3004
J. Phys. Chem. 1980, 84,3604-3608
Mechanism of the Gas-Phase Reactions of C3H6and NO3 Radicals H. Bandow," M. Okuda, and H. Akimoto Division of Atmospheric Environment, National Institute for Environmental Studies, Yatabe-machi, Tsukuba, Ibaraki305, Japan (Received: April 4, 1980; In Final Form: August 5, 1980)
Gas-phase reactions of propylene with NO3 were investigated in the C3H6-Nzo5-o2/N2system by Fourier transform infrared spectrometry. New type of nitrogen-containing compounds, nitroxyperoxypropyl nitrate (NPPN, CH~CH(ONOZ)CH~(OONO~) and/or CH3CH(OONO~)CHz(ONOz)) and nitroxypropyl nitrite (NPN, CH~CH(ONO~)CHZ(ONO) and/or CH&H(ONO)CH2(0N02))were identified for the reaction systems with and without 02,respectively. Both nitroxy compounds were unstable, and their kinetic behaviors suggest that they are intermediate species in the formation of the final product, propylene glycol 1,2-dinitrate (PGDN). The reaction was concluded to be initiated by the addition reaction of the NO3 radical to propylene, and an overall reaction mechanism for the C3H6-N2O5system was proposed.
Introduction There have been only a few studies on the olefin-N2O5 reaction both in the and liquid Morris and Niki' and Japar and Niki2 investigated the gas-phase kinetics of N205-olefin systems and obtained rate constants for the reaction of the NO3 radical with olefins. Although they also reported2 that a product showed an IR absorption band near 1670 cm-l in the case of the propylene-N20, system, identification was not made. Recently, 1,2-propanediol dinitrate, abbreviated as PGDN (propylene glycol 1,2-dinitrate),was found3 to be a major product of a thermal reaction of a propylene-N206-air system at room temperature. The wavenumber of the band reported by Japar and Niki2corresponded closely to that of PGDN. PGDN was also found7y8to be formed as a nitrogen-containing photooxidation product in our smog chamber study of the propylene-nitrogen oxides-air system, and the reaction of propylene with the NO3 radical was thought'ss to be responsible for the formation of the compound in the photooxidation system. In the liquid phase, the olefin-N2O5 reaction was reported4 to give nitroalkyl nitrates and nitroolefins, although the formation of glycol nitrate was also noted in earlier ~ t u d i e s However, .~~~ neither in the gas nor in the liquid phases, product analysis of the olefin-NZO5system has been complete and the mechanism of the reaction is still uncertain. In this study, the gas-phase reaction of the propyleneN205 system was investigated by long-path Fourier transform infrared spectroscopy (FT-IR). Other than the reaction products reported before? new nitrogen-containing compounds, NPPN (nitroxyperoxypropyl nitrate) and NPN (nitroxypropyl nitrite), were found to be formed in the presence and absence of 02,respectively. From the kinetic behavior of the products, both of the new compounds are thought to be produced via the free radical initially formed by the addition of NO3 to propylene and to be intermediate species to give the final products. Overall reaction pathways to give the observed products in the propylene-N,O, system will be proposed. Experimental Section The reaction cell used was an 11-L quartz cylinder (12 cm i.d., 100 cm long) and both sides were teflon-coated metal flanges fitted with an IR multireflection mirror system. Reactants and products were identified and quantitatively analyzed in situ by the long-path FT-IR system (Block Engineering Co., JASCO International Inc., FTS-496s). The IR path length was aligned at 40 m and 0022-3654/80/2084-3604$0 1.oo/o
the resolution used in this study was 1 cm-'. Reactant gases, C3H6,NO2,and N205,were prepared as follows: Commercially available propylene was purified by trap-to-trap distillation (liquid Nz cold trap) several times before using. NO2 was prepared by a thermal reaction of NO with excess 0, and purified by vacuum distillation and trap-to-trap distillation with a liquid N2 cold trap. After this procedure, no other nitrogen oxides except NO2 were detected by FT-IR measurement. Nz05 was synthesized by a two-step dehydration of a concentrated HN03 aqueous solution with P2O5 at low temperature. NzO5was purified by vacuum distillation before using. The air used was either purified air9 (impurities; 2 ppb, hydrocarbons C 100 ppbC, C 0 2 1 ppm, NO, SO2 < 10 ppb, and H20 < 1ppm) or synthesized air from pure N2 (Nippon Sanso, >99.999%) and pure O2 (Nippon Sanso, >99.9%). In the 02-freeexperiment, pure Nz was used after passing through a Molecular-Sieves (5A) cold trap at -100 "C. Kinetic measurements were performed under 1atm of buffer gas. The amounts of the reactant gas were measured by an MKS Baratron capacitance manometer in a constant volume. Propylene was f i s t sampled and flushed into the reaction cell with the buffer gas to a pressure of 0.5 atm. Then NZO5, and NO2 if used, were sampled and introduced in the same way until the pressure became 1 atm. The spectra were obtained about every 3 min by scanning 64 times and this scanning required 2.1 min. Therefore, every spectrum is the average for the scanning time, and the reaction time discussed below is the mean time of each scanning after the NzO5 flush. Experiments were carried out at 25 f 1 "C in the dark.
