The nature of the excited states of p-nitro-N,N-dimethylaniline.

Contrary to numerous derivatives of p-substituted N,N-dimethyl-aniline, p-nitro-N,N-dimethylaniline, does not form the TICT state. This behaviour is predicted by INDO/S calculations. The calculations also reveal an important role of the Coulomb interaction term in the evolution of intramolecular charge-transfer excited-state energy upon twisting of the dimethylamino group

Surface exposure to sunlight stimulates CO 2 release from permafrost soil carbon in the Arctic

Recent climate change has increased arctic soil temperatures and thawed large areas of permafrost, allowing for microbial respiration of previously frozen C. Furthermore, soil destabilization from melting ice has caused an increase in thermokarst failures that expose buried C and release dissolved organic C (DOC) to surface waters. Once exposed, the fate of this C is unknown but will depend on its reactivity to sunlight and microbial attack, and the light available at the surface. In this study we manipulated water released from areas of thermokarst activity to show that newly exposed DOC is >40% more susceptible to microbial conversion to CO2 when exposed to UV light than when kept dark. When integrated over the water column of receiving rivers, this susceptibility translates to the light-stimulated bacterial activity being on average from 11% to 40% of the total areal activity in turbid versus DOC-colored rivers, respectively. The range of DOC lability to microbes seems to depend on prior light exposure, implying that sunlight may act as an amplification factor in the conversion of frozen C stores to C gases in the atmosphere

T^3-Stern-Gerlach Matter-Wave Interferometer

We present a unique matter-wave interferometer whose phase scales with the cube of the time the atom spends in the interferometer. Our scheme is based on a full-loop Stern-Gerlach interferometer incorporating four magnetic field gradient pulses to create a state-dependent force. In contrast to typical atom interferometers which make use of laser light for the splitting and recombination of the wave packets, this realization uses no light and can therefore serve as a high-precision surface probe at very close distances.Comment: Phys. Rev. Lett., in print, https://journals.aps.org/prl

SECONDARY FLUORESCENCES OF 4'-(1-PYRENYL)ACETOPHENONE AND PARA-DIMETHYLAMINOACETOPHENONE

International audienceno abstrac

Intramolecular charge-transfer properties of a molecule with a large donor group: The case of 4'-(1-pyrenyl) acetophenone

International audienceno abstrac

Intramolecular charge-transfer properties of a molecule with a large donor group: The case of 4'-(1-pyrenyl) acetophenone

no abstrac

EXCITED-STATE RELAXATION PROCESSES IN THE CASE OF SOME ACETOPHENONE DERIVATIVES

no abstrac

Effects of long-term climate trends on the methane and CO2 exchange processes of Toolik Lake, Alaska

Methane and carbon dioxide effluxes from aquatic systems in the Arctic will affect and likely amplify global change. As permafrost thaws in a warming world, more dissolved organic carbon (DOC) and greenhouse gases are produced and move from soils to surface waters where the DOC can be oxidized to CO2 and also released to the atmosphere. Our main study objective is to measure the release of carbon to the atmosphere via effluxes of methane (CH4) and carbon dioxide (CO2) from Toolik Lake, a deep, dimictic, low-arctic lake in northern Alaska. By combining direct eddy covariance flux measurements with continuous gas pressure measurements in the lake surface waters, we quantified the k600 piston velocity that controls gas flux across the air–water interface. Our measured k values for CH4 and CO2 were substantially above predictions from several models at low to moderate wind speeds, and only converged on model predictions at the highest wind speeds. We attribute this higher flux at low wind speeds to effects on water-side turbulence resulting from how the surrounding tundra vegetation and topography increase atmospheric turbulence considerably in this lake, above the level observed over large ocean surfaces. We combine this process-level understanding of gas exchange with the trends of a climate-relevant long-term (30 + years) meteorological data set at Toolik Lake to examine short-term variations (2015 ice-free season) and interannual variability (2010–2015 ice-free seasons) of CH4 and CO2 fluxes. We argue that the biological processing of DOC substrate that becomes available for decomposition as the tundra soil warms is important for understanding future trends in aquatic gas fluxes, whereas the variability and long-term trends of the physical and meteorological variables primarily affect the timing of when higher or lower than average fluxes are observed. We see no evidence suggesting that a tipping point will be reached soon to change the status of the aquatic system from gas source to sink. We estimate that changes in CH4 and CO2 fluxes will be constrained with a range of +30% and −10% of their current values over the next 30 years.ISSN:2296-665