Perhaps the most interesting sample encountered was sodium chromate te t rahydrate (Fig. 9). While this yellow material showed no obvious signs of decom- position such as smoking or charring when the sample was scanned in static mode, a significant variation in its spectrum was observed when the sample was rotated. In the 800 to 1000 cm -I region, one band near 800 cm -1 quite reprodueibly vanished and other bands were shifted slightly in frequency when the rotator was stopped. Higher sensitivity scans in the 3300 em -~ region also revealed the disappearance of the OH stretching band of the water of hydration when the sample was static. Evidently, the localized heating produced by absorption of laser radiation was sufficient to dehydrate the sample only in the minute area where the laser struck it. The spectrum of the anhydrous compound (corresponding to static in Fig. 9) was readily reproduced by a sample which was dehydrated in a 110°C oven for several hours.

One drawback of the rotating sample technique should be mentioned. Samples which produce interfer- ing fluorescence exhibit no beneficial effects from rotation. In fact, continual exposure of fresh sample to the exciting laser beam precludes the use of the "drench- quench" technique for alleviation of fluorescence. 7

This method of quenching simply involves exposure of the sample to the focus of the laser for extended periods, whereupon fluorescence often subsides considerably.

III. C O N C L U S I O N

In our experience, the rotating solid sample technique appears to offer the Raman spectroscopist a general solution to the problem of deeply colored samples which decompose from too rapid absorption of laser energy. The wide range of colors and sample types examined is evidence of the techuique's versatility. As originally intended by Kiefer and Bernstein, the technique also offers a new tool in the study of resonance Raman effects.

1. W. Kiefer and H. J. Bernstein, Appl. Spectrose. 25, 500 (1971).

2. W. Kiefer and I-t. J. Bernstein, Appl. Spectrosc. 25, 609 (1971).

3. Supplied by Peter Ford, University of California, Santa Barbara, who kindly granted permission to use the spectrum for illustration.

4. G. Michel, Spectrochim. Acta 25A, 517 (1969). 5. J. A. Topp, H. W. SchrStter, H. Hacker, and J. Brand-

mfiller, Rev. Sci. Instr. 40, 1164 (1969). 6. F. Tuinstra and J. L. Koenig, J. Chem. Phys. 53, 1126 (1970). 7. T. R. Gilson and P. J. Hendra, Laser Raman Spectroscopy

(Wiley-Interscience, London, 1970), p. 157, 169.

Infrared Emission Spectra of Solids

Gianfranco Fabbri and Pietro Baraldi

Laboratorio di Chimica Fisica Applicata, Istituto di Chimica Fisica, Universitg di Modena, 41100 Modena, Italy

(Received 3 April 1972; revision received 5 June 1972)

A simple technique for recording ir emission spectra on nonmodified spectrophotometers is discussed. The effects of support, temperature, sample fineness, and layer thickness on both band intensities and band resolution are stated. Some examples of emission spectra in com- parison with the absorption spectra of the same compounds are given. INDEX HEADINGS: Inorganic infrared emission spectra.

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

Infrared emission spectra have had few applications because of the difficulties in recording them. When working at room temperature or slightly above room temperature, insufficient energy is available, and instrumental modifications for increasing sensitivity are needed. Spectra of samples at room temperature have been recorded making use of modified spectropho- tometers 1 or interferometers, 2, 5 i.e., instruments with high sensitivity detectors and high light-gathering power.

In applied research there are many problems which can be solved by infrared emission methods but not by

absorption spectroscopy. An example of these problems is the study of the catalytic properties of solids. In this case, absorption spectroscopy methods are often limited to a great extent not only by the high reactivity of the compounds h~vestigated with the supports, but also by the high temperatures required in these experiments. I t was precisely these considerations that led Eischens and Pliskin 6 to suggest the evolution of simple tech- niques for infrared emission spectroscopy. Some diffi- culties are also met in absorption spectroscopy on account of the problem of the modifications (decomposi- tions, dehydrations, phase changes, etc.) undergone by both organic and inorganic compounds between 100 and

Volume 26, Number 6, 1972 APPLIED SPECTROSCOPY 593

500°C. This area may be studied with comparative ease by infrared emission techniques, while absorption methods may be unsuitable. Among other things, in these situations the potassium-halide supports may give rise to chemical interference with the compounds investigated.

