Solid Kr Research Articles

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.

The Dioxygen Complexes of VO2

AbstractBy matrix isolation in solid Ne and Kr, VO, VO2, and the complexes VO2(O2) with one superoxo ligand and VO2(O2)2 with one superoxo and one neutral dioxygen ligand, as well as V2O2 and V2O4 have been generated. For VO2(O2), transitions of five vibrational modes have been observed, and for VO2(O2)2, transitions belonging to seven vibrational modes, confirming and extending former Ar matrix results. Attempts to stabilise the cyclic V(O2) peroxide by use of the heavier Kr matrix were not successful. By accompanying MRCI calculations on VO2 and V(O2), vibrational frequencies have been determined. Furthermore, the investigation is assisted by density functional calculations with the TPSS functional. Possibly, also one vibrational transition of the VO3 molecule has been observed.

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.

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.

Local thermal nonequilibrium conjugate natural convection heat transfer of nanofluids in a cavity partially filled with porous media using Buongiorno’s model

ABSTRACTThe natural convection heat transfer in a cavity filled with three layers of solid, porous medium, and free fluid is addressed. The porous medium and free fluid layers are filled with a nanofluid. The porous layer is modeled using the local thermal nonequilibrium (LTNE) model, considering the temperature difference between the solid porous matrix and the nanofluid phases. The nanofluid is modeled using the Buongiorno’s model incorporating the thermophoresis and Brownian motion effects. The governing equations are transformed into a set of nondimensional partial differential equations, and then solved using finite element method in a nonuniform grid. The effects of various nondimensional parameters are discussed. The results showed that the Brownian motion and thermophoresis effects result in significant concentration gradients of nanoparticles in the porous and free fluid layers. The increase in Rayleigh (Ra), Darcy (Da), the thermal conductivity ratios for the solid wall and solid porous matrix, i.e., Kr and Rk, enhanced the average Nusselt number. The increase in the convection interaction heat transfer parameter between the solid porous matrix and the nanofluid in the pores (H) increases the average Nusselt number in the solid porous matrix but decreases the average Nusselt number in the nanofluid phase of the porous layer.

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.

Evolution of Kr Precipitates in Kr-Implanted Al as Observed by the Channelling Method

The evolution of Kr precipitates at room temperature from nucleation to the formation of solid Kr precipitates in Al implanted with 50 keV Kr+ ions has been studied through the site change of Kr atoms determined by the channelling method. A previous channelling study reported that nucleation centres are various types of Kr–vacancy (V) complexes formed at low implantation doses. In this study, the initial stage of growth of Kr precipitates to bubbles and a key process towards the formation of epitaxially aligned solid Kr precipitates are investigated. The growth of Kr precipitates to bubbles proceeds from the accumulation of Kr atoms migrating to Kr–V complexes by radiation-enhanced diffusion. The Kr bubbles are in the fluid state. As to the epitaxial alignment, the following mechanism is proposed. At implantation doses higher than 2 × 1015 Kr/cm2, small clusters of Kr atoms located at octahedral (O) or displaced O sites are formed on the planes parallel to {111} planes at the bubble-matrix interface at th...

Matrix isolation and ab initio study on HCN/CO2 system and its radiation-induced transformations: Spectroscopic evidence for HCN⋯CO2 and trans-HCNH⋯CO2 complexes.

Spectroscopic characteristics and X-ray induced transformations of the HCN⋯CO2 complex in solid Ar and Kr matrices were studied by FTIR spectroscopy and ab initio calculations at the CCSD(T) level. The complex was prepared by deposition of the HCN/CO2/Ng gas mixtures (Ng = Ar or Kr). The comparison of the experiment and calculations prove formation of a linear, H-bonded NCH⋯OCO complex with a substantial red shift of the C-H stretching band and a blue shift of the H-C-N bending band in respect to the monomer. This result is in contrast with the previous gas-phase observations, where only T-shape complex was found. Irradiation of deposited matrices leads to formation of CN radicals and HNC molecules and subsequent annealing results in appearance of H2CN and trans-HCNH in both matrices plus HKrCN in the case of Kr. In the presence of CO2, the strongest absorption of trans-HCNH radical demonstrates an additional blue-shifted (by 6.4 cm-1) feature, which was assigned to the N-coordinated complex of this radical with CO2 on the basis of comparison with calculations. To our knowledge, it is the first experimentally observed complex of this radical. No evidence was found for HKrCN⋯CO2 complex, which was explained tentatively by steric hindrance.

