Solid Xe Research Articles

Automated hyperpolarized 129Xe gas generator for nuclear magnetic resonance spectroscopy and imaging applications

We describe a method and an apparatus for producing hyperpolarized (HP) Xe gas of high concentration without Xe condensation. The HP Xe generator works under atmospheric pressure and employs a quasi-continuous method to provide a continuous supply of HP Xe gas by adopting technologies for supplying a highly pure gas, a gas control system and precise pressure control. The apparatus has a glass cell containing solid Rb metal and solid Xe in vacuum at a low temperature and is heated so that the Xe becomes a gas and Rb exists in a gas-liquid mixture. Then a magnetic field is applied with laser beam irradiation to produce polarized Xe gas of high concentration. The device was evaluated using a 2T magnetic resonance imaging (MRI) scanner. Long-term experimental operation demonstrated the continuous collection of 30 ml syringes of HP Xe gas with a sufficient polarization rate for fast one scan acquisition. A practical device for the automated manufacture of HP 129Xe gas was thus successfully developed.

Infrared spectroscopy of the α-hydroxyethyl radical isolated in cryogenic solid media.

The α-hydroxyethyl radical (CH3·CHOH, 2A) is a key intermediate in ethanol biochemistry, combustion, atmospheric chemistry, radiation chemistry, and astrochemistry. Experimental data on the vibrational spectrum of this radical are crucially important for reliable detection and understanding of the chemical dynamics of this species. This study represents the first detailed experimental report on the infrared absorption bands of the α-hydroxyethyl radical complemented by abinitio computations. The radical was generated in solid para-H2 and Xe matrices via the reactions of hydrogen atoms with matrix-isolated ethanol molecules and radiolysis of isolated ethanol molecules with x rays. The absorption bands with maxima at 3654.6, 3052.1, 1425.7, 1247.9, 1195.6 (1177.4), and 1048.4cm-1, observed in para-H2 matrices appearing upon the H· atom reaction, were attributed to the OHstr, α-CHstr, CCstr, COstr + CCObend, COstr, and CCstr + CCObend vibrational modes of the CH3·CHOH radical, respectively. The absorption bands with the positions slightly red-shifted from those observed in para-H2 were detected in both the irradiated and post-irradiation annealed Xe matrices containing C2H5OH. The results of the experiments with the isotopically substituted ethanol molecules (CH3CD2OH and CD3CD2OH) and the quantum-chemical computations at the UCCSD(T)/L2a_3 level support the assignment. The photolysis with ultraviolet light (240-300nm) results in the decay of the α-hydroxyethyl radical, yielding acetaldehyde and its isomer, vinyl alcohol. A comparison of the experimental and theoretical results suggests that the radical adopts the thermodynamically more stable anti-conformation in both matrices.

An EPR study on the radiolysis of isolated ethanol molecules in solid argon and xenon: matrix control of radiation-induced generation of radicals in cryogenic media.

This paper addresses the basic question of the impact of a chemically inert environment on the radiation-induced transformations of isolated organic molecules in icy media at cryogenic temperatures with possible implications for astrochemical issues. The radicals produced by X-ray irradiation of isolated ethanol molecules (C2H5OH and CH3CD2OH) in solid argon and xenon matrices at 7 K were characterized by electron paramagnetic resonance (EPR) spectroscopy. It was shown that methyl (CH3˙) and formyl (HCO˙) radicals resulting from the C-C bond cleavage were mainly produced in the case of solid argon, which was attributed to the significant role of "hot" ionic fragmentation and inefficient energy dissipation to medium. In contrast, irradiation in xenon results in the predominant formation of α-hydroxyethyl radicals (CH3˙CHOH or CH3˙CDOH(D) in the cases of C2H5OH and CH3CD2OH, respectively). Remarkably, the experiments with selectively deuterated ethanol provide strong indirect evidence for the primary formation of ethoxy (CH3CD2O˙) radicals due to O-H bond cleavage, which convert to the α-hydroxyethyl radicals due to isomerization occurring at 7 K. The α-hydroxyethyl radicals adopt a specific rigid conformation with a non-rotating methyl group at low temperatures, which is an unusual effect for neutral CH3˙CHX species, and exhibit free rotation in solid xenon only at ca. 65 K.