The purpose of the present work is to point out that, using certain simple techniques which employ nonmodi- fled commercial infrared spectrophotometers, it is pos- sible to record high quality infrared emission spectra between 100 and 500°C. (The techniques proposed cannot be used with spectrophotometers that chop the radiation between the source and the sample compart- ment. In any event, these instruments are not common.) This is the range of main interest for the above-men- tioned areas of study. However, it must be pointed out that our results cannot be ascribed only to the emission of the samples. They may be a sum of factors (emission, reflection, self-absorption, etc.), but under the best ex- perimental conditions emission appears as the most important one.

In this paper, therefore, the term "emission" is in- tended as the outcome of these phenomena. An examina- tion of the relative importance of the factors under various experimental conditions will be undertaken in a following paper.

I. EXPERIMENTAL TECHNIQUES

The techniques in question were evolved using a Perkin-Elmer 457 grating spectrophotometer. A section of the cells used is shown in Fig. 1. The support carrying the spread sample as a pure powder was placed inside one cell and the support alone inside the other. The powder was laid on the support by suspending it in isopropyl alcohol which then evaporated, using the

m

0 ~

D

P

wit' 1 ! , J J

w 1

........ i/!

Fro. 1. Section of the ir emission cell: S, support; t~, sample thermocouple; t~, cell thermocouple; R, heating coil; W, water cooling connections; D, KBr disk; O, O-rings; P, vacuum con- nection.

technique of Hunt, Wisherd, and BonhamJ The two cells were placed opposite sample and reference beam slits, respectively. The addition of particular focusing devices, such as a set of mirrors, was intentionally dis- carded in the present experiments. If the cell containing the sample is placed opposite the sample beam slit and the cell containing only the support opposite the reference beam slit, a arrangement is attained, and with positions reversed b arrangement is attained.

A. a arrangement

This arrangement is unsuitable for the recording of the spectra because of several limitations. It is described simply for the sake of completeness. The sample cell is placed opposite the sample beam slit and the support cell is placed opposite the reference beam slit. If E0 is the energy emitted by the support and E~ the energy emitted by the sample at any given wavenumber, the recorded curve will be proportional to:

E0 + E l _ 1-4-El ~o > -- 1 ( 1 ) E0

The response is therefore the sum of two terms. The first (always unity) is due to support emission and is sufficient in itself to bring the curve up to the 100 % "transmittance" value (in this paper the term "trans- mittance" is merely conventional and refers to the printed scale of the chart). The second is due to sample emission, which would naturally send the recorder pen off scale. To avoid this, use of attenuators on the sample beam is needed.

If x is the fraction of energy transmitted by the attenuator, Eq. (1) becomes:

(Eo + E1)x E1 E0 - x + E0-- z ( 2 )

The first term is therefore reduced by the factor x, so that a background line lower than 100 % is obtained; the sample emission, however, is also decreased by the same factor.

The above expression as a function of Eo/E~ for several values of x is reported in Fig. 2. The dashed por- tions of the curves stand for meaningless experimental

x

• o 5 _

O l o

i \ .. X = I

\ \ X : 0.75

X=0.5

X = 0.25

X=0.1

I I 3 4 5

Eo/E1

FIo. 2. Effect of the attenuators on band intensity in a arrange- ment.

594 Volume 26, Number 6, 1972

situations, since transmittance values higher than 100 % are concerned.

