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TIME-DEPENDENT LINEWIDTH AND
RECOILLESS FRACTION OF THE MÖSSBAUER SPECTRUM WITH 57Co2+[Fe III(CN)6]3-
T. Kobayashi, T. Kitahara, S. Shimizu
To cite this version:
T. Kobayashi, T. Kitahara, S. Shimizu. TIME-DEPENDENT LINEWIDTH AND RECOILLESS
FRACTION OF THE MÖSSBAUER SPECTRUM WITH 57Co2+[Fe III(CN)6]3-. Journal de
Physique Colloques, 1979, 40 (C2), pp.C1-411-C1-412. �10.1051/jphyscol:19792143�. �jpa-00218516�
JOURNAL DE PHYSIQUE Colloque C2, supplkment au n o 3, Tome 40, mars 1979, page C2-411
TIME-DEPENDENT LINEWIDTH AND
RECOILLESS F3ACTION OFTHE
MOSSBAUEZ SPECTRUMWITH
5 7 ~ 0 2 + k e 1 1 1 ( ~ ~ )
2
3 -X %
T. Kobayashi, T. Kitahara and S. Shimizu
Medical College of Shiga, Otsu, Shiga, 520-21 Japan
% I n s t i t u t e for Chemical Research and Radioisotope Research Center, Kyoto University,Kyoto, 606 Japan
Rdsu&.- Les spectres Mzssbauer intdgrds et diffdrencids par rapport au temps de 5 7 ~ 0 2 + Fe1" (CN) 3- ont Btd analysds en tenant compte de l'dlargissement des raies dG aux phBnomGnes de relaxation qui suivent la capture dlectronique de 5 7 ~ o . On a observd la variation de la largeur de raie et de la fraction dleffet sans recul en fonction du temps sur le pic de ~e'+ sensible aux effets de relaxation alors que le pic. de Fe3+ semble y Gtre insensible.
Abstract.- The integral and time-differential ~gssbauer spectra of 57~02+pe111 (cN)a3- have been analyzed by taking account of line broadening due to the relaxation phenomena after the electron cap- ture decay of 5 7 ~ o . The time-dependence of both linewidth and recoilless fraction of Fe2+ peaks in- fluenced by the relaxation phenomena is observed, while no effect of the phenomena on Fe3+ peaks is recognized.
Triftshluser and Schroeer /l/ have recognized narrowing of the resonance lines with time which cannot be explained by the time filtering /2,3/, while they have observed no time-dependence of the relative peak intensities. On the other hand, Hoy and Wintersteiner /4/ have observed the time-depen- dence only of the recoilless fraction due to the lo- calized lattice vibration. In this work we present the experimental evidence for the time-dependence of both linewidth and recoilless fraction influenced by the relaxation phenomena following the electron cap- ture decay of 5 7 ~ o . The measurement has been carried out with cobalt ferricyanide 57~02+pe111(~~)
4
3- asa source at room temperature by means of the delayed coincidence technique /5,6/.
In figure I are shown the observed integral Mijssbauer emission spectrum and time-differential
spectrum for a time window of 100-224 ns. The spec- tra are resolved into two doublets of ~e'+ and Fe3+.
The parameters estimated by the method of least- squares are listed intable I. The parameter 1\ is a m$asure of the effect of time-independent nuclear '?&vironmental inhomogeneity and the relaxation phe-
nomena to the spectrum 1 7 1 . The values of A and yield of ~e'* obtained from the time-differential spectrum are 54% smaller and 23% larger, respective- ly, than those obtained from the integral spectrum.
On the other hand A for Fe3+ shows no conspicuous change.
We ascribe the peaks of Fe3+ to the Mgssbauer absorption after the intramolecular electron trans- fer from the high-spin Fe2+, formed by electron
capture decay of 5 7 ~ o , to the low-spin Fe1" as
57Fe2+ pe1"(~N)d 3- L 57~e3+@e11(~~)
4
Q-,because ~ e ' + ~ e ~ ~ ~ ( c N )
a
3- is unstable /8/. Alekseev et al. /9/ estimated a time constant of this elec- tron transfer reaction to be 10-20 ns by observing the integral and time-differential (0-60 ns) spectra at 80 K. However, in our spectrum for the (100-224)- ns delay interval observed even at room temperature we still recognize the Fe2+ doublet of approximatelythe same yield as that in the integral spectrum, as shown in the figure.
