Hydrocarbon Flame Spectra. - Industrial & Engineering Chemistry

December 1951

2739

INDUSTRIAL AND ENGINEERING CHEMISTRY

and measurement of flow, pressure, and temperature of the mixture have been achieved; however, the cause of variation of apparent flame speed with inlet gas velocity must be determined. In addition, further experiments are needed to learn whether the variations of measured flame temperature are due to some defect in the experimental approach or whether they are due to a lack of equilibrium. The spectroscopic methods of measuring the relative light intensities from various intermediate molecules such as OH, CH, and Cp,as well as the equipment for determination of flame speeds, show sufficient promise to warrant future detailed studies in the attempt to gain relevant information about the mechanism of the combustion process. ACKNOWLEDGMENT

The assistance of A. F. Baillie and L. P. Parker of these laboratories and W. C. Johnston of the Westinghouse Research Laboratories in the design and construction of apparatus and instruments is gratefully acknowledged. The cooperation of G. T. Lalos of the Combustion Section of the National Bureau of Standards in the development of the metering systems and in photographing the flames also was most helpful. LITERATURE CITED

(1) Am. Soc. Mech. Engrs., Special Research Committee on Fluid Meters. “Fluid Meters. Their Theory and Amlication.” .. 2nd ed.: Part 1, 1927. (2) Anderson, J. W., and Fein, R. S., J. Chem. Phys., 18, 441 (1950).

Barret, P., Pubs. sei. et tech., direction inds. aeronaut. (France), Notes tech. No. 33 (1950). Coward, H. F., and Payman, W., Chem. Revs., 21, 359 (1937). Denues. .A. R. T.. and Huff, W. J., J . Am. Chem. SOC.,62, 3045 (1940). Diecke, G. H., and Crosswhite, H. M., Johns Hopkins University Applied Physics Laboratorv, Bumblebee Rept. No. 87 ( S o vember 1948). Fastie, W. G., J . Optical SOC.Am., 40, 800 (a)(1950). Gaydon, A. G., Nature, 165, 170 (1950). Gerstein, M., Levine, O., and Wong, E. L., Natl. Advisory Comm. Aeronautics. RM E50G24 (SeDt. 28. 1950). Grove, J. R., Hoare, M. F., and Linnett, J. W.,Trans. Faradau Soc., 46, 745 (1950). Hirschfelder, J. O., and Curtiss, C. F., J . Ch.em. Phys., 17, 1076 (1949). Johnston, W. C., S . A . E . Journal, 55, 62 (December 1947). Kretzschmer, F., Forschungsheff 381B,7 (1936). Lewis, B., and von Elbe, G., J . Chem. Phus., 2,537 (1934). Mallard, E., and Le Chatelier, H., Ann. M i n e s , [8] 4, 274 (1883). Markstein, G. H., “Third Symposium on Combustion,” p. 162, Baltimore, Md., Williams & Wilkins, 1948. Payman, W., and Wheeler, R. V., Fuel, 8,204 (1929). Smith, F. A,, Chem. Reus., 21, 389 (1937). Smith, F. A., and Pickering, S. F., J . Research Natl. Bur. Standards, 3, 65 (1929). Strong, H. M., and Bundy, F. P., Third Symposium on Combustion. KID. _ - 641. 647, Baltimore, Md.. Williams & Wilkins. 1948. Tanford, C., and Pease, R. N., J. Chem. Phys., 15, 431, 861 (1947). ,- - . ,. (22) Wohl, K., and Kapp, N. M., Project Meteor, University of Delaware, Report UAC-42 (October 1949). I

RECEIVED June 7,1951.

HYDROCARBON FLAME SPECTRA. GEORGE A. HORNBECK

AND

ROBERT C. HERMAN

Applied Physics Laboratory, The John Hopkins University, Silver Spring,

Hydrocarbon flame spectra have been surveyed in the range -2000 to -9000 A. in order to establish the identity of band systems obtained under a variety of flame conditions. The sources and techniques required to enhance the spectra of specific molecular species by means of variations in oxygen-fuel ratio are described. The experimental results are presented chiefly in a selected series of densitometer tracings of bands obtained under a wide variety of oxygen-fuel ratios. The spectra of diatomic and polyatomic molecules, particularly the “hydrocarbon” and

“deuterocarbon” flame bands, are discussed and some comments are made concerning the kinetic mechanisms involved. Several electronic (2Z TI) OH bands are reported. The results of this work are significant principally in that they provide the spectroscopic investigator of flames with a pictorial means of rapid identification. This was made possible by the fact that this survey was carried out at fairly high dispersion and with systematic variations of the oxygen-fuel ratio which enhanced specific molecular bands and made their identification relatively simple.

