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HIGH PRESSURE XAS ON BROMINE IN THE DISPERSIVE MODE
J. Itie, M. Jean-Louis, E. Dartyge, A. Fontaine, A. Jucha
To cite this version:
J. Itie, M. Jean-Louis, E. Dartyge, A. Fontaine, A. Jucha. HIGH PRESSURE XAS ON BROMINE IN THE DISPERSIVE MODE. Journal de Physique Colloques, 1986, 47 (C8), pp.C8-897-C8-900.
�10.1051/jphyscol:19868174�. �jpa-00226079�
JOURNAL DE PHYSIQUE
C o l l o q u e C8, s u p p l e m e n t a u n o 1 2 , Tome 47, d e c e m b r e 1 9 8 6
HIGH PRESSURE XAS ON BROMINE IN THE DISPERSIVE MODE
J . P . I T I E , M. JEAN-LOUIS, E. DARTYGE*, A. FONTAINE' a n d A. JUCHA"
LIMHP
-
CNRS, Universite P a r i s - ~ o r d , F-93430 Villetaneuse, France" L U R E (CNRS, CEA, MEN), F-91405 Orsay Cedex, France
Br2 a 6t6 & d B sous haute p r e n par spectroscopic d l a k a p i o n X en dispersion dl&ergie juqdh 57,5 GPa. L s avantages du montage en dispersion d'&ergie s3nt pr&ent&. L g r&ulhts de XANES et dlEXAFS sur le home s n t disc& en kmnes de d t 5 m a n c e avec la pr&n de la longueur de la liaison m o l & d a k e et du p3tentiel kbrstitiel moyen.
High pressure energy disprsive x ray atsorption m o s c o p y has k e n
@armed on Br up to 57.5 GPa. The advantages of the energy d i s m v e set up are premtxd. The
XANES
and EXAFS results on homine are discussed in terms of bond length and average inter&tial p t e n t i a l pressure dependence.The clissdation of diatomic molecules under high preisure, due to the increasing charge &ansEer &om the intramolecular to the intermolecular bond, has been investigated by different m e n t a l techniques : rgitivity measurement (11, Raman spxtrcscopy (2), x ray djfEradion (3,4,5). Through the halogen &es, only the iodine dismiation has k e n observed (3). For tkomine and chloline, using a scaling law between the halogens and the valume &tion with pressure, the transition from a m a l e c d a r to a monoatomic phase has been predicted respedively a t 58 f 6 GPa and 140 f 30 GPa. A . the data on halogens leave the q u d o n s t i l l open, wether ar not the hond length changes with pressure pior the transition. X ray an- w c s x - p y is @ c W y suited to address this issue. W e present preliminary results of energy cfkpesive x ray a t x q t b n s p c t r ~ s c o p y on sdlid homine under high prgsure, using the diamond anvil cell technique.
The pressure was generated by a d a s k a l Bell and Mao type diamond a n d cell w i t h "Drukker standard" diamonds (p( = 4 mm). Bromine was loaded in the hale (p/ = 150 pm, 30 pm thick) af a staides sksd gasket without any pressure transmitting medium. In order tn measure the pressure (6) a ruby chip was added to the sample. The luminescence of the ruby, &tated by the 488 nm line of an air mold argon laser (40 mw), was recorded outside the hutch h ga single monochromatar. T k mount of the cell, w i t h centaing phs, was specially hilt to put back the cell, a f t e r pesnne measurements, a t the same @ace, better than 10 ym. The cell was placed on a three axes tramlatar, m o b driven from outside the hutch.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19868174
C8-898 JOURNAL DE PHYSIQUE
The energy dispersive port of LURE (ORSAY (7) presents important advantages to perform high pressure experiments :
ti) The x ray beam is focused which is very impartant according to the s m d l d z e of the sample.
(ii) An the data are obtained a t once in a very short time. This makg easier the alignment of the cell in the beam and also prevents for some of the distarsions of the spectrum due to a M o m a t i o n of the gasket.
Ciii) The stahilty of the beam is excellent k a u s e of the lack of any mechanical mowement during data collection.
tiv) The acquisition time is very short : for a kame, we need only 800 ms. Six frames are t- to obtain data on the XANES part of the spectrum. For EXAFS up to 100 eames were added to improve statistics.
Though the x ray beam goes through the anvils, we see only a Bragg peak of the diamonds in the preedge part u£ the spectrum. Some glitches due to the extra Bragg reflection d the curved crystal were also o m e d in the spectrum, unfortunately very wax the position of the E2 peak figure 1). -ugh the x ray beam was £ocused, the d z e of the spot was a little hit higger than the gasket hdle so a part of the beam goes directly through the gasket and the spectra were slightly distarted. The main consequence was that oriy a small energy band ~ZIS was available to callect signEkant data. The energy calikation was made using NaBr as a standard. Thus we choose the NaBr treshdd as an arbitrary arigin.
Previous measurements o£ liquid hromine ( 8 ) show that the achieved energy resolution in our experiment is not at the top. This may 12 due to the attempt to d e c t a wide energy band pas; for EXAFS data which leads to a larger radius of curvature and a detectcarpositionclc6etothefccus.
