The properties of ion-water clusters. I. The protonated 21-water cluster

The ab initio atom-centered density-matrix propagation approach and the multistate empirical valence bond method have been employed to study the structure, dynamics, and rovibrational spectrum of a hydrated proton in the "magic" 21 water cluster. In addition to the conclusion that the hydrated proton tends to reside on the surface of the cluster, with the lone pair on the protonated oxygen pointing "outwards," it is also found that dynamical effects play an important role in determining the vibrational properties of such clusters. This result is used to analyze and complement recent experimental and theoretical studies.     

Cycloaddition reactions of some analogs of the acridizinium ion

The 1-aryl-2-imidazo[1,2-b]isoquinolin-4-ium system ( 3 and 4 ), prepared by the action of aniline, or a suitable aniline derivative upon 2-phenacyl-3-chloroisoquinolinium bromide undergoes cycloaddition reactions only with the more nucleophilic alkenes such as cyclopentadiene or 9-vinylcarbazole. The pyrazino[1,2-b]isoquinolin-5-ium-2-oxide ( 8–10 ) system reacts with nucleophilic alkenes more readily than does the acridizinium system 1. For both systems the cycloaddition appears to occur across the meso position of the central ring.     

Exploring the physical,chemical and thermal characteristics of a new potentially insensitive high explosive RX-55-AE-5

Current work at Lawrence Livermore National Laboratory (LLNL) includes both understanding properties of old explosives and measuring properties of new ones. The necessity to know and understand the properties of energetic materials is driven by the need to improve performance and enhance stability to various stimuli, such as thermal, friction and impact insult. This paper will concentrate on the physical properties of RX-55-AE-5, which is formulated from heterocyclic explosive, 2,6-diamino-3,5-dinitropyrazine-1-oxide, LLM-105, and 2.5% Viton A. Differential scanning calorimetry (DSC) was used to measure a specific heat capacity, C _p, of≈0.950 J g⁻¹ °C⁻¹, and a thermal conductivity, κ, of≈0.475 W m⁻¹ °C⁻¹. The LLNL kinetics modeling code Kinetics05 and the Advanced Kinetics and Technology Solutions (AKTS) code thermokinetics were both used to calculate Arrhenius kinetics for decomposition of LLM-105. Both obtained an activation energy barrier E≈180 kJ mol⁻¹ for mass loss in an open pan. Thermal mechanical analysis, TMA, was used to measure the coefficient of thermal expansion (CTE). The CTE for this formulation was calculated to be ≈61 μm m⁻¹ °C⁻¹. Impact, spark, friction are also reported.     

Infrared investigation of the reactions of rhodiumcarbonyl halides and carbon monoxide at elevated pressures

Infrared spectral results at elevated carbon monoxide pressures suggest that rhodiumdicarbonyl halides and carbon monoxide exist in an equilibrium with the corresponding rhodiumtricarbonyl halides.     

Dynamics of water confined in single- and double-wall carbon nanotubes

Using high-resolution quasielastic neutron scattering, we investigated the temperature dependence of single-particle dynamics of water confined in single- and double-wall carbon nanotubes with the inner diameters of 14+/-1 and 16+/-3 A, respectively. The temperature dependence of the alpha relaxation time for water in the 14 A nanotubes measured on cooling down from 260 to 190 K exhibits a crossover at 218 K from a Vogel-Fulcher-Tammann law behavior to an Arrhenius law behavior, indicating a fragile-to-strong dynamic transition in the confined water. This transition may be associated with a structural transition from a high-temperature, low-density (<1.02 gcm(3)) liquid to a low-temperature, high-density (>1.14 gcm(3)) liquid found in molecular dynamics simulation at about 200 K. However, no such dynamic transition in the investigated temperature range of 240-195 K was detected for water in the 16 A nanotubes. In the latter case, the dynamics of water simply follows a Vogel-Fulcher-Tammann law. This suggests that the fragile-to-strong crossover for water in the 16 A nanotubes may be shifted to a lower temperature.     

On the origin of the redshift of the OH stretch in Ice Ih: evidence from the momentum distribution of the protons and the infrared spectral density

Recent measurements of the momentum distribution in water and ice have shown that the proton is in a considerably softer potential in ice Ih than in water or the free monomer. This is broadly consistent with the large red shift observed in the vibrational spectrum. We show that existing water models, which treat the intramolecular potential as unchanged by the hydrogen bonding are unable to reproduce the momentum distribution. In addition, even if they can substantially explain the red shift they are unable to explain the large increase in intensity observed in the infrared spectrum in going from the monomer to ice Ih. We show that the inclusion of a bond dipole derivative term is essential to explain the observed intensities in the infrared spectrum. Though this term is partially responsible for the softening of the effective potential of the proton we show that best agreement with the observed momentum distribution requires a further softening of the harmonic component of the intramolecular potential. We introduce an efficient normal-mode molecular dynamics algorithm for calculating the momentum distribution with path-integrals.     

Multiband generation of mid infrared by use of periodically poled lithium niobate

We report the generation of simultaneous multiband mid-infrared laser output by use of periodically polled lithium niobate pumped by the 1.54-microm output from a KTP optical parametric oscillator. The multiband source is capable of producing three mid-infrared wavelengths ranging from 2.5 to 4microm . In initial experiments we obtained output powers of 542 mW near 2.5microm and 453 mW near 4microm , with power conversion efficiencies of 30% and 25%, respectively. To the best of our knowledge, this is the first demonstration of this kind in the literature.