Using Quantum Rotational Polarization Moments To Describe The Stereodynamics Of The H+d2(v=0,j=0)→hd(v′,j′) + D Reaction

We present results of quantum calculations we have performed on the title reaction in order to study its stereodynamics at collision energies of 0.54 and 1.29 eV. Our theoretical model is based on a representation where directional properties are expressed in terms of real rotational polarization moments instead of magnetic quantum numbers. We analyze the physical meaning of rotational polarization moments and show that, when defined as in the present work, these quantities directly describe the reaction stereodynamics in terms of intuitive chemical concepts related to preferences in the reaction mechanism for particular planes and senses of molecular rotation. Using this interpretation, we identify two distinct regimes for the stereodynamics of the title reaction, observed when HD is formed with low or high rotational excitation. 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Methyl mercury in Lake Superior: Offshore processes and bioaccumulation

The effects of watershed type exert a strong influence on the speciation of mercury and the delivery of mercury to Lake Superior nearshore waters. As a consequence, tributary mixing zones are important locations for enhanced bioaccumulation in Lake Superior. Methyl Hg (MeHg) bioaccumulation, however, is also observed in regions of the lake that are remote from tributary influences. Three cruises aboard the USEPA vessel R/VLake Guardian on Lake Superior revealed that offshore concentrations of total mercury (HgT) were low, similar to Lake Michigan and oceanic waters (0.21 – 1.0 ng L$^{-1}$ HgT). During August 2000, MeHg averaged 3.0 – 12.6 pg L$^{-}$, at least an order of magnitude lower than most tributaries during typical flow régimes. Despite these differences, initial comparisons of phytoplankton revealed only a two to threefold enrichment of MeHg in tributary mixing zones versus offshore regions. MeHg inputs to the open waters of the lake are dependent on three processes: mixing from nearshore zones, direct atmospheric inputs and MeHg diffusion from sediments. Direct sedimentary methylation rates are extremely low and modeling efforts suggest that photodegradation would eliminate tributaryderived MeHg. Therefore, we conclude that atmospheric sources strongly influence MeHg uptake in offshore zones. A detailed profile at a deep-lake station in August 2001 suggests enhanced bioaccumulation at a subsurface chlorophyll maximum, in a zone with close contact to atmospheric fluxes

Two applications of the Divide & Conquer principle in the molecular sciences

Brinkmann G, Dress A, Perrey SW, Stoye J. Two applications of the Divide & Conquer principle in the molecular sciences. Mathematical programming. 1997;79(1-3):71-97.In this paper, two problems from the molecular sciences are addressed: the enumeration of fullerene-type isomers and the alignment of biosequences. We report on two algorithms dealing with these problems both of which are based on the well-known and widely used Divide & Conquer principle. In other words, our algorithms attack the original problems by associating with them an appropriate number of much simpler problems whose solutions can be "glued together" to yield solutions of the original, rather complex tasks. The considerable improvements achieved this way exemplify that the present day molecular sciences offer many worthwile opportunities for the effective use of fundamental algorithmic principles and architectures

Dependence of the scattering length for hydrogen atoms on effective mass

The possibility that the non-adiabatic correction to the scattering length of a pair of hydrogen atoms interacting via the ground state molecular potential, X1Σg +, of H2 could be made by replacing the mass of each nucleus by a different effective mass is explored. The Born-Oppenheimer potential with adiabatic, relativistic and radiative corrections is used in calculations of the scattering lengths and the mass-dependent shifts of the rotationless vibrational levels with fixed and varying effective masses. The shifts are compared with established values and it is demonstrated that the semi-classical formula for the scattering length accounts well for the effect of changing the mass. A perturbing potential that is equivalent to a change in mass is derived and it is compared to a published local non-adiabatic potential