Thermodynamic Analysis of ArxXe1-x Solid Solutions Based on Kirkwood–Buff Theory

Kirkwood–Buff Integral (KBI) theory is an important method for the analysis of the structural and thermodynamic properties of liquid solutions. For solids, the calculation of KBIs has become possible only recently through the finite-volume generalisation of KBI theory, but it has so far only been applied to monoatomic crystals. Here, we show that KBI theory can be applied to solid mixtures and compute the KBIs of a ArxXe1−x solid solution, for 0<x<0.1 and temperature T=84−86 K, from pair distribution functions obtained by Monte Carlo simulation. From the KBIs, the isothermal compressibility, partial molar volumes, and thermodynamic factors are calculated and found to be in good agreement with alternative theoretical methods. The analysis of the KBIs and the partial molar volumes give insight into the structure of the mixture. The KBI of Ar pairs is much larger than that of Xe pairs, which indicates the tendency of Ar impurities to accumulate. The evolution of the partial molar volumes with increasing Ar molar fraction x shows a transition at x≈0.06, which reflects the formation of Ar clusters, precursors of the Ar-rich liquid phase. The calculated thermodynamic factors show that the solid(Xe) phase becomes unstable at x≈0.1, indicating the start of the solid (Xe)–liquid (Ar) equilibrium. The chemical potentials of Ar and Xe are obtained from the thermodynamic factor by integration over lnx, and by fitting the data to the Margules equations, the activity coefficients can be estimated over the whole composition range. The present findings extend the domain of applicability of the KBI solution theory from liquids to solids.

Melting curves and bulk moduli of the solid noble gasses He, Ne, Ar, Kr and Xe

Alternative bulk moduli for He, Ne, Ar, Xe and Kr, which differ from those reported in the literature, are presented. These alternative bulk moduli are based on the Gilvarry-Lindemann criterion, combined with a constraint demanding that the derived bulk moduli parameters will simultaneously fits the equations of state and the melting curves of these solid rare gasses. With increasing pressure, He, Ar, Xe and Kr exhibit a first order crystallographic phase transition from fcc to hcp structures. Ne is an exception and maintains the fcc phase up to 208 GPa. Good fits of the melting data are obtained by separately fitting each phase, allowing the extrapolation of the melting curves to higher pressures and temperatures. The anomalous linear behavior of the melting curve of Helium-4 is explained by assuming that the van der Waals attractive force should be added to the coulomb repulsion force when the distance between the two protons reduces under pressure. As the Grüneisen parameter γ is directly related to the bulk moduli B and B′, it is concluded that the flattening of the melting curves in the hcp region is absolutely dependent on the correct determination of the bulk moduli.

Carbene-insertion noble gas compounds: FKrCF and FXeCF

FKrCF and FXeCF were synthetized in solid krypton and xenon matrices at cryogenic temperatures. These molecules representing a new class of noble-gas compounds are formed as a result of reaction between mobile F atoms and trapped CF fragment in solid Kr and Xe, which occur after X-ray radiolysis of CH2F2 in the corresponding matrices. The assignment was based on comparison with previously published computational data (Chopra et al., Chem. Phys., 2017, 494, 20) and the results of additional quantum chemical calculations. New molecules were found to be sensitive to near-IR, visible and UV light.

Thermal decomposition of the HXeCl···H2O complex in solid xenon: Experimental characterization of the two-body decomposition channel

The thermal decomposition process of HXeCl···H2O in solid Xe is studied, and HCl···H2O is identified as a decomposition product. The production is due to the two-body (2B) decomposition of HXeCl moiety, in agreement with theoretical predictions. Two types of 2B decomposition paths are predicted: catalytic and unimolecular 2B decompositions, where water molecule plays different roles. In an experiment to selectively produce HXeCl···D2O, only HCl···D2O is observed as a thermal decomposition product, indicating the occurrence of unimolecular 2B decomposition, where water molecule serves as a spectator. The activation energy for this decomposition process is experimentally determined to be 15 kJ mol−1.

