Infra-red spectra of some vinyl and ethyl compounds of mercury, cadmium, zinc, tin and phosphorus

Spectrochimica

Acts, 1050, pp. 300 to 377. Pergnmon

I&a-red

Press Ltd.

Printed in Northern

Ireland

spectra of some vinyl and ethyl compounds of mercury, cadmium, zinc, tin and phosphorus H. D. KAESZ*~

Mallinclcrodt

Chemical

Laboratory,

and F. G. A.

Harvard

(Received

University,

23 Jawmy

STONE Cambridge,

Massachusetts

1959)

Abstract-The infrared spectra of divinylmercury, ethylvinylmercury, diethylmercury, divmylzinc, diethylzinc, diethylcadmium, tetraethyltin, tetravinyltm, triethylphosphine and trivinylphosphine have been examined in the liquid state over the region from 650-3500 For each spectrum many of the vibrational frequencies have been assigned. In the cm-l. 1100-3000 pattern the vinyl ETHYL

Periodic

cm-1

region

which is almost or to the ethyl

the

vinyl

independent

and

the

ethyl

of the nature

compolmds

each

of the metal

show

a characteristic

or metalloid

band

atom bonded

to

groups.

derivatives of metals and metalloids of elements of the main groups of the Classification have long been known, but only comparatively recently

have vinyl

compounds of metals and metalloids been prepared in any number. vinylating reagents has been the chief cause of this situation, but recently a number of these reagents have been made. NORMANT [l] prepared [4] have been made in vinyl Grignard, and divinylmercury [ 2, 31 and divinylzinc this laboratory. A new method for preparing sodium vinyl in good yield has also been reported [5]. A natural consequence of discovery of these new compounds has been the isolation of vinyl derivatives of other elements, e.g. Sn [6, 71, Ge [S], B [2, 91, P [lo, 111 and Pb [12]. Divinylmercury was made in this laboratory several months before we reported it in the literature [2, 31. Delay in reporting divinylmercury occurred because we were not obtaining the compound in a pure state. This became evident on examination of the infra-red spectra of various samples of divinylmercury prepared on different occasions by treating mercury-II chloride with vinylmagnesium bromide. These spectra, taken with a liquid-film cell, oftendiffered from each other, but in varying degrees. Differences were especially obvious in the 3300-2700 cm-l and 1600-1100 cm-l regions of the spectrum. Despite this, all samples analysed well (C, H, Hg), and distilled at reproducible temperatures at constant pressure. However, although a particular sample of divinylmercury had an infra-red Lack

of suitable

* This paper represents a part of the work submitted by H. D. KAESZ to the Graduate School of Harvard University in partial fulfillment of the requirements for the degree of Doctor of Philosophy. t Public Health Predoctoral Research Fellow of the National Heart Institute. [l] H. NORMANT, Compt. rend. 239, 1510 (1954). [2] B. BARTOCHA, F. E. BRINCKMAN, H. D. KAIXZ and F. G. A. STONE, J. Chem. Sot. 116 (1958). [3] B. BARTOCEA and F. G. A. STONE, 2. Nalurforsch. 13b, 347 (1958). [4] B. BARTOCHA, H. D. KAESZ and F. G. A. STONE. 2. AWwfors& In press. [6] R. G. ANDERSON, M. B. SILVERMAN and D. M. RITTER, J. Org. Cltem. 23, 750 (1958). [6] S. D. ROSENBERG, A. J. GIBBONS and H. E. RAMSDEN, J. Am. Chem. Sot. 79, 2137 (1957). [7] D. SEYFERTH and F. G. A. STONE, J. Am. Chem. Sot. 79, 515 (1957). [8] D. SEYFERTH, J. Am. Chem. Sot. 79, 2738 (1957). [9] T. D. PARSONS, M. B. SIL~ERM~ and D. M. RITTER, J. Am. Chem. Sot. 79, 5091 (1957) [lo] H. D. KAESZ and F. G. A. STONE. J. Org. &em. In press. [ll] L. MAIER, D. SEYF~RTH, F. G. A. STONE and E. G. ROCHOW, J. Am. Cl&em. Sot. 79, 5884 (1957). [12] E. C. JUENQE and S. E. COOIE, Abstracts of Papers, 135th Meeting American Chemical Society, Boston (1959). 360

Infre-red

spectra

of some

vinyl

and

ethyl

compounds

of mercury,

cadmium,

zinc,

tin

and

phosphorus

spectrum differing from another, when the two samples were used to make a vinyl derivative of another element, the new compound not only analysed corClearly the substance contaminating our rectly, but had a consistent spectrum. divinylmercury was not affecting its use as a vinylating agent; nor significantly Wave number,

1

6040 20

J

I

II

(W&Hg liquid 0.015

film mm

I' J .

