Reaction of Nitrogen Oxides with Black Carbon: An FT-IR Study

t h a t a t ma t r ix - to -ana ly te rat ios of 1000/1 some measure of neares t -ne ighbor interact ions is occurring.

S U M M A R Y A N D C O N C L U S I O N S

Matr ix isolation Fourier t r ans fo rm infrared da ta have been presented, detai l ing the character is t ics of the hydroxyl group for a series of catechols, resorcinols, hy- droquinones, and diols. T rends a t t r ibu tab le to steric and electronic effects have been documented and found t o general ly agree with es tabl ished t rends found for vapor- phase data. The posi t ions of the hydroxyl absorp t ion bands are unique to the mat r ix phase and fall within a window set on the higher energy side by the vapor -phase resul ts and on the lower side by sol id-state results. The very low full width at hal f -height values found in the ma t r ix expe r imen t allow for the observat ion of unique absorp t ion bands not ye t seen before in the vapor -phase or sol id-state exper iments . These new bands confirm the presence of in t ramolecular interact ions not previously documented . The da ta also indicate t ha t in termolecular (aggregation) interactions occur at very low loadings (-< 10 ng) on the cryogenic disk, for diols in part icular .

1. G. C. Pimentel and A. L, McClellon, The Hydrogen Bond (W. H. Freeman Co., San Francisco, 1960).

2. J. March, Advanced Organic Chemistry, Reactions, Mechanisms, and Structure (John Wiley & Sons, New York, 1985), 3rd ed.

3. R. M. Silverstein, G. C. Bassler, and T. C. Morril, Spectrometric Identification of Organic Compounds (John Wiley & Sons, New York, 1974), 3rd ed.

4. R. A. Nyquist, The Interpretation of Vapor Phase Infrared Spec- tra, Group Frequency Data (Sadtler Research Laboratories, Phila- delphia, Pennsylvania, 1984), Vol. 1.

5. "Matrix Isolation Spectroscopy and Molecular Structure--A Trib- ute to George C. Pimentel," L. Andrews and W. J. Orville-Thomas, Eds., J. Mol. Structure 157, 1 (1987) and references therein.

6. G. Mamantov, A. A. Garrison, and E. L. Wehry, Appl. Spectrosc. 36, 339 (1982).

7. P. R. Griffiths and J. A. de Haseth, Fourier Transform Infrared Spectrometry, Chemical Analysis, P. J. Elving and J. D. Wine- fordner, Eds. (John Wiley & Sons, New York, 1986), Vol. 83, p. 502; R. N. Perutz, "Matrix Isolation," in Annual Reports on the Progress of Chemistry, Vol. 82, 1985, Section C: Physical Chem- istry, M. G. R. Symons, Ed. (Royal Soc. Chem., London, 1986).

8. I. R. Dunkin, Chem. Soc. Rev. 9, 1 (1980). 9. (a) W. M. Coleman, III and B. M. Gordon, Appl. Spectrosc. 41,

886 (July 1987). (b) M. L. Rogers and R. L. White, Appl. Spectrosc. 41, 1052 (1987).

10. C. J. Pouchert, The Aldrich Library of FT-IR Spectra (Aldrich Chemical Co., Milwaukee, Wisconsin, 1985), 1st ed., Vols. I and 2.

11. W. M. Coleman III, Appl. Catalysis, 22, 345 (1986). 12. G. T. Reedy, D. G. Ettinger, J. F. Schneider, and S. Bourne, Anal.

Chem. 57, 1602 (1985). 13. W. M. Coleman III and B. M. Gordon, Appl. Spectrosc. 41, 1159

(1987). 14. W. M. Coleman III and B. M. Gordon, Appl. Spectrosc. 41, 1163





(1987).

Reaction of Nitrogen Oxides with Black Carbon: An FT-IR Study

D. M. SMITH,* W. F. WELCH, S. M. GRAHAM, A. R. CHUGHTAI, BRIAN G. WICKE, and KAREN A. GRADY Department of Chemistry, University of Denver, Denver, Colorado 80208 (D.M.S., W.F.W., S.M.G., A.R.C.); and Physical Chemistry Department, General Motors Research Laboratories, Warren, Michigan 48090 (B.G.W., K.A.G.)

