J. Phys. Chem. 1990, 94, 2413-2419 support for a photodecomposition mechanism involving sequential CO elimination from M(CO), in its electronic ground state. Qualitative estimates of the nascent internal energy content of the product fragments M(CO), and CO are also consistent with this mechanism. In addition, we have observed, for the first time, the expected buffer gas pressure effects on the relative yields of Cr(CO)S and Cr(C0)4 in the case of 308-nm photolysis. Our relative fragment yields between Cr and Mo support previous indications that in Cr(C0)6 the first M-CO BDE is not the largest whereas it is in the cases of Mo and W. Unlike W(CO),, presumably as a consequence of the lower CO binding energy, there are no excimer laser wavelengths that ex-
2413
clusively produce a single Mo(CO)~species. Mo(CO), is the major product at 308 nm and may be tractable for reactive studies; however, at 351 nm there is also a significant amount of Mo(CO), produced that may thwart attempts to study Mo(CO),.
Acknowledgment. We thank Patrick Lawrence for his technical assistance and Dr. Steven Mitchell, Dr. Shigeyoshi Arai, and Dr. Toshiaki Munakata for useful discussions. Registry No. Mo(CO),, 13939-06-5; Cr(C0)6, 13007-92-6; W(CO)6, 14040-11-0; Cr(CO),, 26319-33-5; C r ( C 0 ) 4 , 561 10-59-9; Mo(CO),, 44780-98-5; Mo(CO),, 55979-29-8; Mo(CO),, 32312-17-7; CO, 630-
08-0.
Kinetics and Products of the Reactions of NO3 with Monoalkenes, Dialkenes, and Monoterpenes Ian Barnes, Volker Bastian, Karl H. Becker,* and Zhu Tong Physikalische ChemielFachbereich 9, Bergische Uniuersitat-GH (Received: June 2, 1989; In Final Form: September 13, 1989)
Wuppertal, 0-5600 Wuppertal I , FRG
Rate constants for the reactions of NO3 with a number of aliphatic mono- and dialkenes and monoterpenes have been determined in a 420 1 reaction chamber at I-bar total pressure of synthetic air by 298 K with a relative kinetic method. The products of these reactions have been investigated also at I-bar total pressure of synthetic air with in situ FT-IR spectrometry and gas chromatography. In all cases, the initial formation of thermally unstable nitrooxy-peroxynitrate-type compounds containing the difunctional group -CH(OON02)-CH(ON0,)- has been observed. The experimental results are consistent with a mechanism involving the formation of nitrooxy-alkoxy radicals, -CH(0)-CH(ON02)-, via the self-reaction of the nitrooxy-peroxy radicals. The further reactions of the nitrooxy-alkoxy radicals then determine the final products. The main reaction pathways are (i) reaction with O2 to form nitrooxy-aldehydes or -ketones and H 0 2 and (ii) thermal decomposition forming aldehydes/ketones and NO2. The mechanisms leading to the final products are discussed, and their possible relevance for the chemistry in the troposphere is considered
Introduction A large number of hydrocarbons is known to be emitted to the atmosphere from natural sources.] The most important biogenic hydrocarbons released from various types of plants and trees are isoprene and monoterpene^.^-^ Their emission source strengths on a global scale are much larger than those of anthropogenic non-methane hydrocarbons. They represent a significant source of reactive organic compounds to the atmosphere whose role in the chemistry of tropospheric oxidant formation is not well understood. At present, attention is being focused on the degradation processes of these natural hydrocarbons and in particular on those processes leading to the formation of oxidants that might develope phytotoxic properties within forest areas. Isoprene and the monterpenes are known to react rapidly with 036 and OH radicals.' Recently, it has been shown that NO3 also reacts rapidly with these compounds.*-12 These fast reactions taken in conjunction with the atmospheric concentrations of NO3, which have been observed in the nighttime troposphere as high as 350 pptv,I3-I5have led to the suggestion that reaction with NO3 may dominate the nighttime chemistry of volatile biogenic organic compounds. Product studies have so far only been reported in a series the literature for the reactions of NO3 with of sulfur compounds,21formaldehyde,22a ~ e t a l d e h y d eand , ~ ~ tetra~nethylethylene.~~ The aim of the present study was to investigate the mechanisms and products of the reactions of NO3 with atmospherically important alkenyl hydrocarbons. Many of the expected products such as peroxynitrates, nitrates, and organic acids are potential phytotoxicants; a detailed knowledge of their mechanisms of
* Author to whom correspondence should be addressed. 0022-3654/90/2094-2413$02.50/0
formation and product yields will allow a better evaluation of their possible impact on forest ecosystems. (1) Graedel, T. E.; Hawkins, D. T.; Claxton, L. D. Atmospheric Chemical Compounds: Sources, Occurrence, and Bioassay; Academic Press: London, 1986. (2) Rasmussen, R. A.; Khalil, M. A. K. J. Geophys. Res. 1988, 93, 1417. (3) Riba, M. L.; Tathy, J. P.; Tsiropoulos, N.; Monsarrat, B.;Torres, L. Atmos. Enuiron. 1987, 21, 191. (4) Lamb, B.; Guenther, A.; Gay, D.; Westberg, H. Atmos. Environ. 1987, 21, 1695. ( 5 ) Zimmerman, P. R.; Greenberg, J. P.; Westberg, C. E. J. Geophys. Res. 1988. 93. 1407. (6) Aikinson, R.; Carter, W. P. L. Chem. Rev. 984, 84, 437. (7) Atkinson, R. Chem. Rev. 1986, 86, 69. (8) Atkinson, R.; Aschmann, S. M.; Winer, A. M Pitts, J. N., Jr. Enuiron. Sci. Technol. 1984, 18, 370. (9) Atkinson, R.; Aschmann, S. M.; Winer, A. M Pitts, J. N., Jr. Enuiron. Sei. Technol. 1985. 19. 159. (10) Rahman, M. M.; Becker, E.; Benter, Th Schindler, R. N. Ber. Bunsen-Ges. Phys. Chem. 1987, 92, 91. (11) Benter, Th.; Schindler, R. N. Chem. Phys. Lett. 1988, 145. 67. (12) Dlugokencky, E.; Howard, C. J. J. Phys. Chem. 1989, 93, 1091. (13) Platt. U.F.: Winer. A. M.: Biermann. H. W.: Atkinson. R.: Pitts. J. N.,'Jr.'Etwiron. Sci. Technol. 1984, 18, 365. (14) Winer, A. M.; Atkinson, R.; Pitts, J. N., Jr. Science 1984, 224, 156. (15) Atkinson, R.; Winer, A. M.; Pitts, J. N., J r . Atmos. Environ. 1986, 20, 331. (16) Akimoto, H.; Hoshino, M.; Inoue, G.; Sakamaki, F.; Bandow, H.; Okuda, M. J. Enuiron. Sci. Health, Part A 1978, 13, 9677. (17) Hoshino, M.; Ogata, T.; Akimoto, H.; Inoue, G.; Sakamaki, F.; Okuda, M. Chem. Lett. 1978, 1367. (18) Bandow, H.; Okuda, M.; Akimoto, H. J. Phys. Chem. 1980,84,3604. (19) Shepson, P: B.; Edney, E. 0.; Kleindienst, T.E.: Pittman, J. H.; Name, G. R.; Cupitt, L. T. Environ. Sci. Technol. 1985, 19, 849. (20) Akimoto, H.; Bandow, H.; Sakamaki, F.; Inoue, G.; Hoshino, M.; Okuda, M. Environ. Sci. Technol. 1980, 14, 172.