From Fig. 2 it can be seen that intense emission bands may be recorded only with the use of low transmittance attenuators. Also, for constant values of x and E~, a decrease of E0 causes an increase of band intensities. We may conclude that with this experimental arrange- ment the use of low emission supports is useful, but the continuous recording of a whole spectrum is not generally convenient since each band would need the use of an at tenuator appropriate to its intensity. However, an at tenuator subtracts a portion of the available energy so that an increase of the gain is needed, and this causes a decrease of signal to noise ratio.

B. b arrangement

In the b arrangement the sample cell is placed opposite the reference beam slit and the support cell is placed opposite the sample beam slit. In this case, the recorded quanti ty is proportional to:

E0 (3) E1 "~- E0

activity features even at high temperatures, apart from its catalytic effects.

D. Cell Temperature Regulation

Cell temperature steadiness is an important factor in achieving tfigh quality emission spectra, for the energy amount emitted by the sample depends greatly on temperature, as is stated by the Stefan-Boltzmann law. In practice, it is observed that, even with small varia- tions of sample temperature, the recorded spectrum changes considerably. Copper sulfate emission spectra at 250°C between 1000 and 300 cm -1 are reported in Fig. 5. In all the figures the ordinate (emission) is in arbitrary units. The spectra reported here, therefore, have only a qualitative meaning.

Spectrum a is obtained with a periodical in phase variation of about ± i ° C for both the sample and the reference temperature, and spectrum b is obtained under the same conditions with variation of about ±5°C.

The spectra in Fig. 5 indicate that , if the sample temperature is not precisely regulated during the re- cording of spectra, weak bands or shoulders may appear,

At zero sample emission the transmittance is 100 %, while at every wavenumber at which the sample emits, it will be lower than 100 %. Attenuators are not required for this arrangement; hence all energy available reaches the detectors, giving maximum signal to noise ratio.

The above quantity, Eo/E1 + Eo as a function of Eo/E1, is reported in Fig. 3. I t can be seen that, for constant values of E1, the recorded band intensities in- crease as E0 decreases, and thus, in practice, supports ~dth minimum emission are to be preferred.

C. Supports

To evaluate the suitability of various materials for use as supports, emission spectra on iron, brass, alu- minium, platinum, glass, and potassium bromide disks were recorded at different temperatures, using the Nernst glower as reference. The spectra recorded at 300°C are reported in Fig. 4. I t is observed that all the metals have a weak emission of practically the same value, while glass and potassium bromide have a marked emission especially at low wavenumbers.

From this we conclude that, because of their spectral features, the metals tested are very suitable as supports. Platinum is particularly useful because of its low re-

I -

W +

qs_ %

l I I I o 1 2

Eo/E1 FiG. 3. Effect of the support on band intensity in b arrange- ment.

Ec/En

0 C _ _ C ol

4000 3000 20100 ~ I 1500 10100 500 cm-1

Fro. 4. Emission spectra at 300°C of: a, brass; b, alu- minium; c, iron; d, platinum; e, potassium bromide; and f, glass, under the same conditions, with the Nernst glower as reference.

Z O

O~

W

I I I

1000 800 600 400

cm-1

FIG. 5. Emission spectra of copper sulfate at 250°C obtained with a temperature variation of :=t=l°C (a) and ::k5°C (b).

APPLIED SPECTROSCOPY 595

which really do not exist. On the other hand, it is clear from our experiments that a sample temperature varia- tion of about :t:: l°C eliminated these effects.

E. Sample Preparation

Two factors need to be borne in mind when preparing the crystalline solid samples on which emission spectra were recorded, namely the degree of powder fineness and the layer thickness, both of which influence the spectra. To ascertain what effect these two factors have on the quality of the spectra, two series of experiments were carried out on samples kept at the same tempera- ture under identical conditions.

