REGION OF OH DEFORMATION VIBRATIONS

IN MICAS

M. S. Metsik, T. I. Shishelova, G. F. Golovko, and Z. N. Epifantseva

UDC 539.194

It mus t be noted that, while the va l ence -v ib ra t ion region of the OH band in micas has been adequately studied [1-3], the l i t e r a t u r e contains ve ry l i t t le in format ion on the de fo rma t ion -v ib ra t i on region . On the other hand, the de fo rma t ion -v ib ra t i on region of the OH bond, like the va l e nc e - v i b r a t i on region , is c h a r - a c t e r i s t i c in micas , i . e . , d ioc tahedra l and t r i oc t ahed ra l micas yield absorp t ion at d i f ferent f requencies ; there is a r e l a t ionsh ip between the absorpt ion constant at the maximum of the OH de fo rma t ion -v ib ra t i on band and the degree of spec imen hydra t ion . The form of the spec t rum also changes subs tan t ia l ly with the angle of the spec imen to the incident rad ia t ion . These c i r cums tances n e c e s s i t a t e an inves t igat ion of the OH-bond de fo rma t ion -v ib ra t ion reg ion in micas in g r e a t e r de ta i l .

The measu remen t s were made in an IKS-14 in f ra red s p e c t r o m e t e r with NaC1 opt ics . Our r e s e a r c h subjects were spec imens of phlogopite and muscovi te f rom S ibe r i an depos i t s .

Our invest igat ions showed that phlogopite exhibited a broad a s y m m e t r i c absorp t ion band ( a symmet r i c in the h igh- f requency di rect ion) with its maximum at 1620-1640 cm -I (Fig. 1, curve 1) in the OH-bond de- fo rma t ion -v ib ra t i on region for spec imens more than 0.03 mm thick. As the spec imen became thinner , this band was reso lved and three maxima with f requencies of 1600, 1690, and 1800 cm - I (Fig. 1, curve 4 )became

Fig. i. Deformation-vi-

bration region of OH bond

in micas. Phlogopite with

thickness of 0.3 mm (i),

0.15 mm (2), 0.03 mm (3),

and 0.018 mm (4). Musco-

vite with thickness of 0.2

mm (5), 0.04 mm (6),

0.025 mm (7), and 0.01 mm

(8).

l# 17 /'5 J/'/Ba, cm -I

Trans la ted f rom Zhurnal Pr ik ladnoi Spekh 'oskopi i , Vol. 15, No. 4, pp. 750-752, October , 1971. Original a r t i c l e submit ted July 6, 1970; r ev i s ion submit ted March 26, 1971.

�9 1974 Consultants Bureau, a division of Plenum Publishing Corporation, 227 g'est 17th Street, New York, N. Y. 10011. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any .form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission of the publisher. ~1 copy of this article is available from the publisher for $15.00.

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K

18

Fig. 2.

70~

_1

IR spectra of tabular phlogopite (a) and muscovite (b) crys ta ls oriented differently with respec t to incident radiation.

visible against its background for specimens 0.02 mm thick. The presence of three absorption bands indi- cated that there were three types of vibrations for the water molecules in phlogopite, which interacted with the mica crysta l lattice in different ways. Similar resul ts have been obtained for the valence-vibrat ion region [3].

The degree of hydration of the specimen was a direct function of its hardness . The intensity of the absorption band in the OH-bond deformation region increased as the specimen hardness decreased for the phlogopite.

In contrast to phlogopite, the OH-bond deformation-vibrat ion region of muscovite contained a broad absorption band asymmet r ic on the low-frequency side, the maximum of which lay at 1800 cm -1 (Fig. 1, curves 5-8). As the specimens became thinner, this band split into two bands with maxima at 1850 and 1690 em -i.

It can be hypothesized that the molecular deformation-vibrat ion frequencies of 1690 and 1640 cm -1 in micas correspond to centrally symmet r i c (,cs) and m i r r o r - s y m m e t r i c (~ms) water-molecule vibrations. Adjoining these is the absorption maximum with v ~ 1800 cm -1, which can probably be attributed to m i r r o r - symmet r i c vibrations of water molecules strongly perturbed by the crys ta l - la t t ice fields (Vpert).

Study of the spectra of oriented tabular muscovite and phiogopite crysta ls in the OH-bond deformation- vibration region showed that, when a phlogopite crystal was sufficiently thin (d = 0.018 mm) and was or ient - ed perpendicular to the incident radiation, the spect rum consisted of a broad band with maximum frequen- cies of 1600 (~ms), 1690 (Vcs), and 1800 (~pert) cm-I (Fig. 2a). When the crysta l was positioned obliquely with respec t to the beam, the intensity of the ~pert absorption band decreased and the band was displaced in the high-frequency direction. The band virtually disappeared with incidence angles of 45-60 ~ while the Pros and ~cs bands became equal in intensity and merged into a single broad band. M i r r o r - s y m m e t r i c vibrations could not be excited when the light vector was parallel to the OH bond in the water molecule and the absorption at 1800 cm -t was produced by molecules the dipole moments of which were oriented at an angle of about 75 ~ to the (001) cleavage plane. These molecules might have been OH localized in vacant octahedra[ positions and held in the lattice hydrogen-bonding forces . Such molecules cannot be excited by incident radiation at an angle of 40-45 ~ so that gradual degeneration of the absorption bands would occur when the crystal was rotated to these angles, as was observed in our experiments on phlogopite crystals (Fig. 2a) and especial ly clearly in those on muscovite crysta ls (Fig. 2b).