0 1990 American Chemical Society
2414
The Journal of Physical Chemistry, Vol. 94, No. 6, 1990
Reported here are product studies on the reactions of NO, with a number of monoalkenes, dialkenes, and the monterpenes apinene, @-pinene,A3-carene, and D-limonene performed in a large reaction chamber under simulated atmospheric conditions using FT-IR and GC analytical techniques. Since many of the rate constants for these compounds are still uncertain or have only been investigated once, rate constant determinations using a relative method were also performed and compared with the available literature data.
Experimental Section The experiments were carried out at 298 f 2 K in a 420 1 cylindrical Duran glass reaction chamber, which has been described in detail e l ~ e w h e r e . ~A~relative * ~ ~ kinetic technique using the thermal deomposition of N2O5 into NO, and NO2 was applied as the NO3 radical source8s9to determine rate constants of the radical reactions with ethene, 1-butene, isobutene, 1,3 butadiene, isoprene, and the monoterpenes a-pinene, @-pinene,A'-carene, and D-limonene. Provided that the substance X and a reference hydrocarbon Y, whose rate constant with NO, is known, are removed solely by reaction with NO3, NO3 + X products, k, NO,
+Y
--
products, k ,
then the rate constant ratio k l / k 2 is given by eq I, where [XI, ki log ( [ x l ~ / [ X l O -= (1) k2 log ([YlO/[Yl,) and [Y], denote the initial concentrations of the substance under investigation and the reference hydrocarbon at time t = 0. [XI, and [Y], are the corresponding values at time t . If eq I holds, then plots of log ([X]o/[X],) against log ([Y],/[Y],) should give straight lines with zero intercept and a slope k , / k 2 . It is known ~ that NO2 reacts slowly with conjugated d i a l k e n e ~ . ~Control experiments showed that the range of NO, concentrations used in the present kinetic studies (up to 2.4 X lOI4 molecules cm-,) had a negligible effect upon the rate constants measured for the dialkenes. Consequently, no corrections have been made to these rate constants for reactions with NO,. Typical mixtures for the kinetic experiments consisted of the substance under investigation and a reference hydrocarbon each in the concentration range (2.5-25) X I O l 3 molecules cm-j in 1-bar total pressure of synthetic air. Up to 5 incremental amounts of N 2 0 5(1-2) X I O i 3 molecules contained in an external 20 1 bulb pressurized to 1.1 bar with nitrogen were added to the chamber during the course of the experiments. Homogeneous distribution of N2O5 in the chamber was attained within approximately 1 min by rapidly mixing with use of a fan. A FT-IR analysis of N205showed that 2.4 X IO1, molecules c r f 3 contained approximately 0.6 X IO', molecules cmm3of NO2 and 0.2 X 1013 molecules of HNO,. The concentrations of the monoalkenes and dialkenes were measured by gas chromatography with flame ionization detection after separation on a Porasil-C column (100/120 mesh, in. X 2 m). The monoterpenes and 2methyl-2-butene were monitored by GC-FID using a i/4-in. X (21) MacLeod, H.; Aschmann, S. M.; Atkinson, R.; Tuazon, E. C.; Sweetman, J . A,; Winer. A. M.; Pitts, J. N . , Jr. J . Geophys. Res. 1986, 91, 5338. (22) Cantrell, C. A.; Stockwell, W. R.; Anderson, L. G.; Busarow, K . L.; Perner, D.; Schmeltekopf, A.; Calvert, J. G.; Johnston, H . S. J. Phys. Chem.
--.
1985. 89. -- - ,139 ---
(23) Cantrell, C. A.; Davidson, J. A.; Busarow, K. L.; Calvert, J . G. J. Geophys. Res. 1986, 91, 5347. (24) Niki, H.; Maker, P. D.; Savage, C. M.; Breitenbach, L. P.; Hurley, M. D.J . Phys. Chem. 1987, 91, 941.(25) Barnes, 1.; Bastian, V.; Becker, K. H.; Fink, E. H.; Klein, Th.; Nelsen, W.; Reimer, A.; Zabel, F. Untersuchung der Reaktionssysteme NO,/ CIO,/HO, unter tropospharischen Bedingungen BPT-Bericht; Gesellschaft fur Strahlen und Umweltforschung mbH, Munchen, FRG, 1984; Vol. 11/84; ISSN 01761077. (26) Barnes, 1.; Becker, K. H.; Fink, E. H.; Reimer, A,; Zabel, F.; Niki, H.Inr. J. Chem. Kiner. 1983, 15, 631. (27) Atkinson, R.; Aschmann, S. M.; Winer, A. M.; Pitts. J . N . , Jr. Inr. J. Chem Kinet. 1984. 16, 697.
Barnes et al. 0.5
0.4
-
0.3
-
0.2
-
lag ([2-methyl-2-butene)d[2-methyl-2-butene]~)
Figure 1. Plot of the data according to eq I taken from experiments on the reaction of NO, with A'-carene measured relative to NO, with 2methyl-2-butene.