The layer thickness effect on several copper sulfate samples is shown in Fig. 6. Each sample was prepared with powder with a mean crystal size of 10~. Layer thicknesses were measured microscopically, the support plane and outer layer surface being focused in turn. Repeat measurements at several points of the layer gave a mean value for the thickness. From Fig. 6 it may be observed that the layer thickness effect on both band intensity and band resolution is very clear and is such that the quality of spectra increases visibly as the layer thickness decreases. Such a correlation was found for all

2,

l

I 4

1500 1000 5OO cm-1

Fro. 6. Emission spectra of copper sulfate for different layer thicknesses: a, 100 t~; b, 25 tL; c, 10 t~.

1500 1000 ' 5O0 Cm -1

Fro. 7. Emission spectra of copper sulfate of different mean crystal sizes: a, 200 ~; b, 100 u; c, 30 t,; d, 10 t~.

the solid compounds examined. We may reasonably de- duce that the quality of spectra is greatly dependent on powder layer thickness.

The powder fineness effect is shown in Fig. 7, which reports some spectra obtained from copper sulfate powders of different mean fineness and of the same layer thickness. Fig. 7 shows that crystal size is a very im- portant factor in achieving good quality spectra, as was found for all the solid samples investigated. It may therefore be supposed that powder fineness is not only important in the case of absorption techniques but also in that of emission techniques, and is a determining factor in the recording of good quality spectra.

II. SOME APPLICATIONS OF THE TECHNIQUE

To illustrate the applications of the above techniques, emission spectra for some compounds are reported in comparison with the corresponding absorption spectra gleaned from the literature.

The emission spectra of stoichiometric vanadium oxides, copper sulfate, and silver nitrate are discussed in detail. These compounds were chosen because their reactivity with alkaline halides, especially above room temperature, does not allow absorption spectra to be obtained. Moreover, complex experimental contrivances must sometimes be devised, as shown later. These diffi- culties are completely overcome by emission techniques.

A. Vanadium Oxides

The absorption spectra of vanadium oxides V203, V20~, and V205 at room temperature were published in a previous note? The spectrum of V205 was reported also by Frederickson and Hausen 9 and in a series of papers by Japanese workers. ~°-'3 At room temperature these oxides are stable, while above 100°C they react rapidly with alkaline-halide supports. Even at this temperature range, the recording of their absorption spectra becomes nearly impossible. On the other hand, their spectroscopic behavior up to about 500°C is im- portant for the study of their catalytic activity in oxidation reactions.

Emission spectra of the oxides in air at 200 and 400°C, with platinum as support, are reported in Figs. 8, 9, and 10. Emission peak wavenumbers are summarized in Table I.

At 200°C both the number of bands and the band frequencies correspond exactly to those of the absorption spectra at room temperature. At higher temperatures

I I I I

1000 800 600 400 cm-1

FIo. 8. Emission spectra of V~O3 at 200°C (a) and 400°C (b).

$96 Volume 26, Number 6, 1972

g

J a , c _ _ y . I I I I

1000 800 600 400 cm-1

FIG. 9. Emission spectra of V~O4 at 200°C (a) and 400°0 (b).

the vanadia spectrum is unchanged, and this may mean that vanadia does not undergo any modification, which is supported by Kosuge's findings on differential thermal analysis (DTA)24

As the temperature rises above 200°C, V203 and V204 spectra undergo an increasingly rapid and irre- versible change. At 200°C, however, the change is slow, so that a series of spectra may be recorded. The V205 spectrum from both oxides is the last to be ob- tained. At 400°C the rate of change is high enough to allow the vanadia spectrum to be immediately recorded. A discussion of this subject will be undertaken in a following note. I t is only necessary here to mention that the use of emission techniques enables the oxida- tion of V:03 and V~O4 to V205 to be traced and ex- plained with relative ease. This is important if we are to understand the behavior of these oxides in catalytic oxidation reactions and recognize possible intermediate nonstoichiometric oxides, to which the catalytic activity of vanadia has been ascribed by some authors25, ~6