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The a b s o r p t i o n a t the f r e q u e n c y ~ms d e c r e a s e d s l i g h t l y for ph logop i te as the c r y s t a l was tu rned and b e c a m e equal to that a t the f r e q u e n c y ~cs (for c r y s t a l a n g l e s of 40-50~ I t then i n c r e a s e d r a p i d l y and d o m - ina ted the a b s o r p t i o n a t o ther f r e q u e n c i e s .

A m o r e c o m p l e x p a t t e r n was o b s e r v e d for the o r i e n t a t i o n - r e l a t e d changes in the a b s o r p t i o n s p e c t r a of m u s c o v i t e c r y s t a l s . Only two a b s o r p t i o n b a n d s , v . (1800 cm -~) and ~ms(1640 cm -1) a p p e a r e d when the p e r t s p e c i m e n was o r i en t ed p e r p e n d i c u l a r to the i n c i d e n t r a d i a t i o n . The s t r o n g ~pert band i nd i ca t ed the p r e s - ence of a c o n s i d e r a b l e n u m b e r of w a t e r m o l e c u l e s in m u s c o v i t e that a r e p e r t u r b e d by h y d r o g e n bonds and f o r m an angle of 75 ~ to the c l e a v a g e p lane . When the c r y s t a l was o r i e n t e d ob l ique ly , this band was d i s - p laced in the h i g h - f r e q u e n c y d i r e c t i o n by abou t 50 cm -1 and d e g e n e r a t e d a t ang l e s of 37-40~ i t then r e - a p p e a r e d a t c r y s t a l o r i e n t a t i o n ang les of m o r e than 45 ~ .

With c r y s t a l o r i e n t a t i o n ang les e x c e e d i n g 45 ~ cond i t ions w e r e c r e a t e d for d e g e n e r a t i o n of the m i r r o r - s y m m e t r i c v i b r a t i o n s of m o l e c u l e s f o r m i n g an ang le of 75 ~ with r e s p e c t to the c r y s t a l s u r f a c e and the v i b r a - t ions of m o l e c u l e s with axes p a r a l l e l to the c l e a v a g e p l ane . At l a r g e a n g l e s , the a b s o r p t i o n - b a n d m a x i m u m of these v i b r a t i o n s was d i s p l a c e d toward h i g h e r f r e q u e n c i e s .

Thus , the e x i s t e n c e of a d e f o r m a t i o n - v i b r a t i o n s p e c t r u m for w a t e r m o l e c u l e s in ph logop i t e and m u s - cov i t e c r y s t a l s i n d i c a t e s the p r e s e n c e of m o l e c u l a r w a t e r in t h e s e c r y s t a l s . T h e s e m o l e c u l e s might be l o - ca l i zed at s t r u c t u r a l l a t t i c e po in ts (in p l ace of h y d r o x y l s ) o r in i n t e r s t i t i a l zones of the c rys ta l~and might f o r m mono- or p o l y m o l e c u l a r s a l t s a t d e f e c t i v e l a t t i c e s i t e s [4 ,5] .

The f i l m - w a t e r content is h i g h e r in ph logop i t e than m u s c o v i t e and i n c r e a s e s as the s p e c i m e n h a r d n e s s d e c r e a s e s . C o n v e r s e l y , m u s c o v i t e c r y s t a l s exh ib i t w a t e r m o l e c u l e s that a r e m o s t l y s t r o n g l y l o c a l i z e d in the l a t t i c e and o r i e n t e d a t an angle of a p p r o x i m a t e l y 75 ~ with r e s p e c t to the c l e a v a g e p l ane .

The i n t e r s t i t i a l m o l e c u l e s can be o r i e n t e d e i t h e r p a r a l l e l or p e r p e n d i c u l a r to the c l e a v a g e p lane . The bonding e n e r g y of the w a t e r m o l e c u l e s v a r i e s with t h e i r o r i e n t a t i o n in the c r y s t a l l a t t i c e .

I.

2. 3. 4.

5.

LITERATURE CITED

M. S. Metsik and T. I. Shishelova, Zh. Prikl. Spektr., 8, 821 (1968). I. I. Plyusnina, Infrared Spectra of Silicates [in RussianV, Izd. MGU (1967). M. S. Metsik, T. I. Shishelova, and V. A. Liopo, Zh. Prikl. Spektr., I0, 788 (1969). M. S. Metsik, Physics of the Cleavage of Mica [in Russian], Vostochno-Sibirskoe Knizhnoe Izd., Irkutsk (1962). T. I. ShisheIova, Author's Abstract of Candidate's Dissertation [in Russian], Irkutsk (1969).

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