-
Results and Discussion Products of the C3H6-N2o5-Air System. Figure l a shows the IR absorption spectrum of the reaction products at t = 7 min when C3H6(35.8 mtorr) and N205 (22.1 mtorr) were mixed under 1atm of synthetic air ([N,] = 650 torr and [O,] = 100 torr). The spectrum was obtained by subtraction of the remaining reactants and products (NOz, HCHO, and CH3CHO) from the IR spectrum of the reaction mixture. The IR spectrum shown in Figure l b is an authentic spectrum of PGDN, which is known to be a major product of this reaction systema3Comparing Figure l a with lb, one can see that there exist other unknown products in addition to PGDN. Subtraction of spectrum l b from l a with appropriate multiplying factor gives the spectrum shown in Figure IC.It is noteworthy that there still remain bands whose wavenumbers are very close to 0 1980 American Chemical Society
Gas-Phase Reactions of
The Journal of Physical Chemistry, Vol. 84, No. 26, 1980 3005
C3H6and NO3
@Fr-+ Products
+!I I i!l Y
3
z 40
1
- 1 5+~
z
h
t
0
0
1400
li00
Id00
ab0 A 0 1
b,
-&-+&a0
-
( Products) ( PGDN)
1400 HAVENUMBERS 1200
Id00
ab0 ;c0
Flgure 2. (a) Product spectrum of the C3H, (35.7mtorr)-N20, (18.4 mtorr)-N, (750torr) system. Reaction time was 12 min under dark conditions, temperature = 24 OC. (b) Product spectrum obtained by subtracting the authentic spectrum of PGDN from (a). The spectrum is due to NPN. See text. -17-
1400
1200 HAVENUMBERS
I000
eCO 7b0
Flgure 1. (a) Product spectrum of the C3HB(35.8 mtorr)-N,0, (22.1 mtorr)-N2 (650 torr)-0, (100 torr) system. Reaction time was 7 min under dark conditions, telmperature = 26 OC;. (b) Authentic spectrum of PGDN. (c) Product spectrum obtained by subtracting the authentic spectrum of PGDN from (a). The spectrum is mainly due to NPPN. See text.
those of PGDN. The wavenumbers and relative intensity ratio of the bands, 1670, 1284, and 845 cm-l, are in good agreement with the ONOz group bands of PGDN (1672, 1280, 840 cm-l) and ethyl nitrate (1667, 1291,855 cm-l). The other intense bands at 1726, 1295, and 790 cm-l correspond well to 0 0 N 0 2 bands of methyl peroxynitrate (1724, 1299, 791 cm-l)l0and PAN (1'736, 1302, 793 cm-l). Further, the intensity of these two sets of absorption bands varies in parallel, suggesting that all of these bands are ascribed to a single compound. From these considerations, the IR spectrum shown in Figure ICis assigned to NPPN, although some other carbonyl compound could be included, as will be discussed below. As for the structure of NPPN, CH3CH(ONOz)CHz(OONOz)and CH&H(OONOZ)CH2(0NO2)are possible. Since the absorption spectrum and the absorption coefficients of ONOz and OON02 bands of the two isomers of NPPN are thought to be scarcely affected by the positions on which the functional groups are attached, isolation was not possible from the IR spectra. Efforts to determine the structure were done by using the methods of gas chromatography (GC)and GC-MS but were unsuccessful because of its thermal instability. In Figure IC,a weak band can be seen at about 1760 cm-l in the region which is characteristic for the carbonyl group. In our previous study of the C3H6-N205-air system: the formation of l-formylethyl nitrate, CH3CH(ONOZ)CHO, was suggested from the mass fragment pattern in the GC-MS analysis. Thierefore, the carbonyl compound in Figure ICis presumably this compound. No mass fragment pattern expected from the other possible carbonyl com-
