147.0 10.0 3.2 15.2 1. 55 2.61 147.0 20.0 2.6 16.8 0.89 4.64 147.0 30.0 2.5 17.1 0.58 7.27
123.6 5.0 ndb 8.48 9.37 3.62 123.6 10.0 5.6 8.45 6.64 7.17 123.6 20.0 5.7 8.05 5.77 10.57 123.6 30.0 5.8 7.56 3.96 12.87
106.7-4.8 5.0 ndb 5.43 11.5 3.55 106.7-4.8 10.0 7.2 4.73 9.43 6.52 106.7-4.8 20.0 5.8 4.00 7.00 9.85 106.7-4.8 30.0 4.1 3.22 4.88 12.6
"Torr. b Not determined.
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2164 A. A. SCALA AND D. G. BALLAN
8.0 D' IOS.7- 4.8 NM 6' 123.S NM
7.0 o • 147.0 NM
S.O
5.0 C3HS
C-C3HS 4.0
3.0
2.0
1.0
" 10 20 30
CYCLOBUTANONE PRESSURE (TORR)
FIG. 2. The dependence of the ratio l-CaH6/c-CaH6 upon the cyclobutanone pressure.
of the cyclobutanone pressure. The data presented in Fig. 1 indicate that there is a slight preference for the formation of Cs products at higher pressures. The data for the 147.0 nm photolysis appears to be the resultant of two separate Cs species undergoing secondary decomposition. The species which is quenched at low pressures is less sensitive to pressure than the one which is quenched at higher pressure. Although at 147.0 nm the ratio CS/C2 changes by 0.125, this corresponds to only a 0.08 change in the quantum yield of the Cs products. Figures 2 and 3 present the ratios CSH6/c-CsH6
and CSH4/c-CsH6 respectively as a function of pressure. It is worthy of note that in Fig. 2 the succession of lines representing the photolysis wavelengths is reversed from the succession observed in Fig. 3.
When cyclobutanone was photolyzed in the presence of 5% ethylene at 147.0 nm both I-pentene and cyclopentane were observed as products. The ratio c-CsHlO/total Cs was 0.05 in this experiment. There were no detectable amounts of either I-pentene or cyclopentane when cyclobutanone was photolyzed in the absence of ethylene. When a mass spectrum was
4.0
o 3.0
10
0=106.7-4.8 NM A • 123.S NM o • 147.0 NM
20 30 CYCLOBUTANONE PRESSURE ITORR)
FIG. 3. The dependence of the ratio CaH./c-CaH6 upon the cyclobutanone pressure.
run on the entire reaction mixture from high conversion experiments at all wavelengths a peak could be detected at m/e=84. This peak could only be observed after high conversion> 1%.
The quantum yields reported in Table I at 123.6 and 106.7-4.8 nm are based upon the measured cyclobutanone ionization efficiencies of 0.24 and 0.22 respectively and the measured ionpair yields of ethylene. The quantum yield at 147.0 nm was determined from carbon dioxide actinometry.8
DISCUSSION
The majority of the products observed in the vacuum ultraviolet photolysis of cyclobutanone (Table I) can be explained in terms of the two primary processes, Reactions (1) and (2), which have been observed in the near ultraviolet photolysis of cyclobutanone. The data from the near ultraviolet photolysis of cyclo-
o • IOS.7-4.8 NM I.S
1.4
1.2
1.0
C3HS 0.8
C-C3HS 0.6
0.4
0.2
:~ /~ 2~7
0.1 0.2
0.05 O,{O 0.15 0.20
I PCYCLOBUTANONE
FIG. 4. The dependence of the ratio l-C3H6/c-C3H6 upon the reciprocal of the cyclobutanone pressure.
butanone indicate that the ratio of the extent of Reaction (2) relative to Reaction (1) is about 0.44 at 313 nm and 0.77 at 253.7 nm. This ratio for the present study obtained by extrapolation of the CS/C2
ratio to infinite pressure (Fig. 1) is 0.28 at both 123.6 and 106.7. The ratio for the 147.0 photolysis is approximately 0.35 but the steep slope in this line prevents accurate extrapolation to infinite pressure. These values for the ratio reaction (2)/reaction (1) clearly do not follow the trend expected from the near ultraviolet data. This observation indicates that the decomposition of cyclobutanone in the vacuum ultraviolet is occurring from an excited state other than the first singlet or triplet states. It also makes the involvement of a vibrationally excited ground state unlikely. The involvement of excited states higher than n--t7r* is consistent with the assignment of the 150 nm absorption band in ketones to the 1l-+7r* transition.9 The observation that the high pressure intercept in Fig. 1 is the
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PHOTOCHEMISTRY OF CYCLOBUTANONE 2165
same for 123.6 and 106.8-4.8 nm suggests that almost all of the decomposition at these wavelengths is from the same excited state which is of higher energy than the 'II"-t1r* state involved in the 147.0 nm photolysis. This is also suggested by the pressure dependence of the ratio CaRa/c-CaRa for each wavelength (Fig. 2). At 147.0 nm there is much more propylene than at either of the higher energy wavelengths.