II

cm-’

/I I /" 1

.J

\ LJ

/

108

80 60

80 60 40 20 0 CL Fig.

1

affecting its boiling point, or analytical data. Because of this it seemed likely that the contaminant of our divinylmercury was the ethyl compound. This idea was amply confirmed when a few different spectra were compared. For example, relative intensities of certain bands, those of 1468, 1430, 13'i5, 1232 and 1188 cm-l, varied in the spectra of the different samples of “divinylmercury” prepared. On the other hand, in the spectrum of vinylethylmercury (Fig. 1) these five 4

361

H. D. KaEsz

and F. G. A. STONE

-Furthermore, this same series of bands was bands became especially prominent. also prominent in the spectrum of an authentic sample of diethylmercury (Fig. 1). SEYPERTH [l3, 141 has shown that a number of reagents will preferentially A similar preferential cleavage cleave vinyl groups from vinylethyltin compounds. of vinyl groups accounts for the fact that our impure divinylmercury could give pure vinyl compounds of certain other elements. Ethyl-group contamination of our divinylmercury arose because the vinyl bromide* used to make vinyl Grignard contained appreciable quantities of ethyl bromide. We have recently reported [4] a method for removing ethyl bromide from vinyl bromide, and purified vinyl bromide was used in our preparations of spectrum of pure divinylmercury [2, 31 and divinylzinc [4]. In the infra-red divinyl mercury, the various bands mentioned above (1468-1188 cm-l) observed in the spectra of impure samples vanish, or become very weak (Fig. 1). As a consequence of the ethyl contamination of our first samples of divinylmercury and our use of infra-red spectra to demonstrate this fact, we became interested in the spectra of vinyl and ethyl compounds in general. Such spectra are of interest for identification purposes, and could conceivably supply information about structure and the nature of chemical bonds. The initial treatment of spectra reported here frequently involves tentative band assignments which are Better data through accumulation of more information on often incomplete. similar molecules should lead to complete assignments. In many instances, for a particular type of compound the spectra were strikingly similar over the region studied, e.g. (CH,:CH),Hg and (CH,:CH),Zn; or (C,HJ,Cd and (C,H,),Zn.

Experimental (a) Preparation

of vinyl

and ethyl derivatives

of the metals and metalloids

Using either pur
D. SEYFERTH, J. Am. D. SEYFERTH,N~~WIU~.W.

Chem. Sot. 79, 2133 (1957). 44, 34 (1957).

362

claiming that Matheson

99.0 per cent most Matheson Company has

Infra-red

spectra

of some

vinyl

and

ethyl

compounds

of mercury,

cadmium,

zinc,

tin

and

phosphorus

All spectra are those of liquid films which were held in a demountable cell In the case of air-sensitive compounds with silver spacer of 0.015 mm thickness. such as those of phosphorus, zinc and cadmium, the cell was loaded under nitrogen in a dry box.* In this manner oxidation was reduced to a minimum, but perhaps not completely avoided in the case of divinylzinc. Partial oxidation of organozinc compounds would result in the appearance of a strong absorption in the region 1030-l 140 cm-l, due to the C-O stretch in either R-Zn-OR or Zn(OR) 2. These compounds are formed when zinc alkyls come into contact with a deficiency Owing to its similar, though diminished, reactivity the same of oxygen [15]. behavior but to a lesser degree might be expected for diethylcadmium. Absence of a strong band in the region 1030-l 140 cm-l in the infra-red spectrum of diethylcadmium, and presence of only a weak shoulder at 1025 cm-r in the spectrum of diethylzinc attests to the fact that oxidation has been held to a minimum for these substances. In the case of divinylzinc, however, the whole region 920-1050 cm-l indicates a much greater relative absorption intensity than that observed in the spectra of any of the other alkyls or vinyls of the metals. This would arise from the absorption of the Zn-O-R and (R-O),Zn systems, in addition to the normal bands of that region due to divinylzinc alone. This supports tentative assignment of the 1035 cm-l band in the spectrum of divinylzinc as indicating Zn-O-C bonds [16]. As the presence of this absorption did not interfere with our main purpose, no attempt was made to see whether this band really belonged to divinylzinc, or whether it could be eliminated by adopting even greater precautions in loading the cell. Band assignments presented in Tables l-9 were made by reference to BELLAMY [17], to JONES and SANDORPY [ 151 and to NAKAGAWA[~~], and to papers cited by these authors. The following abbreviations are used in the Tables. Band characteristics and relative intensities w weak m medium s strong c possible combination or overtone band

