Electronic and vibrational spectra and thermodynamic functions of 3- and 4-methoxy benzonitriles

Spectrochimica Acta, Vol. 38A, No. 6, pp. 583-590, 1982 Printed in Great Britain.

0584-8539[821060583-08503.0010 © 1982 Pergamon Press Ltd.

Electronic and vibrational spectra and thermodynamic functions of 3- and 4-methoxy benzonitriles R. K. GOEL* and M. L. AGARWALt Department of Physics, D. N. College, Meerut-250002, India

(Received 23 June 1981) Abstract--The i.r. absorption spectra of 3- and 4- methoxy benzonitriles have been recorded on a Perkin-EImer 521 sPectrophotometer, while the Raman spectrum of 4-methoxybenzonitrile was recorded on CODERG Raman spectrometer T800 triple monochromator. The near ultraviolet absorption spectra of both the molecules in vapour phase have been recorded on Medium Quartz Hilger spectrograph and that of 4-methoxybenzonitrile on DK-2A ratio recording spectrophotometer also. The assignment of fundamental frequencies to various modes of vibration have been proposed and on the basis of free internal rotation and assigned vibrational frequencies, the thermodynamic functions of the molecules have been computed on a VAX-I 1/780 computer. The analysis of the electronic spectra has been given in terms of fundamentals, their combinations and overtones. 4-Methoxy benzonitrile has exhibited two band systems corresponding to tAlg-tB2u(2600A) and IAlg-IBlu(2100,~) system of benzene, while 3-methoxybenzonitrile exhibited only the former system. The red shift of 0,0 bands has been discussed.

INTRODUCTION

EXPERIMENTAL

The i.r. and Raman spectra of benzonitrile, its mono- and di- derivatives have been studied in detail by various w o r k e r s [ l - l l]. The vibrational spectra of anisoles and substituted anisoles have been studied extensively[12-16]. Recently CHATTERIEE et al.[17] reported the complete vibrational analysis of para-methylbenzonitrile and TYLLI et aL[18, 19] reported the low frequency vibrations of anisole and its various deuterated analogues. The analysis of the near ultraviolet absorption spectra of benzonitrile and mono-halogenated benzonitriles also appear in literature[20-22]. PADHYE and VARADARAJAN[23] have reported the electronic absorption spectrum of three isomeric toluenitrile where in CH3 group was electron donating and CN the electron withdrawing. The present paper includes the complete assignments of frequencies to various modes of vibration of m- and p-methoxybenzonitriles from their i.r. and Raman spectra, which have not been reported earlier. The study of changes involved in excited state electronic energies due to OCH3 group (electron donating) has also been made with the help of vapour phase near u.v. absorption spectra of these molecules. It also includes the statistically computed thermodynamic properties of these molecules using assigned frequencies assuming hindered internal rotation of the OCH3 group about Caryl-O bond on a VAX-11/780 computer.

The spec-pure chemicals 3- and 4-methoxybenzonitriles (hereafter referred as 3-MB and 4-MB respectively) obtained from M/S Aldrich Chemical Co., U.S.A., which were in liquid and solid phases respectively, were used as such. The i.r. spectra have been recorded on a Perkin-Elmer 521 spectrophotometer in the region 2504000cm 1. The spectrometer was calibrated by running the spectra of a thin sheet of polystyrene. The laser Raman spectra of 4-MB have been recorded on a CODERG Raman spectrometer T800 triple monochromator, using argon laser of wavelength 514.5 nm at I W and slit width 500 microns. The Raman spectrum of 3-MB could not be observed because of its colour. The near ultraviolet absorption spectra of these molecules were photographed on a Hilger medium quartz spectrograph, path length varying from 50 to 150cm and temperature varying from 10 to 100°C. As 4-MB vapour phase spectra gave some indication of some weak bands around 2400 A, this was also tried on Beckman DK-2A ratio recording spectrophotometer with scanning time 100s, using a cell of 10cm path length at temperatures varying between 20 to 55°C.