0.wl '
' I3 - 2 - 1 0 I 2 3
VELOCITY (mm/*)
Fig. 1 : Integral (a) and time-differential (b) spectra. The solid curves are least-squares fits to the experimental data and two resolved doublets of Fe2+ and Fe3+.
The structure of Co2+Fe I11 (CN)
a3-
is shown in figure 2, where the unit cell is cubic with - CO'+ions and low-spin Fe1" arranged in a NaCl structure which has bridging CN groupes of the form -CO-N-C- Fe-. In this paper, we call these CO'+ ions to be at
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792143
C2-412
A-type position.
JOURNAL DE PHYSIQUE
Table I : M6ssbauer parameters
1
:
Isomer Shift:
l Quadrupole:
Integral Spectrum:
Differential Spectrum; ;
Splitting:
A Yield A YieldI (mm/s)
:
S (%l (mm/s> ( W )1 I
1 I I
Fe3+
;
-0.34+0.03:
0.49t0.03:
1.23t0.24 81.3 1.15t0.34 77 .Ol I 1 l
1 I
Fe2+
:
-0.95t0.06:
2.16k0.06 10.48t0.11 18.7i
0.22t0.06 23 .Ol t I l
t I l l
Fig. 2 : The structure of C ~ ~ + D ~ I I I ( C N ) ~ ~ - . Single and double circles indicate CO'+ at A- and B-type
ositions, respectively. Black spots are F ~ I I I of fke111(CN) G]
'-
ions.Additional two CO'+ ions situated inside two of the octants for charge balance, we call to be at B-type position. The ratio of numbers of A- to B-type CO'' ions in the source is 2. Fe2+ formed immediately after the electron capture of 5 7 ~ o at A-position should become Fe3+, because iron ions at A-position are in stronger negative Coulomb field and interact with their surroundings more strongly than ions at B-position. Considering this fact and the yields of Fe2+ end Fe3+ given in table I, we can estimate that more than half of the iron ions at B-position are
in the Fe2+ state.
A change of A of Fe2+ from the inkegral to differential spectra means that the width of the
~ e peaks decreases with time more rapidly than as ~ + expected from the time-filtering theory /2,3/. The increasing-of the yield 6f Fe2+ cannot be explained by a change of ~ e to Fe2+, because Fe3+ is more ~ + stable in the sample used in the present work 181, and, therefore, can be understood by the fact that the recoilless fraction of ~e'+ increases in time scale comparable to the lifetime of the resonance state. 'The line narrowing of Fe2' with time beyond that expected by the time filtering as well as the increasing of the recoilless fraction of Fe2+ are
-
dings
.
It is also noted that the observed line broade- ning of Fe3+ peaks expressed by a nearly constant value of A is caused by the time-independent nuclear environmental inhomogeneity. This effect can be un- derstood by the inherent characteristic of the sam- ple crystal; owing to the lattice distortion by Cou- lomb force, etc., the electric field and its gradient at the Fe3+ site contributed partially from E e I1 (CN)d4- depend on the site where this complex ion is formed by the intramolecular electron transfer from an ~''e ion at A-position to one of F e I11
(CN)
67
3-ions.References
/l/ Triftshaiiser, W.and Schroeer, D., Phys. Rev.
187 (1969) 491.
/2/ Lynch, F.J., Holland, R.E. and Hamermesh, M., Phys. Rev.
2
(1960) 513./3/ Harris, S.M., Phys. Rev.
124
(1961) 1178./4/ Hoy, G.R. and Witersteiner, P.P., Phys Rev. Lett.
28 (1972) 877.
-
/ S / Hoy, G.R., Hamill, D.W. and Wintersteiner, P.P.,
"Mijssbauer Effect Methodology", I.J. Gruverman ed., (Planum Press, New York) 1971, p. 109.
/6/ Kobayashi, T. and Shimizu, S., Phys. Lett.
54A
(1975) 311.
/7/ See Appendix of the report, in this proceedings, entitled "Gamma-X ray coincidence ~6ssbauer sepctroscopy with cobalt chloride1'.
/8/ Chadwick, B.M. and Sharpe, A.G., Adv. Inorg.
Chem. Radiochem.
8
(1966) 83./g/ Alekseev, V.P., Gol'danskii, V.I., Prusakov,V.E., Nefed'ev, A.V. and Stukan, R.S., Pislma Zh.
Eksp. Teor. Fiz.
5
(1972) 65 (JETP Lett.16
(1972) 43).
due to the relaxation phenomena connected strongly with the loose bondings of Fe2+ with its surroun-