Qualitative and quantitative studies of the reaction of black carbon with the oxides of nitrogen, including NO, NO2/N204, N20 , and N203, have been carried out with the use of Fourier transform infrared spectroscopy (FT-IR). The active reactant is shown to be NO2, whether it acts as a disproportionation product or as an impurity in the gas under study. FT- IR spectra of the surface species identify them as resulting from reaction of carbon with NO2. For paraffin candle soot which was exposed simultaneously to oxygen atoms, and nitric oxide at 298 K, the surface species also are due to NO2, formed by oxidative adsorption of NO on the soot surf~tce.

Index Headings: Black carbon; Nitrogen oxides; FT-IR.

I N T R O D U C T I O N

T h e oxides of nitrogen, especially with regard to the pa ths of thei r fo rmat ion and deplet ion, current ly hold

Received 7 December 1987. * Author to whom correspondence should be sent.

the a t t en t ion of env i ronmenta l chemists. Fo rma t ion of the oxides of ni t rogen th rough such means as the high- t e m p e r a t u r e combus t ion of fuels and electrical s to rms in the a tmosphe re are well known. The deplet ion of these oxides in the a tmosphe re is th rough a var ie ty of processes such as n i t ra te aerosol format ion, pho tochemica l reactions, and reduct ion of NO2 by carbonaceous substances. 1 Addi t ional pa thways for deplet ion of ni t rogen oxides are suspec ted to be i m p o r t a n t bu t are not fully unders tood; one example is the react ion of these oxides with par t ic- ulates in the a t m o s p h e r e - - t h e subject of this work.

Research by the Univers i ty of Denver (DU) authors has focused on the s t ruc ture of black carbon (soot) and its react ions with the oxides of ni t rogen (NOJN204 , NO, N20, and N2Os), oxides of sulfur, and ozoneY -s Studies by the Genera l Motors Research (GMR) authors have examined the oxidat ion of soot by oxygen a toms at 298 K, the effects of this oxidat ion on the poros i ty and the s t ruc ture of soot, and the inhibi t ion of this oxidat ion by

674 Volume 42, Number 4, 1988 0003-7028/88/4204-067452.00/0 APPLIED SPECTROSCOPY © 1988 Society for Applied Spectroscopy

GAS INLET

ZERO AIR

NO~ INLET

FIG. 1. Apparatus for mixing and purifying gases interfaced with the FT-IR cell.

nitric oxide. 1°-12 The kinetics of the reaction of NO2/N204 with black carbon at 298 K have already been estab- lished. 5 During the study of the reaction of N20 with black carbon under flow conditions, the infrared absorption bands for the species formed on the carbon were identical to the IR bands observed in the reaction of black carbon with NO2/N204, which were identified (with isotopic substitution techniques) as arising from NO2) This result was somewhat surprising in light of the non- reactive nature of N20. It is speculated that the IR bands produced with the use of N20 were due to the reaction of carbon black with trace quantities of NO2 and/or NO present in the reagent N20. Since both NO and NO2 have one unpaired electron, comparable reactivity for NO and NO2 with carbon appeared feasible. The present experiments were undertaken to identify the reaction responsible for the formation of the IR absorption bands observed on black carbon exposed to NO, and to identify the nitrogen-containing adsorbed species responsible for the inhibition by nitric oxide of the oxidation of soot by oxygen atoms at 298 K. As will be shown, adsorbed NO2 is involved in both cases.

EXPERIMENTAL

Samples of the nitrogen oxides used in the present study--nitric oxide (NO), nitrogen dioxide (NO2 in equi- librium with its dimer N204), dinitrogen trioxide (N203), and nitrous oxide (N20)--and their analytical compo- sitions were acquired from Matheson Gas Products. The FT-IR spectra of the individual gases for reference pur- poses, with the exception of NO2/N204, were obtained by allowing the gas to pass through the flit/soot assembly shown in Fig. 1. Spectra of binary gas mixtures were obtained by passing the mixtures through mixer I and mixer II into the FT-IR cell in the spectrometer sample chamber.