The role of spin-orbit coupling in the optical spectroscopy of atomic sodium isolated in solid xenon

Molecular dynamics calculations, based on the diatomics-in-molecules method, have been used to probe the manifestations of spin-orbit (SO) coupling in the experimental absorption bands of atomic sodium isolated in solid xenon. Inclusion of SO coupling of –320 cm−1 in spectral simulations of the 3 p 2 P ← 3 s 2 S transition leads to unequal band spacings which very closely match the asymmetrical bandshape observed for blue single vacancy (SV) site occupancy. This SO value, extracted in a previous MCD study, reveals the dramatic change in the effective SO coupling constant of the Na atom (from the gas phase value of +17 cm−1) in solid Xe when it is close to the 12 xenon atoms in the first surrounding sphere. In contrast, the symmetrical three-fold split band of the red tetra vacancy (TV) site in Na/Xe is not affected nearly as much by SO coupling. This reflects a greatly reduced “external heavy atom” effect when the 24 Xe atoms surrounding the Na atom in TV are located at greater distances. The contrasting behavior of sodium in the SV and TV sites suggests a strong dependence of the SO coupling strength on the Na–Xe distance.Molecular dynamics calculations, based on the diatomics-in-molecules method, have been used to probe the manifestations of spin-orbit (SO) coupling in the experimental absorption bands of atomic sodium isolated in solid xenon. Inclusion of SO coupling of –320 cm−1 in spectral simulations of the 3 p 2 P ← 3 s 2 S transition leads to unequal band spacings which very closely match the asymmetrical bandshape observed for blue single vacancy (SV) site occupancy. This SO value, extracted in a previous MCD study, reveals the dramatic change in the effective SO coupling constant of the Na atom (from the gas phase value of +17 cm−1) in solid Xe when it is close to the 12 xenon atoms in the first surrounding sphere. In contrast, the symmetrical three-fold split band of the red tetra vacancy (TV) site in Na/Xe is not affected nearly as much by SO coupling. This reflects a greatly reduced “external heavy atom” effect when the 24 Xe atoms surrounding the Na atom in TV are located at greater distances. The contra...

Triplet emission of atomic ytterbium isolated in a xenon matrix

The electronic transitions of ytterbium atoms in a solid Xe matrix grown at 4.8 K are investigated. Absorption bands are detected in the regions of the gas-phase 6s2 1S0 → 4f135d6s2 and 6s2 1S0 → 6s6p 1P1 transitions. Both bands indicate that Yb atoms occupy multiple trapping sites, of which three are identified. Emission induced by the 6s2 1S0 → 6s6p 1P1 excitation is found to be concentrated entirely in the region of the 6s6p 3PJ → 6s2 1S0 decay, whereas the singlet emission is completely quenched. Multiple emission peaks are observed and the effects of annealing and prolonged irradiation on their amplitudes are found to be significant and are interpreted as a consequence of Yb population transfer from one type of site to another. Modeling of the ground-state site structure and stability predicts three Yb/Xe occupation types, substitutional (ss), tetravacancy (tv) and hexavacancy (hv), in order of decreasing stability. Their tentative associations with observed absorption and emission features are discussed. Time correlated single photon spectroscopy is used to determine the lifetimes of the individual emission bands. They are found to be different from each other with indications of a mixture of short- and long- lived 6s6p 3PJ fine-structure components and demonstrate distinct temperature dependencies. A dramatic decrease in the lifetime of the emission peak tentatively assigned to the most stable site with temperature is explained by a competition between the radiative and non-radiative decay paths of the 6s6p 3P1 state. The mechanism of the latter can be attributed to electron–phonon coupling as confirmed by a model of the temperature-dependence of the lifetime.The electronic transitions of ytterbium atoms in a solid Xe matrix grown at 4.8 K are investigated. Absorption bands are detected in the regions of the gas-phase 6s2 1S0 → 4f135d6s2 and 6s2 1S0 → 6s6p 1P1 transitions. Both bands indicate that Yb atoms occupy multiple trapping sites, of which three are identified. Emission induced by the 6s2 1S0 → 6s6p 1P1 excitation is found to be concentrated entirely in the region of the 6s6p 3PJ → 6s2 1S0 decay, whereas the singlet emission is completely quenched. Multiple emission peaks are observed and the effects of annealing and prolonged irradiation on their amplitudes are found to be significant and are interpreted as a consequence of Yb population transfer from one type of site to another. Modeling of the ground-state site structure and stability predicts three Yb/Xe occupation types, substitutional (ss), tetravacancy (tv) and hexavacancy (hv), in order of decreasing stability. Their tentative associations with observed absorption and emission features are discu...