H E combustion of hydrocarbons has been studied intensively for many years because of its theoretical and practical in; terest. As a matter of fact flame spectroscopy in general is a subject which has held the attention of both physicists and chemists for many years. Flames have been used as sources of particular band systems for the study of molecular spectra but perhaps more generally by the chemist or investigator of combustion reactions for obtaining spectra or spectral variations in the hope that these might be useful in understanding kinetic mechanisms. A rather complete survey of the field of spectroscopy as applied to the theory of combustion has been given by Gaydon (8). The spectroscopic technique is a useful one for studying flame sources in that it clearly does not in any way affect the conditions under which the reaction occurs. It allows the identification of a t least some of the radicals and molecules that exist in the flame and a determination of their ewrgy states. Furthermore, while difficult, the examination of relative intensities affords information concerning the relative concentrations of the various species

as well as indicating the degree of thermal equilibrium. On the other hand, it is not clear in many cases whether or not all the molecular species detected in flames by spectroscopic means have significance with respect to the chemical mechanisms involved in flame reactions. Another difficulty is that frequently one readily obtains spectra which are not so easily identified because of their complexity. Also, many flame sources are so weak that adequate spectra are indeed difficult to obtain and, as will be mentioned later, one of the problems in this field is the development of suitable flame sources which yield spectra of high intensity and good contrast. An examination of the literature concerning hydrocarbon flame emission spectra in the photographic regions reveals the almost complete absence of high dispersion work. Most of the spectroscopic studies have been either a t low or moderate dispersion because of the speed of prism instruments, the paucity 6f grating instruments in the past, and because a t lower dispersion it has been felt that band heads are more easily observed. However, it is found under these conditions that while many of the most in-

T II

Md.

-


2740

tense bands are easily obtained, many bands as well as band systems have been overlooked. The reason for this lies in the high degree of band overlap coupled with the fact that many bands do

r - - , u r n aF c e Quartz Tube

Com mercial

\Torch Figure 1.

/"slit\

Compressed Air Jet

Schematic Diagram of Burner Used for High Oxygen-Fuel Ratios

not have sharp heads or are headless. Therefore, i t appeared worth~hileto study emission spectra from flames a t sufficiently high dispersion, so that the spectra which are dealt with may be more fully identified. The first step was to obtain high dispersion spectrograms for purposes of identification, then to vary flame conditions such as pressure, temperature, fuel-oxygen ratio, eto., to observe the spectral changes, and finally to attempt to correlate all this information with a view to understanding the kinetic mechanisms. Although considerable progress has been made in obtaining and identifying additional band systems in hydrocarbon flame spectra, the ramifications of the over-all problem are so great that only limited progress in kinetic interpretation ' h a s been possible. The principal purpose of this paper is to present a discussion of the kinds of spectra yielded by hydrocarbon flames and the means of obtaining them. A selected set of densitometer tracings of many of the molecular bands is presented as an aid in the identification of spectra.

Vol. 43, No. 12

served in somewhat better contrast However, continuous einission is considerably less troublesome a t higher dispersion so that attention in this paper has been confined to sources operating a t atmospheric pressure. In these studies a limited number of the simpler hydrocarbons have been utilized-namely, methane, acetylene, acetylene-d, and ethylene. Most of the work to be described concerns the acetylene flame, because it has been found that this flame yields with greater intensity and better contrast all the spectra that are obtained using methane and ethylene. The particular fueloxygen ratio, p , determined the type of burner necessary to obtain a stabilized flame. Ordinary coinmercial oxyac~tylenetorches were used unless p became small ( p 0.05). In such cases the mixing baffles and tip were removed from the nozzle of the torch in order to accommodate a greater mas8 flow of gas a t speeds which permit flame stabilization. The tank fuel, oxygen, and diluent, if added, were of the highest purity obtainable commercially. The acetylene-d was prepared from DzO and dehydrated calcium carbide. A mass spectronietric analysis of the acetylened is given in Table I. The sample also contained small amounts of carbon diovide and hydrogen sulfide but there m r e no heaviei hydrocarbons present. The gases were metered accurately with Hoke Flowrators and then premixed before burning. For the case where p is small-e.g., p 5 0.03-it was necessary to stabilize the flame inside ~t quartz tube heated in a furnace a t about