In order that the uniformity of the black carbon sample could be ensured, specific optimum soot generation and collection conditions have been maintained throughout

183.1067

160.084

136.961d

11).889

.,=

90.8165

67.744(

FTIR-Specfrum of N20{gas}ot lower concentrations

44.671'

3800 3600 3400 3200 3000 2800 86(~0 8400 2200 Z000 1800 16(;0 1400 12130 P~O WAVENUMBER

FIG. 2. FT-IR spectrum of N20 at room temperature.

these experiments. As described elsewhere, 9 black carbon is generated at the DU laboratory by the burning of n-hexane and is collected on a CaF2 support through a stemless inverted funnel with a base diameter of 7.5 cm and a top diameter of 1.2 cm. The funnel length is 5.7 cm. The CaF2 support is positioned 1.2 cm above the top opening, while a hexane-containing 100-mL beaker is placed directly under the funnel; the distance between the funnel and the rim of the beaker is 2.5 cm. This black-carbon-generating apparatus is operated under minimum air turbulence. It has been noticed in our laboratory that black carbons prepared under the least turbulent conditions have lower density than the black carbon prepared under turbulent conditions (such as in exhaust-fume hoods). At the same time, the combustion rate is higher under turbulent conditions. These different collection conditions affect the oxygen-containing func- tionalities on the black carbon, both quantitatively and qualitatively, s and therefore may modify the potential extent of reaction with a particular gas.

The black carbon is allowed to deposit on the CaF2 support for approximately 10 min, so that the carbon black sample is partially transparent to the IR beam of the Digilab-Biorad FTS-20B. It is important for the sample to be free of any pinholes; this requirement is ensured by observation of the desiccator-cooled sample over a light.

The sample then is positioned in the quartz/CaF2 cell assembly (Fig. 1). After collecting the spectrum of the black carbon, one allows the gas of interest to flow over the sample at a rate of 20 mL/min for a specific period of time. The system is once again purged with nitrogen, and the IR spectra are collected. Experiments were con- ducted with the use of nitrous oxide and nitric oxide under identical conditions. For nitrogen dioxide and dinitrogen trioxide, however, it was not necessary to flow

APPLIED SPECTROSCOPY 675

400.000

385.8220

a Spectrum of N20(gos) with NO2(gos) as o contominant

311.8440

267.4661

==

~ 223.2881

179.1101

90.7542

46.5762 ~ ~ 2~)0 2200 2tO0 2000 1900 1800 1700 ]600 1500 1400 1360 1200 HO0

WAVENUMBER

FIG. 3a. FT-IR spectrum of N20 at higher concentration to show NO2 contamination.

50 F i i i i i i i r i

3 NO- - -~N02 + N20

A : NO spectrum

41.25 8 B: NO spectrum ofler the soot lfop

32.5

23.75 8 B

t5

6.25 8 l A

-2.5

-H.25

' 'oo ' ' 'oo ' ' ' ,' ~'oo ~ - 2 0 2300 2200 2l 2000 1900 t8 tT00 16(30 1500 I O0 1 ] 00 I100

WAVENUMBER

Fro. 4. FT-IR spectrum of NO: (A) NO gas flowing directly into the cell; (B) NO gas flowing through black carbon bed first (see text).

200 - - 'T ' - - 'T-~ I = t l I [ ~ i I ' I ' I ' I I I ' I ' I i

b FTIR-$pecfrum of N02(gosl.

172.. =

t45

i I

- 2 0 ~ _ , i i I i I i I t I i I i I , [ , I i I i I i I i 3800 36(;0 3400 3200 30~0 2800 2600 2400 2200 2000 t800 1600 1400 1200 I000

WAV£NUMBER3

Fro. 3b. FT-IN spectrum of NO 2 at room temperature.