pound, CH3(CO)CHZ(0NO2), was detected by GC-MS.3 Other than PGDN, NPPN, and l-formylethyl nitrate, HCHO, CH3CH0, NOs, and HNOBwere detected by FTIR. Products of the C3H6-Nz05-N2System. If the reaction of C3H6+ Nz05proceeds via radical intermediates, the OZ-freesystem is expected to give different products from the Oz-includedsystem. The IR spectrum of the reaction products of C3H6(35.7 mtorr) + N2O5 (18.4 mtorr) under 1 atm of Nz is shown in Figure 2a. Reactants, C3H6and N205, and NOz produced have been subtracted in this spectrum. Subtiraction of PGDN from Figure 2a gives Figure 2b, which shows the bands due to the ONOz functional group, 1672,1282, and 843 cm-l, and the other bands, 1692,15801, and 768 cm-', which are very similar to those of organic nitrites in their wavenumbers (e.g., CzH50NO: 1665 (trans), 1618 (cis),778 cm-l; n-C4H90NO: 1668 (trans), 1618 (cis), 785 cm-') and relative intensities. Since these nitrate bands and nitrite bands in Figure 2b vary in parallel and are thus thought to be ascribed to a single compound, the product was deduced to be NPN. The splitting of ~ ~ between ~ - cis 0 and trans isomers is somewhat larger as compared with other organic nitrites. This shift is thought to be caused by an intersection with a bulky ONOz group. Although two structural isomers, CH3CH(ON02)CIHzON0and CH3CH(ONO)CH20NO2, are possible for this compound too, its structure was not determined in this work. The main products of this system were PGDN and NPN. Formation of nitro compounds for the reaction of Nz05with olefins in the liquid phase has been r e p ~ r t e d . ~ In our experiment.,however, IR spectra of the products did not show the two marked bands of nitro compounds in the regions of 1556-1545 and 1390-1355 cm-l.ll Other reaction products, such as aldehydes, which were obtained in the 02-includedsy,stem,were not detected by FT-IR. This result reveals that, the reaction of C3H6+ N2O5 proceeds via a radical intermediate, presumably the radical formed
3606
The Journal of Physical Chemistry, Vol. 84, No. 26, 1980
Bandow et ai. 4
,
I
50
100
3 h
L
EE Y
C
.o 2 c
c2
.c
---------_---__
2 c C
e
c
Q,
0
C
0
U C
V
0 V
1
0
100
50
Time
250
zeo
0
(min)
Figure 3. Concentrations of reactants and products as a function of reaction time in the C3H, (35.8 mtorr)-N,0, (22.1 mtorr)-N, (650 torr)-O, (100 torr) system. Temperature = 26 OC.
by the C3H6+ NO, radical reaction. Kinetic Measurements. The time profile of reactants and main products in the reaction of [C3H6I0= 35.8 mtorr, [N205],= 22.1 mtorr, [N,] = 650 torr, and [O,] = 100 torr a t 26 "C is shown in Figure 3. The concentration of NPPN was calculated from the absorbance of the 790-cm-' band under the assumption that its absorption coefficient was equal to that of the 793-cm-l band of PAN (1.36 X torr-l cm-l.l2 For the concentration of PGDN, since all the main bands of PGDN overlapped those of NPPN, a calculation was carried out for the 840-cm-' band after subtracting the contribution of the 845-cm-' band of NPPN. The absorption coefficient used was 3.8 X torrT1cm-' for the 840-cm-l band.' The concentrations of C3H6,N2O5, HCHO, and CH3CH0 were also calculated by IR absorption in the same manner as previously describeda8 Reactants, C3H6and Nz06,were rapidly consumed at the initial stage, and NPPN was formed and reached its maximum concentration within 5 min and then decreased. PGDN was successively produced after NPPN. Addition of NO2to this sytem was found to decelerate the reaction. Figure 4 shows the result when 26.7 mtorr of NO2 was added. The result agrees well with the finding of Morris and Nikil and Japar and Niki2 that the decay of N2O5 in the presence of olefins is slowed by the addition of NOz. These results strongly suggest that the reactions are initiated by the NO, radical which is rapidly equilibrated with N2O5and NOz as follows: NzO5 ==NOz + NO, Kp = 1.70 X
torr
1
(1)
The addition of 26.7 mtorr of NOz reduced the initial concentration of NO, by about two orders of magnitude. Figure 4 also indicates that the formation of PGDN had an induction period, and the time profile suggests that PGDN was formed through NPPN. As for HCHO and CH,CHO, their formation curve seems to be equal and also nearly parallel to that of PGDN, as shown in Figures 3 and 4, suggesting that HCHO, CH3CH0, and PGDN were formed from the same intermediate. The carbon balance of these experiments was 0.7 and 1.0 at the initial stage of the reactions in Figures
150
Time (mini Figure 4. Concentrations of reactants and products as a function of reaction time in the C3H, (35.5 mtorr)-N,0, (22.1 mtorr)-NO, (26.7 mtorr)-air system. Temperature = 25 OC.