2-m stainless steel column packed with 10% Carbowax 600 on 100/120 mesh Chromosorb-P. The reactions of NO, with isobutane, propene, tram-2-butene, and 2-methyl-2-butene with rate constants at 298 K of (9.7 f 2.5) X 10-'7,28,29(9.4 f 1.2) X 10-'5,29 and (9.3 f 1.2) X cm3 s-',,~ re(3.8 f 0.4) X 10-13,12330 spectively, were used as reference reactions. The k values for isobutane, propene, and 2-methyl-2-butene have recently been put on a firm absolute basisz9with the now well-established absolutely determined rate constant for the NO3 reaction with trans-2b ~ t e n e , 'thus ~ . ~allowing ~ them to be used as reference compounds in relative rate measurements. Previously, relative rate determinations have depended, in many cases, on the equilibrium constant for N 2 0 5e~ NO3 NO2,which is uncertain by a factor of 2.31~32 For the product studies, one increment of (10-24) X I O i 3 molecules of N 2 0 Swas added to approximately 5 X l o i 4 molecules cm-, of the reactant contained at 1-bar total pressure of synthetic air in the chamber. A White mirror system (base length 1.4 m, optical pathlength 44.8 m) mounted in the chamber and coupled to a FT-IR spectrometer (Nicolet Model 7199; Globar light source, HgCdTe detector) allowed in situ analysis of both reactants and products. The IR absorption spectra were recorded at 1a n - ' resolution by madding 10-30 interferograms over periods of 2C-60 s. Typical time-resolved data were obtained by recording 10-1 5 such spectra successively. Concentrations of identified species were determined by computer-aided subtraction of calibrated reference spectra of authentic samples of the compounds. N 2 0 5was prepared in situ by titrating 0, in an external 20 1 bulb with NO,. This method was preferred to the procedure described by Schott and Davidson3, for preparing pure N205 since the impurity levels of HNO, were found to be much lower. The nitrates used for the FT-IR product identification were prepared by published ~ n e t h o d sby ~ ~treatment .~~ of an appropriate alcohol with HNO, and H2S04.
+
(28) Atkinson, R.; Plum, C. N.; Carter, W. P. L.; Winer, A. M.; Pitts, J . N . , Jr. J. Phys. Chem. 1984, 88, 2361. (29) Atkinson, R.; Aschmann, S. M.; Pitts, J. N., Jr. J . Phys. Chem. 1988, 92, 3454. (30) Ravishankara, A. R.; Mauldin, R. L., 111. J. Phys. Chem. 1985,89, 3144. (31) Finlayson-Pitts, B. J.; Pitts, J. N . , Jr. Atmospheric Chemistry: Fundamentals and Experimental Techniques; Wiley: New York, 1986. (32) Cantrell, C. A,; Davidson, J. A,; McDaniel, A . H.; Shetter, R. E.; Calvert, J . G. J. Chem. Phys. 1988, 88, 4991. (33) Schott, G.; Davidson, N . J. A m . Chem. SOC.1958, 80,1841. (34) Boiteau, J.; Bouchez, R.; Frejaques, C.; Jacta, C.; Pujo, A. M. Bull. Soc. Chim. Fr. 1957, 338. (35) McKay, A. F.; Meen, R. H.; Wright, G F. J. Am. Chem. SOC.1948, 70, 430.
NO, Reactions with Mono- and Dialkenes and Monoterpenes
The Journal of Physical Chemistry, Vol. 94, No. 6, 1990 2415
TABLE I: Experimental Results in Synthetic Air at 1-bar Total Pressure and Literature Values of the Rate Constants for the Reactions of NO3 with a Number of Alkenes, Dialkenes, and Monoterpenes All at Room Temperature but Different Total Pressures
literature ( k , ) values, cm3 s-I
k , , cm3s-I
reactant ethene
reference isobutane
1.78 f 0.37
(1.7 f 0.4) X
I-butene
propene
1.34 f 0.20
(1.3 f 0.2) x
1044
isobutene
trans-2-butene
0.86 f 0.13
(3.3 f 0.5) x
10-13
1,3-butadiene
isoprene
trans-2-butene
trans-2-butene
kllk2
0.50 f 0.10
3.1 f 0.5
(1.9
(1.2
0.4) x 10-13
0.2) x 10-12
a-pinene
2-methyl-2-butene
0.70 f 0.10
(6.5 f 1.0) X
P-pinene A3-carene D-limonene
2-methyl-2-butene 2-methyl-2-butene 2-methyl-2-butene
0.30 f 0.05 0.87 f 0.13 1.20 f 0.18
(2.8 f 0.5) X (8.1 f 1.2) X (1.1 f 0.2) X lo-”
Results and Discussion I . Kinetic Studies. Plots of the experimental data according to eq I for the various systems studied showed reasonable linearity. Figure 1 shows an example of such a plot with data taken from experiments on the reaction of NO, with A,-carene relative to NO, with 2-methyl-2-butene. Table I lists the kl/k2 ratios obtained from such plots from a minimum of five experiments and the values of k i derived from these ratios with use of the appropriate k2 values for the reference hydrocarbons. The quoted errors for k,/k2 and ki values are l o and represent experimental precision only; any uncertainties in the reference rate constants have not been taken into account. In Table I, a comparison is also made with the k values available in the literature. The k values quoted under Atkinson et al. are the revised values for these compounds given by these workers in ref 29. In most cases, there is good agreement between the rate constants determined in this study and those given in the more recent literature. Discrepancies only exist for the reactions of NO, with 1,3-butadiene and isoprene. The k value measured here for NO, 1,3-butadiene is in good agreement with the recent absolutely determined values of Rahman et a1.,I0 Benter and Schindler,” and Canosa-Mas et al.;38however, it is a factor of 2 higher than the value of Atkinson et al.8929who used a similar technique as applied in the present work. Similarly for NO, + isoprene, the rate constant determined here agrees well with the absolutely determined value of Benter and Schindler” but is again a factor of 2 higher than the relatively determined value of Atkinson et al.8929However, the most recent determination of this rate constant by Dlugokencky and Howardi2 using a fast-flow system at low pressure with LIF detection of NO, leads to a k value that supports the results of Atkinson et a1.8329 At present, no obvious reason can be given for the discrepancy between the various determinations. 2. Product Studies. In order to simplify the discussion on the pathways leading to the products detected in the reactions of NO, with the various alkenyl hydrocarbons, a generalized reaction mechanism applicable to all of the systems studied is given below. The group names for the more important radicals and compounds produced in the reactions are indicated in brackets. Continual
+
( 3 6 ) Japar, S. M.; Niki, H. J . Phys. Chem. 1975, 79, 1629. (37) Atkinson, R.; Plum, C. N.; Carter, W. P. L.; Winer, A. M.; Pitts, J. N., Jr. J . Phys. Chem. 1984, 88, 1210. (38) Canosa-Mas, C.; Smith, S . J.; Toby, S.; Wayne, R. P. J . Chem. Soc., Faraday Trans. 2 1988, 84, 247. (39) Canosa-Mas, C.; Smith, S.J.; Toby, S.;Wayne, R. P. J . Chem. Soc., Faraday Trans. 2 1988, 84, 263. (40) Carrington, R. A. G. Spectrochim. Acta 1960, 16, 1279.
