ГА ZS- SW
KFKI
30/1968 Ш9 J 4 n/ ;д
PMR STUDIES OF FROZEN AQUEOUS F.C Ij SOLUTIONS
A. Jánost/, G. Grilnar and K. Tompa
HUNGARIAN ACADEMY O F SCIENCES CENTRAL RESEARCH INSTITUTE FOR PHYSICS
BUDAPEST
2017
P r in t e d i n t h e C en tra l R e se a rc li I n s t i t u t e f o r P h y s i c s , B udapest Kiadja. a KFKI Könyvtár é s K ia d ó i O s z t á ly . O v.: Parkas I s tv á n n á Szakm ai l e k t o r t D é zsi I s t v á n . N y e lv i le k t o r t Monori Jenöné
Példányszám : 12 0 Munkaszám: 4 0 8 6 B u d a p est, 1 9 6 8 . november 1 9 . K é s z ü lt a KFKI h á z i s o k s z o r o s ít ó j á b a n , P . v . : Gyenes Imre
A. J á n o s s y , G, Grüner and K. Tompa
C en tra l R esea rch I n s t i t u t e f o r P h y s i c s , B u d ap est, Hungary
R e c e n tly Mössbauer r eso n a n ce exp erim en ts o f D é z s i e t . a l . [1] and N o z ik e t . a l . [2] showed t h a t on warming up quenched d i l u t e aqueous s o l u t i o n s t o ab ou t -80°C an i r r e v e r s i b l e change o f th e arrangem ent o f i c e m o le c u le s around th e c a t io n s ta k e s p l a c e . T hese auth ors s u g g e s te d t h a t i c e , c o n t a in in g a sm a ll amount o f im p u r ity , on quenching from l i q u i d s t a t e t o -1 9 6 °C has a c u b ic s t r u c t u r e w h ich on warming up tr a n sfo r m s a t a b o u t -80°C t o norm al h exagon al i c e .
W hile th e Mössbauer r eso n a n ce g iv e s in fo r m a tio n on th e c a t i o n s i t e s , t b s p r e s e n t p ro to n m agn etic reso n a n ce /PMR/ ex p erim en ts were perform ed i n o rd er t o s tu d y th e p r o c e s s e s a s o b serv ed in th e i c e m a tr ix .
The measurements were made on s o l u t i o n s o f 0 ,4 7 M fe r r o u s c h lo r id e i n d i s t i l l e d w a te r . In th e fe w ml sam ples th erm al e q u ilib r iu m was r e a c h e d in ab o u t a m inute a f t e r q u en ch in g .
A w id e l i n e NMR sp e c tr o m e te r was u se d a t a fr e q u e n c y o f 26 MHz, th e modula
t i o n am p litud e was 0 ,5 G au ss, th e am p litud e o f th e r a d io fr e q u e n c y f i e l d was c h o sen s o low t h a t s i g n a l d i s t o r t i o n caused b y r e la x a t i o n e f f e c t s ap p eared o n ly a t tem p eratu res lo w e r th an -1 2 0 °C ,
F ig u r e 1 . shows two c h a r e c t e r i s t i c PMR s p e c t r a .
a . / At -196°C th e sp ectru m d id n o t d i f f e r from t h a t o f quenched d i s t i l l e d w a te r . The measured sec o n d moment o f th e PMR l i n e , i n agreem ent w ith
131 pure i c e , was 30^-2 G auss2 , th e p e a k t o peak l i n e w id th 14^0>5 G auss.
b . / On warming up from -196°C th e spectrum decom poses t o two l i n e s . At about -100°C a s t r o n g l y asym m etric l i n e w it h a w id th o f >^-0.5 Gauss appears a t th e c e n t e r o f th e sp ectru m . The b roader component o f th e
PMR S T U D IE S OF FROZEN AQUEOUS F e ö l 2 SO L U T IO N S
spectrum rem ains up t o —6 0 °0 unchanged, a t h ig h e r tem p era tu res I t shows a m o tio n a l narrow ing [ 4 ] . The i n t e n s i t y o f t h e narrow l i n e in c r e a s e s up t o -7 0 °C and a lth o u g h th e r e p r o d u c i b i l i t y was n o t v e r y good i t n e v e r e x ce e d e d 10 % o f t h a t o f t h e w hole Spectrum *
K eeping th e tem p era tu re a t -7 0 °C th e narrow l i n e v a n is h e s w it h in a h a l f t o a few hours and does n o t rea p p ea r agRin* The change i s
i r r e v e r s i b l e , on r e c o o l i n g t o low er tem p era tu res t h e spectrum rem ains unchanged, th e narrow l i n e i s m is s in g .
c . / On c o n tin u in g th e h e a tin g from - 7 0 ° c a f t e r th e d isa p p e a r a n c e o f th e narrow l i n e , a new narrow er sym m etric l i n e w ith a w id t h o f ab ou t 1*5 Gauss appears a t -5 0 ° C , w ith an i n t e n s i t y r a p id ly in c r e a s in g w it h tem p erature* By r e c o o lin g from -30°C t h e i n t e n s i t y o f t h i s narrow l i n e d e c r e a s e s s lo w ly and i s s t i l l w e l l o b s e r v a b le a t -9 0 °C .
