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Infrared spectroscopic studies of weakly bound clusters isolated in solid parahydrogen (pH2) that exhibit large-amplitude tunneling motions are needed to probe how quantum solvation perturbs these types of coherent dynamics. We report high resolution Fourier transform infrared absorption spectra of (HCl)2, HCl–DCl, and (DCl)2 isolated in solid pH2 in the 2.4–4.8 K temperature range. The (HCl)2 spectra show a remarkable amount of fine structures that can be rigorously assigned to vibration–rotation–tunneling transitions of (HCl)2 trapped in double substitution sites in the pH2 matrix where end-over-end rotation of the cluster is quenched. The spectra are assigned using a combination of isotopically (H/D and 35Cl/37Cl) enriched samples, polarized IR absorption measurements, and four-line combination differences. The interchange-tunneling (IT) splitting in the ground vibrational state for in-plane and out-of-plane H35Cl–H37Cl dimers is 6.026(1) and 6.950(1) cm−1, respectively, which are factors of 2.565 and 2.224 smaller than in the gas phase dimer. In contrast, the (DCl)2 results show larger perturbations where the ground vibrational state IT splitting in D35Cl–D37Cl is 1.141(1) cm−1, which is a factor of 5.223 smaller than in the gas phase, and the tunneling motion is quenched in excited intramolecular vibrational states. The results are compared to similar measurements on (HCl)2 made in liquid helium nanodroplets to illustrate the similarities and differences in how both these quantum solvents interact with large amplitude tunneling motions of an embedded chromophore. [ABSTRACT FROM AUTHOR]

In this study, the thermal stability of Au–Al2O3 core–shell and Au nanowires was investigated by in situ scanning transmission electron microscopy and other techniques. The nanowires were synthesized by the helium droplets method and deposited on various substrates. The in situ characterization of Au–Al2O3 thermal stability demonstrated a substantially enhanced stability as compared to that of pure Au nanowires, which can be a transformative approach to design more durable Au-based nanocatalysts. Our study also revealed the existence of strong metal–support bonding in the Au/Al2O3 system. [ABSTRACT FROM AUTHOR]

Atomic and molecular clusters are a unique class of substances with properties that differ greatly from those of the bulk or single atoms due to changes in surface to volume ratio and finite size effects. Here, we demonstrate the ability to create cluster matter films using helium droplet mediated cluster assembly and deposition, a recently developed methodology that condenses atoms or molecules within liquid helium droplets and then gently deposits them onto a surface. In this work, we examine magnesium nanocluster films, which exhibit growth behavior comparable to low-energy cluster beam methods, and demonstrate physical properties and morphology dependent on helium droplet size. [ABSTRACT FROM AUTHOR]

We report the first rotationally resolved and completely assigned rovibrational spectrum for a nonhydride molecule rotating in the solid phase: carbon monoxide (CO) monomers isolated in cryogenic solid parahydrogen (p-H2). We employ a modified crystal field theory model, in which the CO molecular spectroscopic constants are taken as adjustable parameters, to make good spectroscopic assignments for all the observed features. We discuss the limitations of this approach and highlight the need for improved theoretical models of molecular rotation dynamics in quantum solids. [ABSTRACT FROM AUTHOR]

The ionization and charge transfer processes, which occur when a doped helium droplet undergoes electron impact, are studied for droplets doped with van der Waals complexes with various structures and electrostatic moments. The mass spectra of the two isomers of hydrogen cyanide complexed with either cyanoacetylene or acetylene in helium droplets were obtained using optically selected mass spectrometry, and show that the structure of the complex has a large effect on the fragmentation pattern. The resulting fragmentation pattern is consistent with an ionization process in which charge steering strongly influences the site of initial ionization. The observed dissociation products may also be subject to caging by the helium matrix. [ABSTRACT FROM AUTHOR]

We report polarized infrared absorption spectra of water isotopologues isolated in solid parahydrogen (pH2) which reveal the crystal field induced splittings of the 101←000 R(0) lines in the ν1 HDO, ν3 D2O, ν3 HDO, and ν3 H2O fundamental bands. For annealed pH2 solids, these spectra also reveal a strong alignment of the hexagonal-close-packed crystallites’ c axes with the deposition substrate surface normal. This alignment effect explains our failure to detect the parallel-polarized components of these R(0) lines in spectra of pH2 solids produced on a transparent deposition substrate [M. E. Fajardo et al., J. Mol. Struct. 695, 111 (2004)]. This lesson applies more generally to comparison of solid pH2 spectra obtained in different laboratories. The spectra are consistent with water monomers existing in solid pH2 as very slightly hindered rotors. The individual components of the R(0) absorption lines show a Lorentzian lineshape, with vibrational depopulation the most important source of line broadening. [ABSTRACT FROM AUTHOR]

The process of electron impact ionization of a helium atom in a helium nanodroplet is studied for the cases of hydrogen cyanide, acetylene, and cyanoacetylene in helium by using a new experimental method called optically selected mass spectroscopy. This method is used to study the charge migration in helium and reveals that the probability of charge transfer to a solvated molecule does not approach unity for small droplets and depends on the identity of the solvated molecule.