(1.1 f 0.1) X (2.1 f 0.3) X (1.9 f 0.2) X (9.1 f 1.0) x (1.2 f 0.2) x (1.3 f 0.1) x (3.1 f 0.4) X (3.3 f 0.4) x (3.3 f 0.5) x (3.4 f 0.7) x (9.8 f 1.2) x (1.7 f 0.3) X (2.1 i 0.4) x (2.2 f 0.6) x (5.9 0.7) x (1.3 f 0.2) X (6.5 f 0.8) X (5.8 f 0.8) X (6.2 f 0.7) X (2.4 f 0.3) X (1.1 f 0.2) X (1.3 f 0.3) X
Japar and Niki36 Atkinson et al.29537 Canosa-Mas et al.38-39 Japar and Niki36 Atkinson et a1.29,37 Japar and Niki36 Atkinson et Ravishankara and Mauldin III’O Rahman et a1.I0 Canosa-Mas et al.38 Atkinson et al.8329 Rahman et a1.I0 Benter and Schindler” Canosa-Mas et al.38 Atkinson et al.8*29 Benter and Schindler” Dlugokencky and Howard12 Atkinson et al.839,29 Dlugokencky and Howardi2 Atkinson et Atkinson et al.839329
10-l6
10-15 10-14 1043
10-13 10-13 10-13
10-14 1043
10-13 10-13 lo-’’
lO-I3 lo-’’
al.899.29
lo-” IO-”
Atkinson et al.899-29
reference will be made to this reaction scheme during the course of the discussion. The initial reactions are, R-CH=CH-R R-CH-CH(ONO),-R
-
+ NO3 (MI R-CH-CH(ON02)-R + 02 (M) R-CH(O,)-CH(ONO,)-R
-
R-CH(O,)-CH(ONO,)-R
(1)
nitrooxy-peroxy radical (2)
-
(M)
+ NO2 R-CH(02NO,)-CH(ONOJ-R nitrooxy-perox ynitrate
(3, -3)
Further reactions of the nitrooxy-peroxy radical species are, 2R-C H (02)-C H (ON O&R 2R-CH(0)-CH(ON0,)-R + 0, (4a) nitrooxy-alkoxy radical -+
-
R-CHOH-CH(ON02)-R hydroxy-nitrate
R-CH(O,)-CH(ONO,)-R
+ R-CO-CH(ON02)-R + 02 nitrooxy-aldeh yde/-ketone
-
+ NO
(4b)
+
R-CH(0)-CH(ON0,)-R NO2 (sa) nitrooxy-alkoxy radical
(M)
R-CH(ONO,)-CH(ONOZ)-R dinitrate The nitroxy-alkoxy radical reacts further, R-CH(O)-CH(ONO,)-R
+0 2
---*
(5b)
+
R-CO-CH(ON02)-R H 0 2 (6a) nitrooxy-aldehyde/-ketone R-CH(O)-CH(ONO,)-R R-CH(O)-CH(ONO,)-R
+A
+ NO2
--c
-
2RCHO
+ NO2
(6b)
(M)
R-CH( ON02)-CH(ON02)-R ( 6 ~ ) dinitrate Although the present investigations were performed under atmospheric conditions, the use of N205as the NO, radical source precludes the presence of NO in the reaction system since the fast reaction NO3 + NO 2N02 suppresses NO as long as NO, is present in excess. Thus, reactions involving NO in the above scheme do not occur under the NO-free conditions employed in the present study but have to be taken into consideration for an assessment of the chemistry in the real atmosphere. Because of difficulties in the synthesis of many of the nitrate-type products expected in the reactions and in addition
-
2416
The Journal of Physical Chemistry, Vol. 94, No. 6, 1990
Barnes et al. N03/trans-2-butene/air reaction system
TABLE 11: Spectral Positions of the Major IR Absorption Bands Observed in the Initial Stage of Reactions of NO3 with Various Oreanics" ~~
(a) after 5 min reaction time ~
wavenumber, cm-l reactant propene 1 -butene trans-2-butene
isobutene 1,3-butadiene
I 1723 1726 1725 1725 1725
I1
111
IV
v
1671 1669
1283 1284
845
788
845
791
1666
1282
848
790
1671
1296 1285
848
790
1668
1293 1284
846
791
I298 1286
845
792
845 860 850 844
790
isoprene
1719
1667
a-pinene @pinene
1720
1667 1660 1656 1656
A)-carene o-limonene
1725 1740 1744
1299 1288 1283 1261
1287
1725
I
I
( b ) after 120 min reaction time
790
791
790
"Bands at positions I, 11, and V indicate the presence of peroxynitrates while bands at positions 11, 111, and IV indicate the presence of nitrates.
because of the similarity of their absorption spectra, it has only been possible to achieve complete product analyses for the reactions of NO, with trans-2-butene and isobutene. The reaction of NO, with ethene was too slow to allow sufficient conversion of the reactant for a detailed product analysis. Although for the monoalkenes propene and l-butene, the dialkenes butadiene and isoprene, and the monoterpenes a-pinene, @-pinene,A3-carene, and D-limonene the product analyses are incomplete, valuable information concerning the nature of the products and some mechanistic details have been deduced by a comparison with the results obtained from the studies on the reactions of NO, with trans-2-butene and isobutene. In the following discussion, the general characteristics of the recorded IR product spectra for all of the reactions studied will first be presented. This is then followed by a discussion of the observed products and their mechanistic implications for the different classes of organics in the order monoalkenes, dialkenes, and monoterpenes. 2. I . General IR Spectral Characteristics. For all the organics studied, characteristic bands about 1725, 1660, 1290, 845, and 790 cm-' appeared in the initial stages of their reaction with NO,. At 1290 cm-I, two bands were often discernable. The wavenumbers of the bands observed for the various reaction systems are listed in Table 11. Because of the overlap of product spectra due to similar functional groups, the accuracy of their positions is about f3 cm-I. Figure 2a shows an absorption spectrum of a N03/frans-2-butene/air mixture after 20 min of reaction time in which the absorptions due to the NO3 radical source N 2 0 , have already been subtracted. Bands around 1725. 1290, and 790 cm-' are characteristic for peroxynitrate-type compound^^^-^^ (I, 111, and V in Table 11) and bands around 1660, 1290, and 845 cm-I for nitrates/dinitrates40 (11, 111, and IV in Table 11). Figure 2b shows the absorption spectrum for the NO,/trans2-butene/air reaction mixture after 120 min of reaction time. Although the absolute intensities of all the bands have decreased, evidently the intensities at 1725 and 790 cm-' have decayed faster than for the other bands and a new absorption has appeared at 1755 cm-', which is typical for a carbonyl functional group. Addition of NO to the reaction mixture after completion of the NO, reaction caused a rapid disappearance of the bands at 1725 and 790 cm-I. Thermal instability and rapid reaction with NO(41) Zabel, F.; Reimer, A.; Becker, K. H.; Fink, E. H . J . Phys. Chem. 1989, 93, 5500.