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.

Formation and spectroscopy of dicyanotriacetylene (NC₈N) in solid Kr.

Thermally induced creation of dicyanotriacetylene (NC8N) was observed in solid krypton. Samples were obtained by cryogenic trapping of gaseous cyanoacetylene/Kr mixtures subjected to electric discharges. Strong a (3)Σ(+)(u) → X (1)Σ(+)(g) phosphorescence of NC8N is reported here for the first time; its vibronic structure permitted the measurement of several ground-state vibrational frequencies. Other chemical species, mostly smaller than the precursor molecule, have also been formed, among them the dicarbon molecule (C2), and these may serve as indispensable building blocks in the NC8N synthesis. Processes leading to the elongation of cyanoacetylenic chains are of potential importance for the chemistry of icy grains present in the interstellar gas clouds.

CH3 spin probe in solid Kr: Matrix structure and guest–host interaction

Experimental EPR data obtained for the methyl, CH3, radical trapped in quench condensed solid Kr are analyzed rendering the radical a probe for determination of regional disorder in Kr and similar solid matrices. Formation of regions of a highly disordered local matrix structure is proved. An attempt is presented of assessing a disorder parameter, based on the line broadening. The new structure is shown to be very effective in accumulating the radicals which are transiently mobile at the Kr 4.2K surface. We discuss a model of the trapped radical rotation, which includes somewhat different mechanism than the hindrance of the rotation about the C3 axis and the rotation about the in-plane C2 axes. The level of the thermal contact of the radical spin-rotation motion with the lattice degrees of freedom in regions of varying order in the Kr solid matrix was assessed by progressive saturation curve-fitting parameters related to the spin-lattice relaxation time T1 of the radical.

Solidification and fcc to metastable hcp phase transition in krypton under variable compression rates

We present time-resolved synchrotron x-ray diffraction measurements to study kinetics associated with the liquid-solid and solid-solid high-pressure phase transitions in Kr under dynamic loading in a dynamic-diamond anvil cell. The results show a strong compression-rate dependence of the solidification/melting process in liquid Kr. The analysis of the compression-rate dependent melting/solidification, using an Avrami equation with the parameter $n=1$, indicates a spontaneous nucleation and one-dimensional growth mechanism. In contrast, the face-centered-cubic to metastable hexagonal close-packed transition in solid Kr occurs rapidly at \ensuremath{\sim}0.8 GPa near the melting line, which has negligible compression-rate dependence within the range of compression rates studied $(0.004--13 \mathrm{GPa}/\mathrm{s})$.

Spectroscopy of Mn atoms isolated in solid ⁴He.

We present an experimental study of the laser-induced luminescence spectra of Mn atoms in solid helium matrices. We observe transitions of the valence electron and of inner-shell electrons. We find that the Mn-He interaction perturbs the inner-shell transitions to a lesser extent than the valence-electron transitions. The observed lineshapes of the inner-shell transitions of Mn are similar to those of an inner-shell transition in Ba studied earlier. At the same time, they are more strongly perturbed than the corresponding transitions in Au and Cu under the same conditions. We suggest a qualitative explanation of these observations based on the atomic bubble model. Our results also suggest that the inner-shell transitions of Mn in solid He are more strongly perturbed than the same lines of Mn isolated in solid Ar or Kr matrices.

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.