*Present address: Department of Physics, College of Science, University of Sulaimaniyah, Sulaimaniyah, Iraq. tDepartment of Physics, D. S. College, Aligarh-202001, India. SAA VoL 38A, No. 6---A

583

RESULTSAND DISCUSSION group as a single mass point the 4-MB may be considered to possess C2~ symmetry and 3-MB as C, and as such a 13 particle system will have (12a~+ 10b2) in-plane (a') and (3a2+8b,) out-of-plane (a") vibrations, with the X-axis of the reference system perpendicular to the plane of the molecule and the Z-axis along the para substituents. While all these modes are active in Raman, all except a2 are i.r. active. The fundamental frequencies of 3-MB and 4-MB are shown and correlated with benzonitrile [24] and p-chloroanisole [12] in Table 1 along with the proposed assignment. The position of the observed bands and their analysis in vapour phase near u.v. spectra of 3-MB and 4-MB are given in Tables 2 Assuming

OCH3

584

R . K . GOEL and M. L. AGARWAL

%%%%%~%%

~

I~

~-

~

I

I ~~

~

~_

,..~'1

~.~ I " ' ~

~-

~

I I ~~

& .£

~,~

~-~

I ~

Z [..

l

.~o

o,,1~

I ~

~'#

.~

III

I

I

I

I

I I

III

Electronic and vibrational spectra and thermodynamic functions of 3- and 4-methoxy benzonitriles

,..&

"d

__.~,,d

¢,q

_=

._qo =

<

~

I I

I

I

"T>

= 8,.,..q

°~

.~

1

~

I .-~

~

~

:~

~, ~

"~

" ~

~

"~

"~

= ~'N

585

586

R. K. GOEL and M. L. AGARWAL Table 2. Analysis of the electronic absorption bands of p-methoxybenzonitrile

Intensity*

Position of the bands (cm -I)

Separation from 0,0 band (cm -1)

Assignment

vs vsb mw ms m s s ms m ms ms mw ms mw w

34222 34405 34630 34801 35060 35330 35545 35757 35987 36323 36524 36770 36995 37315 38150

t At~ - 1B2, 0 - 1108 0 - 925 0 - 700 0 - 529 0 - 270 0,0 0+215 0 + 427 0 + 657 0 + 993 0 + 1194 0 + 1440 0 + 1665 0 + 1985 0 + 2820

m ms

38466 38609

0 + 3136 0 + 3279

mw

38951

0 + 3621

w

39172

0 + 3842

(2600/~) s y s t e m 0 - 1108 0 - 925 0 - 925 + 215 0 - 2 x 270 0 - 270 0,0 0+215 0 + 2 x 215 0 + 3 x 215 0 + 993 0 + 1194 0 + 993 + 2 x 215 0 + 1665 0 + 2 x 993 0 + 1665 + 1194 + 215 - 270 -0 + 1665 + 1194 +2×215 0 + 2 x 993 + 1194 +2×215 0 + 1665 + 1194 + 993

41494 41876 42159 42230 42355 42608 42662 42790 42974 43403 43554 43679

0,0 0 + 382 0 + 685 0 + 736 0 + 861 0 + I 114 0 + 1168 0 + 1296 0 + 1480 0 + 1909 0 + 2050 0 + 2185

aAls - tBt = vvs m vw vs vvw vw ms m mw ms m mw

0,0 0 + 382 0 + 685 0 + 736 -0 + 736 + 382 0 + 1168 0 + 1296 0 + 2 x 736 0 + 1168 + 736 0 + 1296 + 736 0 + 3 × 736

*Symbols as given in Table 3.

a n d 3, r e s p e c t i v e l y . T h e a s s i g n m e n t o f t h e f u n d a m e n t a l s to t h e p r o b a b l e m o d e s o f v i b r a t i o n is r e p r e s e n t e d in T a b l e 4, w h i l e T a b l e 5 s h o w s t h e values of thermodynamic functions of these m o l e c u l e s in t h e t e m p e r a t u r e r a n g e 1 0 0 - 1 5 0 0 K . T h e v a r i a t i o n o f e n t h a i p y f u n c t i o n (H°-~oo)/T and heat capacity C ° with absolute temperature a r e s h o w n in Fig. 1 w h i l e t h o s e o f t h e f r e e e n e r g y f u n c t i o n s - ( F ° - E°)/T a n d e n t r o p y S o a r e s h o w n in Fig. 2.