(42) Niki, H . ; Maker, P. D.; Savage, C. M.; Breitenbach, L. P. Chem. Phys. Lett. 1979, 61, 100. (43) Bruckmann, P. W.; Willner, H. Enoiron. Sci. Technol. 1983,17, 352. (44) Barnes, I.; Becker, K. H.; Fink, E. H.; Reimer, A.; Zabel, F.; Niki, H . Chem. Phys. Lett. 1985, 115, I . (45) Barnes, I.: Bastian. V.: Becker, K . H.; Niki. H. Chem. Phys. Lett. 1987, 140, 451,
I14 I '
lc) reference spectrum of9.6 ppm 3.nitrooxg-2-butanone in 1 bar air
; :;I
848
. ~-
L1 I ' 19w
1750
1600
1450
1300
1150
loo0
850
700
550
wavenumber ( cm.l)
Figure 2. IR absorption spectra in the range 1900-500 cm-' for a
NO~/trans-2-butene/airreaction mixture. The initial concentrations of N 2 0 5and trans-2-butene were 1.2 X 10'' amd 2.4 X I O l 4 molecules cm-3, respectively. Trace a is a spectrum recorded after a 5-min reaction time in which absorptionsdue to N,05 and HNO, have been subtracted; trace b is a spectrum recorded after 120-min reaction time, and trace c is a reference spectrum obtained from 9.6 ppm 3-(nitrooxy)-2-butanonein 1 bar of synthetic air. scavenging ROO radicals are characteristic features for peroxynitrate-type compounds, (MI
+ M w ROO + NO2 ROO + NO R O + NOz
ROONO,
--*
It would appear that under the present experimental conditions compounds each containing a stable nitrate and an unstable peroxynitrate functional group are being formed in the early stages of the reaction. As the peroxynitrate decays, a band attributable to a carbonyl functional group builds up. This behavior was observed for all of the organics studied. Whereas the nitrate bands showed little variation in position from compound to compound, the spectral position of the carbonyl group formed after the decay of the peroxynitrate varied from 1760 to 1710 cm-I. The primary reaction of NO3 is expected to proceed mainly via addition forming radicals of the general type R-CH-CH(ON02)-R. The present results are most consistent with a mechanism involving consecutively the addition of O2 to these radicals to form nitrooxy-peroxy radicals, which with NO2,under the present experimental conditions, establish an equilibrium with thermally unstable nitrooxy-peroxynitrate-typecompounds. This sequence corresponds to reactions 1-3 in the general reaction scheme. The experimental results suggest that the further reactions of the nitrooxy-peroxy radicals then lead to the final products. The concentration-time behavior of the nitrooxyperoxynitrates formed in the reactions of NO3 with the monoalkenes, dialkenes, and monoterpenes could be followed over time
The Journal of Physical Chemistry, Vola94, No. 6,1990 2417
NO, Reactions with Mono- and Dialkenes and Monoterpenes
TABLE III: Measured and Estimated (est) Yields for the Products Formed in the Reactions of NO3 with Alkenes and Dialkenes in 1 bar of Synthetic Air products (% yield on a molar basis) reactant
HCHO (8). C H X H O (12). total nitrates ( 5 8 est) DroDene HCHO ( l l ) , CH,CH,CHO (12), total nitrates (60 est) i -butene trans-2-butene CH,CHO (70),CH3COCH(ON02)CH, (55), CH,CH(ON02)CH(ONOJCH3 (4) HCHO (80), CH,COCH, (85), total nitrates ( 2 5 est) isobutene 1.3-butadiene CO (4), HCHO (12), CH2=CHCH0 (12), total nitrates (60 est) isoprene CO (4), HCHO ( 1 l), total nitrates (80 est)
periods of 60-120, 30-60, and 1-5 min, respectively. From experiments in which an excess of N O was added to the system after completion of the reaction of NO, to destroy the nitrooxy-peroxy radicals, R-CH( O2)-CH (ON02)-R
+
(M)
NO2 R-CH(02)-CH(ON02)-R
-
R-C H (02N02)-CH (ON02)-R
Q
+
NO R-CH(O)-CH(ONO,)-R
+ NO2
it has been estimated that at room temperature the unimolecular decay rate constants for the nitrooxy-peroxynitrates are of the same order of magnitude or smaller than those reported in the literature for simple alkyl-peroxynitrates. For example, ethyl peroxynitrate has an unimolecular decay rate constant of approximately 1 s-l at I-bar total pressure and 288 K.41 2.2. Products from NO3 Monoalkenes. All the product analyses were performed after completion of the decay of the thermally unstable nitrooxy-peroxynitrate compounds formed initially in the reaction systems. In cases where the lifetimes of the nitrooxy-peroxynitrate intermediates were particularly long, minor corrections had to be made for wall loss of the products. The results for the monoalkene product studies will be discussed in the order propene, 1-butene, trans-2-butene, and isobutene followed by a comparison with other product studies on NO, + monoalkene reactions reported in the literature. 2.2. I. NO, + Propene and NO3 I -Butene. For propene and 1 -butene, only aldehydes could be quantitatively determined. HCHO and C H 3 C H 0 were formed in the NO, propene reaction and HCHO and CH3CH2CH0in the NO, + 1-butene reaction. These aldehydes accounted in both cases for only about 12% of the total products (Table 111). On the basis of the information derived from the more detailed analyses of the N03/?rans-2-butene/air and NO,/isobutene/air reaction systems, the aldehydes are most probably being produced by the thermal decomposition of nitrooxy-alkoxy-type radicals formed in reaction sequences corresponding to reactions 1-4 in the general mechanism CH,-CH(O)-CH,(ONO,) + A CH3CHO HCHO NO2
+
'