(4-3)(3-2) (2-1)

,

(1-0)

EXPERIMENTAL

The purpose of this section is to reinark briefly about the experimental techniques which have been found useful in obtaining the hydrocarbon flame spectra to be discussed late1 In the photographic spectral region there is no characteristic hydrocarbon flame spectrum. It will be seen that the spectrum is very dependent on flame conditions. principally the fuel-oxygen ratio and the temperature. While the fuel-oxygen ratio affects the temperature. significantly l o v w temperatures can also be produced by the introduction of diluents such as nitrogen, carbon dioside, and the inert gases (14). A great variety of hydrocarbon flame sources have been investigated including low pressure burners. The latter have the disadvantage of low light intensity and like others (Q), the authors have found that the spectra differ little from those obtained from burners operating a t a t m o s p h i c pressure. The principal advantage, in some cases, is that low pressure spectra contain less continuum and the rotational fine structure is ob-

4dOOL

Figure

4d50

2. Densitometer Tracing of a Portion of Two Sequences of C2 Swan Band System Obtained from inner cone of oxyacetylene flame

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I

I

1 Figure 3.

2330

2390

9310

9300

9990 A.

Densitometer Tracing of the

CZMulliken Band at 231 4 A.

Insert drpicts appearance of this band at lower dispersion

I

I

2820

6 I

1

1 3060d

I

I

I

3080 Figure

I

I

2860

2840

I

I

2880

I

I

2900

I

I

h

I

3100

I

I

3120

I

I

3140

4. D.enritometer Tracing of (1-0) and (0-0) OH Bands at 4 M I and 3064 A,, Respectively

I

I

3160

INDUSTRIAL A N D ENGINEERING CHEMISTRY

2742

I

I

I

3440%

I

3460

I

I

3480

I

I

3500

Vol. 43, No. 12

I

I

3520

I

(0-2) OH

I

3920i

I

1

3930

I

I

I

3940

3950

3970

3960

Figure 5. Densitometer Tracing of (0-1) OH Band at 3428 A. and the (0-2) and (1-3)

A

4200 A.

4250

A

4300

1

3980

OH Bands

A

4350

Figure 6. Densitometer Tracing of the (0-0)CH Band of the 4300 A. ( z A - Q) System Band essentially free from ovetlap with Swan bands because of the very lean oxyacetylene mixture used

4000

INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY

December I951

I

I

I

I

3900 Figure

1

I

3920

Figure 8.

4075 Densitometer Tracing

- TI)System

4100

of (1-1) CH Band of the 3900 A. ('2

1000° C. as shown schematically in Figure 1(80). The rates of flow of the premixed gases in the ordinary torches was -7 to -20 2 per minute whereas for the open quartz tube it was -80 to -100 I per minute. These high rates of flow provided flame sources of relatively high intensity although the latter type gives a flame of considerably lower temperature. The above types of flames have been viewed spectroscopically from all aspects and spectra have been obtained of both the inner and outer cones. The results to be discussed are primarily concerned with the inner cone or reaction zone. The spectra have been obtained using a medium quartz Bausch and Lomb spectrograph, a 2-meter Baird grating spectrograph (Eagle mounting) in the first (8 A. per millimeter) and second orders, and a 21-foot 10inch Jarrell Ash grating spectrograph (Wadsworth mounting) in the first (4.8 A. per millimeter), second, and third orders. Conventional plates of the highest contrast suitable for the particular

I

3966

3940

7. Densitometer Tracing of (0-0)CH Band of the 3900 A. (?2

4050

1

I

I

4025 A.

2743

-

2Q

I

I

4125

41 50

System

spectral region and source intensity were used. The lower temperature source described above provided considerably higher intensities than heretofore reported for the hydrocarbon flame bands. For example, exposure times of -30 seconds are sufficient to obtain well exposed plates with a medium quartz spectrograph and -3 minutes with a 2-meter Baird grating spectrograph in the second order using 25,u slits and 11-0 plates.

