EPR and ENDOR of the PO
4
2?
radical in anhydrite,celestite and barite |
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| Authors: | I D Ryabov I A Potashnyi |
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| Institution: | 1. Institute of Litosphere, Academy of Sciences of Russia, Staromonetniy 22, 109180, Moscow, Russia
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| Abstract: | Electron paramagnetic resonance (EPR) and eletron nuclear double resonance (ENDOR) low temperature measurements of natural anhydrite CaSO4, celestite SrSO4 and barite BaSO4 have revealed the presence of PO
4
2–
radical. The principal values of the g tensor and the A tensor MHz] of hyperfine interaction (HFI) are found to be g
xx
=2.0124, g
yy
=2.0159, g
zz
=2.0098, A
xx
=82.1, A
yy
=81.4, A
zz
=77.2 in CaSO4, g
xx
=2.0250, g
yy
=2.0070, g
zz
=2.0131, A
xx
=84.8, A
yy
=82.7, A
zz
= 90.5 in SrSO4, g
xx
=2.0302, g
yy
=2.0079, g
zz
=2.0135, A
xx
=85.2, A
yy
=82.3, A
zz
=90.0 in BaSO4. The principal axes A
xx
, A
yy
and A
zz
are parallel to the crystallographic axes a, b, c in all three matrices. In anhydrite the principal g axes coincide with the A axes. In celestite and barite such coincidence is found to be only along the b axis (a low symmetry effect). The coherence effect of splitting of ENDOR lines by a strong microwave field has been detected. From the analysis of the relative intensities of the ENDOR lines of the PO
4
2–
radical in CaSO4 the relation of probabilities of cross-relaxation processes W
x/W
xx
=3.5 are evaluated. |
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| Keywords: | |
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