04
4
PGDN
h
L
b 3 t
E
aJ
Y
U
C
0
c
fl
2
v) n
.-c
0
02
;:2 u
Q
Z
c
n z
V
3.1
1
I
100
50
Time
150
(min)
Figure 5. Concentrations of reactants and products as a function of reaction t h e in the C,H, (71.2 mtorr)-N2O5 (44.0 mtorr)-N2 (750 torr) system. Temperature = 25.5 OC. Concentration of NPN is plotted in absorbance units for the 788-cm-' band.
3 and 4, respectively, being obtained by the amounts of [PGDN] + [NPPN] + ([HCHO] + [CH&H0])/2 to -A[C3H6]. These values decreased with the reaction time, indicating the involvement of some secondary processes and/or adsorption. This would explain the difference of the time profile between HCHO, CH,CHO, and PGDN at the later stage of the reaction. Figure 5 shows the time profile of reactants and main products in the reaction of the 02-free system, [C3H6I0= 71.2 mtorr, [N,O,], = 44.0 mtorr, and [N,] = 750 torr at
The Journal of Pihysical Chemlstty, Vol. 84, No. 26, 1980 3807
Gas-Phase Reactions of C3H, and NO3
--
Scheme I. Proposed Reaction Mechanism for the Reactions of the C,H[,-N,O,-Air System
I
1
I
100
150
->-
f
H02
25.5 "C. NPN is pllotted in absorbance units. C3H6and N205were rapidly consumed as in the OZ-addedsystem, accompanying the formation of NPN. PGDN seems to be produced after NPN. NPN was also found to be easily photolyzed when exposed to a fluorescent lamp. This behavior is analogous to other organic nitrites and thus supports the identification of NPN. The Reaction Sch(eme. The reaction scheme proposed in this study is depicted in Scheme I[. In a C3H6+ Nz06 reaction system, the NO3 radical is the reactive species which initiates the reaction as mentioned above. Addition of the NO3 radical to olefin is plausibly the main reaction pathway, and then C3H6yields the nitroxypropyl radical (CH3CHCHz0N0zilnd/or CH3CH(ONOz)CHZ). Under atmospheric conditims, the nitroxypropyl radical is considered to combine easily with excess Oz. The nitroxypropylperoxy radical (CH3CH(OO)CHzONOZand/or CH3CH(ON02)CH200) thus formed would react in large part with NOz which exists in the Eiystem from the decomposition of Nz05and/or by intentional addition. Thus, one of the main products, NPPN, its formed. Peroxyalkyl nitratatype compounds have recently been studied13J4with respect to their thermal stabilities for decomposition and have been found to be in equilibrium with ROz and NO, at room temperature:
3ROz + NO2
ROONOZ
(2)
The unimolecular decomposition rate constant of HOON0, under atmospheric pressure was given by Graham et al.13as 1.4 X 1014expi(-20700 f 500/RT) s-l, giving a decay rate of 0.12 s-l at 300 K. Similarly, the decomposition rate constant of C3H700N02was obtained by Edney et al.14 as 5.0 X 1014exp(-191800/RT) s-l, giving a value of 1.9 s-l at 300 K. If one assumes that the unimolecular decomposition rate constant for NPPN is comparable to that for C3H700N02,and the backward reaction rate is the same as that for the reaction of C2H5O2 + NOz, 1.3 X cm3 molecule-l s-l as reported by Adachi and Basco,15 NPPN is thought to be in fast equilibrium with the nitroxypropylperoxy radical and NO2, with an estimated equilibrium constant of K = kz/k+ = 1.5 )I: 1Ol2 molecule ~ r n - ~ . Then, one can assume the formation of PGDN via reactions of the type ROZ -t ROz 2R0 t- 0 2 (3) (4) RO -t NO2 RON02 where RO and RONOZ represents the nitroxypropoxy radical and PGDN, respectively, in the present case. The apparent half-life of NPPN after Nz05was consumed can 4
+
--
50
Time
(rnin)
Figure 6. ?lot of l/[NPPN] vs. reaction time. Plots A and B correspond to Figures 3 and 4, respectively. Each slope was obtained in the region where N,05 was almost consumed.