B. Copper S u l f a t e

The recording of the absorption spectra of copper sulfate in the form of KBr pellets or pure powder spread on KBr disks is hindered by a fast double exchange reaction which leads to brown copper bromide even at room temperature. The copper sulfate infrared spectra reported in the literature 17.18 were obtained on nujol mulls with KC1, BaF2, or polyethylene windows, direct contact with the supports thus being avoided. They were recorded at room temperature on partially or totally dehydrated samples. Spectra at the dehydration tem- perature, i.e., between 100 and 200°C, have not yet been recorded. This may be due to some difficulties en- countered using the absorption technique at high temperatures. Using emission techniques between 130 and 400°C, this problem may be solved. In this temper- ature range, two different spectra were recorded, cor- responding to monohydrated (between 130 and 230°C) and anhydrous (between 230 and 400°C) copper sul- fates. These spectra are reported in Fig. 11. Emission peak frequencies and estimated intensities are listed in Table II, together with Ferraro and Walker's absorption values. ~

Monohydrate dehydration is observed at about 230°C in agreement with Wendlandt 's findings. ~9 There-

.P. E

U.I

L I 1 I I

1000 800 600 400 Cm-1

FIG. 10. Emission spectrum of V~O~ at 400°0.

TABLE I. Emiss ion wavenumbers of vanadium oxides (cm-t) . ~

V208 (200°C) 990 s 790 m 490 s (400°C) 1010 vs 800 s 590 w 510s

V~04 (200°C) 980 s 850br 540 w 500s (400°C) 1010 vs 800 s 590 w 510s

V205 (400°C) 1010 vs 980 w 800s 590 w 510s

Abbreviations: s = strong, m = medium, w = weak, br = broad.

I I 3000 2000 15'00 1000 500

cm-1

FIG. 11. Emission spectra of copper sulfate at 180°C (a) and 250°C (b).

fore, emission techniques overcome the difficulties in- volved in absorption techniques and enable spectra of the same quality to be obtained. Thus, here too, it is proved that emission spectra are qualitatively equiv- alent to absorption spectra. Moreover, the difficulties met in absorption spectroscopy no longer arise. Data on dehydration temperatures may be obtained simply.

C. S i l v e r Ni tra te

Emission spectra of silver nitrate recorded at different temperatures are shown in Fig. 12. Table I I I gives emission peak wavenumbers close to absorption peak values for the solid and liquid silver nitrate reported in the literature. ~°-~2 Silver nitrate gives a fast reaction with the alkaline halide supports. The absorption spectra reported in the literature were recorded using

APPLIED SPECTROSCOPY 597

TABLE II. Emission spectra of copper sul fate compared to absorption spectra. ~

TABLE III. Emiss ion spectra of s i lver nitrate compared to absorption spectra.~

Monohydrate salt (cm -1) Anhydrous salt (cm -1) Emission Absorp- Emission 21Absorption (130°C) tion 20 (1 6 0 °C) (220°C)

Emission spectra Absorption Emission Absorption (180oC) values '7 spectra (300°C) values ~7 2160 m 2160 m

2020 m 2020 m 1750 s 1760 s 1750 m 1745 1755

2000 w 2100 m 1400 m 1430 vs 1420 s 1448 1900 m 1333 1390 1395 1750 w 1340 1310

1650 w 1620 vw 1650 m 1260 s 1230 s 1270 s 1520 s 1520 m 1540 m 1070 m 1070 m 1070 w

1420 w 1015 m 1015 m 1030 s 1180 m 1190 s 1220 m 1215 sh

1153 s 1085 s

1068 1042 1003

800 s 798 800s 800 vs 780 w 782 790 w 735 s 750 740 sh 740

962 s 715 s 728 720m 720 m 727 709 713

680w 672 670 w 704 m

613 m ~ Values in em-L Abbreviat ions as in Table I. 593 m

500m 395m 345m

g

E W

l l 0 0 s 1090m 1060 s 1075 s

1015 s 970m 840w 863m 795m 800m 670m 675m 700 s 625m 632m 610 s 590m 598m 590 s 550 w 550 vw 460 s 485m 495 s

410 m 390m 330 s

300m 299m 305w

~Abbrevia t ions as in Table I.