Further, preliminary studies on a number of nitrooxy-aldehyde/-ketone compounds synthetized in this laboratory show that the absorption coefficients for the carbonyl group in such compounds are also quite similar, and a value of e = (1.6 f 0.3) X ppm-' m-I (basis e) has been estimated for the carbonyl band in the 1720-cm-' region. With these two absorption coefficients, it has been estimated that nitrate-containing products comprise approximately 60% of the total products for both of the reactions and that they are probably present mainly in the form of nitrooxy-aldehyde/-ketone isomers. Preliminary experiments show that also (nitrooxy)acetone and l-(nitrooxy)-2-butanone are products of the reaction of NO, with propene and 1-butene, respectively. However, because of the instability of these compounds, it has not been possible to carry out a quantitative analysis. 2.2.2. NO3 trans-2-Butene. For the NO, reaction with trans-2-butene, the final products were 3-(nitrooxy)-2-butanone (CH,C(O)CH(ONO,)CH,), 2,3-butanediol dinitrate (CH,CH(ON02)CH(ON02)CH3),and acetaldehyde (CH,CHO). The products 3-(nitrooxy)-2-butanoneand 2,3-butandiol dinitrate were identified by comparison with both GC-ECD chromatograms and FT-IR spectra of authentic samples of the substances prepared according to procedures reported in the l i t e r a t ~ r e . , ~A. ~gas-phase ~ spectrum of 9.6 ppm 3-(nitrooxy)-2-butanone is presented in Figure IC. A comparison with the spectra from the NO3/ trans-2-butenelair reaction system clearly shows the formation of 3-(nitrooxy)-2-butanone. The carbon mass balance was approximately 94%, and the product yields are listed in Table 111. The yields for most of the other stable products could be determined with an accuracy of approximately *lo%. As discussed in section 2.1, the results are in line with the general mechanism involving first the addition of NO3and consecutively of O2 resulting in the formation of 3-(nitrooxy)-2-butylperoxy radicals, which with NO2 finally establish an equilibrium between 3-(nitrooxy)-2-butyl peroxynitrate corresponding to reactions 1-3 in the general mechanism,
+
+ NO,
CH,-CH=CH-CH,
-+
CH,CH2CH(O)-CH2(ON02)
+ A .--* CH3CH2CHO
+
+
+ HCHO + NO2
The other isomeric forms of these radicals are expected to lead to the same products (see section 2.2.2). The residual IR absorption spectra in both reaction systems after subtraction of the absorption from the aldehydes show the presence of carbonyl and nitrate functional groups. From the NO3 trans-Zbutene reaction studied in the present work, it is observed that nitrooxy-aldehyde/-ketone compounds are major products in such reaction systems. A comparison of the spectra of 14 aliphatic organic nitrate compounds synthetized in this laboratory shows that the absorption coefficients for each of the characteristic nitrate bands around 1666, 1280, and 850 cm-l corresponding to the - 0 N 0 2 asymmetric stretch (11), the - 0 N 0 2 symmetric stretch (111), and the 0-NO2 stretch (IV), respectively, do not differ significantly for the different compounds. From a comparison of these 14 nitrate compounds, an averaged absorption coefficient ppm-I m-' (basis e) has been estimated of e = (3.6 f 0.8) X for the O N 0 2 symmetric stretch (111) at about 1280 cm-I.
+
(M)
CH3-CH-CH(ON02)-CH3
+
+
-
-
+
(M)
CH,--CH-CH(ON02)-CH3 0 2 CH,-CH(02)-CH(ONO2)-CH, CH,-CH(02)-CH(ON02)-CH, NO2
(MI
+
CH,-CH(02N02)-CH(ONO2)-CH3
In the reaction system, NO, is rapidly consumed and the majority of the products are observed to come from the thermal decay of 3-(nitrooxy)-2-butylperoxynitrate. Since the experiments were carried out under NO-free conditions, reactions between N O and the (nitrooxy)butylperoxy radicals can be excluded in the present mechanistic considerations. The self-reaction of the 3(nitrooxy)-2-butylperoxyradicals to form 3-(nitrooxy)-2-butoxy radicals seems to represents the major loss channel most consistent with the experimental results and corresponds to reaction 4a of the general scheme, 2CH3-CH(02)-CH(ON02)-CH3 2CH,-CH(O)-CH(ONO2)-CHj + 0 2
-
The other reaction channel (4b) can lead directly to the formation of nitrooxy-aldehyde/-ketone and hydroxy-nitrate compounds. In this particular case, the reaction would result in the formation of 3-(nitrooxy)-2-butanone and 3-hydroxy-2-butyl nitrate, 2CH,-CH(02)-CH(ON02)-CH, CH,-CO-CH(ONO2)-CH, CH,-CHOH-CH(ON02)-CHj + 0 2
-
+
However, because of the observed carbon mass balance and the lack of evidence for the formation of 3-hydroxy-2-butyl nitrate in the IR product spectrum, reaction 4b is considered, in this case, to be only of minor importance. In the real atmosphere, reactions with N O have to be considered in addition. This leads to two
2418
The Journal of Physical Chemistry, Vol 94, No. 6, 1990
additional reaction channels, one forming nitrooxy-alkoxy radicals and the other a dinitrate product, corresponding to reactions 5a and 5b in the general scheme, CH,-CH(02)-CH(ONO2)-CH,
+ NO
4
(MI
CH,-CH(O)-CH(ON02)-CH, + NO2 CH3-CH(ONOJ-CH(ON02)-CH, From a comparison with reactions of other peroxy radicals, the first channel leading to the formation of nitrooxy-alkoxy radicals is expected to dominate. In the initial stage of the reaction process, the NO, radical concentration is high and the reaction of NO3 with the nitrooxy-peroxy radicals may also result in the formation of nitrooxy-alkoxy radicals. The reaction of NO3 with H 0 2 is known to be f a ~ t , 4 ~and * ~ ’recent experimental observations of Hjorth et aL4*suggest that NO3 also reacts fairly fast with nitrooxy-peroxy radicals,
-
+
CH,-CH(O2)-CH(ONO2)-CH3 NO3 CH,-CH(O)-CH(ONO,)-CH,
+ NO2 + 0 2
However, the observation that under the present experimental conditions the products mainly originate from the decay of the initially formed nitrooxy-peroxynitrate makes this a minor pathway although it may have some importance under tropospheric nighttime conditions. The observed products 3-(nitrooxy)-2-butanone,acetaldehyde, and 2,3-butanediol dinitrate are most probably formed by the further reactions of the 3-(nitrooxy)-2-butoxy radicals,