Vibrational spectra The correlation of the presently assigned frequencies with benzonitrile and parac h l o r o a n i s o l e a r e e v i d e n t l y s a t i s f a c t o r y ( T a b l e 1). However, some of the discussions are given below:

al Vibrations. T h e v i b r a t i o n s 1 a n d 12 w h i c h c o r r e s p o n d to a l s ( 9 9 5 ) a n d bl=(1010) m o d e s o f b e n z e n e , u n d e r r e d u c e d s y m m e t r y b e l o n g to t h e s a m e s y m m e t r y t y p e a~ o r a ' a n d a s t h e m a g -

4 - I~B 3-~B 7O 7O

5¸

,~ 4o 3

"4

fO o

0

-

I 200

i 600 Temperature,

I

I

lOOP

1500

K

Fig. 1. Variation of enthalpy function ( H ° - Eg)/T and heat capacity C~p of 3-MB and 4-MB with absolute temperature.

Electronic and vibrational spectra and thermodynamic functions of 3- and 4-methoxy benzonitriles

587

Table 3. Analysis of the electronic absorption bands of m-methoxybenzonitrile

Intensity*

Position of the bands (cm_~)

Separation from 0,0 band (cm_J)

Assignment

34220 34425 34622 34787 35143 35329 35525 35657 35847 35968 36252

0 - 923 0 - 718 0 - 521 0 - 356 0,0 0 + 186 0 + 382 0 + 514 0 + 704 0 + 825 0 + 1109

0 - 923 0 - 718 0 - 923 + 2 × 186 0 - 718 + 2 x 186 0,0 0 + 186 0 + 2 x 186 0 + 514 0 + 514 + 186 0 + 825 0 + 1109

vsb vsb w m s s m s mw m m

s--strong; ms--medium strong; vs--very strong; vsb---very strong and broad; m--medium; mw--medium weak; w--weak.

Table 4. Correlation of the fundamental vibrational frequencies of m- and p-methoxybenzonitriles in i.r., Raman and u.v. spectra and their assignment* 3-MB

I.r.

Electronic GS ES

270 690

718

987

923 --

1264

I.r.

Raman 4-MB Electronic GS ES

186 514 -825

690 837 1032

266 684 828 1012

270 --925

215 685t 7365 861t

-1109

1122 1264

-1254

1108 --

993 1194 1168f

-

-

Assignment CH3 Torsion C-C o.p.b. Ring breathing C-C-C Trigonal bending CH3 Rocking C-OCH3 Stretching

*All values in cm-L tValues from tAmg--lBlu system.

200 y.

190--

j

160 160

II

8(3 80

5C 5C

.......

I I00

I 500 900 Tempera'ture, K

1500

Fig. 2. Variation free energy function - ( F ° -E~o)/T and entropy S o of 3-MB and 4-MB with absolute temperature.

n i t u d e s of t h e s e are quite close, t h e r e m a y b e a n a p p r e c i a b l e i n t e r a c t i o n b e t w e e n t h e two. M a n y w o r k e r s [ 8 , 17,25] h a v e utilized this a r g u m e n t in assigning the different m o d e s . GARRIGOU-LANGRANGE et a/.[26] h a v e o b s e r v e d a s e q u e n c e of v e r y i n t e n s e a n d s t r o n g l y p o l a r i z e d R a m a n lines in the r a n g e 844-690 cm -1 c o r r e s p o n d i n g to m o d e 1. JAKOBSEN a n d BREWER[27] a s s i g n e d this m o d e as s u b s t i t u e n t s e n s i t i v e in s o m e parR s u b s t i t u t i o n s in b e t w e e n 820 a n d 8 6 0 c m - L T h e s e h a v e led us to assign a v e r y s t r o n g R a m a n b a n d at 8 2 8 c m -~ ( h a v i n g a c o r r e s p o n d i n g v e r y s t r o n g i.r. v a l u e 837 cm -t) in 4-MB a n d v e r y s t r o n g i.r. b a n d at 870 cm -~ in 3-MB to vm m o d e a n d t h o s e at 1012 a n d 9 8 7 c m -I in the t w o m o l e c u l e s r e s p e c t i v e l y to v i b r a t i o n 12. OWEN a n d HESTER[12] h a v e a s s i g n e d Cary~--O s t r e t c h i n g m o d e 13 b e t w e e n 1260 a n d 1 2 4 4 c m -m in v a r i o u s m o n o - h a l o g e n a t e d anisoles. In view of this the b a n d s at 1264 ( 1 2 5 4 R ) a n d 1 2 6 4 c m -~ h a v e b e e n a s s i g n e d to this m o d e in 4-MB a n d 3-MB r e s p e c t i v e l y . JAKOBSEN[4]