2000 1500 1000 500 Cm-1

Fro. 12. Emission spectra of silver ni t ra te at 130°C (a), 190°C (b), and 220°C (c).

single crystals for solid samples is and attenuated total reflectance (ATR) and reflection techniques for liquid samples.2t, 22 Fig. 12 shows that up to about 160°C silver nitrate spectra are nearly equal to the absorption spectrum at room temperature recorded by James and Leong. 20

At 160°C a modification takes place wlfich leads to spectrum B. A second modification at about 220°C leads to spectrum C, which corresponds to the fused salt spectra recorded by reflection 2~ and ATR 21 techniques.

1025 1029 1015 800 800

695

Using DTA, Ropoport and Pistorius 23 established that silver nitrate has a crystalline transformation at 159°C followed by melting at 212°C. Therefore, emission tech- niques allow a detailed and accurate study of both crystalline and phase transitions (see Fig. 12).

III. CONCLUSIONS

The above examples allow us to conclude that de- tailed emission spectra may easily be recorded. They agree with absorption spectra to a large extent. The temperature range in which emission techniques are applicable is very interesting both for applied research (e.g., the study of catalytic activity) and theoretical problems (e.g., the study of phase transitions). Used in conjunction with DTA and thermogravimetric analy- sis (TGA), complete sets of data on solid behavior above room temperature could be obtained. Moreover, as in the case of silver nitrate, the study of melting at high temperatures by recording infrared spectra is shown to be possible.

1. It . J . Low and H. I. Inowe, Anal. Chem. 35, 2397 (1964). 2. H. J . Low and H. I. Inowe, Can. J . Chem. 43, 2047 (1965). 3. H. J . Low and I. Coleman, Spectrochim. Acta 22, 369

(1966). 4. I. Coleman and H. J. Low, Spectrochim. Acta 22, 1293

(1966). 5. M. Gebbie, G. Roland, and L. Delbonille, Nature 191,264

(1961). 6. R. P. Eischens and W. A. Pliskin, Advance. Catalysis 9,

1 (1958). 7. J . M. Hunt , 1VL P. Wisherd, and L. C. Bonham, Anal.

Chem. 22, 1478 (1950). 8. G. Fabbr i and P. Baraldi, Anal. Chem. 44, 1325 (1972). 9. M. L. Frederickson and D. Hausen, Anal. Chem. 35, 818

(1963). 10. Y. Kera, S. Teratani , and K. t t i ro ta , Bull. Chem. Soc.

Japan 40, 2458 (1967). 11. Y. Kera and K. Hirota, J. Phys. Chem. 73, 3973 (1969). 12. K. Terama, S. Teranishi, and S. Yoshida, Bull. Inst . Chem.

Res. 4-5, 185 (1968). 13. K. Terama, S. Yoshida, S. Ishida, and H. Kakioka, Bull.

Chem. Soc. J apan 41, 2840 (1968).

5 9 8 Volume 26, Number 6, 1972

14. K. Kosuge, J. Phys. Chem. Solids 28, 1613 (1967). 15. G. L. Simard, J. F. Steger, R. J. Arnott, and L. A. Siegel,

Ind. Eng. Chem. 47, 1424 (1955). 16. V. Satava, Coll. Czech. Chem. Commun. 24, 3297 (1959). 17. J. 1~. Ferraro and A. Walker, J. Chem. Phys. 42, 1278 (1965). 18. L. Ben Dor and R. Margalith, Inorg. Chim. Acta 1, 49

(1967). 19. W. W. Wendlandt, Anal. Chim. Acta 27, 309 (1962).

