Formaldehyde of known, near-natural isotopic composition was photolyzed in the SAPHIR atmosphere simulation chamber under ambient conditions. The isotopic composition of the product H2 was used to determine the isotope effects in formaldehyde photolysis. The experiments are sensitive to the molecular photolysis channel, and the radical channel has only an indirect effect and cannot be effective...

Through characterization of the solvent isotope effect on protein dynamics, we have examined determinants of the rate limitation to enzyme catalysis. A global conformational change in Ribonuclease A limits the overall rate of catalytic turnover. Here we show that this motion is sensitive to solvent deuterium content; the isotope effect is 2.2, a value equivalent to the isotope effect on the cat...

We report the influence on the superconducting critical temperature Tc in doped SrTiO3 of the substitution of the natural 16O atoms by the heavier isotope 18O. We observe that for a wide range of doping this substitution causes a strong (~50%) enhancement of Tc. Also the magnetic critical field Hc2 is increased by a factor ~2. Such a strong impact on Tc and Hc2, with a sign opposite to conventi...

We explain the origin of the unusual large isotopic dependence found in charge-transfer cross sections for H(D,T)+ + Be collisions. We show that this large effect appears in a semiclassical treatment as a consequence of the mass dependence of the charge-transfer transition probabilities, which is due to the variation of the radial velocity in the region where the nonadiabatic transitions take p...

In this study, we develop and test a method to determine the rate of particle transfer and kinetic isotope effects in enzymatic reactions, specifically yeast alcohol dehydrogenase (YADH), from first-principles. Transition path sampling (TPS) and normal mode centroid dynamics (CMD) are used to simulate these enzymatic reactions without knowledge of their reaction coordinates and with the inclusi...

We report on the observation of weak satellites of the strong and sharp parity-forbidden, but symmetry-allowed 1s(A1)-1s(T2) doublet of the infrared electronic spectrum of S + in silicon. The low-energy satellites are ascribed to a Si isotope effect and the high-energy ones to an S isotope effect. We also show that the profile of the low-energy component of the same transition of Se can be repr...

Hydrogen atom transfer reactions between the aldose and ketose are key mechanistic features in formose chemistry by which formaldehyde is converted to higher sugars under credible prebiotic conditions. For one of these transformations, we have investigated whether hydrogen tunneling makes a significant contribution to the mechanism by examining the deuterium kinetic isotope effect associated wi...

Population growth and watershed deforestation in northwestern Tanzania threaten the biodiversity of Lake Tanganyika through erosion and habitat degradation. We used cores collected offshore from Gombe Stream National Park and a deforested watershed to reconstruct how land-use changes in the Gombe Stream area since A.D. 1750 have affected lake biodiversity. Paleoenvironmental and paleoecological...