EFFECT OF PRESSURE ON RAMAN-SPECTRA OF SOLID HCl AND HBr

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EFFECT OF PRESSURE ON RAMAN-SPECTRA OF SOLID HCl AND HBr

P. Johannsen, W. Helle, W. Holzapfel

To cite this version:

P. Johannsen, W. Helle, W. Holzapfel. EFFECT OF PRESSURE ON RAMAN-SPECTRA OF SOLID HCl AND HBr. Journal de Physique Colloques, 1984, 45 (C8), pp.C8-199-C8-201.

�10.1051/jphyscol:1984836�. �jpa-00224336�

JOURNAL DE PHYSIQUE

Colloque C8, supplément au n ° l l , Tome * 5 , novembre 198* page C8-199

EFFECT OF PRESSURE ON RAMAN-SPECTRA OF SOLID HC1 AND HBr

P.G. Johannsen, W. ttelle and W,B. Holaapfel

FacsHbereieh Pkysik, Universitat'GH-Paderbom, D-47S0 Padevbovn, P.H.G.

Résumé - Des résultats de diffusion Raman sur HC1 et HBr, a des températures de 100 à 250 K et des pressions jusqu'à 40 GPa sont présentés. Une nouvelle procédure de chargement avec ces produits réactifs est décrite. L'argon et l'azote sont utilisés comme milieux transmetteurs de pression. Dans HBr, une nouvelle phase a été détectée -probablement avec des liaisons hydrogène symétriques-à 100 K et è des pressions supérieures à 32 GPa.

Abstract - Raman data are presented f o r HC1 and HBr at temperatures between 100 and 250 K and pressures up to 40 GPa. A new procedure i s described f o r loading a DAC with these reactive materials. Argon and nitrogen are used .as pressure media. A new phase, probably with symmetric hydrogen bonds, i s detected i n HBr at 100 K and pressures above 32 GPa.

Three phases a r e r e p o r t e d f o r each HC1 and HBr a t ambient p r e s s u r e . I n t h e h i g h t e m p e r a t u r e phase I , t h e halogen atoms occupy face-centered c u b i c p o s i t i o n s w h i l e t h e H atoms e x h i b i t a 1 2 - f o l d d i s o r d e r . Phase I I I i s o r t h o r h o m b i c , space group C1 2, mith planar zig-zag hydrogen bonded chains /1 / . The orthorhombic "phase I I " has been considered as a seperate phase with proton disorder, however, the differences between "phase I I " and I I I may be very gradual without any c r y s t a l l o - graphic phase t r a n s i t i o n .

fl new loading procedure had to be developed for loading the diamond a n v i l c e l l (DAC) with the chemically reactive HC1 and HBr. The reactive gas i s f i r s t l i q u i f i e d by c o n t r o l l i n g the temperature of a small glass tube ( f i g . 1 ) . A glass c a p i l l a r y i s f i l l e d up with the l i q u i d and kept i n l i q u i d Hz u n t i l i t i s needed for the next preparation. To load the gasketed DAC, i t i s cooled to l i q u . fJ2-temperature i n an insulated box ( f i g . 2 ) . Turbulences i n the N2-atmosphere are prevented by covering the box with two transparent p l a t e s . A glass c a p i l l a r y with the crys-

Fig. 1 - L i q u i f i c a t i o n of the gases. F i g . 2 - Apparatus for loading the DAC at l i q u . N²-temperature.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984836

C8-200 JOURNAL DE PHYSIQUE

talline s a m p l e s i s cracked beside the cell. A c r y s t a l i s selected and brought into t h e s a m p l e chamber. E i t h e r N 2 o r Ar a r e used a s pressure media.

The present e x p e r i m e n t s were performed with a D A C t h a t h a s b e e n d e - scribed previously 1 2 1 . ^{T h e}

nm and 5 1 4 nm l i n e s of an a r g o n - i o n laser were used t o excite the Raman-spectra and the ruby fluorescence.

Back-scattered l i g h t was analysed using a double monochromator and photon counting techniques. T h e resulotion w a s k e p t a t

cm

T y p i c a l R a m a n - s p e c t r a of HBr under pressure a t

K are s h o w n in fig. 3. At a b o u t 32 GPa a drastic c h a n g e i s s e e n i n the spectra. T h e strong intramolecular peaks a s well a s two peaks i n the l a t t i c e r e g i o n vanish. O n the other hand, a new l a t t i c e peak appears. From group theoretical a r g u m e n t s i t can be concluded, t h a t these c h a n g e s indicate a t r a n s i t i o n i n t o a phase with s y m m e t r i c hydrogen bonds. U n d e r the assumption of a zellengleich transition into a phase with s p a c e group D:;, the three remaining peaks of t h i s phase

can be assigned a s shown i n fig.

Fig.

- T y p i c a l R a m a n - s p e c t r a Fig.

- Effect of pressure on of H B r under pressure a t 1 0 0 K. Raman-frequencies of HBr.

( * :

Oiamond).

T h e temperature variation of t h e intramolecular m o d e s of H B r a t 3 . 4 G P a i s illustrated in fig. 5. T h e s p e c t r a a t temperatures below 1 6 5 K can be assigned to the orthorhombic phase 111. S p e c t r a a t temperatures above 2 0 0 K a r e typical f o r phase I. T h e phase boundary between the cubic and the orthorhombic phase i s represented by the continuousline in the P - T - p h a s e diagram o f HBr (fig. 6).

The Raman-spectra o f HCl a r e very s i m i l a r t o the s e c t r a o f HBr. T h e

effect of pressure on the Raman-frequencies of H C 1 a t 1 0 0 K i s given

in fig. 7. Fig.

s h o w s the P - T - p h a s e diagram of HC1. A phase tran-

s i t i o n i n t o a s y m m e t r i c phase w a s n o t observed f o r H C 1 in the present

pressure r a n g e up to

GPa.

Wavenumbers (cnil)

F i g . 5 - T e m p e r a t u r e v a r i a t i o n o f t h e i n t r a m o l e c u l a r modes i n H B r .

PIGPal

F i g . 6

-

F i g . 7 - E f f e c t o f p r e s s u r e o n F i g . 8 P - T - p h a s e d i a g r a m o f HC1.

R a m a n - f r e q u e n c i e s o f HC1.

R e f e r e n c e s :

/ I / ANDERSON A . , TORRIE B.H. a n d TSE W.S., J. o f R a m a n S p e c t r o s c o ~ i e ~ ~ ( 1 9 8 1 ) ; 1 4 9

/ 2 / HIRSCH K.R. a n d HOLZAPFEL W.B., R e v . S c i . I n s t r u m .

52,

) , 52