~~

Table 1.

Mass Spectrometric Analysis of Acetylene-d

Component

Mole yo

CzDz

94.2 5.1 0.7

CzHD CzHz

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Vol. 43, No. 12

I

3640 A.

3660

Figure 9.

3680

Densitometer Tracing of (1 -0)

CH Band of the 3900 A. (zZ- 'TI) System

/(

0-0) CH

M I

I

I

'

I

3100 A.

I

i

I

I

1

'

31 50

Figure 10. Densitometer Tracing of (0-0) CH Band of the 31 43 A. ('9-TI)System Infonrity o( this band relative to the (0-0) OH is high%oeauro a fuel-rich Rame was omdoved

3700

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2745


1950 A.

eo00 Figure 11.

2050

2100

pensitometer Tracing of a Portion of Fourth Positive CO (A‘n-X’z)

DIATOMIC SPECTRA

Prior to high dispersion investigations of hydrocarbon flames, the diatomic spectra reported (8) from these sources were as follows: From the inner cone have been reported the Swan ( allo and Mulliken (12: - 9:)band systems of CZ,the ( 22: - Q) and system of OH, and the 4300 A. (zA - V ) ,3900 A. (‘2 3143 A. (22 - 2n) band systems of CH. In addition, the CO Fourth Positive bands (.41ll - XlZ) and the line of atomic carbon a t 2478.6 A. have been observed with the oxyacetylene flame (8). In certain cases the impurity spectra of CN, NH, and the ybands of NO may also be obtained. The spectrum of the outer cone was reported to contain the OH band system, continuum, and perhaps in some instances the so-called CO flame spectrum. A selected portion of the band systems of CZ,OH, CH, and CO are given in the form of densitometer tracings in Figures 2 to 11and 15. Densitometer tracings were chosen for illustrative purposes because of the difficulty of adequate reproduction of spectrograms. However, it was necessary to obtain many of the densitometer tracings a t a rather high scan rate in order to cover the spectral range required. In many instances this gives tracings which do not reflect the true resolution of the spectrograms. It has not been practical to illustrate all the bands of interest but this work can be supplemented with the information on band positions and molecular constants given by Herzberg (16) and Pearse and Gaydon ( 2 6 ) . Studies a t higher dispersion have revealed a number of additional known band systems hitherto not reported in flames (19, 1’7, 18), as well as several new individual bands. Figure 12 consists of a set of densitometer tracings of the acetylene-oxygen flame, burning with various fuel-oxygen ratios, in the region -3000 to -4000 A. These spectra were photographed a t a dispersion of 2.4 A. per millimeter and the densitometer tracings were obtained a t a rapid scan rate in order to cover so extended a spectral region. Examination of Figure 12 ( B )reveals the prominence of the Deslandres-D’Azambuja system in this spectral region. The Deslandree-D’Azambuja band system (‘no- ‘nu) of G had been obtained originally in both condensed and uncondensed dischargas and were analyzed by a number of investigators (8, 16, 28). This band system is obtained readily from the inner

2150 System

cone of the flames of methane, acetylene, and ethylene burning with oxygen in an ordinary torch with a fuel-oxygen ratio in the vicinity of stoichiometric proportions. However, the intensity is greatest when using acetylene. All the bands of this system reported by Herzberg and Sutton (16) have been identified. In Figures 13 and 14 densitometer tracings are presented which show a sequence of these bands near 3600 A. and the bands which head near 3850 A., respectively. Figure 14 exhibits the character of the rotational structure. If the fuel-oxygen ratio for the oxyacetylene flame is about unity, then the Fox-Herzberg system (3& - 317,) of the Cn molecule also becomes a prominent feature in the region between -2400 A. and the head of the (0-0) OH band at 3064 A. To longer wave lengths the structure is confused with that of other bands and is not easily distinguished because the bands of this system have rather weak heads. In Figure 15 is shown a densitometer tracing of GI OH, and CO bands lying in the short wave-length region between the Mulliken and the (0-0)OH bands when p S 1. It is easy to see why it is difficult to ascertain the presence of the Fox-Herzberg bands even at moderate dispersion. However, they are most readily seen in the vicinity of the short wave-length side of the 3064 A. OH band. Figure 16 is a densitometer tracing of the region -3005-3064 A. which shows the rotational structure of a portion of the (0-4) band of the Fox-Herzberg system mixed with lines of OH. A portion of this band is labeled so as to identify the R and P triplets. These bands degrade to the red, do not have pronounced heads, and are known to extend from 2378 A. (4-1) to 3283 A. (0-6) (4,28). In view of the close rotational structure and lack of sharp heads it is not surprising that the Fox-Herzberg system has not been evident in low dispersion spectra of Barnes. Under these same conditions p 1, the Phillips band system (‘11, - ‘2,)of the CZmolecule is observed as the most prominent feature of the photographic infrared region between -7700 to -9000 -4.(27). Since, as can be seen from Figure 17, the Phillips band system involves a transition from the lower state of the (In, - In,,) Deslandres-D’hambuja system to the lower state of the (12: - %;) Mulliken system, the Phillips bands would be expected to appear when flame conditions are such as to produce the Deslandres-D’Azambuja bands. If p is about stoichiometric


