ly. The oxygen fugacity (/02) of the experiments was not buffered externally. However, /02 calculations based on biotite-sanidine-magnetite-H20-02 equilibrium [D. R. Wones, Kozan Chishitsu 31, 191 (1981)] yield /02 values 1.5 to 2 log units above the nickel-nickel oxide buffer. This is consistent with the estimated f02 conditions of natural epidote-bearing magmas {6, 16). Quenched experimental charges were sectioned longitudinally, polished, and examined with reflected-light microscopy and backscattered electron imaging. Rim widths were measured with an optical microscope equipped with a graduated ocular lens; the rim widths reported are the average of 20 to 30 measurements. Rim width data are as follows: experiment Ep-10, t = 51.17 hours, rim width = 2.74 ± 0.9 fjim; experiment Ep-12, t = 141.20 hours, rim width = 4.95 ± 0.8 fjtm; and experiment Ep-11, t = 378.78 hours, rim width = 8.18 £ 1.3 fjtm. 9. D. C. Rubie and A.

Abstract:The cavity inside fullerenes provides a unique environment for the study of isolated atoms and molecules. We report encapsulation of hydrogen fluoride inside C 60 using molecular surgery to give the endohedral fullerene HF@C 60 . The key synthetic step is the closure of the open fullerene cage while minimizing escape of HF. The encapsulated HF molecule moves freely inside the cage and exhibits quantization of its translational and rotational degrees of freedom, as revealed by inelastic neutron scattering and infrared spectroscopy. The rotational and vibrational constants of the encapsulated HF molecules were found to be redshifted relative to free HF. The NMR spectra display a large 1 H-19 F Jcoupling typical of an isolated species. The dipole moment of HF@C 60 was estimated from the temperature-dependence of the dielectric constant at cryogenic temperatures and showed that the cage shields around 75% of the HF dipole.Molecular endofullerenes consist of fullerene cages encapsulating small molecules, which are free to rotate and translate inside the cage. 1 The dihydrogen and water endofullerenes H 2 @C 60 , H 2 O@C 60 , and their isotopologues, have been synthesized by the procedure known as 'molecular surgery', in which synthetic operations are used to open a hole in the fullerene allowing encapsulation of the guest, followed by a suturing technique to reform the pristine fullerene shell. [2][3][4] Recently the approach has been extended to C 70 and C 59 N. [5][6][7] The confined molecules display quantization of their coupled translational and rotational degrees of freedom, and exhibit phenomena such as nuclear spin isomerism and orthopara conversion. [8][9][10][11][12] Recently it was shown that nuclear spin conversion of the encapsulated water molecules in H 2 O@C 60 leads to a change in the dielectric constant of the material. 13 One system of great interest is HF@C 60 , in which each fullerene cage contains a single hydrogen fluoride (HF) molecule. This material offers the possibility to study the spectroscopic properties of nearisolated and freely rotating HF molecules under a wide range of conditions, free from the complications of dimerization and hydrogen bonding. Predictions of the properties of HF@C 60 have been made using classical, 14 semiempirical 15,16 and quantum chemistry techniques. [17][18][19][20] Furthermore it has been postulated that endofullerenes containing freely rotating electric dipoles could exhibit ferroelectricity, due to cooperative alignment of the interacting electric dipole moments. 21 2The first examples of open-cage endofullerenes encapsulating a hydrogen fluoride molecule have recently appeared, including HF@1. 22,23 Herein we report the successful suturing of HF@1 to give the closed-cage species HF@C 60 . We present NMR, infrared, and neutron scattering data on HF@C 60 which show that the translational and rotational motions of the HF molecule inside the cage are quantized. Interactions with the cage modify the rotational and vibrational constants of the encapsula...

We report on terahertz spectroscopy of quantum spin dynamics in α-RuCl_{3}, a system proximate to the Kitaev honeycomb model, as a function of temperature and magnetic field. We follow the evolution of an extended magnetic continuum below the structural phase transition at T_{s2}=62  K. With the onset of a long-range magnetic order at T_{N}=6.5  K, spectral weight is transferred to a well-defined magnetic excitation at ℏω_{1}=2.48  meV, which is accompanied by a higher-energy band at ℏω_{2}=6.48  meV. Both excitations soften in a magnetic field, signaling a quantum phase transition close to B_{c}=7  T, where a broad continuum dominates the dynamical response. Above B_{c}, the long-range order is suppressed, and on top of the continuum, emergent magnetic excitations evolve. These excitations follow clear selection rules and exhibit distinct field dependencies, characterizing the dynamical properties of a possibly field-induced quantum spin liquid.