Although ketene is indicated as a product in Reaction (1) at these energies ketene will certainly decompose to carbon monoxide and methylene. The insertion of methylene into cyclobutanone is the major reaction of the methylene and accounts for the presence of a peak at m/e=M+14 (methylcyclobutanone) in the mass spectrum of the reaction mixture. The origin of the methyl radicals present in the system is probably the decomposition of a fraction of the methylcyclobutanone produced by methylene insertion. It can be seen from Table II that the variation of the methane yield with pressure is consistent with this interpretation at 147.0 and 106.7-4.8. The invariance of the methane yield with pressure at 123.6 could conceivably be experimental error.
If we assume consistent with our previous studies of the photolysis of cyclohexanone and cyclopentanone that the trimethylene diradical is an intermediate in Reaction (2), then cyclopropane and propylene may be accounted for by the cyclization and isomerization of the trimethylene diradicaF ,10:
CH2CR2CH2~C-CaHa, (3)
~1-CaHa. (4)
The postulation of the trimethylene diradial in this system is verified by the observation of cyclopentane among the products when 5% ethylene was added to the ketone prior to photolysis. Although the presence of I-pentane in these experiments could be rationalized in a number of ways which do not involve the trimethylene diradical, it is difficult to imagine any route
O' 106.7- 4.8 NM 16 A' 123.6 NM
o • 147.0 NM 14
12
4
2~~~~ 10 20 30
CYCLOBUTANONE PRESSURE (TORR)
FIG. 5. The dependence of the ratio C-CaH6/CaH4 upon the cyc1obutanone pressure.
30 0 • 106.7 - 4.8 NM A • 123.6 NM
28 0 • 147.0 NM
26
24
22
_-.--4 --0--0
__ ---tr' o o
10 20 30
CYCLOSUTANONE PRESSURE (TORR)
FIG. 6. The dependence of the ratio l-CaH6/CaH4 upon the cyc1obutanone pressure.
for the production of cyclopentane other than Reaction (5) followed by Reaction (6):
CH2CH2CH2+ C2R4~CH2CH2CH2C H2CH2, (5)
(6)
The data in Table II which are plotted for clarity in Figs. 4, 5, and 6 indicate that the products, propylene, cyclopropane, and allene are linked together probably through the intermediacy of the trimethylene diradical. It can also be seen from the high pressure limit of CaHa/c-CaHs at 147.0 nm (Fig. 2), that there is a large amount of propylene produced at 147.0 nm which is significantly reduced at 123.6 and almost absent at 106.7-4.8, which does not originate from cyclopropane isomerization. It is this primary propylene which probably accounts for the curvature of the 147.0 nm line in Fig. 1, since primary propylene should be more susceptible to secondary decomposition probably to methyl and vinyl radicals, than propylene which is formed by secondary reaction of the trimethylene diradical after a number of collisions. The value placed upon the quantum yield of primary propylene based upon the high pressure limit in Fig. 2,0.09, is consistent with the difference in the intercepts of the two dotted lines in Fig. 1. Since the 150.0 nm absorption band has been attributed to the 'II"~* transition, we conclude it is this state which leads to the production of propylene in a primary reaction and that photolysis at 106.7-4.8 nm does not produce this state to any appreciable extent. This point is demonstrated further by the observation
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2166 A. A. SCALA AND D. G. BALLAN
that at any pressure the ratio CaH6/ c-CaH6 is increased as the incident energy is decreased. This is clearly opposite to the effect expected if propylene originated entirely from cyclopropane isomerization. Although the observed trend in the ratio CaH6/ C-CaH6 could be explained by some additional source of cyclopropane at higher energies, this would require that the value observed for the ratio CaH6/c-CaH6 extrapolated to infinite pressure on an inverse pressure plot (Fig. 4) would be lower than that observed in the thermal and mercury sensitized decompositions of cyclopropaney,I2 The intercept of the 106.7-4.8 line in Fig. 4 is within experimental error identical to the values of 0.08 and 0.03, respectively, observed in the latter systems. However, at 123.6 and 147.0 nm, the intercepts are higher indicating an additional source of propylene as proposed, rather than additional source of cyclopropane.