588

R . K . GOEL and M. L. AGARWAL

L~ % °~

t. °~ ttq ee~

e~

d~

o

._=

._t2 ¢¢ e-

a~

vo e~

.o

e~

Electronic and vibrational spectra and thermodynamic functions of 3- and 4-methoxy benzontriles assigned a band at 1192 cm -~ in benzonitrile-d5 to C - C N stretching mode 2. We have assigned this mode at 1179 cm -~ (having a corresponding Raman value 1176cm -~) in 4-MB and 1172cm -~ in 3-MB. The twelfth a~ mode in benzonitrile corresponding to C=N stretching vibration is characteristically observed around 2225cm-1; very strong i.r. and Raman bands around 2225 cm -1 in the spectra of present molecules have been assigned to this mode. b2 Vibrations. Out of the ten in-plane b2 modes, two v2ob and vTb, could not be observed in the i.r. spectra of 3-MB. 18b Vibrations corresponding to C-OCH3 bending, in view of the OWEN and HESTER[12] assignment, have been identified at 505 and 484 cm -~ in 4-MB and 3-MB respectively. HIDALGO[28] found a characteristic i.r. band between 380 and 400cm -t for several nitriles. G R E E N [ I ] o n this basis assigned a frequency 380cm -~ to in-plane C - C N bending mode 9b. In proponitrile[29] and acrylonitrile[30], the bands observed at 378 and 362 cm -~ were assigned to this mode. This mode has been identified at 386 and 390 c m -t in 4-MB and 3-MB respectively. b, Vibrations. All these six modes of b~ species are well correlated to the benzonitrile and anisole frequencies (Table 1), except C - C N and C-OCH3 vigrations which are well correlated to the frequencies of acrylonitrile[30] and anisole[12] respectively. JAKOBSEN[4] assigned the C---N bending mode at 551 and 552cm -~ in C6HsCN and C6DsCN respectively. SHURVELL et al.[6] assigned this mode at 468 cm -I in C6FsCN. Strong Raman and i.r. frequencies near 550 cm -j have been correlated to this mode in the present spectra. No frequency corresponding to C - N deformation mode has observed either in 4-MB nor in 3-MB. a2 Vibrations. Only one Raman band has been observed corresponding to a2 species in 4-MB; however, weak i.r. bands have been assigned to the other modes in this molecule. Under C, symmetry all these modes are allowed in the infrared, as a result of which all the three bands have been identified in the i.r. spectra of 3-MB belonging to C~ symmetry.

OCH3 Group vibrations Out of the twelve fundamental frequencies arising due to the OCH3 group, all except CH3 torsion about C,tky~--O axis and OCH3 torsion about C,rytO axis have been well identified and correlated to p-anisole frequencies[12]. OWEN and HESTER[12] have assigned frequencies between 97 and 112 cm -l to OCH3 torsional mode and between 177 and 240 cm -~ to CH3 torsional mode in various mono-halogenoanisoles. TYLLI et al.[18, 19] have observed phenyl torsion around 140cm -1 in various deuterated anisoles (which is lower than 148 cm -t, anisole value) and methyl torsion around 280 cm -~ in anisole-ds. In view of these, the very strong Raman shift of 155cm -~ and medium in-

589

tensity band at 266 c m -I have been assigned to phenyl and methyl torsional modes respectively in 4-MB. The i.r. band at 270 cm -~ in 3-MB has also been assigned to methyl torsion.