In this study, the production of particulate films of iodine (V) oxides is investigated. The influence that sonication and solvation of suspended particles in various alcohol/ketone/ester solvents have on the physical structure of spin or drop cast films is examined in detail with electron microscopy, powder x-ray diffraction, and UV-visible absorption spectroscopy. Results indicate that sonicating iodine oxides in alcohol mixtures containing trace amounts of water decreases deposited particle sizes and produces a more uniform film morphology. UV-visible spectra of the pre-cast suspensions reveal that for some solvents, the iodine oxide oxidizes the solvent, producing b and lowering the pH of the suspension. Characterizing the crystals within the cast films reveal their composition to be primarily HI3O8, their orientations to exhibit a preferential orientation, and their growth to be primarily along the ac-plane of the crystal, enhanced at higher spin rates. Spin-coating at lower spin rates produces laminate-like particulate films versus higher density, one-piece films of stacked particles produced by drop casting. The particle morphology in these films consists of a combination of rods, plates, cubes, and rhombohedra structure. [ABSTRACT FROM AUTHOR]

In the first of a series of papers on the iodine(V) oxide system, the chemical and physical properties associated with iodine(V) oxide in its anhydride (I2O5) and hydrated states (HI3O8 and HIO3) are examined. The three forms of the oxide have been investigated utilizing differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and powder X-ray diffraction (PXRD). Furthermore, the hydration rates governing the conversion of the anhydride (I2O5) to the initial hydrate (HI3O8) and later to the final hydrated state (HIO3) are reported and discussed. Results from this study suggest that the hydration mechanism for I2O5→HI3O8 begins with an accelerating period described as a nucleation and growth phase followed by a decelerating period that is diffusion limited. The initial rate of hydration was observed to be governed by a nucleation and growth mechanism, which was inhibited by covering the surface of the particle with an inert metal. Based on this investigation the initial rate of hydration appears to be strongly dependent on the anhydride's available surface area which facilitates nucleation and growth of HI3O8. The final step, HI3O8→HIO3, proceeds through an initial induction period followed by a continuous acceleratory period unlike the first hydration step. [ABSTRACT FROM AUTHOR]

Exothermic reactions between metals and fluorinated polymers are found in a variety of energetic materials, including reactive binder systems and the Magnesium-Teflon-Viton incendiary composition. This paper describes the reactions between a high molecular weight perfluoropolyether, Fomblin Y 140/13, and magnesium in a variety of morphologies including μm-scale powders and nano-scale layered films. Using Temperature Programmed Desorption and Temperature Programmed Reaction we have found that the magnesium-perfluoropolyether interaction is characterized by: (1) competition between Fomblin decomposition and desorption, and (2) magnesium passivation by the formation of magnesium fluoride. Differential Scanning Calorimetry measurements establish a lower-bound estimate of the specific reaction energy of 9.2 kJ g−1. High molecular weight Fomblin (6500 amu) undergoes a competitive reaction/desorption process with desorption occurring at 550 K and decomposition at 610 K. Decomposition becomes more favorable relative to desorption for higher heating rates and thicker films. Perfluoropolyethers produce several characteristic ions in the 70 eV election ionization mass spectra, with the CF3+ ion being the most abundant ion observed during both the molecular desorption and decomposition. Larger fragment ions with masses of 235 and 285 amu are observed in relatively high concentrations during desorption and low concentrations during decomposition. The reaction between magnesium and Fomblin begins at 400 K, producing CF3+, CO+, and C2F5+ in the electron ionization mass spectrum. We propose that these reactions form a passivating layer of magnesium fluoride that protects the remaining metal as it approaches the magnesium melting point. Most of the reaction takes place at 800 K and above when the magnesium fluoride film ruptures. [ABSTRACT FROM AUTHOR]

In this study, the thermal stability of Au-Al 2 O 3 core-shell and Au nanowires was investigated by in situ scanning transmission electron microscopy and other techniques. The nanowires were synthesized by the helium droplets method and deposited on various substrates. The in situ characterization of Au-Al 2 O 3 thermal stability demonstrated a substantially enhanced stability as compared to that of pure Au nanowires, which can be a transformative approach to design more durable Au-based nanocatalysts. Our study also revealed the existence of strong metal-support bonding in the Au/Al 2 O 3 system.

Infrared spectroscopic studies of weakly bound clusters isolated in solid parahydrogen (pH 2 ) that exhibit large-amplitude tunneling motions are needed to probe how quantum solvation perturbs these types of coherent dynamics. We report high resolution Fourier transform infrared absorption spectra of (HCl) 2 , HCl-DCl, and (DCl) 2 isolated in solid pH 2 in the 2.4-4.8 K temperature range. The (HCl) 2 spectra show a remarkable amount of fine structures that can be rigorously assigned to vibration-rotation-tunneling transitions of (HCl) 2 trapped in double substitution sites in the pH 2 matrix where end-over-end rotation of the cluster is quenched. The spectra are assigned using a combination of isotopically (H/D and 35 Cl/ 37 Cl) enriched samples, polarized IR absorption measurements, and four-line combination differences. The interchange-tunneling (IT) splitting in the ground vibrational state for in-plane and out-of-plane H 35 Cl-H 37 Cl dimers is 6.026(1) and 6.950(1) cm -1 , respectively, which are factors of 2.565 and 2.224 smaller than in the gas phase dimer. In contrast, the (DCl) 2 results show larger perturbations where the ground vibrational state IT splitting in D 35 Cl-D 37 Cl is 1.141(1) cm -1 , which is a factor of 5.223 smaller than in the gas phase, and the tunneling motion is quenched in excited intramolecular vibrational states. The results are compared to similar measurements on (HCl) 2 made in liquid helium nanodroplets to illustrate the similarities and differences in how both these quantum solvents interact with large amplitude tunneling motions of an embedded chromophore.