R~~ and discussion
In figure 1, we &ow the spectra a t the lowest pressure (4.8 GPa) and the highest pressure (57.5 GPa) performed on s3.d txomine. In bath spectra we can see the
shape resonance peak (E which means that wen a t 57.5 GPa, komine is still a mdlecukc ayskil. Cornpahg the h r o qectm w e mte that El and E2 are sbXted to higher energy by 4 and 9 eV. W e note also that the peaks koaden and decrease in intensity with increasing pressure. The energy p t i o n E of the peaks is related to the bond length R according to the relation (E-EO)R = constant where Eo is the true energy &gin (average in-tid. patentiau (9).
If we compare the salid hromine spectrum a t 4.8 GPa to the liquid spectrum fig. 2), we o& that the peaks are shifted by 5 eV. Since we don't expect a dramatical
t
Fi 2. LIQUID BROMINE ABSORPTIONchange in the mdmular bond length w i t h d d i f i c a t i o n and also &ce E. remains almost a n s t a n t up to 20 GPa (fig. 41, we a m t e the shift of the peaks energy& a shift of the migin due to the change in the htemiitial potential when you go kom liquid to sdlid state.
T k Fourier transEom of the liquid spectrum using E =
-
12 e V and the Fourier transEorm a€ the salid one using E =-
5 e V (a 5 eV s h i f t of &e energy arigin) give about t h e s a m e bond length (fig. 3) wh& is co-nt w i t h the position of the shape resonance in bothFh-.
To interprete the results on d d komine w i t h increasing presnne we can do two alternative hypthesis :
ti) The energy migin E is constant with pressme in the salid phase. In this case the shift to higher energy of
4
and E2 peaks (fig. 4) is entirely due to a decrease ofF a j 3 BOND LENGTH CHANGE WtTH P R E S S U R E ASSUMING EO=CST
the bxx3 length and then we can determine its variation versus the applied pressure (fig.
3). The Fourier t r a n s E o r m s of the spectra Uig. 5) show also a decrease of t h e bond length with haeasing gressure in agreement w i t h the fhst pr-e fig. 3). Amxding to this line of reasoning, a t 57.5 GPan we obtain a Mliation of 13 % in the bond length, which is u n w .
(iil The bond does not vary with Wesmre. In this case the shift of the El psak is entirely due to a shift of the energy d g i n which can be explained by an i n d g d ' tion of the tainding ekctrons. But, the E peak should have the same shift which is= case and if we Bo a Fouier transform
2
the d i d h o r n b e .5pzkaI we obtain a decrease a€ the bond Mgth with inaeasi.ng p r e s u r e which is also unfounded.In f a c t we think t h a t b t h parameters, Eo and R change w i t h Fgsure. To fit their variation we need to compare the results of the XANES and the EXAFS treatments.
The quality of t h e present EXAFS data is too poor to g e t a d h l e e t i o n of the two
e f E e c t s (distorted q@xa lead to a F d e r tramEarm calculated in a small k range).
JOURNAL DE PHYSIQUE
W a
L 3
ii!
Q t
FL8 4 SHAPE RESONANCE SHIFT WITH PRESSURE J.
DISTANCES fl
~ 4 5 SOLID BROMINE FOURIER TRANSFORM EO=-7eV
We have &own that XAS c a n be p e r f o r m e d a t very high pressme and that the energy dispersive m e t h o d is very w e l l adapted to s u c h a e x p e r i m e n t . T o obtain better dak~
on the EXAFS part of the spectrum, .%me improvments are n e e d e d (ketta focus of the beam, h a r m o n i c r e j e z t b n ) . T o interprete t h e results af solid h o m i n e b t h XANES and EXAFS are necessary, s i n c e b t h E and R c a n bs pressme dependant. A theoretical support is also n e e d e d to really und& the data.
1
-
R.W. LYNCH and H.G. DRICKAMER, J. Chem. Phys.45,
1 0 2 0 (1966) 2-
P.G. JOHANNSEN and W.B. HOLZAPFEL, J. Phys. C8, 1 9 1 (1984)3
-
H. D'AMOUR-STURM and W.B. HOLZAPFEL, P h M a 1 3 9 & 1 4 0 B, 328 (19861.4
-
E.-Fr. DUSNG, W.A. GROSSHANS and W.B. HOLZAPFEL, J. Phys. C8, 203 (1984).5
-
K. TAKEMURA, S. MIMOMURA, 0. SHIMOMURA, Y. FUJlIand J.D. AXE, Phys. Rev. B& 998 (1982).
6
-
H.K. MAO, P.M. BELL, J.W. SHANER and D J . STEhTER, J. App. Phys. 49 3276 (1978).7
-
E. DARTYGE, C. DEPAUTEX, J.M. DUBUISSON, A. FONTAXNE, A. JUCHA, P-LEBOUCHER arad G. TOURILLON, NLM. A 246, 452 (1986).8
-
B.M. KINCAID and P. ELSENBERGER, Phys. Rw. Lett.34,
1 3 6 1 (1975).9