v very sh shoulder b broad

Scale of relative intensities in percentage transmission

(%I

vvw 90-95 VW 55-90

m 30-60 s

O-30

w 60-55

vs band center off the paper Noise level corresponds to about 2 per cent. * Professor P. D. BARTLETT was kind enough to lend us a dry box which could be evacuated and then refilled with prepurified nitrogen. This cycle was repeated two or three times so as to eliminate as completely as possible all traces of oxygen. [15] G. E. COATES, Organometo.ZZic Compounda, Methuen, London (1956). [IS] J.V. BELL, J. HEISLER, H. TANNENBAUM and J. GOLDENSON, And. Chem. 25, 1720 (1953). [17] L. J. BELLAMY, The Infru-red Spectra of Complex Alolecules (2nd. Ed.) Methuen, London (1956). [18] R. N. JcIvns and C. SANDORFY, Technique of Organic Chemistry (Edited by A. WEISSBEROER) Vol. IX, p. 247. Interscience, New York (1956). [19] I. NAKAQAWA,N~~~~~ Kugaku Zm& 77, 602 (1956).

363

H. D. KAESZ

and F. G. A. STONE

rock = deformation, in-plane, in-phase scissor = deformation, in-plane, out-of-phase wag = deformation, out-of-plane, in-phase twist = deformation, out-of-plane, out-of-phase The vibrational frequencies for diethyland divinylmercury are listed in Tables 1 and 2. The spectra are shown in Fig. 1. The Raman spectrum of diethylmercury has been reported [20], and the frequencies are included in Table 1. C-H

deforlnatiolzs

Wave 3000 I

10

2000

1500

number

cm-’

1200

1000 I

900 I

800

750

700

650

nI

\A/

7

/

\

‘20 108 80 60 40 20

80 60 40 20 O

I

I 3

I

I 5

I

I 7

I

I 9 P Fig.

I

I 11

I

13

I

I 15

I

2

For purposes of further comparing the series of bands characteristic of the vinyl group with those characteristic of the ethyl group (vide i@a), the spectra of ethylvinylmercury and of phenylvinylmercury are also given (Fig. 1). The infra-red spectra of diethyl- and divinylzinc, and of diethylcadmium are shown in Fig. 2. Vibrational frequencies for the zinc compounds are listed in Tables 3 and 4 respectively. Table 3 lists also the Raman frequencies of diethylzinc [20]. Vibrational frequencies in liquid diethylcadmium are given in Table 5. Vibrational frequencies of tetravinyland tetraethyltin are recorded in Tables 6 and 7. The spectra of the tin compounds are given in Fig. 3. [20] [Zl]

N. GOPALA PAI, G. F. REYNOLDS,

Proc. Roy. Sot. London A 149,29 (1935). R. E. DESSY and H. H. JAFF& J. Org. Chem.

364

23, 1217

(1953).

I&a-red

spectra

of some

vinyl

and

ethyl

compounds

of mercury,

cadmium,

zinc,

-

tin

> 2-

i-

--9

-40

--Q

ON NOISSIY

365

I v kll %

and

phosphorus

H. D. I(4Es.z

and F. a. A. STONE

NOISSIWSNVU%

366

Infm-red

spectra, of some vinyl and ethyl comp6unda

The infrared spectra are shown in Fig. 4. Table The Raman spectrum of GUNDLACH [22], and the vibrational frequencies in

of mercury, cadmium,

zinc, tin and phosphorus

of Methyland trivinylphosphine in the liquid phase 8 lists the vibrational frequencies of trivinylphosphine. triethylphosphine has been reported by BAUDLER and frequencies are listed in Table 9 together with the the i&a-red, obtained in this work.

