The effect of variable electronic transition moment on the EELS intensity distribution within a vibrational progression: use of the R-centroid approximation to analyze results for the CO B-X and O2B′-X transitions

The CO B-X and O₂ B′-X transitions are analyzed with the help of ab initio MRD-CI calculations. In both cases a violation of a well-known rule in electron energy loss spectra (EELS) is observed, namely that the intensity distribution of vibrational bands is normally independent of both the scattering angle and the incident electron energy. In both cases strongly avoided crossings are shown to be responsible for the unusual appearance of the EELS. The analysis is simplified by making use of the R-centroid approximation, which was originally developed to organize and systematize optical absorption and emission data. It is concluded that a breakdown of the intensity distribution invariance in EELS should occur for a wide class of transitions in which avoided crossings lead to rapid variations in the electronic transition moment as a function of internuclear separation.     

A Short Synthesis of d-Sotalol

Asymmetric synthesis of d-Sotalol (2) was accomplished by chiral homogenous hydrogenation of (4-isopropylaminoacetyl)methane-sulfonanilide hydrochloride (1).     

Hydrogen bonding and short contacts in [2,4,6‐tris(trifluoromethyl)phenyl]phosphinic acid

In the title compound, C₉H₄F₉O₂P, molecules are linked by a single O—H...O hydrogen bond into chains related to those in phenylphosphinic acid. There are short intramolecular F...P contacts.     

Hydrogen storage using carbon adsorbents: past, present and future

Interest in hydrogen as a fuel has grown dramatically since 1990, and many advances in hydrogen production and utilization technologies have been made. However, hydrogen storage technologies must be significantly advanced if a hydrogen based energy system, particularly in the transportation sector, is to be established. Hydrogen can be made available on-board vehicles in containers of compressed or liquefied H₂, in metal hydrides, via chemical storage or by gas-on-solid adsorption. Although each method possesses desirable characteristics, no approach satisfies all of the efficiency, size, weight, cost and safety requirements for transportation or utility use. Gas-on-solid adsorption is an inherently safe and potentially high energy density hydrogen storage method that could be extremely energy efficient. Consequently, the hydrogen storage properties of high surface area “activated” carbons have been extensively studied. However, activated carbons are ineffective in storing hydrogen because only a small fraction of the pores in the typically wide pore-size distribution are small enough to interact strongly with hydrogen molecules at room temperatures and moderate pressures. Recently, many new carbon nanostructured absorbents have been produced including graphite nanofibers and carbon multi-wall and single-wall nanotubes. The following review provides a brief history of the hydrogen adsorption studies on activated carbons and comments on the recent experimental and theoretical investigations of the hydrogen adsorption properties of the new nanostructured carbon materials. Received: 16 October 2000 / Accepted: 15 November 2000 / Published online: 9 February 2001