2146

Vol. 43, No. 12

3872i CH

OH

Figure 12.

Rapid Densitometer Tracings of the Spectrum of Oxyacetylene Flame from Fuel-oxyeon ralior.

A.

1;

8.

thePhillips bands appear, but in addition there is anothci, structure in this region n-hich as yet has not been identified. In Figure 18 is shown a densitometer tracing of some of the Phillips bands obtained at a dispersion of 4.8 A. per niillimeter from the inner cone of an oxyacetylene flame burning s-ith p E 1. The band heads lying in the region 7700 to 8500 A. aw indicated. ;2 new ultraviolet band system of thc CZmolecule (e12: - b lau)has been reported by Freymarli (6). The Runge bands t3Z; - %;j and the "atmospheric absorption bands" (l2; - "2,j of the osj-gen molecule were obt'ained in emission recently from the caI bon monoside-oxygen explosion and stationary flames (29, 91). These band systems of oxygen are also present in the emission spectrum of oxyhydrocarbon flames when burning on the lean side of stoichiometric, p < p (stoichiometric), and are found particularly in the outer cone. The Runge bands lie in the region -2500 to ~ 4 5 0 0A. and are more intense the great'er the oxygen-fuel ratio ( 3 , 8.4). Ho-ivever, if p is very much smaller than about 0.05, the Runge bands are either weak or absent because there is an appreciably cooler flame and oxygen is not excited readily. A densitometer tracing of the

0.4;

C.

0,Ij

-3000

to -4000

A.

D. 0.02

Runge bands in the region 4 2 0 0 to -4000 A. is given in Figure 19. The intensity of the oxygen bands bet,\Teen 4 3 2 0 0 t o -3900 A., relative to the OH and CH bands, can be seen in the spectrum of the oxyacetylene flame in Figure 12 (C). The rotational structure of the (0-14) and (0-15) Runge bands of oxygen is s h o m in Figure 20. These tT7-o oxygen bands are particularly useful hecause of their relatively open structure in identifying t'he presence of the Runge system. In the spect,ral range below -3200 A. the oxygen bands are mixed TT-ith OH bands. The Runge bands have also been reported in the oxyhydrogen flame spectrum by Gaydon and Wolfhard (10). It is difficult to suppress the Runge bands in the oxyhydrogen flame unless it is cooled by a high excess of oxygen or the introduction of a diluent such as nitrogen. Under similar conditions to those giving rise t'o the Runge bands in the oxyacetylene flame, the (1Zi - 3Zij system of oxygen is also found. -41though this system involves a forbidden transition, it persists more than the Runge system as a flame is made leaner because less excitation energy is required, The densitometer tmcing shown in Figure 21 was obtained from the carbon monoxitie--