If we take the data at 106.7-4.8 nm where molecular propylene formation and secondary decomposition of C3 species, as indicated by the invariance of the Ca yield (Table II), are both unimportant and make the reasonable assumption that the trimethylene diradical is an intermediate in the production of propylene, cyclopropane, and allene, we can write the following mechanism (Scheme I) to account for these products:
k,
-tCO+· CH2CH2CH2·-t 1-CaH6
kcl 1kd
k.
C-CaH6 *-tc-CaH6
k.I~C,II':H' This mechanism, exclusive of the photodecomposition and the allene producing step, has been suggested previously to explain the mercury sensitized decomposition of cyclopropane.I2 If we make a steady state assumption for excited cyclopropane, the following expressions result:
c/JCaH6 _ ki + k i kd+ke M-I (A) c/J~ - kc kc --,;:- , c/Jc-CaH6/c/JC'H4= (k./ke)M, (B)
CPC.H6 = '!!. 1+ ~ + kik· M . c/JC.H 4 kc ke kcke
(C)
The appropriate plots of the data for Eqs. (A), (B), and (C) are presented in Figs. 4-6. Using the 106.7 nm data where the data is not complicated by the production of primary propylene in a step unrelated to Scheme I and using a strong collision assumption such that ksM = w, from the slopes in Figs. 4-6 which are 0.010 atm, 67.8 atm-r, and 5.68 atm-I, respectively, and the intercept in Fig. 6 which is 0.431 the following
rate constants may be obtained: k8=2.2XlO11 liter mole-I'seei , ke= 1.3 X 108 seeI, kd= LOX 109 seeI, k;/kc=8.2±2XlO-2• The relatively large uncertainty in k;/kc is due to the fact that slightly different values for ki/kc are obtained depending upon which data is used to evaluate ki/kc. The ratio ki/kc is quite close to values observed for this ratio in the thermal and mercury sensitized decompositions of cyclopropaney,l2 The correlation coefficients for the 106.7-4.8 lines in Figs. 4-6 which were used to evaluate the rate constants are 0.998,0.993, and 0.997, respectively. If we now take ke+kd as the rate constant for unimolecular decomposition of excited cyclopropane, we may evaluate the energy content of the excited cyclopropane. The energy of the excited cyclopropane which corresponds to a rate constant for decomposition of 1.13 X 109 seel depends upon the method of calculation. The simple Kassel equation
k = A [(E- Ea) / EJs-r,
using A;' 1015.17 seeI, Ea=65 kcal/mole, s= 13, and k = 1.13 X 109 seer, gives a total energy for the excited cyclopropane of 94 kcal/mole. The more accurate calculation of this quantity based upon RRKM theory as described by Rabinovitch and Setserla gives a slightly lower energy of 88 kcal/mole. In view of the photon energy at 106.7-4.8 (270 kcal/mole) and the thermochemistry of Reaction (2) (~H = + 7 kcal/mole) the carbon monoxide and CaH6 produced in this reaction must partition 263 kcal/mole between them. The fact that the cyclopropane only contains 88 kcal/mole as an average excess vibrational energy, requires that the carbon monoxide must be produced with excess energy in the vicinity of 175 kcal/mole. This energy is sufficient to produce carbon monoxide in either of two electronically excited states. The possible states are a a1l" and aI 32;+,14 The lifetime of the a a1l" state makes it impossible to observe emission from this state under our experimental conditions.I5 Since the quantum yield of carbon monoxide is less than unity at 106.7-4.8 nm it is impossible to determine whether any of the excited carbon monoxide molecules sensitize further decomposition of cyclobutanone. This nonstatistical distribution of energy in the products of a photodecomposition has been observed before by Campbell and Schlag in the near ultraviolet photolysis of cyclobutanone, however the present system is a severe divergence from a statistical distribution compared to the relatively minor divergence observed in the near ultraviolet.I6 The present system strongly suggests that the photon energy is localized in the carbonyl group and that decomposition occurs without complete loss of electronic excitation in the product carbon monoxide.
Despite the fact that there is no theoretical justification for doing so, it is often assumed and frequently observed that photochemical excitation is distributed among the products of a photodecomposition statistically according to the number of vibrational degrees
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PHOTOCHEMISTRY OF CYCLOBUTANONE 2167
of freedom in the products,l7 This is a reasonable assumption for thermal energy and is a fundamental assumption in RRKM theory. The recent elegant experiment by Rabinovitch18 has demonstrated the validity of this assumption for thermal systems. In photochemical systems, it is usually impossible to determine the distribution of energy in the products.