Pore Size Dependence of Melting Point for Kr Confined in Crystalline Carbon Pores

To elucidate the origin of the large depression in the melting point of Kr in the crystalline carbon pores, we examined the pore-size dependence of the melting point for the Kr confined in the hexagonally shaped pores of turbostratic carbon, compared with the cylindrical pores of amorphous silica of comparable size, by means of X-ray diffraction (XRD). For the amorphous silica pores of cylindrical shape with radius R, the melting-point depression of the confined solid Kr showed a usual 1/R dependence. However, for the solid Kr confined to the crystalline carbon pores, a plot of the melting-point depression against 1/R seems to cross the ordinate at a finite positive value. This strongly suggests that a bulk component of the confined solid has a melting point lower than that for a bulk solid. In accord with this observation, simulation studies (Maddox, M. W.; Gubbins, K. E. J. Chem. Phys.1997, 107, 9659–9667; Kanda, H.; Miyahara, M.; Higashitani, K. Langmuir2000, 16, 8529–8535) have suggested that, in the ...

Electronic spectroscopy of I2–Xe complexes in solid Krypton

In the present work, we have studied ion-pair states of matrix-isolated I(2) with vacuum-UV absorption and UV-vis-NIR emission, where the matrix environment is systematically changed by mixing Kr with Xe, from pure Kr to a more polarizable Xe host. Particular emphasis is put on low doping levels of Xe that yield a binary complex I(2)-Xe, as verified by coherent anti-Stokes Raman scattering (CARS) measurements. Associated with interaction of I(2) with Xe we can observe strong new absorption in vacuum-UV, redshifted 2400 cm(-1) from the X → D transition of I(2). Observed redshift can be explained by symmetry breaking of ion-pair states within the I(2)-Xe complex. Systematic Xe doping of Kr matrices shows that at low doping levels, positions of I(2) ion-pair emissions are not significantly affected by complexation with Xe, but simultaneous increase of emissions from doubly spin-excited states indicates non-radiative relaxation to valence states. At intermediate doping levels ion-pair emissions shift systematically to red due to change in the average polarizability of the environment. We have conducted spectrally resolved ultrafast pump-probe ion-pair emission studies with pure and Xe doped Kr matrices, in order to reveal the influence of Xe to I(2) dynamics in solid Kr. Strikingly, relaxed emission from the ion-pair states shows no indication of complex presence. It further indicates that the complex escapes detection due to a non-radiative relaxation.

Dissipative quantum coherent dynamics probed in phase-space: Electronically resonant 5-color 4-wave mixing on I2(B) in solid Kr

Spectrally resolved, 4-wave mixing measurements in five resonant colors are used to interrogate vibronic quantum coherences in phase-space. We highlight the principles through measurements on the B-state of I(2) in solid Kr--a prototype of a system strongly coupled to its environment. The measurements consist of preparing a superposition of wavepackets on the B-state and interrogating their cross-coherence as they get entangled with the environment. The study provides direct realizations of fundamental quantum principles in the mechanics of molecular matter, among them: the distinction between quantum and classical coherent dynamics of a system entangled with the environment, coherent dissipation, event-driven decoherence, environment selected coherent states, and non-local mechanics.

Transient thermal effects in solid noble gases as materials for the detection of Dark Matter

Noble solid gases are promising detector materials to be used in the search for dark matter. In the present paper a systematic analysis of the transient phenomena associated with the stopping of recoils in noble gases in the solid phase is performed for the first time. The investigated energy range of the recoils corresponds to the elastic scattering of WIMPs from the galactic halo in these materials. A thermal spike model, previously developed by the authors, is extended and applied to solid noble gases. Ionization, scintillation and nuclear energy loss processes are considered and included in the model, as well as the coupling between the subsystems. The development of the temperature pulse in space and time in solid Ar, Kr and Xe is analysed for different energies of the WIMP, and for different initial temperatures of the material. Phase transitions are possible in particular cases. The results of the model could be used as supplementary information in respect to ionization and scintillation, for detection and particle identification.