1172,

E 90

<

62.5

these gases for extended times, because their reactions with black carbon are rapid. ~

The single exception to this black carbon deposition technique, in the experiments reported here is the case of the candle soot sample exposed simultaneously to oxygen atoms and nitric oxide at GMR. 1°-12 The collection technique.' for this sample has been described previously, to Following exposure to oxygen atoms and nitric

676 ~/olume 42, Number 4, 1988

oxide, the soot sample was carefully removed from the quartz plate and mixed into a KBr pellet to obtain IR spectra.

RESULTS AND DISCUSSION

The infrared spectrum of pure nitric oxide (NO) gas is difficult to obtain, in part because nitric oxide is ther-

119.9999

115.43~5

90,9050

76.3576

6].8101 m

47.2626

32.7192

I I I I I [

NzO3(gos)

18.1677

3.6202 I ] ~ 2300 2200 2tO0 2000 I900 t800 1700 1600 tSO0 1400 1300 1200 H(~O

WAVENUMBER

FIG. 5. FT-IR spectrum of N2Oa at room temperature.

43.8688

37 .2T40

NO

30.5591

23.9043

]0.5946

3,9398

2800

c,:' (No2) I '~l

-2.715] ,- i ~ , [ 2300 2200 2100 2000 1900 ]BO0 1700 1600 ]500 1400 190(~ ]200 II00

WAVENUMBER

FIG. 6a,b. (a) FT-IR spectrum of NO gas immediately upon entering the cell; (b) FT-IR spectrum of NO gas after flowing through cell for 30 rain (not much disproportionating).

modynamically unstable with respect to disproportionation at 25°C and 1 atmospheric pressure--

3NO -~ N20 + NO2 (1)

- -and in part because of the nearly instantaneous reaction nitric oxide undergoes with oxygen: ~3

2NO + 02 -~ 2N02. (2)

79.6600

69.5595

59.4590

49.3584

8

39,2579

I I f

,1622m'l(N02)

: NzO 2 9 . ] 5 7 4 P 3 1 0 ( C m - i )

I

19.0369 IcNOl 1~.1260(cm "l}

- I , t 4 4 2 I t I I I 2300 Z200 2100 2000 1900 ]800 1700 ]60£] ]500 I400 ]300 1200 1100

WAVENU•BER

FIG. 6c. FT-IR spectrum of NO gas after remaining in the cell over night (brown coloration observed in the cell).

NO2 FORMATtON (]650- i6f8 CM-I ) V/S TIME

+

2400

ZOO0

i ]600

1200

800

400

5 0 . 5 2 3 7 I I I 3~00

I I I I 40 810 rZ0 ~60 ~ 0 Z40

TIME IN M]N.

Fro. 7. Integrated absorption of NO= (1650-1618 cm -1) as a function of time formed during the course of NO disproportionation.

These experimental difficulties probably explain why there is limited information in the literature about the IR spectrum of pure nitric oxide. The FT-IR spectra of nitrous oxide, nitrogen dioxide, nitric oxide, and dinitrogen trioxide with "unde tec tab le con taminan t s " (Matheson Gas Products) are shown in Figs. 2-6. The FT-IR spectrum of N20 at higher concentration (Fig. 3a) shows the presence of NO2 as a contaminant, the FT- IR spectrum of which is shown in Fig. 3b. Figure 4 shows the removal of NO2 after the gas has passed through the black carbon filter. Also seen from the spectrum in Fig. 5 are the major bands of N203, essentially due to NO2 (1628-1595 c m -1 , 1755-1740 cm -1, and 1268-1252 c m -1) and NO (1909-1845 cm-~). The spectrum of NO in Fig. 6a shows the extent to which the gas dispropor- tionates immediately upon entering the cell; while the spectrum of NO, after it has come to a steady state of flow, is shown in Fig. 6b. It is therefore essential that, for a representative composition of these nitrogen oxides, the system be brought to a steady state.