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2747

Deslandres-D’Azambuja bands, become rather weak and the Runge bands of oxygen become more evident. For even p E 0.02-diatomic smaller p-say spectra are generally suppressed and in the region -2350 to -4000 A,, there appear complex bands undoubtedly polyatomic in nature. Figure 12 (D) shows a portion of these bands, which are generally referred to as the hydrocarbon flame bands, in the region 3000 to 4000 A. The only obvious diatomic band is the (0-0) OH a t 3064 A. but this is considerably suppressed. The hydrocarbon flame bands are discussed in the next section. In order to illustrate the appearance of flame spectra from several different sources taken a t moderate dispersion (medium quartz prism spectrograph), Figure 22 is given. The difficulty of identifying all the bands shown a t lower dispersion without previous knowledge of their existence is quite evident. This is caused by the serious overlapping of the many band systems that lie in this region. The spectrum of the inner cone of a split burner using ethylene and air is most similar in character to that in Figure 12 (D). Note the presence of the 3872 A. C H and 3064 A. OH bands in the former and the almost complete absence of these bands in the latter case because of the lower effective temperature of the source. The ethylene-oxygen flame spectrum in Figure 22 is comparable to the acetylene-oxygen flame spectrum shown in Figure 12 ( B ) . The low dispersion instrument, however, is indeed useFigure 13. Densitometer Tracing of a Sequence of Deslandres-D’Azambuja Bands of the Cz Molecule in Vicinity of 3600 A. from Oxyethylene Flame ful for the general mapping of spectra. over a large spectral range, in particular 4 A, per millimetr when studying the effects produced by varying burning conditions. This is predicated on a knowledge of the spectra with which one is dealing. oxygen explosion flame where these bands appear free from the Considering the wide limits used for the fue!-oxygen ratio, i t vibration-rotation spectrum of water. would be expected that the temperature of the inner cone, whatFrom the foregoing discussion it becomes clear that variations ever this may mean, would be quite different from flame to flame. in the fuel-oxygen ratio, p, produce rather marked changes in the An attempt was made to determine “temperatures” by the isooxyhydrocarbon flame spectrum. In Figure 12 are shown a set of intensity method (1) using the (0-0) OH band. The temperadensitometer tracings of the spectrum of the inner cone of the tures were found to vary far less than expected as p was changed oxyacetylene flame in the region between the head of the (0-0) from -0.02 to -1.0. The chief reason for this result may lie in OH a t 3064 A. and the (0-0) CH band a t 3872 A. for four characthe fact that as p deviates widely from stoichiometric proportions teristic ratios p. When burning rich in fuel-e.g., p E 1-the the OH lines become seriously blended with the lines of other spectrum appears as in Figure 12 ( A ) from which it is strikingly evident that the 3143 A. system of CH t is more intense than the Av = 0 sequence of OH. The 3900 A. system of C H is also moderately strong. Although relatively weak, the Deslandres-D’Azambuja bands are evident and the head of the (2-2) CN band ( 2 2 - 22) a t 3862 A. appears very weakly because of the diffusion of atmospheric nitrogen into the flame. The spectrum in Figure 12 ( B ) is for p = p (stoichiometric), in which case the OH, CH, and Cz bands are quite prominent. When p E+ 0.1, as 3830 3840 3850 38*0 A. in Figure 12 (C), the principal difference over the case in Figure 12 ( B ) is that Figure 14. Densitometer Tracing of (0-0) 3852 A. Deslandres-D’Azambuja Band all of the bands of CZ, particularly the Obtained from the ox~acetyleneRome at 2.4 A. per millimeter

,


2148

2

Vol. 43, No, 12

ATOMIC CARBPN LINE ( 2 4 7 8 A )

MULLIKEN C,

f 2325140

n

\

Figure 15.

Densitometer Tracing

OF

the Short Wave-Length Region -2300

to -3064

A. OF the Spectrum OF Oxyacetylene Flame

p = i

4.8 A. per millimeter

Table ti. Wave Length OF QIBranch Lines OF the (2-3), (0-2), and (1-3) Bands OF the (a ZII) OH System

-

Line

X, A. (Obsvd.)

X, Cm.-l

(Obsvd.)

X.Cm.-l (Calcd.)

