Phase transitions reflected in HF-EPR spectra

Doctoral thesis OPEN
Horst, E. van der;
(2006)
  • Publisher: Nijmegen : [S.n.]

EPR is a technique limited to unpaired electrons. Current state of the art set-ups operate at frequencies of 130 GHz or higher. The benefits are increased resolution and the ability to measure large D systems. Using EPR data combined with other techniques systems in whi... View more
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    22 references, page 1 of 3

    1 High Frequency-EPR 11 1.1 Introduction to EPR . . . . . . . . . . . . . . . . . . . . . . 11 1.1.1 The g-value . . . . . . . . . . . . . . . . . . . . . . . 12 1.1.2 Interaction with the nuclear spin . . . . . . . . . . . 14 1.1.3 Zero field splitting and rhombicity . . . . . . . . . . 15 1.2 Benefits of high(er) frequencies . . . . . . . . . . . . . . . . 17 1.2.1 Increased g-tensor resolution . . . . . . . . . . . . . 17 1.2.2 Large zero field splittings . . . . . . . . . . . . . . . 18 1.2.3 Theoretical increase of sensitivity . . . . . . . . . . . 19 1.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

    2 HF-EPR techniques 23 2.1 Transmission lines . . . . . . . . . . . . . . . . . . . . . . . 23 2.2 Circulators and directional couplers . . . . . . . . . . . . . . 26 2.3 Resonators . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.3.1 Single mode resonators . . . . . . . . . . . . . . . . . 29 2.3.2 Whispering gallery resonators . . . . . . . . . . . . . 30 2.3.3 Fabry-Perot resonators . . . . . . . . . . . . . . . . . 31 2.3.4 Oversized resonators . . . . . . . . . . . . . . . . . . 32 2.3.5 Non resonant sample holders . . . . . . . . . . . . . 32 2.4 The Nijmegen HF-EPR set-up . . . . . . . . . . . . . . . . 33 2.4.1 Source and detection . . . . . . . . . . . . . . . . . . 33

    3 The ground state of Ni:Zn(en)3(NO3)2 43 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 3.2 Crystallography of Ni:Zn(en)3(NO3)2 . . . . . . . . . . . . . 46 3.3 Experimental set-up . . . . . . . . . . . . . . . . . . . . . . 46 3.4 The S = 1 resonances of Ni:Zn(en)3(NO3)2 . . . . . . . . . 47 3.4.1 190 K data . . . . . . . . . . . . . . . . . . . . . . . 47 3.4.2 115 K data . . . . . . . . . . . . . . . . . . . . . . . 47 3.5 The central resonance of Ni:Zn(en)3(NO3)2 . . . . . . . . . 50 3.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 3.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

    4 The ground state of Mn(C5H5)2 61 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 4.1 Manganocene as an unusual metallocene . . . . . . . . . . . 62 4.1.1 Structural anomaly of Mn(C5H5)2 . . . . . . . . . . 63 4.1.2 The ground state of Mn(C5H5)2 . . . . . . . . . . . 64 4.2 Experimental methods . . . . . . . . . . . . . . . . . . . . . 65 4.3 Magnetization of Mn(C5H5)2 . . . . . . . . . . . . . . . . . 66 4.4 (HF)-EPR measurements on Mn(C5H5)2 . . . . . . . . . . . 67 4.4.1 S = 52 resonances . . . . . . . . . . . . . . . . . . . . 67 4.4.2 The S = 12 like resonance . . . . . . . . . . . . . . . 70 4.5 Antiferromagnetic resonance of Mn(C5H5)2 . . . . . . . . . 71 4.5.1 General antiferromagnetic resonance . . . . . . . . . 72 4.5.2 AFMR of quasi 1-D systems . . . . . . . . . . . . . . 73 4.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 4.6.1 EPR active dimer systems . . . . . . . . . . . . . . . 74 4.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

    5 The ground state of molecular oxygen 81 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 5.1.1 A short history of oxygen . . . . . . . . . . . . . . . 82 5.1.2 The ground state of O2 . . . . . . . . . . . . . . . . 83 5.2 Contradicting indications . . . . . . . . . . . . . . . . . . . 86 5.2.1 Pure molecular oxygen . . . . . . . . . . . . . . . . . 86 5.2.2 Diluted molecular oxygen . . . . . . . . . . . . . . . 87 5.3 Experimental set-up . . . . . . . . . . . . . . . . . . . . . . 88 5.4 The ground state at low temperatures . . . . . . . . . . . . 89 5.4.1 Determination of the zero field splitting . . . . . . . 89 5.4.2 Temperature dependence of the S = 1 resonances . . 91 5.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 5.5.1 Pure oxygen . . . . . . . . . . . . . . . . . . . . . . . 96 5.5.2 Dilution in a host . . . . . . . . . . . . . . . . . . . . 97 5.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

    [1] D.R. Lide (editor in chief ). Handbook of Chemistry and Physics, 72nd special student edition. The Chemical Rubber Company, 1991.

    [2] Encyclopedia Brittanica. WWW.Brittanica.com, 1999-2000.

    [11] G.M. Graham, J.S.M. Harvey, and H. Kiefte. EPR of O2 impurity in solid N2. J. Chem. Phys, 52:2235-2237, 1970.

    [12] J.R. Byberg. Detection by ESR of oxygen molecules formed as defects in single crystals. Chem. Phys. Lett., 57:579-581, 1978.

    [13] N. Bjerre. ESR study of the librations of O2 defects in NaClO3 and KClO4 single crystals. J. Chem. Phys., 76:3347-3351, 1982.

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