The decomposition of nitric oxide to nitrogen dioxide and nitrous oxide under static (closed cell) conditions is illustrated by results from our having run a few nitric oxide disproportionation kinetics experiments (Fig. 6c). The growth with time of nitrogen dioxide as a disproportionation product of nitric oxide under these conditions is shown in Fig. 7. Note that the zero-time intercept is greater than zero, indicating the initial presence of some NO2 in the flowing NO.

During the study of the nitrous oxide-black carbon reaction, infrared absorption bands at 1660 c m -1, 1565 c m -1, 1540 c m -1, 1340 cm-L 1305 cm -1, and 1280 cm -1 were observed, bands which are identical to the absorption bands observed in our study of the reaction of nitrogen dioxide with black carbon2 These bands appeared

A P P L I E D S P E C T R O S C O P Y 677

12.5

11.25

o 8.75 o

<_ 7.5

1535

i i

1324 C Jl3CO / 277

6.25

5.

3.75 ~ ~ " ' % ~ , , . ~ J

' ,600 , 14100 1/00 121 riO0 2"~000 19100 18'0C '700 15(~0 WAVENUMSER

Fro. 8. FT-]R spectrum of hexane soot: (A) subtraction baseline; (B) 72 h exposure to NO after flowing through black carbon prefilter; (C) 5 rain exposure to NOJN204.

3.9281

3.7362

3.5443

J

2.96e4- " I ~ " ' ~ -

2.7765 8 8

2 . 5 8 4 6 ' l l l l l t = l l l l l l l { l l I ' l ' l l l J ' I 1 ' ' 2000 1900 1800 1700 1600 1500 1400 1300 1200 II00

WAVENUt~BER

Fro. 9a. FT-IR spectrum of GMR paraffin candle soot exposed simultaneously to oxygen atoms and nitric oxide from which the spectrum of soot exposed to oxygen atoms has been subtracted.

regularly in the FT-IR spectra of carbon after nitrous oxide exposure, even though the analytical data supplied by Matheson Gas Products indicated nitric oxide and nitrogen dioxide concentrations below their detection limits (less than 0.5 ppm). These same strong bands were observed while the reaction of nitric oxide with black carbon was being studied. In this case, however, the analytical data showed 500 ppm nitrogen dioxide impurity present in the nitric oxide. For black carbon exposure to nitric oxid.e, therefore, it remained unclear whether adsorption of NO or adsorption of the N02 impurity was responsible for the observed IR absorption. The reactivity of nitrogen dioxide with black carbon at 298 K already has been examined in detail, 5 but the potential reactivity of nitric oxide on black carbon required further exami- nation.

In order to examine the reaction of these nitrogen oxides with black carbon, we take advantage of the fact o that the reaction of black carbon with NO2 is very rapid. Nitrous oxide gas (with possible NO2 and NO impurities) was first passed through a bed of black carbon to remove traces of :NO2(g) (Fig. 1) before it was allowed to come in contact with the black carbon sample on the CaF2 support. This "prepurified" nitrous oxide gas was allowed to pass over the black carbon sample for 72 h, and then the sample was purged with nitrogen for several hours. The expanded FT-IR spectrum showed no bands in the 1100-2000 cm -1 region.

Similar experiments were run in which nitric oxide was passed through the purifying bed of black carbon before contacting a black carbon sample on a CaF2 support. After three hours of exposure to the flowing prepurified nitric oxide, weak bands in the 1100-2000 cm -~ region were observed (Fig. 8B). These bands are those resulting from the reaction of black carbon with NO2/N204 (Fig.

8C is the spectrum of soot exposed to N O 2 / N 2 O 4 for 5 min). These observations show that the disproportionation of nitric oxide to nitrogen dioxide and nitrous oxide, followed by subsequent rapid reaction of this nitrogen dioxide with the black carbon, 5 is responsible for the IR bands at 1660 cm -1, 1565 cm -1, 1540 cm -1, 1340 cm -1, 1305 cm -1, and 1285 cm -~ on exposure of black carbon to nitric oxide.

FIG. 9b.