+
-
CH,-CH(O)-CH(ON02)-CH3 02 CH3-CO-CH(ONO,)-CH, CH,-CH(O)-CH(ON02)-CH,
+A
+
+
2CH3-CHO
-
+ HO2 + NO2
(M)
CH,-CH(O)-CH(ON02)-CH3 NO2 CH3-CH(ONOJ-CH(ON02)-CH, which correspond to reactions 6a-6c in the general reaction scheme. The observed yield of C H 3 C H 0 of 70% (molar basis) can only be explained by postulating that the thermal decomposition of one 3-(nitrooxy)butoxy radical results in the formation of two CH,CHO molecules and one NO2 molecule. Unfortunately under the experimental conditions of the present study, the IR absorption band of NO2 was quickly saturated preventing a quantitative analysis of the concentration-time behavior of NO2 that would be helpful in confirming this reaction. On the basis of the above mechanism, which has been deduced from the product yields presented in Table 111, it can be concluded that under NO-free conditions reaction with O2 and thermal decomposition seem to represent the main pathways for the 3(nitrooxy)-2-butoxy radicals formed in the reaction of NO3 with trans-2-butene, the former being slightly more important. The addition of further NO2 to form a dinitrate is only of minor importance. 2.2.3. NO3 Isobutene. For isobutene, the two main products are CH3COCH3and HCHO with yields of 85% and 80%, respectively (Table 111). The residual spectrum after subtraction of absorptions of CH3COCH3and HCHO shows the presence of carbonyl and nitrate functional groups. CH3COCH3 and HCHO can be formed from the decomposition of either of the possible isomeric nitrooxy-alkoxy radicals formed in reaction sequences corresponding to reactions 1, 2, and 4 in the general scheme. As in the case for NO3 + trans-2-butene, the observed
+
(46) Mellouki, A,; Le Bras, G.;Poulet, G . J . Phys. Chem. 1988, 92, 2229. (47) Hall, I . W.; Wayne, R. P.; Cox, R. A,; Jenkin, M . E.; Hayman, G . D. J . Phys. Chem. 1988, 92, 5049. (48) Hjorth, J.; Cappellani, F.; Lohse, C.; Nielsen, C.; Restelli, G . ;Skov, H. In Air Pollution Research Report 17: Mechanisms of Gas Phase and Liquid Phase Chemical Transformations in Tropospheric Chemistry; Cox, R. A,, Ed.; Commission of the European Communities, [Report] EUR 12035; Commission of European Communities: Luxembourg, 1988: pp 85-89.
Barnes et al. yields of CH3COCH3 and HCHO can only be explained by postulating that thermal decomposition occurs with the formation of NOz,
(CH,),C(o)-CH2(oNo2)/(CH,),C(ONO2)-CH,(O) A CH3COCH3 + HCHO +
+
+ NO2
The only carbonyl- and nitrate-containing compound that can be formed is 2-(nitrooxy)isobutyraldehyde ((CH3),C(ON02)-CHO), which should come from the reaction of O2 with the corresponding nitrooxy-alkoxy radical, (CH,),C(ONO,)-CH,(O) + 0 2 (CH3)2C(ON02)-CHO + HO2 -+
With the procedure outlined in section 2.2.1 for the reactions of NO3 with propene and I-butene, it has been estimated that approximately 25% of the products of the NO, isobutene reaction can be accounted for by nitrate-containing compounds present mainly in the form of nitrooxy-aldehydes. 2.2.4. Comparison with Literature Data on the Products of NO, + Monoalkene Reactions. The results of the product analyses presented here for the reaction of NO, with the various alkenes can only be compared with the literature studies of the reaction of NO3 with propene.16-20(Nitrooxy)propyl peroxynitrate has been detected as an intermediate in the reaction of NO, with propene by Bandow et a1.18 The stable end products observed in these studiesis included HCHO, CH,CHO, NO2, H N 0 3 , and 1,2-propanediol dinitrate as the major nitrate-containing compound. However, Shepson et aI.l9 report in a later study with [NO2]/[O,] ratios closer to atmospheric conditions than those used in the study of Bandow et al. that (nitro0xy)acetone is the major nitrate-containing product, which qualitatively agrees with the observations of the present study. Shepson et a l l 9 have also reported the formation of 2-hydroxypropyl nitrate and 2-(nitrooxy)propyl alcohol in small yields. No evidence could be found in the IR product spectra of the NO3 reactions studied in the present work for the formation of alcohol-containing nitrates from which can be concluded that their yields must be small under the present experimental conditions. Recently, Jay and S t i e g l i t ~ ~ ~ have reported the formation of 1,2-hexanediol dinitrate and 1(nitrooxy)-2-hexanone by the reaction NO, I-hexene with yields of 40% and 50%, respectively. It is, at this stage in the discussion, interesting to note that the OH-initiated oxidation of alkyl nitrates also yields alkoxy nitrate radicals via H abstraction, which by further reaction with O2would presumably lead to the formation of nitrooxy-aldehyde/-ketone compounds,
+
+
-CH,-CH(ON02)-
+ OH
01
+ NO
-CHO*-CH(ONO2)-CH(O)-CH(ONO,)-
-CHOZ-CH(ON02)-
+ H20
-CH(O)-CH(ONO,)-
+NO2
---*
+0 2
-+
-CO-CH(ONO+
+ HO2
Also, the reaction of O H with ketones in the presence of NO, should yield nitrooxy-ketone compounds as has been observed in unpublished work from this laboratory on the reaction of OH with butan-2-one where 3-(nitrooxy)butan-2-one was observed as a product,
CH,-CO-CH,-CH,
+ OH
0 2 .-*
CH3-CO-CH(02)-CH3 CH,-CO-CH(O,)-CH,
+ NO
+ H20
-+
CH3-CO-CH(ON02)-CH3 2.3. Products from NO3 + Dialkenes. For NO3 + butadiene, the identified products were CO, HCHO, and CH,=CH-CHO (acrolein) and for the NO3 + isoprene reaction CO, HCHO, and (49) Jay, K.; Stieglitz, L. Statuskolloquium des PEF; Kernforschungszentrum Karlsruhe: Karlsruhe, F’RG, 1988; pp 601-613; KfK-PEF 35, ISSN 093 1-2749.