3566.75 3568.51 3570.38 3572.43 3574.70 3577.14 3579.58 3582.87

28028.7 28014.9 28000.2 27984.2 27966.4 27947.2 27926.1 27902.6

28028.63 28014.66 27999.91 27983.91 27966.29 27947.06 27926.72 27902,37

3920.03 3921.54 3922.75 3923.85 3924.77 3925.65 3926.49 3927.33 3928.20 3929.11 3930,07 3931.12 3932.28 3933.55

25502.8 25493 .O 25485.1 26478.0 25471.4 25466.3 25460.9 25153,4 25449,8 25443.9 25437,6 25430.8 25423.4 23415.2

2S03.44 25493.40 25485.22 25478.25 25472.27 25466.61 25461.04 25455. 60 25449.96 25444.08 25437 76 25430,99 28423.66 26415.47

3959.17 3960.78 3962.19 3963.43 3964.60 3965.79 3966.97 3968.18 3969.48 3970.86 3972.33 3974.00

25250.7 25240.4 25231.4 25223.6 25216.1 25208.6 25201.1 25193.4 25186.1 25176.4 28167.1 23166.5

25280.73 26240.66 25231.77 25223.76 25216.23 25208.73 25201.29 25193.46 25185.31 25176.54 25167.08 25156.70

bands. A complete discussion of this subject is not given since it is not within the scope of this paper. Sevcral new electronic and vibration-rotation bands of the OH radical were found during this survey. The electronic bands are the (2-3), (0-2), (1-3), and (2-4) bands of t'he ( % - 211) system. These bands are relatively weak and are blended either with other OH lines or wit'h lines of other band systems. Neasurements were carried out and compared with positions calculated with the aid of term values given by Dieke and Crosswhite ( 1 ) . The differences between calculated and observed positions generally agree to better than 0.5 em.-' The positions of some of the Q1 branch lines are given in Table I1 for aid in identification. The QI and QZ branches of the (0-2) and (1-3) OH bands can be seen in the lower portion of Figure 5, Recently, the (4!-0), (5-1)) and (6-2) vibration-rotation bands of OH m r e obtained from the outer cone of the oxyacetylene flame a t a dispersion of 8 A. per millimeter in the photographic infrared (19). Spectrograms of good contrast and density were obtained with exposure times of about l l / z hours using a 25p slit and ammonia hypersensitized I-N plates. In Figure 23 is shown a densit'ometer tracing of a portion of the (4-0) and (5-1) bands, with some of the P-branch lines of the former band indicated. In the P-branch the spin doublets are well resolved as are the A-doublets for high K values. The weaker lines in Figure 23 are vibration-rotation lines of water which become more intense a t longer wave lengths and in cooler flames. These OH bands can also be obtained from the outer cones of flames of other hydrocarbons, although in these cases the OH lines are badly overlapped by the intense water spectrum. Best results have

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December 1951

rnrn

3005

30'15

3010

3020

I

3025

3030'

3035

3040

(0;O)OH I'

30'45 Figure 16.

3050

Densitometer Tracing of Spectrum

3055

3060

of Oxyacetylene Flame Showing Portion of the (0-4) Fox-Herzberg Band of Ca 2.4 A. Der mllliarkr

I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY

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Vol. 43, No. 12

been achieved with the oxyacetylene flame at stoichiometric proportions when viewing the region of the outer cone closest to the tip of the reaction zone.

l6

POLYATOMIC HYDROCARBON FLAME BANDS

I t has been known for some time that complex band spectra are emitted by the flames of ammonia, carbon monoxide, hydrogen, and hydrocarbons burning with air or oxygen (8). I t has been suggested that the @-bands of the ammonia-oxygen flame spectrum are emitted by the NH2 radical, that the CO flame bands are emitted by carbon dioxide, that the long wave-length complex bands in the hydrogen-oxygen flame spectrum are emitted by water, and that the hydrocarbon flame bands are emitted by the HCO radical. The hydrocarbon flame bands mere first investigated in detail under low dispersion by Vaidya (SO). He described the appearance of a system of bands which are degraded to the red and lie between 2500 to 4100 -4. These bands were arranged in a vibrational array and it was suggested that the emitter was the HCO radical. Vaidya obtained these bands with many hydrocarbons burning with both air and atomic oxygen (8). While Vaidya employed the technique of separating the inner and outer cones in the former case, this is not necessary since the production of the band system from hydrocarbons requires a cooler flame which can be obtained in various ways. Gaydon has also produced these bands by the technique of what he termed a

dl

&/w (3-c

Figure 18.

1

I 7800

-4 -3

-2

-I

SINGLET Figure 17.

TRIPLET Energy Level Diagram of Molecule

CZ

chilled flame (8). The authors have been able to obtain these bands with high intensity by stabilizing an oxyacetylene flame in a heated quartz tube using p

Hydrocarbon Flame Spectra. - Industrial & Engineering Chemistry

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