Laser plasma vacuum ultraviolet light source using solid rare-gas targets

The laser plasma emission spectra in a broadband from 30 to 200 nm of solid Ar, Kr, and Xe targets are presented for the first time. The spectra are composed of a broadband continuum and lines. A broadband vacuum ultraviolet (VUV) spectrometer that can measure spectra in the wavelength range from 30 to 200 nm is developed and the measured spectra are able to be calibrated over the entire broad band. The spectral intensity integrated from 30 to 200 nm indicates that the VUV average power generated in the wavelength range is 30 mW when the laser energy is 1 J at 1 Hz. The number of photons of monochromatic light after passing through the spectrometer is estimated to be more than 5 × 106 photons/nm/pulse over the wavelength range and is considered to be useful for applications of broadband VUV spectroscopy.

Magnetically Bistable Nitrenes: Matrix Isolation of Furoylnitrenes in Both Singlet and Triplet States and Triplet 3-Furylnitrene

Two simple acylnitrenes, 2-furoylnitrene (2) and 3-furoylnitrene (6), were generated through 266 nm laser photolysis of the corresponding azides. Both are magnetically bistable in cryogenic matrices, as evidenced by the direct observation of the closed-shell singlet state with IR spectroscopy in solid Ne, Ar, Kr, Xe, and N2 matrices (3-40 K) and the triplet state in toluene (10 K) with EPR spectroscopy (32: |D/hc| = 1.48 cm-1 and |E/hc| = 0.029 cm-1; 36: |D/hc| = 1.39 cm-1 and |E/hc|c = 0.039 cm-1). Subsequent visible-light and UV laser irradiations led to the formation of furyl isocyanates (3 and 7) and ring-opening product 3-cyanoacrolein (9-E and 9-Z), respectively, in which the elusive 3-furylnitrene (38) was also identified by IR and EPR spectroscopy (|D/hc| = 1.12 cm-1 and |E/hc| = 0.005 cm-1).

Infrared Spectroscopic and Electronic Structure Investigations of Beryllium Halide Molecules, Cations, and Anions in Noble Gas Matrices.

Laser-ablated Be atoms, cations, and electrons were reacted with F2, ClF, Cl2, NF3, CCl4, CF2Cl2, HCl, DCl, and SiCl4 diluted in noble gases. The major products were the dihalides BeF2, BeClF, BeCl2, and the hydride chloride HBeCl, whose identities were confirmed by comparison with previous evaporative work, deuterium substitution, and vibrational frequency calculations. The matrix-isolated fundamental frequency of the BeF molecule is higher, and the frequency of BeCl is lower, than that determined for the gas-phase molecules. The BeF+ and BeCl+ cations formed strong dipole-induced dipole complexes in solid Ne, Ar, Kr, and Xe with stepwise increase in computed noble gas dissociation energies. Going down the family NgBeF+ and NgBeCl+ series (Ng = Ne, Ar, Kr, Xe) the Mulliken charges q(Be) decrease, while q(Ng) increases, and the dipole moments decrease, which suggests covalent bonding in the xenon species. We find that the largest intramatrix shift is Ne to Ar which follows the largest factor increase for the Ng atomic polarizabilities. Extra electrons produce Cl-, which reacts with HCl to form the stable HCl2- anion and possibly with BeCl2 to give BeCl3-. A weak band observed in neon experiments with F2 is probably due to BeF3-.

Modeling of Manganese Atom and Dimer Isolated in Solid Rare Gases: Structure, Stability, and Effect on Spin Coupling.

Structures and energies of the trapping sites of manganese atom and dimer in solid Ar, Kr, and Xe are investigated within the classical model, which balances local distortion and long-range crystal order of the host and provides a means to estimate the relative site stabilities. The model is implemented with the additive pairwise potential field based on the ab initio and best empirical interatomic potential functions. In agreement with experiment, Mn single substitution (SS) and tetrahedral vacancy (TV) occupation are identified as stable for Ar and Kr, whereas the SS site is only found for Xe. Stable trapping sites of the weakly bound Mn2 dimer are shown to be the mergers of SS and/or TV atomic sites. For Ar, (SS + SS) and (TV + TV) sites are close in energy, whereas (SS + TV) site lies higher. The (SS + SS) accommodation is identified as the only stable site in Kr and Xe at low energies. The results are compared with the resonance Raman, electron spin resonance, and absorption spectroscopy data. Reproducing the numbers of stable sites, the calculations tend to underestimate the matrix effect on the dimer vibrational frequency and spin-spin coupling constant. Nonetheless, the level of agreement is found to be informative for tentative assignments of the complex features seen in Mn2 matrix isolation spectroscopy.