-2.2361

-2.3295

-2.4228

-2.5162

-2,6296

- 2 . 7 0 2 9

b eve =Sin cvf : 2

/

/%. ONO~ 1669' CFz "T

-~-0H .-I

I

-2.8897

-?.9830 I i i J I I I 1800 1720 1640

WAVENUMBER

Expanded Fig. 9a in the region 1800--1640 cm -1.

678 Volume 42, Number 4, 1988

27.6861

24.7224

1660 (;m -1

Zl.7587

<z 16.7949 m o <=

15.B312

I2.9674

9.9037

6.9399

]660 ¢m~t

)

1800 1700 1600 I500 1400 13(]0 1200 WAVENUMBER

FIG. 10. FT-IR spectrum of DU hexane soot exposed to NO2 from which the spectrum of soot has been subtracted.

In experiments at GMR using paraffin candle diffusion flame soot, small quantities of gas-phase nitric oxide have been shown to inhibit the oxidation of soot by oxygen atoms at 298 K. Thermogravimetric experiments and thermal desorption mass spectra showed that rapid, re- versible adsorption of NO on the oxygenated soot surface was responsible for the observed inhibition. H An FT-IR spectrum of paraffin candle soot exposed simultaneously to oxygen atoms and nitric oxide from these GMR experiments is shown in Fig. 9. Fresh soot as collected from the candle flame and then exposed to only atomic oxygen for the same time period was used as a reference (Fig. 9A); deliberate over-subtraction of the reference is observed at 1400 cm -1, to ensure elimination of its inter- ference with product bands. The complex absorption bands seen here are very similar to those observed in experiments with NO2 on hexane soot 5 and shown in Fig. 10. The unresolved strong absorption at 1800-1640 cm -~ seen in Fig. 9b (smoothed at cvf = 2) is due to the 1660 cm -~ (nitrito-) and 1740 cm -1 (carboxylic) functionali- ties, created on the soot upon exposure to oxygen atoms and nitric oxide simultaneously. 1° The first derivative maximum of this band is 1669 cm -~, while the actual peak postion for the nitrito- group is at 1665 cm -1. For comparison, Fig. 11 shows the FT-IR spectrum of hexane soot (from the DU laboratory) which has been exposed to NO2 at 298 K and then ozonated.

In contrast to the cases discussed earlier, in which small NO2 impurities in nitrogen oxide gas samples led to the observed IR features, NO2 contamination is not a contributing factor in these oxygen atom experiments. 1°,~1 The reaction of oxygen atoms with nitric oxide--

O + N O ~ N 0 2 (3)

20.7995 I r I

17.6438

14,4875

11.3315

8.t755 ?740

5.0195

1.9635

-1.2925

"4"448~000 r900 1800 1700

1625

34781

3.0146 t 2.554f

i f 300 ¢m-1

1340 c~

L t

\

, , 2® ,2'~ , 0 o 1600 ]500 1400

WAVENUMBER

FIG. 11. FT-IR spectrum of DU hexane soot, first exposed to NOJ N204 and then ozonized, from which the spectrum of soot has been subtracted.

- - i s very slow under the GMR experimental conditions, 1°,11,14-16 whereas the reaction of oxygen atoms with nitrogen dioxide--

0 + NO2 -~ NO + 02 (4)

- - i s extremely rapid. 1°,11,14,~6 Hence, the presence of ex-

1780 cm - I

2.0935

1.6330

~.f724

I I

1665 ¢11~ -t

V

30.6499

o.7119 II

II

0.2514

-0'209~000 1900 ,8~0 ]700 ]600 1500' 14~0 ,3100 ,2~X) I ICO

WAVENU~BER

Fm. 12. F T - I R spectrum of D U hexane soot, exposed to ozone and then to NOJN204, from which the spectrum of soot has been subtracted.

APPLIED S P E C T R O S C O P Y 679

cess oxygen atoms and the introduction of nitric oxide well upstream of the soot sample ~0,~ eliminates any NO2 in the gas stream.