Electronic spectra Under reduced symmetry C2~ or Cs, the forbidden transitions of benzene ~Aig-~ IB2. (2600 ]k) and 1AIs~'B,, (2100,~) become allowed. The spectrum of 4-MB observed on medium quartz spectrograph apart from main band system around 2800 ,~ gave some weak bands around 2400 A but these could not be improved on this spectrograph. With this its spectra was tried also on a u.v. spectrophotometer in vapour phase in which clear bands were observed between 2290 and 2410 A.The 2800A system could not be resolved on the u.v. spectrophotometer; however, the intense band observed about 2830A, towards the higher wavelength side also enabled to assign the 0,0 band at 35330cm -~ in 4-MB. Because the spectra of 4-MB and 3-MB are similar, the corresponding strong band at 35143cm -~ has been assigned to 0,0 band in 3-MB. These correspond to ~A,g ~ IBz, (2600 A) system of benzene. The system corresponding to ~A~8->~B2u extends from 2921.25 to 2590/~ in 4-MB and from 2921.42 to 2757 A in 3-MB. The system corresponding to ~Aig--*~Biu transition could not be observed in 3-MB. The analysis of the spectra indicates more red shift in meta(3-MB) than in para(4-MB) substitutions compared to that in benzonitrile (0,0 band at 36516 cm-~). Such a trend has also been reported in literature [21]. The excited state (E.S.) values 215 and 186 cm -1 in 4-MB and 3-MB respectively, supported by ground state (G.S.) value 285 cm -I in 4-MB have been assigned to CH3 torsional mode which find support from the corresponding Raman shift at 266 cm -~ in 4-MB and i.r. value 270 cm -~ in 3-MB. E.S. fundamental 215 cm -~ has been traced up to three quantas and combines with other fundamentals also. The other G.S. fundamentals identified at 718 and 923 cm -~ in 3-MB and at 925 and 1108 cm -1 in 4-MB, while E.S. fundamentals are identified at 514, 825 and 1109 in 3-MB and at 993, 1194cm -~ in 4-MB. These have been correlated to the i.r. and Raman values and assigned to probable modes in Table 4.

1A,,-1B,. (2100 A) System It is interesting to observe the second system in 4-MB between 2290 and 2410 ]k, which has been correlated to the 2100]k (~A1~-IB~.) system of benzene. The strongest band towards the higher wavelength observed at 41494 cm -1 has been correlated to the 0,0 band. The other very strong band at 42230cm -~ having a separation of 736cm -j which has been traced up to three quantas and which also combine with a number of fundamen-

R. K. Cow

590

and M. I.. AG~RWAL

tals, has been correlated to the ring breathing mode. Since the spectrum does not extend towards the higher wavelength side, the corresponding G.S. value was nut observed. However, it finds support from the i.r. and Raman values at 837 and 828 cm-’ respectively. AMMA et ul.[31] and NAIR et al. [32] have also observed such an additional band system in benzene derivatives. The other E.S. fundamentals are very well correlated to the fundamentals of 2600 A system which is clearly exhibited in Table 4. THERMODYNAMIC FUNCTIONS

Thermodynamic functions of 3-MB and 4-MB molecules have been calculated by using standard expressions [33,34]. For determining rotational contribution the following structural parameters were used[l2,17]: c-C = 1.4A, C-H = 1.08A, CL,,,0 = l.37A,@Cmsthy, = 1.47A,C-H(methyl) = l.O9A, QCOC = 120”, C-CtictiI. = 1.42A, C-N = l.l57A, QOCH = 109.5”, QCCN = 180”, all other angles were taken as 120”. Thermodynamic functions shown in Table 5 were calculated at several temperatures between 100 and ISOOK using 45 fundamental frequencies assuming rigid rotor harmonic oscillator approximation. The calculations were performed for an ideal case at 1 atmosphere pressure. The symmetry number for overall rotation was taken as 1 and for internal rotation as 3 for both the molecules, The principal moments of inertia for 3-MB are 122.65, 83.29, 39.69 x 10~“9gcm* 119.33, 136.97, for 4-MB are and 17.97 x 10m3’gcm* respectively. The reduced moment of inertia for the two molecules are 2.5857 and 2.4177 x lo-j9 gm cm-* respectively. The values of reduced moment of inertia agree well with the values given by OVEN and HESTER[~~] for various mono-halogenoanisoles. The values of barrier height for 3-MB and 4-MB are 1.588 and 1.485 kcal/mole respectively. The higher value in meta compared to para substitution also finds support from the similar trend reported in literature [12]. The trend of variation of various thermodynamic functions with absolute temperature (Figs. 1 and 2) is similar to that reported in literature [17,35,36]. Acknowledgement-The authors are thankful to Dr. B. N. KHANNA. Department of Physics, A. M. University, Aligarh (India) and to Dr. P. L. Gorxn~, School of Chemistry, University of Bristol. Bristol (England) for providing necessary facilities for n.v. and Raman spectra respectively, One of the authors (M.L.A.) is also thankful to U.G.C., New Delhi (India) for financial

assistance. REFERENCES [I] J. H. S. GREEN,Spectrochim. A&

17,607 (1961). [2] J. M. LEBAS, J. Chem. Phys. 59, 1072 (1962).

[3] B. BAK and J. T. NIELSON, Z. Efectrochem.