Hydrogen is produced with a quantum yield of 0.20,0.21, and 0.27 at 147.0, 123.6, and 106.7--4.8 nm, respectively. One source of hydrogen in the present system is shown in Scheme I to be the secondary decomposition of excited cyclopropane to produce allene and a hydrogen molecule. A second source of hydrogen is the secondary decomposition of ethylene which results in the production of acetylene and hydrogen. Acetylene is produced at each wavelength and the quantum yield of acetylene is increased. as the energy is increased. The sum of the acetylene and allene is not, however, sufficient to account for all of the hydrogen and it is likely that
---+H+C4H50,
---+H2+ C4H40
(7)
(8)
contribute to the production of hydrogen. The fact that the quantum yield of carbon monoxide is 1.0 at 147.0 and 123.6 nm indicates that essentially all of the C4H50 and C4H40 produced in these reactions decomposes to produce carbon monoxide. This should also be true of these species produced at 106.7-4.8 nm.
Although we are unable to conclusively account for the low (0.81) quantum yield of carbon monoxide at 106.7-4.8 nm, we can suggest a tentative explanation. Despite the fact that the ionization quantum yield is 0.2, we have not been able to demonstrate the occur· rence of an ion molecule reaction. At 123.6 nm (10.0 eV) it is likely that only the parent ion, C4H60+, is produced. If the parent ion is unreactive, it will even· tually undergo neutralization and decompose, pro· ducing carbon monoxide in the same manner as other neutral excited molecules. At 106.7-4.8 nm ("-'11.7 eV) the photon energy is probably above the appearance potential of the C2H20+ ion which accounts for 60%
of the total ionization in the 70 eV mass spectrum of cyclobutanone.19-
21 The deficiency in the quantum yield of carbon monoxide at 106.7-4.8 nm could be due to the failure of the C2H20+ ion produced in Reaction (9)
(9)
to decompose to carbon monoxide.
* This research was supported by the U.S. Atomic Energy Commission [AT(30·1).3945].
1 For a review see (a) R. Srinivasan, Advan. Photochem. 1,83 (1963). (b) J. Calvert and J. N. Pitts, Jr., Photochemistry (Wiley, New York, 1966), p. 406.
2 N. E. Lee and E. K. C. Lee, J. Chern. Phys. 50, 2094 (1969). 3 H. O. Denschlag and E. K. C. Lee, (a) J. Am. Chern. Soc.
89,4795 (1967); (b) 90,3628 (1968). 4 T. M. McGee, J. Phys. Chern. 72, 1621 (1968). 5 R. J. Campbell, E. W. Schlag, and B. W. Ristow, J. Am. Chern.
Soc. 89, 5098 (1967). 6 Robert A. Sandsmark, dissertation, Northwestern University,
August 1967. 7 A. A. Scala and D. G. Ballan, J. Phys. Chern. 76, 615 (1972). 8 J. Y. Yang and F. M. Servedio, Can. J. Chern. 46, 338 (1968). 9 H. L. McMurry, J. Chern. Phys. 9, 231 (1941). 10 A. A. Scala and D. G. Ballan, Can. J. Chern. (to be pub·
lished) . 11 (a) E. W. Schlag and B. S. Rabinovitch, J. Am. Chern. Soc.
82, 5996 (1960). (b) J. W. Simons and B. S. Rabinovitch, J. Phys. Chern. 68,1322 (1964). (c) S. W. Benson, J. Chern. Phys. 34,521 (1961). (d) W. B. DeMore and S. W. Benson, Advan. Photochem. 2, 219 (1964).
12 O. P. Strausz, P. J. Kozak, G. N. C. Woodall, A. G. Sherwood, and H. E. Gunning, Can. J. Chern. 46,1317 (1968).
13 D. W. Setser and B. S. Rabinovitch, Can. J. Chern. 40, 1425 (1962).
14 G. Herzberg, Molecular Spectra and Molecular Structure. [. SPectra of Diatomic Molecules (Van Nostrand, New York, 1950), p.452.
15 T. G. Slanger and G. Black, J. Chern. Phys. 55, 2164 (1971). 16 R. J. Campbell and E. W. Schlag, J. Am. Chern. Soc. 89,
5103 (1967). 17 B. C. Roquitte, J. Am. Chern. Soc. 91, 7664 (1969). 18 J. D. Rynbrandt and B. S. Rabinovitch, J. Phys. Chern. 74,
4175 (1970). 19 Y. Wada and R. W. Kiser, J. Phys. Chern. 66, 1652 (1962)
have determined an appearance potential of 9.8±0.4 eV for the C2H20+ ion produced from 3, 4-epoxy·l·butene (C2HsO). The appearance potential for this ion produced from cyclobutanone (C.H60) should be similar, especially since the neutral product is the same (C2H4) in both cases.
20 H. J. Hofman, Tetrahedron Letters 1964, 2329. 21 H. Audier, J. M. Conia, M. Fetizon, and J. Gore, Bull. Soc.
Chim. Frace 1967, 787.
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