Absorption spectroscopy of heavy alkaline earth metals Ba and Sr in rare gas matrices--CCSD(T) calculations and atomic site occupancies.

Isolation of the heavier alkaline earth metals Ba and Sr in the solid rare gases (RGs) Ar, Kr, and Xe is analysed with absorption spectroscopy and interpreted partly with the assistance of ab initio calculations of the diatomic M ⋅ RG ground state interaction potentials. The y(1)P ← a(1)S resonance transitions in the visible spectral region are used to compare the isolation conditions of these two metal atom systems and calcium. Complex absorption bands were recorded in all three metal atom systems even after extensive sample annealing. Coupled cluster calculations conducted on the ground states of the nine M ⋅ RG diatomics (M = Ca, Sr, and Ba; RG = Ar, Kr, and Xe) at the coupled cluster single, double, and non-iterative triple level of theory revealed long bond lengths (>5 Å) and shallow bound regions (<130 cm(-1)). All of the M ⋅ RG diatomics have bond lengths considerably longer than those of the rare gas dimers, with the consequence that isolation of these metal atoms in a single substitutional site of the solid rare gas is unlikely, with the possible exception of Ca/Xe. The luminescence of metal dimer bands has been recorded for Ba and Sr revealing very different behaviours. Resonance fluorescence with a lifetime of 15 ns is observed for the lowest energy transition of Sr2 while this transition is quenched in Ba2. This behaviour is consistent with the absence of vibrational structure on the dimer absorption band in Ba2 indicating lifetime broadening arising from efficient relaxation to low-lying molecular states. More extensive 2D excitation-emission data recorded for the complex site structures present on the absorption bands of the atomic Ba and Sr systems will be presented in future publications.

Unraveling the conformational landscape of triallyl phosphate: matrix isolation infrared spectroscopy and density functional theory computations.

The conformations of triallyl phosphate (TAP) were studied using matrix isolation infrared spectroscopy and density functional theory (DFT) calculations. TAP was trapped in N2, Ar, and Xe matrixes at 12 K using an effusive source and the resultant infrared spectra recorded. The computational analysis on conformers of TAP is a challenging problem due to the presence of the large number of conformations. To simplify this problem, conformational analysis was performed on prototypical molecules such as dimethyl allyl phosphate (DMAP) and diallyl methyl phosphate (DAMP), to systematically arrive at the conformations of TAP. The above methodology discerned 131 conformations for TAP, which were found to contribute to the room temperature population. The computations were performed using B3LYP/6-311++G(d,p) level of theory. Vibrational wavenumber calculations were performed for the various conformers to assign the experimental infrared features of TAP, trapped in solid N2, Ar, and Xe matrixes.

Structure and stability of solid Xe(H2)n.

Mixtures of xenon and molecular hydrogen form a series of hexagonal, van der Waals compounds at high pressures and at 300 K. Synchrotron, x-ray, single crystal diffraction studies reveal that below 7.5 GPa, Xe(H2)8 crystallizes in a P3̄m1 structure that displays pressure-induced occupancy changes of two pairs of xenon atoms located on the 2c and 2d sites (while the third pair on yet another 2c site remains fully occupied). The occupancy becomes 1 at the P3̄m1 to R3 transition and all the xenon atoms occupy the 3d sites in the high-pressure structure. These pressure-induced changes in occupancy coincide with volume changes that maintain the average Xe:H2 stoichiometry fixed at 1:8. The synchrotron x-ray diffraction and Raman measurements show that this unique hydrogen-bearing compound that can be synthesized at 4.2 GPa and 300 K, quenched at low temperatures to atmospheric pressure, and retained up to 90 K on subsequent warming.

Non-stationary Luminescence as a Probe of Charged Species

We have developed a new approach – non-stationary luminescence (NsL), for probing charged species in irradiated solids. This original two-stage technique is based on some kind of “pump-probe” experiments with controlled in situ “injection” of electrons via their release from the traps stimulated by the sample heating. The ionic species of interest are first generated by an intense electron beam. The species produced are then probed by recombination luminescence under low-density beam to minimize production of new charged species. The “probing” – detection of NsL spectra, is performed under gradual heating of the irradiated sample in order to release electrons from progressively deeper traps and initiate the recombination with positively charged species. The approach developed is demonstrated by examples D2-doped solid Xe and solid N2.

Infrared identification of proton-bound rare-gas dimers (XeHXe)⁺, (KrHKr)⁺, and (KrHXe)⁺ and their deuterated species in solid hydrogen.