be obtained from Figures 3 and 4 as 46 and 130 min for runs with and without initially added NOa. Such a dependence of the apparent decay rate of NPPN on NO, concentration stirongly suggests that the main decay of NPPN proceeds through reactions 2 and 3 rather than the other possible reaction
ROO NO^ 5 RO + NO^
(5)
Although the dissociation energy of RO-ONO, bond is not known for NPPN, it can be expected to be more than a few kcal mol-l higher than D0(ROO-NO2),which would be about 20 kcal mol-l judging from the data for other peroxyalkyl n i t r e ~ t e s . ~Thus, ~ J ~ reaction 5 would not be very significant ats the decomposition mode of NPPN at room temperature. If we assume that the decay of NPPN proceeds only through reactionai 2 and 3, the following equation should hold after the coxlsumption of Nz06:
where K is the equilibrium constant of reaction 2 and approximately constant NOz concentration is assumed during the period. Figure 6 shows plots of eq 6 for the runs shown in Figures 3 and 4. From the slope of the plots, P k 3 may be deduced t o be 2.6 X 1Ol2 and 2.7 X 1Ol2 molecule s-l if we take [NO,], = 18 and 44 mtorr for the runs of Figures 3 and 4, respectively. If we further take the equilibrium constant estimated above, the value of k3 can cm3molecule-l This value be deduced to be 11.2 X is about an order of magnitude larger than the reported rate constant for CH3OZ,l6k3 = (1.6 f 0.4) X cm3 molecule-' s-l. Poadbly, the assumed equilibrium constant would be lower than the real value. CH3CH(ONO2)CHz0,one of the nitroxypropoxy radicals, is considered to give l-formylethyl nitrate by hydrogen atom abstraction by Oz, and to give HCHO, CH3CH0, and NOz by decomposition, which competes with reaction 4 to give PGDN. In a similar way, the other nitroxypropoxy raldical, CH3CH(O)CH20NO2,is supposed
3608
The Journal of Physical Chemistry, Vol. 84, No. 26, 1980
to give 2-oxopropyl nitrate (CH3(CO)CH2(ON02)) instead of 1-formylethyl nitrate by hydrogen atom abstraction by 02.Although 2-oxopropyl nitrate was not detected in our experiments even in high c~ncentration,~ this does not necessarily exclude the possibility of the addition of the NO3 radical to the terminal carbon atom of the propylene double bond. Baldwin et a1.l' estimated the unimolecular decomposition rates of selected RO-type radicals and showed that the 1-hydroxy-2-propoxy radical (CH3CH(O)CH,OH) decomposes -100 times faster than the 2hydroxy-1-propoxy radical (CH3CH(OH)CH26).In accord with the estimate, Carter et al.'* reported that a good fit was obtained in their computer simulation study of smog chamber data when they assumed that the l-hydroxy-2propoxy radical primarily decomposes while the 2hydroxy-1-propoxy radical is primarily hydrogen abstracted by 0, to give a carbonyl compound. If we assume that the reactivity of nitroxypropoxy radicals i s analogous to that of hydroxypropoxy radicals, CH3CH(O)CHZ0NO2 may decompose primari!y to give HCHO and CH3CH0, and CH3CH(ON02)CH20 may be primarily hydrogen abstracted to give 1-formylethyl nitrate or recombine with NOz to give PGDN. Thus, NO3 radical addition toward the terminal carbon atom cannot be ruled out, and both reaction pathways are included in Scheme I. As a route to 1-formylethyl nitrate, direct elimination of nitric acid from NPPN is also possible, as suggested by Hendrylg for alkylperoxy nitrate, reaction 7, and included in Scheme I.
In the 02-free system, the initial step is the same as in the 02-added system; NO3addition to C3&. However, the second step is thought to be NOz addition, instead of O,, to the nitroxypropyl radical to give NPN. NPN could be an intermediate species to PGDN, judging from its time profile as shown in Figure 5. Although detailed analysis was not done, conversion of NPN to PGDN is assumed to be oxidation by NO3 or N206.