64, 560

[4] (~%J?AKOSSEN. Spectrochim. Acta 21, 127 (1965). [5] D. STEELE and D. H. WHIFFEP;, Spectmchim. Acto 16, 368 (1960). [6] H. F. SHURVELL.A. S. BLAIR and R. J. JAKOBSEN, Specrrochim. Acta 2dA, 1257 (1968). [7] J. H. S. GREEN and D. J. HARRISON,Specrrochim. Acta 32A, 1279 (1979). [S] R. R. RANDLEand D. H. WHIFFEN, Proceedings of the Symposium on Molecular Spectroscopy (Institute of Petroleum, London), p. 111 (1955). [9] S. P. SINHA and C. L. CHATTERJEE,Spectrosc. Left. 9, 461 (1976). 1101 P. D. SINGH. Indiun J. Pure Appl. Phys. 7, 430 - . (1969). [Ill R. K. GOEL, S. D. SHAMRMand S. N. SHARMA, Indian _I. Pure Appl. Phys. 17, 55 (1979). 1121 N. L. OWEN and R. E. HESTER, Spectrochim. Acta 25A, 343 (1969). [13] E. F. MOONEY,Spectmchim. Acta 19, 877 (1963). 1141 M. HORAK, E. R. L~PPINC~TTand R. K. KHANNA, Spectrochim. Actu 23A, 11I1 (1967). [IS] C. P. D. DWIVEDIand S. N. SHARMA,Indian J. Pure Appl. Phys 11,787 (1973). 1161 R. K. GOEL. K. P. KANSALand S. K. SHARMA,Actu Physica Polonico %A, 453 (1980). [I71 C. L. CHATTERIEE,P. P. GARC and R. M. P. JAISWAL, Spectrochim. Acta 34A, 943 (1978). .1181 . H. TYLLI and H. KONSCHIN.J. Mol. Struct. 42, 7 (1977). [I91 H. TYLLI, H. KONSCHINand G. F. CAROLA,J. Mol. Slrurt. 55. I57 (1979). [20] M. Bass. J. &em. ihys. 18, 1403 (1958). 1211 S. M. PANDKYand S. J. SINGH, fndian I. Pure Appl. Phys. 14, 587 (1976). [22] T. S. VARA~ARAJANand S. PARATHASARATHY, Indian .I. Pure Appl. Phys. 11, 341 (1973). 1231 M. R. PA~HYE and T. S. VARADARAJAN,L Scient. Ind. Res. 218, 241 (1962). .1241 H. W. Wrrso~ and J. E. BLOOR. Soectrochim. Acta 21.45 (1965). [25] M. R. PADHYEand B. G. VILADKAR,I. Scient. Ind. Res. 188, 504 (19F9). [26] C. GARRIGOU-LAGRANGE, J. M. LESAS and M. L. JOSIEN, Spectrosc. 16, 32 (1958). [27] R. 1. JAKO~SENand E. J. BREWER,J. Appl. Spectrosc. 16, 32 (1962). [28] A. HIDALGO, Crhebd Seonc. Acad. Sci. Paris 249, 395 (19S9). [29] N. E. DUNCANand G. 2. JANZ, J. Chem. Phys. 23, 434 (1955). [30] F. HALVERSTON,R. F. STAMMand J. J. WHALEN, J. Chem. Phys. 16, 808 (1948). [31] R. A. AHMA, K. P. R. NAIR and D. K. RAI, Appl. Spectrosc. 23, 616 (1969). [32] K. P. R. NAIR, R. A. AMMA and M. P. SRIVASTAVA. Appl. Specfmsc. 23, 550 (1969). [33] G. HERZBERG, Molecular Spectra and Molecular Structure, Vol. II, Infrared and Raman Spectra, p. 510. T. Van Nostrand, Reinhold, New York (1%6). [34] K. S. PITZER and W. D. CWINN, 3. Chem. Phys. 10, 428 (1942). .1341 _ K. S. P~TZERand W. D. CWINN. .I. Chem. Phys. 10, 428 (1942). [35] R. K. GOEL, S. K. GUPTA, R. M. P. JAISWAL. and P. P. GARG. Indian I. Pure Aool. Phvs. 18. 223 (1980). [36] S. G. FRANKISS,D. I. HARMON and W. KYNASTON, Spectrochim. A& 3OA, 1225 (1974).