Abstract
Using pulsed electron paramagnetic resonance (EPR) techniques, the low-temperature magnetic properties of the NO radical being confined in two different modified open -derived cages are determined. It is found that the smallest principal value , being assigned to the axis of the radical, deviates strongly from the free electron value. This behaviour results from partial compensation of the spin and orbital contributions to the value. The measured values in the range of 0.7 yield information about the deviation of the locking potential for the encaged NO from axial symmetry. The estimated 17 meV asymmetry is quite small compared to the situation found for the same radical in polycrystalline or amorphous matrices ranging from 300 to 500 meV. The analysis of the temperature dependence of spin relaxation times resulted in an activation temperature of about 3 K, assigned to temperature-activated motion of the NO within the modified open -derived cages with coupled rotational and translational degrees of freedom in a complicated three-dimensional locking potential.
Highlights
In a series of recent publications, the Kyoto Group has shown that it is possible to encapsulate small and even reactive molecules in a modified C60 cage with tailored entrance and exit holes (Hasegawa et al, 2018a; Futagoishi et al, 2017; Hashikawa et al, 2018)
The estimated 17 meV asymmetry is quite small compared to the situation found for the same radical in polycrystalline or amorphous matrices ranging from 300 to 500 meV
electron paramagnetic resonance (EPR) data published previously by Hasegawa et al (2018a) for NO@C60-OH1 were obtained in cw mode at a microwave frequency of 9.56 GHz
Summary
In a series of recent publications, the Kyoto Group has shown that it is possible to encapsulate small and even reactive molecules in a modified C60 cage with tailored entrance and exit holes (Hasegawa et al, 2018a; Futagoishi et al, 2017; Hashikawa et al, 2018). It was remarkable that the very small value quoted for the axial component (Hasegawa et al, 2018a) of 0.225 deviates significantly from the value determined for NO radicals trapped in a single crystal host (Ryzhkov and Toscano, 2005) or NO radicals adsorbed in zeolites (Poeppl et al, 2000) This very small value of g3 = 0.225, deduced by an analysis of a continuous wave (cw) measurement, necessitated confirmation by pulse EPR experiments, better suited for the study of very broad spectra. The anticipated effects of a nonspherical cage potential on the radical are explored, and effects due to the structural modification of the cage are studied
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