Discussion Band assignments listed in Tables l-9 should be regarded as tentative, although in the region from 3000 cm-l to about 1100 cm-l they are fairly reliable. As is well known, in this region frequencies are due to vibrations of individual groups or specific bonds in the molecule, and are more or less independent of the structure of the molecule as a whole. This, of course, is borne out by the comprehensive assignment correlations that have successfully been made [ 17, 18-J for organic Below 1200 cm-l spectra arise more from molecules of widely varying structure. skeletal frequencies, and are much more dependent on mass effects and overall molecular structure. CM-’

3500

3000

II MICRONS

2500

17po

,

,500

‘4/O

“p”

l2po

II00

I

:

6

-----

ETHYL

-

VINYL

=c

=dH,

C”, ;dH

Fig. 5. Summary of the group-characteristic band patterns of ethyl- andvinyl-sub&it&d compounds.

This is fully confirmed by the spectra reported here. Above about 1100 cm-l there is a striking similarity in the spectra of Et,Hg, Et,Zn, Et&d, Et,Sn and E&P; and in the spectra of (CH,:CH),Hg, (CH,:CH),Zn, (CH,:CH),Sn and (CH,:CH),P. The vinyl and the ethyl groups both have their characteristic band pattern. These patterns are illustrated in Fig. 5. Small frequency shifts due to [22] M. BAUDLER

and H. GENDLACH,

Naturwiss.

42, 152 (1955).

367

H. D. KAESZ and F. G. A. STONE Table Freq. (cm-l)

Raman* Relative intensity

140 212 259 329 486 562 633

1. Vibrational

frequencies

in liquid

diethylmercury

Infrared freq. (cm-l)

Assignment

1D 2 3 0 8 0 OD 662 s 671 s I

958

2

1008 1055

3 2

1178

6D

942 959 998 1017

CH, rock

wbsh m wbsh I 6

C-C stretch C-CH, rock

1188 6

C-CH,

rock

1232 m

CH, wag

1370

1

1305 w 1375 6

CH, twist CH, deformation

1421

3

1430 6

CH, scissor

1455

3

1460 ssh 1468 I

2857 2896 2942

1 3 1

CH, scissor I CH, deformation

1605 1680 1885 1915 2155 2390 2560 2625 2710 2750

w w vw vw w w w w wsh m

c c c c c c c c c c

2850 2900 2930 2975 3180

ssh vs vs vs wsh

CH, CH, CH, CH,

* See reference [20].

368

stretch stretch stretch stretch

symmetrical

anti-symmetrical

m-phase symmetrical out-of-phase anti-symmetrical

Mm-red

spectra of some vinyl and ethyl compounds

Table Freq. * (cm-l) 938 s 1010 8 1250 s 1400 m

2. Vibrational

frequencies Freq. t (cm-l) 948 to 943 1008 1165 1255 1398 1465 1588 1650 1740 1793

in liquid

zinc, tin and phosphorus

divinylmercury Assignment

bs

CH, wag

s w s s w w VW vw vw

CH wag

1890 m 1955 vw 2025 w

overtone c overtone

2260 2660 2805 2850 2900 2980 s

of mercury, cadmium,

CH rock CH, rock

2 x 943 2 x 1008

w VW w msh msh

2975 ssh

CH, stretch

3010 9

CH stretch

3100 s

CH, stretch

symmetrical

3040 m 3200 w * From reference [21]. t This work.

369

anti-symmetrical

H. D I-s.2

Table Raman* Relative Freq. (cm-l) intensity ill(?) 176 255 476 533 579 938 990

3. Vibrational

and F. G. A.

frequencies

STONE

in liquid

diethylzinc

Infrared freq. (cm-l)

&&nment

2 2 2 5 1 2 2 2

C-C stretch C-CH, rock

950 m 988 w8 1 922 1025 wsh

C-O

stretch

1176 w

C-CH,

1225 m

CH, wag

in ZnOR impurity(?)

rock

1175

5

1336

0

1403

1

1373 m 1415 w

CH, deformation CH, scissor

1458

1

1465 m

CH, ecissor I CR, deformation

2125 vvw

2879

3

symmetrical

anti-symmetrical

c

2735 w 2825 msh 2850 to 5 2998 1

I CH, CH, CH, CH,

+ See reference [ZO].