The above d e s c r ib e d tem p era tu re dependence o f th e PMR sp ectru m can b e w e ll c o r r e l a t e d t o th e p r e v io u s o b s e r v a t io n s , where a t r a n s i t i o n tem p eratu re lo w e r th a n -7 0 ° C , b u t w it h u s u a ll y a s lo w e r t r a n s i t i o n r a t e was r e p o r t e d . One o f th e m ost im p o rta n t f e a t u r e o f th e r e s u l t s i s t h a t t h e PMR s p e c t r a o f sam p les w it h g iv e n tem p era tu re h i s t o r i e s e x h i b i t two l i n e s i n d i c a t in g th e p r e s e n c e o f i c e m o le c u le s i n tw o d i f f e r e n t s t a t e s o f m o tio n . The asymmetry o f th e noprow l i n e a p p e a r in g a t tem p era tu res from -1 0 0 t o - 7 0 °0 can b e a t t r i b u t e d t o moving i c e m o le c u le s su rro u n d in g t h e p a ra m a g n etic fe r r o u s io n s [51* I t f o ll o w s from t h e i n t e n s i t y m easurem ents, assum ing th e sy ste m t o b e hom ogeneous, t h a t e v e n at-maximum i n t e n s i t y o f th e narrow l i n e o n ly p a r t o f th e sy ste m undergoes a ch an ge, nam ely th e i c e m o lecu les w hich a re in th e f i r s t or s e c o n d c o o r d in a t io n s h e l l o f ir o n a to m s . The p ea k t o peak lin e w id t h o f 3 Gauss p r e c lu d e s th e p o s s i b i l i t y o f d i f f u s i o n a t tem per
a tu r e s lo w er th a n - 70 °G [ 6 ] , th e m otion i s b e l i e v e d t o b e o f a h in d e r e d r o t a t i o n a l or o s c i l l a t i o n a l t y p e .
The ind ep en dence o f th e shape o f t h e broad l i n e from tem p era tu re su p p o r ts b u t does n o t p ro v e unam biguously t h e a b sen ce o f phase tr a n s fo r m a tio n in th e b u lk o f i c e . I t i s p r o b a b ly im p o s s ib le t o d i s t i n g u i s h c u b ic and h ex a g o n a l
i c e [7 ] by PMR se c o n d moment m easurem ents, b e c a u s e o f t h e i r s t r u c t u r a l s i m i l a r i t y . In s p i t e o f t h i s f a c t t h e asymmetry and s m a ll i n t e n s i t y o f th e narrow l i n e i n th e c r i t i c a l tem p era tu re r e g io n makes h i g h l y u n lik e ly a c u b ic -h e x a g o n a l t r a n s i t i o n in th e b u lk o f i c e . Aqueous f e r r o u s c h lo r id e s o l u t i o n s have f o r 30 w % c o n c e n t r a t io n an e u t e c t i c p o in t a t -36°C [ 8 ] . The narrow l i n e c h a r a c t e r i s t i c o f r a p id m otion o b serv ed a t -50°C su p p o r ts th e assumed s e p a r a t io n [2] o f an e u t e c t i c p h a se a t t h i s te m p e r a tu r e .
- 3 -
The a u th o rs are in d e b te d t o D r. L, K e s z t h e ly i and D r. I . D é zsi f o r h e l p f u l d is c u s s io n s and Mr. P . Bánki f o r v a lu a b le t e c h n i c a l a s s i s t a n c e .
R e f e r e n c e s /
[11 I . D é z s i, L . K e s z t h e ly i , L . Pécs and L . K orecz, P h y s .L e t t e r s , 1 4 , 14 /1 9 6 5 /
[2] A. J . N ozik and M. K aplan,
J.C hem .P hys. 4 £ , 2960 /1 9 6 7 / [5] D. E. B a rn a ll and I . J . Lowe,
J.C hem .P hys. 4 6 , 4 8 0 0 /1 9 6 7 / [4] K. Kume,
J .P h y s .S o c . Japan 1 £ , 1495 / I 9 6 0 / [5 ] E. R. Andrew,
N u clea r M agnetic R esonance p , 175«
Cambridge U n iv e r s t iy P r e s s , 1 9 5 6 .
[6] I . D é z s i, L . K e s z t h e ly i , В . Molnár and L . P é c s , P h y s .L e tte r s 1 8 , 2 8 /1 9 6 5 /
[7] N. D. L is g a r te n and M. Blackman, Nature 1 7 8 , 59 / 1 9 5 6 /
[8] S o l u b i l i t i e s o f In o r g a n ic quad Organic Compounds
V o l . l . E d ite d by H. Stephen and M. S tep h en Pergamon P r e s s , 1965«, J
*
Cl Í33
-6 0 -40 -20 0 20 40 60
F i g . 1
S p e c tr a o f quenched aqueous FeC]^ s o l u t i o n h e a te d t o -71°C a , / 10 m inutes ,Ъ / 2 hours a f t e r th erm al e q u ilib r iu m was r e a c h e d . /Ho=6100 G a u ss/