Proton-bound rare-gas dimer (RgHRg)(+), in which Rg represents a rare-gas atom, serves as a prototypical system for proton solvation by inert-gas atoms. Until now, only centrosymmetric species with Rg = Ar, Kr, or Xe have been identified with infrared spectra. We employed electron bombardment during deposition of a mixture of Xe (or Kr) in p-H2 at 3.2 K to prepare (RgHRg)(+). Lines at 847.0 and 972.1 cm(-1) are assigned as the Rg-H-Rg antisymmetric stretching (ν3) mode and its combination with the Rg-H-Rg symmetric stretching (ν1 + ν3) mode of (XeHXe)(+) in solid p-H2, respectively. Lines at 871.1 and 974.0 cm(-1) are assigned as the ν3 and ν1 + ν3 modes of (KrHKr)(+) in solid p-H2, respectively. Slightly shifted and broadened lines were observed for these species in solid n-H2. These results agree satisfactorily with reported experimental values of (XeHXe)(+) and (KrHKr)(+) in solid Xe, Kr, and Ar, and with the quantum-chemically predicted anharmonic vibrational wavenumbers of these species in the gaseous phase; the significant spectral shifts in various matrixes are rationalized with the proton affinities of the hosts. When a mixture of Xe and Kr in p-H2 was used, an additional broad feature at 1284 cm(-1) was observed and assigned as the ν3 mode of (KrHXe)(+) in solid p-H2. This line shifted to 1280 cm(-1) in solid n-H2 and the corresponding line of (KrDXe)(+) was observed at 954 cm(-1) in n-D2. The observations of these lines are new; the wavenumbers significantly blue shifted from those of the centrosymmetric (RgHRg)(+) agree with the quantum-chemically predicted anharmonic vibrational wavenumbers of 1279 cm(-1) for (KrHXe)(+) and 916 cm(-1) for (KrDXe)(+). Analysis of the computational results shows that electronic correlation effects play a much greater role for the asymmetric than for the symmetric species. An interpretation for this is provided.

Laser plasma cryogenic target on translating substrate for generation of continuously repetitive EUV and soft X-ray pulses.

To generate continuously repetitive EUV and soft X-ray pulses with various wavelengths from laser-produced plasmas, a one-dimensionally translating substrate system with a closed He gas cryostat that can continuously supply various cryogenic targets for ~10 Hz laser pulses has been developed. The system was successfully operated at a lowest temperature of 15 K and at a maximum up-down speed of 12 mm/s. Solid Ar, Kr, and Xe layers were formed, and their growth rates and the laser crater sizes on them were studied. By optimization of the operational parameters in accordance with our design rule, it was shown that stable output power was achieved continuously from the plasma emission at frequencies of 1-10 Hz. The average soft X-ray and EUV powers obtained were 19 mW at 3.2 nm, 33 mW at 10.0 nm, and 66 mW at 10.8 nm, with 10% bandwidths, from the Ar, Kr, and Xe solid targets, respectively, with a laser power of 1 W. We will be able to achieve higher frequencies using a high beam quality laser that produces smaller craters, and can expect higher powers. Although only Ar, Kr, and Xe gases were tested in this study, the target system achieved a temperature of 15 K and can thus solidify almost all target gases, apart from H and He, and can continuously supply the solid target. The use of various target materials will enable expansion of the EUV and soft X-ray emission wavelength range.

129Xe nuclear resonance scattering on solid Xe and 129Xe clathrate hydrate

Nuclear inelastic and nuclear forward-scattering experiments utilizing the 129Xe Mössbauer resonance were performed on solid Xe and enriched 129Xe clathrate hydrate. The lifetime and energy of the nuclear resonance were determined to be and , respectively. Nuclear inelastic scattering spectra could be obtained with an instrumental resolution of . Despite low Lamb-Mössbauer factors, Xe specific densities of phonon states were derived for solid Xe and Xe clathrate hydrate. Their reliability was investigated using 1-phonon terms obtained by fixing Lamb-Mössbauer factor values within the applied Fourier-Log decomposition. ABINIT calculations of the density of phonon states in solid Xe supplement the interpretation of the experimental data for fcc Xe and good agreement with published densities of phonon states could be achieved below . Results for the Xe clathrate hydrate essentially confirm the rattling nature of the Xe guests and indicate that Xe modes do not contribute to lattice dynamics above .