370

stretch stretch stretch s+etch

in-phase sy&netrical out-of-phase anti-symmetrical

Infra-red

spectra of some vinyl snd ethyl compounds

Table

4. Vibrational freq. (cm-l)

of mercury, cadmium,

frequencies

in liquid

zinc, tin and phosphorus

divinylzinc

Assignment -

880 m 952 vbvs 990 s 1035 8

CH, wag CH wag C-0 stretch

1258 8

CH rock

1390 8 1458 w

CH, rock impurity

1565 m

C=C

in ZnOR impurity

stretch

1638 w 1905 m 1980 w 2070 VW

overtone overtone overtone

2240 w 2360 VW

c c

2630 VW

c

2900 2930 3000 3100

CH, stretch CH stretch CH, stretch

s 8 6 m -

371

2 x 952 2 x 990 2 x 1035

symmetrical anti-symmetrical

(?)

H. D. KUESZ and F. G. A. Table

5. Vibrational

STONE

fret fuencies in liquid

Freq. (cm-l)

diethylcadmium

Assignment

063 m 670 m 1

CH, rock

922 m 954 8 1002 8 1

C-C stretch C-CH, rock

1157 8 1186 m I

C-CH,

1226 m

CH, wag

1373 8

CR, deformation

1421 m

CH, scissor

1465 s

CH, deformation

1600 vw

C

2210 w

C

2730 w

C

2840

CR, stretch CH, stretch

m-phase . symmetrical

CH, stretch CR, stretch

out-of-phase anti-symmetrical

to

1

symmetrical

anti-symmetrical

8

3010 Table

rock

6. Vibrational

frequencies

Freq. (cm-l) 948 1000 1248 1397 1460 1588 1910 1960 2010 2240 2910 2955 3025 3125 3325

vs vs s 8 w w m w w w 8 8 s w VW

in liquid

tetravinyltin

Assignment CH, CH CH CH,

wag wag rock rock

C=C stretch overtone 2 x 948 C

overtone

2 x 1000

C

CH, stretch CH stretch CH, stretch

372

symmetrical anti-symmetrical

Infrared

spectra

of some vinyl

Table

and ethyl

7. Vibrational

compounds

of mercury,

frequencies

cadmium,

in liquid

Freq. (cm-l)

zinc,

tin

tetraethyltin

Assignment

673 660

vs vs I

813

vvw

945 960 990 1005 1015

s s mbsh vs vs

1118 1188 1235 1257 1380 1428 1465 1472

w s m vwsh 8 s ssh vs I

1600 1679 1695 1885 1905 2150 2385 2560 2620 2720 2755

ww ww vvw vvw vvw w vvw vvw vvw ww w

2850

ssh

to 3005 2900 3180

8 I vwsh

CH,

I

C--C C-CH,

rock

stretch rock

C-CH, rock CH, wag CH, CH, CH, I CH,

deformation scissor scissor deformation

symmetrical

anti-symmetrical

C C C C C C C C C C C

CH, CH, CH, CH,

373

stretch stretch stretch stretch

in-phase symmetrical out-of-phase anti-symmetrical

,

and

phosphorus

H. D. KAESZ and F. G. A.

Table S. Vibrational

frequencies

STONE

in liquid

trivinylphosphine

I

Freq . (cm-l) 663 s 670 s 1, 102 to vbvs 71s J

Assignment

P-C bond C=C twist skeletal vibrations

91s 948 982 1020 1262 1392 1595 1850 1905 1965 2215

vs vs vs s s s 6 w w vw w

CH, wag in-phase ‘CR wag CH, wag out-of-phase

2970 3005 3095 3200

m s 8 VW

CH, stretch CH stretch CH, stretch

CH rock CH, rock out-of-phase C=C stretch overtone 2 x 925 overtone 2 x 948 _ overtone 2 x 982 C

374

symmetrical anti-symmetrical

Infra-red

spectra

of some Table

Raman* Freq. (cm-l)

vinyl

and

ethyl

compounds

9. Vibrational

frequencies

of mercury, in liquid

cadmium,

zinc,

tin

and

phosphorus

triethylphosphine

Infrared* Relative intensity

Assignment

freq. (cm-l) -

249 278 306 333 368 410 619

1 1 1 5 3 1 8

669 697

7 4

757

2

934 982

1 6

1041

4

1243 1260 1301 1350 1384 1425

4 4 3 3 3 6

1464

7

2736

1

2821 2873 2896 2926 2963

2 10 8 10 9

* From

reference

655 657 670 690 717 748

m 1, m m s m 9

765

s I

975 1003 1023 1043 1095 1185

m m m s vs w

1231 1245

m msh

1380 1423 1458 1468

skeletal modes P-C stretch CH, rock

G-C

stretch

CCH,

I

rock

CH,

wag

s s 8 s

CH, CH,

deformation scissor

symmetrical

CH,

deformation

anti-symmetrical

2220 2350 2430

VW VW VW

C

2750 2845 2900 to 2998

VW m 9

C

C C

CH, CH, CR, CH,

s I

[22].