Atmospheric Implication The NO3 radical has recently been observed20spectroscopically in ambient polluted air. Particularly, Platt et found that the NO3 concentration increased up to a few hundred ppt in early nighttime during an air pollution episode. If we consider the case that propylene and the NO3 radical coexist at concentrations of 10 ppb and 200 ppt, respectively, in the polluted atmosphere, the rate of disappearance of propylene due to NO3 is obtained to be 0.9 ppb h-l. This implies that a major product such as PGDN accumulates up to ppb levels in a few hours in nighttime.
Bandow et al.
On the other hand, the NO3 concentration during daytime is expectedz0to be much lower than in early nighttime. If we assume that the typical concentration of the NO3 radical in daytime to be about ten times of that of OH (-3 X lo6molecule cm-3)21the relative contribution of C3H6decay due to the former radical is only about 0.2% of that due to the latter radical taking into consideration the rate constant2,22of the reactions of the respective radicals with C3H6. Thus, product formation due to the NO3 reaction would not be significant during daytime. The reaction of the NO3 radical with olefins has sometimes been taken into account in computer modeling studies of photochemical smog reactions. Thus, the reaction schemes proposed by Demerjian et and Hov et aLN include sequences initiated by H-atom abstraction from C3H6by NO3,while a recent study by Carter et assumed the addition reaction of NO3to C3H,. Since the present study established that the NO3 radical initiates the reaction by addition, the addition pathway sequence should be taken into account in future computer-modeling studies.
References and Notes (1) E. D. Morris and H. Niki, J . Phys. Chem., 78, 1337 (1974). (2) S. M. Japar and H. Niki, J . Phys. Chem., 79, 1629 (1975). (3) M. Hoshino, T. Ogata, H. Akimoto, G. Inoue, F. Sakamaki, and M. Okuda, Chem. Lett., 1367 (1978). (4) T. E. Stevens and W. Emmons, J. Am. Chem. Soc., 79, 6008 (1957). (5) L. B. Hains and H. Adkins, J . Am. Chem. Soc., 47, 1419 (1925). (6) N. Y. Dem'yanov, C . R . Acad. Sci. URSS, Ser. A , 1930, 447 (1931); Chem. Absfr., 25, 1215 (1931). (7) H. Akimoto, M. Hoshino, G. Inoue, F. Sakamaki, H. Bandow, and M. Okuda, J. Environ. Sci. Health, Part A , 13, 677 (1978). (8) H. Akimoto, H. Bandow, F. Sakamaki, 0. Inoue, M. Hoshino, and M. Okuda, fnvlron. Sci. Technol., 14, 172 (1980). (9) H. Akimoto, M. Hoshino, G. Inoue, F. Sakamaki, N. Washida, and M. Okuda, Environ. Sci. Technol., 13, 471 (1979). (10) H. Niki, P. D. Maker, C. M. Savage, and L. P. Breitenbach, Chem. Phys. Lett., 55, 289 (1978). (11) N. B. Coithup, L. H. Daly, and S.E. Wiberley, Ed., "Introduction to Infrared and Raman Spectroscopy", Academic Press, New York, 1964. (12) E. R. Stephens, Anal. Chem., 38, 928 (1964). (13) R. A. Graham, A. M. Winer, and J. N. PHts, Jr., Chem. fhys. Lett., 51, 215 (1977). (14) E. 0. Edney, J. W. Spence, and P. L. Hanst, J . Air Pollut. Control Assoc., 29, 741 (1979). (15) H. Adachi and N. Basco, Chem. Phys. Leff., 87, 324 (1979). (16) D. A. Parkes, Int. J . Chern. Kinet., 9, 451 (1977). (17) A. C. Baldwin, J. R. Barker, D. M. Golden, and D. G. Hendry, J. phys. Chem.. 81. 2483 11977). (18) W.b. L. Carter, A.'C. Llbyd, J. L. Sprung, and J. N. Pitts, Jr., Int. J. Chem. Kinet., 11, 45 (1979). (19) D. G. Hendw, Natl. Bur. Stand. S m c . Publ., No. 557, 77 (1978). (20i U. Piatt. D. Perner. A. M. Winer. G. W. Harris, and J. N. Pitts. Jr.. Cieophys. Res. Leff., 7, 89 (1980). J. G. Caivert, fnviron. Sci. Technol., 10, 257 (1976). R. Atkinson and J. N. Pms, Jr., J . Chem. Phys., 83, 3591 (1975). . . K. L. Demerjian, J. A. Kerr, and J. 0. Caivert, Adv. Environ. Sci. Technol., 4, 1 (1974). (24) 0. Hov, I. S. A. Isaksen, and E. Hesstvedt, Atmos. fnviron., 12, 2469 (1978).