We suggest two reasonable kinetic mechanisms for the formation of adsorbed NO2 from NO in these oxygen atom experiments: (1) a concerted oxidative adsorption step involving an NO molecule and an oxygen atom may lead directly to adsorbed NO2 and subsequent products; or (2) direct NO adsorption may occur on the soot, followed by surface oxidation of this adsorbed NO by a chemisorbed oxygen atom. The experiments with ozonized soot suggest that the latter possibility does not occur. When ozonized hexane soot is exposed to NO2 for 5 min, strong IR absorption is observed, due to chemisorbed NO2 (Fig. 12). When ozonized hexane soot is exposed to NO (after the NO is passed through the black carbon bed described earlier) for 90 rain, only extremely weak IR bands are observed, due to nitration (doubtless from the slow disproportionation producing a small amount of NO2). The surface carbon-oxygen function- alities observed in IR spectra of DU ozonized hexane soot and GMR oxygen atom exposed candle soot are very similar; it is unlikely that oxygen atom exposed soot would oxidize adsorbed NO but that ozonated soot would not. It is more likely that the oxygen atoms present in the gas phase in the GMR experiments participate directly in a concerted oxidative adsorption step to give chemisorbed NO2.

CONCLUSIONS

The reaction of black carbon with nitrogen dioxide-- and not a reaction with NO--is predominantly responsible for the formation of species resulting in the IR absorption at 1660 cm -1, 1565 cm -1, 1540-1535 cm -1, 1325 cm -J, 1300 cm -1, and 1277 cm -1. For candle soot exposed simultaneously to oxygen atoms and nitric oxide

at 298 K, the adsorbed nitrogen oxide species also ap- pears to be from NO2, formed by oxidation of NO at the oxygen-atom covered soot surface.

ACKNOWLEDGMENTS

The University of Denver authors are grateful to the National Science Foundation for Grants MPS-7506209 and ATM-8600871 in support ot this work, and to R. H. Allen and Company for glassware fabrication.

1. H. Nishimura, T. Hayamizu, and Y. Yanagisawa, Environ. Sci. Technol. 20, 413 (1986).

2. J. R. Keifer, N. Novicky, M. S. Akhter, A. R. Chughtai, and D. M. Smith, SPIE 289, 184 (1981).

3. M. S. Akhter, A. R. Chughtai, and D. M. Smith, Appl. Spectr0sc. 39, 143 (1985).

4. M. S. Akhter, A. R. Chughtai, and D. M. Smith, Appl. Spectrosc. 39, 154 (1985).

5. M. S. Akhter, A. R. Chughtai, and D. M. Smith, J. Phys. Chem. 88, 5334 (1984).

6. M. S. Akhter, A. R. Chughtai, and D. M. Smith, Carbon 23, 589 (1985).

7. M. S. Akhter, A. R. Chughtai, and D. M. Smith, Carbon 23, 593 (1985).

8. J. A. Jassim, H. P. Lu, A. R. Chughtai, and D. M. Smith, Appl. Spectrosc. 40, 113 (1986).

9. C. A. Sergides, A. R. Chughtai, and D. M. Smith, Appl. Spectrosc. 41, 482 (1987).

10. B. G. Wicke, C. Wong, and K. A. Grady, Combust. and Flame 66, 37 (1986).

11. B. G. Wicke and K. A. Grady, Combust. and Flame 69, 185 (1987). 12. B. G. Wicke and K. A. Grady, Carbon, 26; accepted for publication

(1987). 13. F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry

(Interscience Publishers, John Wiley and Sons, New York, 1972), 3rd ed., p. 355; G. Herzberg, Infrared and Raman Spectra of Poly- atomic Molecules (D. Van Nostrand Co., Princeton, New Jersey, 1968).

14. F. Kaufman, Proc. Royal Soc. (London) A247, 123 (1958). 15. M. Sutoh, Y. Morioka, and M. Nakamura, J. Chem. Phys. 72, 20

(1980). 16. A. P. Ongstad and J. W. Birks, J. Chem. Phys. 81, 3922 (1984).

680 Volume 42, Number 4, 1988

Documents

Reaction of Nitrogen Oxides with Black Carbon: An FT-IR Study