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Register a new userHigh pressure electron spin resonance of the endohedral fullerene $^{15}mathrm{N@C}_{60}$
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We measure the electron spin resonance spectrum of the endohedral fullerene molecule $^{15}mathrm{N@C}_{60}$ at pressures ranging from atmospheric pressure to 0.25 GPa, and find that the hyperfine coupling increases linearly with pressure. We present a model based on van der Waals interactions, which accounts for this increase via compression of the fullerene cage and consequent admixture of orbitals with a larger hyperfine coupling. Combining this model with theoretical estimates of the bulk modulus, we predict the pressure shift and compare it to our experimental results, finding fair agreement given the spread in estimates of the bulk modulus. The spin resonance linewidth is also found to depend on pressure. This is explained by considering the pressure-dependent viscosity of the solvent, which modifies the effect of dipolar coupling between spins within fullerene clusters.
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The endohedral fullerene $^{15}mathrm{N@C}_{60}$ has narrow electron paramagnetic resonance lines which have been proposed as the basis for a condensed-matter portable atomic clock. We measure the low-frequency spectrum of this molecule, identifying and characterizing a clock transition at which the frequency becomes insensitive to magnetic field. We infer a linewidth at the clock field of 100 kHz. Using experimental data, we are able to place a bound on the clocks projected frequency stability. We discuss ways to improve the frequency stability to be competitive with existing miniature clocks.
Infrared absorption spectroscopy study of endohedral water molecule in a solid mixture of H$_2$O@C$_{60}$ and C$_{60}$ was carried out at liquid helium temperature. From the evolution of the spectra during the ortho-para conversion process, the spectral lines were identified as para- and ortho-water transitions. Eight vibrational transitions with rotational side peaks were observed in the mid-infrared: $omega_1$, $omega_2$, $omega_3$, $2omega_1$, $2omega_2$, $omega_1 +omega_3$, $omega_2 +omega_3$, and $2omega_2+omega_3$. The vibrational frequencies $omega_2$ and 2$omega_2$ are lower by 1.6% and the rest by 2.4%, as compared to free water/. A model consisting of a rovibrational Hamiltonian with the dipole and quadrupole moments of water interacting with the crystal field was used to fit the infrared absorption spectra. The electric quadrupole interaction with the crystal field lifts the degeneracy of the rotational levels. The finite amplitudes of the pure $v_1$ and $v_2$ vibrational transitions are consistent with the interaction of the water molecule dipole moment with a lattice-induced electric field. The permanent dipole moment of encapsulated water/ is found to be $0.5pm 0.1$ D as determined from the far-infrared rotational line intensities. The translational mode of the quantized center of mass motion of water/ in the molecular cage of C$_{60}$ was observed at 110cm$^{-1}$ (13.6meV).
We report the observation of quantized translational and rotational motion of molecular hydrogen inside the cages of C60. Narrow infrared absorption lines at the temperature of 6K correspond to vibrational excitations in combination with translational and rotational excitations and show well resolved splittings due to the coupling between translational and rotational modes of the endohedral H2 molecule. A theoretical model shows that H2 inside C60 is a three-dimensional quantum rotor moving in a nearly spherical potential. The theory provides both the frequencies and the intensities of the observed infrared transitions. Good agreement with the experimental results is obtained by fitting a small number of empirical parameters to describe the confining potential, as well as the ortho to para ratio.
The molecular compound K$_6$[V$^{IV}_{15}$As$^{III}_6$O$_{42}$(H$_2$O)] $cdot$ 8H$_2$O, in short V$_{15}$, has shown important quantum effects such as coherent spin oscillations. The details of the spin quantum dynamics depend on the exact form of the spin Hamiltonian. In this study, we present a precise analysis of the intramolecular interactions in V$_{15}$. To that purpose, we performed high-field electron spin resonance measurements at 120 GHz and extracted the resonance fields as a function of crystal orientation and temperature. The data are compared against simulations using exact diagonalization to obtain the parameters of the molecular spin Hamiltonian.
The defect in diamond formed by a vacancy surrounded by three nearest-neighbor nitrogen atoms and one carbon atom, $mathrm{N}_{3}mathrm{V}$, is found in $approx98%$ of natural diamonds. Despite $mathrm{N}_{3}mathrm{V}^{0}$ being the earliest electron paramagnetic resonance spectrum observed in diamond, to date no satisfactory simulation of the spectrum for an arbitrary magnetic field direction has been produced due to its complexity. In this work, $mathrm{N}_{3}mathrm{V}^{0}$ is identified in $^{15}mathrm{N}$-doped synthetic diamond following irradiation and annealing. The $mathrm{^{15}N}_{3}mathrm{V}^{0}$ spin Hamiltonian parameters are revised and used to refine the parameters for $mathrm{^{14}N}_{3}mathrm{V}^{0}$, enabling the latter to be accurately simulated and fitted for an arbitrary magnetic field direction. Study of $mathrm{^{15}N}_{3}mathrm{V}^{0}$ under excitation with green light indicates charge transfer between $mathrm{N}_{3}mathrm{V}$ and $mathrm{N_s}$. It is argued that this charge transfer is facilitated by direct ionization of $mathrm{N}_{3}mathrm{V}^{-}$, an as-yet unobserved charge state of $mathrm{N}_{3}mathrm{V}$.
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