20. D. W. James and W. H. Leong, J. Chem. Phys. 49, 5089 (1968).

21. J. P. Devlin, K. Williamson and GG. Austin, J. Chem. Phys. 4-4, 2203 (1966).

22. J. K. Wilmshurst and S. Senderoff, J. Chem. Phys. 35, 1078 (1961).

23. E. Ropoport and R. Pistorius, J. Chem. Phys. 44, 1514 (1966).

The Vibrational Spectra of Cyanoacetic Acid and Sodium Cyanoacetate

Deepali Sinha and J. E. Ka ton

Department of Chemistry, Miami University, Oxford, Ohio 45056

(Received 4 M a y 1972; revision received 26 June 1972)

The complete vibrational spectra of cyanoacetic acid and sodium cyanoacetate have been re- corded. A tentative vibrational assignment for both molecules is proposed. The results appear to be most consistent with a hydrogen-bonded polymer structure of cyanoacetic acid. The marked effect of temperature on the infrared spectrum of the acid has been explained in terms of an order-disorder transition involving the position of the bydrogen atoms forming the hy- drogen bonds in the crystal. INDEX HEADINGS: Cyanoacetic acid; Infrared spectra; Raman spectra; Molecular structure; Hydrogen bonding.

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

The vibrational spectra of carboxylic acids as a class have been a subject of interest for many years. Although they have been studied by numerous investigators, de- tailed analysis of the spectra has been carried out for only a few. Though carboxylic acids are generally ex- pected to exist as hydrogen-bonded dimers in their condensed phases, some exist as hydrogen-bonded polymers?, 2 Thus, it is of interest to investigate the structures of simple substi tuted carboxylie acids in their condensed phases. The structures of iodoacetic acid 3 and bromoacetic acid 4 have already been studied in this laboratory. This paper reports the vibrational spectra of eyanoacetic acid and sodium cyanoacetate along with their proposed assignments. The assignments have been made by comparing the spectra with the infrared spectra of cyanoacetyl chloride and cyanoacetamide; by comparison to the assignments of iodo- and bromoacetic acids; and by utilizing well known group frequencies. The detailed assignment should be considered as tenta- tive, but the major features are well founded. The results are most consistent with a hydrogen-bonded polymer structure of cyanoacetic acid.

I. E X P E R I M E N T A L M E T H O D

Commercial cyanoacetic acid (Eas tman Organic Chemical) was recrystallized from ether. Sodium cyano- acetate was prepared by reacting stoichiometric quanti- ties of cyanoacetic acid and sodium carbonate in water

and crystallized by evaporation of the water. The product was thoroughly washed with ethanol and dried in a vacuum. Cyanoacetyl chloride was prepared by the method described by Schroeter and Seidler, ~ and com- mercial cyanoacetamide (Aldrich Chemical Co.) was purified by decolorization with charcoal and crystalliza- tion from water.

Infrared spectra of cyanoacetic acid (Nujol mull and hexachlorobutadiene mull), sodium cyanoacetate (Nujol mull, hexachlorobutadiene mull and KBr pellet), cyanoacetyl chloride (capillary film), and cyanoacet- amide (Nu]ol mull and hexachlorobutadiene mull) were recorded on a Perkin-Elmer model 180 infrared spec- t rophotometer which had been previously calibrated with indene. 6 The estimated maximum frequency error is ~ 2 cm -1. The acid is not sufficiently soluble in CC14, CS2, C6H6, or CHC13 to allow a solution infrared spectrum to be obtained. Far infrared spectra (Nujol mull) were recorded on a Digilab FTS-14 interferometer. R a m a n spectra of the solid acid were obtained on a Spex-Ramalog instrument and a Cary model 83 laser R a m a n spectrometer. Those of the salt were obtained on Cary model 83 and Cary model 81 laser Raman spectrometers. All of the compounds were studied both at room temperature and at near liquid nitrogen tem- perature in the mid-infrared region, and the R a m a n spectrum of the acid was obtained at both these tem- peratures. The infrared spectrum of cyanoacetic acid (Nujol mull) was also studied a t 5 and --69°C using ice-water and dry ice-acetone as cooling agents. Tem-

Volume 26, Number 6, 1972 APPLIED SPECTROSCOPY 599