NO, Reactions with Mono- and Dialkenes and Monoterpenes
The Journal of Physical Chemistry, Vol. 94, No. 6, 1990 2419
CH2=CH(CH,)CH0 (methacrolein). As the yields in Table I11 show, these compounds account for only a small fraction of the products in both reactions. An accurate yield determination of methacrolein formed in NO, isoprene was not possible because of an insufficient detection limit for this compound. The residual IR spectra for both systems after subtraction of the absorptions due to these compounds showed, as for the monoalkenes, the presence of carbonyl and nitrate functional groups. At present only a rough estimation can be made of the total nitrates being formed with the procedure outlined for the alkenes. The estimations lead to values of 60% and 80% as yields for nitratecontaining compounds formed in the reactions of NO, with butadiene and isoprene, respectively. Again, the estimations indicate that the bulk of the nitrate-containing products is in the form of nitrooxy-aldehyde/-ketone isomers. The aldehydes formed in the reactions of NO3with the dialkenes can be explained by the thermal decomposition of the related nitrooxy-alkoxy radicals as described in section 2.2.1 for the reaction of NO3 with alkenes. The formation of small quantities of C O in both the NO, dialkene reaction systems is difficult to explain. At present it is unclear whether the CO is formed directly in the reaction of NO, with the dialkenes or whether it is a product of secondary reactions of NO, with acrolein or methacrolein. 2.4. Products f r o m NO, Monoterpenes. As mentioned in section 2.1, IR absorption bands corresponding to nitrooxy-peroxynitrate-type compounds were observed in the initial stages of the reactions of NO3with all the terpenes studied. However, their rapid decay resulted in the formation of aerosols probably via the condensation of products that have low vapor pressures. The expected products from these reactions are known to have lower vapor pressures than the initial reactants. Because of the rapid formation of aerosols, a detailed product analysis using FT-IR spectroscopy was not possible. However, for a-pinene and 8-pinene some spectral features in the FT-IR analysis were discernable, indicating the presence of carbonyl- and nitrate-containing compounds, but to date no positive identification of products has been possible. To our knowledge, no product studies on these reactions have ever been reported in the literature.
kylperoxy radicals, which with NO, establish an equilibrium between thermally unstable nitrooxy-alkyl peroxynitrates. For the monoalkenes and dialkenes, under the NO-free conditions employed in the study, the self-reactions of the nitrooxyalkylperoxy radicals lead to the formation of nitrooxy-alkoxy radicals. The nitrooxy-alkoxy radicals can either thermally decompose to form aldehydes or react with O2 to form nitrooxyaldehyde/-ketone-type compounds (-C(0)CH(ON02)-) and H 0 2 . Evidence was found that the thermal decomposition pathway also results in the release of NO,. Further addition of NO, to form a dinitrate is also observed, but under the conditions of this study, it is only of minor importance. For the dialkenes, CO was also observed as a minor product, but the reactions leading to its formation are unclear. Although in the case of the monoterpenes aerosols formed after the decay of the initial nitrooxyperoxynitrate compounds prevented a detailed product analysis, indications have been found for the presence of carbonyl and nitrate groups in the products for the reactions of NO, with a-pinene and 6-pinene. Under atmospheric conditions, the nitrooxyalkylperoxy radicals formed in NO, reactions reported will react to form nitrooxyalkoxy radicals mainly by reaction with NO but also via selfreaction or reaction with NO,, depending on the atmospheric concentrations of NO and NO3. Decomposition of the nitrooxy-alkoxy radicals will lead to the formation of aldehydes, and the release of NO2 and their reaction with 0, forms stable nitrooxy-aldehyde/-ketone compounds and H 0 2 . The branching ratio for reaction with O2against decomposition appears to be slightly greater than 1 for the simple alkenes under atmospheric conditions. However, for isoprene the experimental evidence suggests that reaction with O2to form nitrooxy-aldehyde/-ketone compounds clearly dominates. In the nighttime atmosphere, the NO2 released can react with O3re-forming NO, radicals. In the presence of high NO2concentrations, a fraction of the nitrooxy-alkylperoxy radicals formed in the NO3reactions may form thermally unstable nitrooxy-peroxynitrates. The atmospheric lifetimes of these peroxynitrates are strongly temperature dependent. At the low nighttime temperatures, they may live sufficiently long to act as reservoirs for NO,. In the morning as the temperature rises, they will decompose forming NO2 and peroxy radicals those further reactions could result in the formation of H202. To date nothing is known about nitrooxy-aldehyde/-ketone compounds in ambient air. It is well-known that peroxyacetyl nitrate (PAN) is a phytotoxicant, and therefore, it is possible that the nitrooxy-aldehyde/-ketones formed in the reaction of NO, with unsaturated organics will also be phytotoxic. Preliminary screening tests on 3-(nitrooxy)-2-butanone are in progress.
+
+
+
Conclusions The rate constants determined for the reactions of NO, with various monoalkenes, dialkenes, and monterpenes are in reasonable agreement with most literature data except those for 1,3-butadiene and isoprene where a discrepancy of a factor of 2 exists between the various measurements. N o indication can be found in the present work for the occurrence of systematic errors in the rate constant determinations. The discrepancy for the reaction of NO3 with isoprene is of particular concern since the present result is in agreement with one absolute determination but disagrees with another relative determination and also an absolute measurement. In the case of the reaction of NO, with 1,3-butadiene, the present result is in good agreement with the absolute determinations but in disagreement with the relative measurement. New determinations of the rate constants for these reactions are necessary with preferably a technique different from those applied in previous investigations. The product studies of all NO3 reactions indicate the initial addition of NO, followed by O2addition to form nitrooxy-al-
Acknowledgment. This work was financially supported by Der Minister fur Umwelt, Raumordnung und Landwirtschaft des Landes Nordrhein- Westfalen, Forschungsprogramm Luftverunreinigungen und Waldschaden. Registry No. NO3, 12033-49-7; H,C=CH,, 74-85-1; H,C=CHCH2CH3, 106-98-9; H2C=CMe2, 115-1 1-7; H2C=CHCH=CH2, 10699-0; H,C=CHCH,, 1 15-07-1; (E)-CH,CH=CHCH,, 624-64-6; CHSCHO, 75-07-0; CH3COCH(ON02)CH,, 124855-10-3;CH,CH(ONO,)CH(ONO,)CH,, 6423-45-6; HCHO, 50-00-0; CH3COCH3, 6764- 1; isoprene, 78-79-5; a-pinene, 80-56-8; P-pinene, 127-91-3; Akarene, 13466-78-9; &limonene, 5989-27-5.
