B. Rajeswari et al. / Spectrochimica Acta Part A 79 (2011) 405–411
411
O–O bond direction) and it exhibited mobility. It may be noted
that EPR investigations on thorium oxalate containing NO3 as an
impurity (incorporated during sample preparation by oxalate pre-
cipitation from nitric acid) gave NO2 on irradiation and exhibited
similar rotational mobility as observed in the present case [38].
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[
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2
3
[
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4
. Conclusion
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[
[
[
EPR studies on gamma irradiated Th(NO ) ·5H O gave evidence
3
4
2
for the stabilization of NO2 at three different sites with slightly
different spin Hamiltonian parameters. NO2 at one of these sites
exhibited molecular dynamics transforming from a slow motion
region to fast motion region with increase in temperature thereby
leading to a change in EPR spectrum from orthorhombic to axial.
This indicated preferred rotation of NO2 molecule about the O–O
bond direction. The NO2 molecule at the second site was found to
be rigid throughout the entire temperature range. The mobility of
NO2 at Site2 is suppressed if it is bound to thorium either through
two oxygen atoms or by one oxygen atom bound to thorium on one
side and a hydrogen bonded oxygen on the other side. On the other
hand, if NO at Site is formed from NO trapped at interstitial sites
(
1995) 673.
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8
[
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[
[
[
[
[
2
1
3
(
non coordinated NO group) or NO adsorbed on the surface, it will
3 3
be weakly bound in the lattice and will be amenable to molecular
dynamics resulting in the observed change in the EPR spectra from
orthorhombic to axial.
[
27] M.D. Sastry, Chapter X, in: N.M. Gupta, V.B. Kartha, R.A. Rajadhyaksha (Eds.),
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Acknowledgements
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28] R.T. Weber, WINEPR SimFonia Manual, Ver. 1.2, Bruker Instruments, Inc., Bil-
lerica, MA, 1995, and references therein.
Authors wish to thank Dr. V.K. Manchanda, Head, Radiochem-
istry Division, BARC for his keen interest and encouragement during
the course of the present study. Thanks are also due to Dr. A.K.
Tyagi, Chemistry Division, BARC for providing the XRD data of the
samples.
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