In porous materials the molecular confinement is often realized by means of weak Van der Waals interactions between the molecule and the pore surface. The understanding of the mechanism of such interactions is important for a number of applications. In order to establish the role of the confinement size we have studied the microscopic dynamics of molecular hydrogen stored in the nanocages of cl...

We present the spectroscopic identification of the binary hydrogen and 1,4-dioxane clathrate hydrates in which H2 molecules are encapsulated in small cages of the structure II hydrate framework. X-ray diffraction, solid-state NMR and Raman spectroscopy were used to confirm the mixed hydrate structure and more importantly the occupancy pattern of hydrogen in clathrate cages. The corresponding pr...

A new genus of Pteridaceae subfamily Cheilanthoideae is established for what has long been known as Doryopteris ludens. The newly erected genus is named Calciphilopteris in reference to its substrate specificity to limestone. Calciphilopteris can be found throughout Southeast Asia, from Indo-China to New Guinea and Australia. New combinations are established for the four known species (Calciphi...

The lattice thermal conductivity of Ge clathrates is investigated by evaluating the linear response theory heat current correlation functions using molecular dynamics. Clathrate crystals with and without guest atoms in their fullerane cages are studied. In comparison with that of diamond-phase Ge, the clathrate conductivity is reduced by approximately 1 order of magnitude due to the open framew...

We present optical conductivity studies of the type-I clathrate Ba8Ga16Sn30, using a terahertz time-domain spectrometer (0.3-3.0 THz). The lowest-lying spectral peak at 0.72 THz due to the Ba(2) ion's off-center vibration in the oversized cage shows a drastic and anomalous temperature dependence. Below about 100 K, the single broad peak splits into two subpeaks, and with further lowering of the...

We report transient grating measurements carried out on single crystals of bromine clathrate hydrates and on bromine dissolved in water. In all cases, excitation into the B-state of Br2 leads to prompt predissociation, followed by cage-induced recombination on the A/A' electronic surfaces. In liquid water, the vibrationally incoherent recombinant population peaks at t=1 ps and decays with a tim...

The stable and metastable melting relations for silicon in the diamond and Si136 clathrate-II structures at positive and negative pressures are calculated by molecular dynamics computer simulation. The simulated liquid and crystalline clathrates undergo cavitation at approximately -3 and -12 GPa. Between these limits a stretched crystal would transform directly to gas in response to a mechanica...

The D2 clathrate hydrate crystal structure was determined as a function of temperature and pressure by neutron diffraction for the first time. The hydrogen occupancy in the (32+X)H2.136H(2)O, x=0-16 clathrate can be reversibly varied by changing the large (hexakaidecahedral) cage occupancy between two and four molecules, while remaining single occupancy of the small (dodecahedral) cage. Above 1...

We present a mechanistic model for the distribution of methane clathrate in marine sediments, and use it to predict the sensitivity of the steady-state methane inventory to changes in the deep ocean. Themethane inventory is determined by binning the seafloor area according to water depth, temperature, and O2 concentration. Organic carbon rain to the seafloor is treated as a simple function of w...