375

stretch in-phase stretch.symmetrical stretch out-of-phase stretch anti-symmetrical

-

H. D. KAESZ

and F. G. A.

STONE

100 I

I200 I

\

/-f

60%El2Hg (CH2

40-

20

:‘iH,2

-

4

60

Hg

L

7 %

\

1’

60-

9.9

L

%

60-

40-

2020

so

%

60

6040 40

20

eo-

50.

I % !!!!I!

2.5

6.5

6.5

and diethyl-mercury

mixtures.

MICRONS

Fig.

6. I&a-red

spectra

of divinyl-

376

Infrared

spectra

of some vinyl

and

ethyl

compounds

of mercury,

cadmium,

zinc,

tiu’and

phosphorus

mass effects will cause these absorptions to move, but not by such a displacement In this laboratory the band patterns (Fig. 5) as to disturb the overall pattern. Fig. 6 shows how this has been done for have been used for analytical work. Authentic mixtures of the two mercury mercury-divinyl and -diethyl mixtures. compounds were made from the pure compounds, and the infra-red spectra of these mixtures were taken. Relative band intensities, especially in the 7-9 ,U region, were used to determine the extent of ethyl contamination of various divinylThis infra-red analytical technique has also been used in this mercury samples. laboratory to determine whether the vinyl groups in vinyl compounds become saturated in certain chemical reactions. It is interesting to note that although there is a very significant difference in the 3000-1100 cm-l region between the spectra of vinyl metal or vinyl metalloid compounds on the one hand and their ethyl analogs on the other (Fig. 5), there is not a great difference between the spectrum of pure vinyl bromide and the spectrum of vinyl bromide which contains as much as 20 per cent ethyl bromide. Difference in spectra of vinyl and ethyl groups are much more prominent in organometal and organometalloid compounds than they are in vinyl and ethyl bromide because the spectrum of vinyl bromide is perforce taken in the gas phase. In the gas phase bands are broadened and, moreover, rotational fine structure becomes These factors cause the band of an impurity superimposed on the band envelopes. in a mixture to be well camouflaged if the impurity band is located near an absorption due to a principal constituent of the mixture. In the spectrum of a liquid on the other hand, a small peak due to an impurity often can be seen if it is close to a peak due to the major compound. Consequently, except for bands near 3000 cm-l the spectrum of pure vinyl bromide resembles that of a grossly impure sample remarkably well. This is so because every absorption in ethyl bromide save those in the 3000 cm-l- region is paralleled by one for the vinyl bromide, very close by, and usually of greater intensity. Hence a 20 per cent impurity of vinyl bromide in ethyl bromide shows up mwh more prominently than does 20 per cent ethyl bromide impurity in the vinyl bromide. It is interesting to note that a complete analysis of the infra-red spectrum of vinyl bromide has recently been reported by GULLIKSON and NIELSEN [23]. These workers used Matheson “vinyl bromide”, and in their paper [23] quote the Matheson claim that the substance was 99 per cent pure. However, GULLIXSON and NIELSEN detected some impurity bands although they apparently did not know what the impurity was, nor suspect that it was present to such an extent as of vinyl bromide at 2990 cm-l 16-20 per cent. Bands in the reported [23] spectrum (shoulder), 2553 cm-l and 1451 cm-l are due to ethyl bromide impurity. -In addition, due to the presence at the same frequency of an absoiption of ethyl bromide, the band at 3030 cm-l in the GULLIKSON and NIELSEN vinyl bromide spectrum has an enhanced relative intensity. Acknowledgemnt-It made possible

[23]

by the

C. W. GULLIKSON 5

is a pleasure to acknowledge that the work award of a grant (G5106) from the National

and

J.

NIELSEN,

J. Mol.

Speclro.swpy

377

described in this Science Foundation.

1, 158 (1957).

paper

was