Observation of Femtosecond Molecular Dynamics via Pump-Probe Gas Phase X-ray Scattering

We describe a gas-phase x-ray scattering experiment capable of capturing molecular motions with atomic spatial resolution and femtosecond time resolution. X-ray free electron lasers can deliver intense x-ray pulses of ultrashort duration, making them suitable to study ultrafast chemical reaction dynamics in an ultraviolet pump, x-ray probe scheme. A cell diffractometer balances sample flow with gas density and laser focusing conditions to provide adequate scattering vector resolution with high signal intensity and near-uniform excitation probability. Images from a pixel-array x-ray detector, spatially and electronically calibrated, allow for detection of scattering intensity changes below 1%. First experiments on the ring-opening reaction of 1,3-cyclohexadiene to form 1, 3, 5-hexatriene show a rapid initial reaction on an 80 fs time scale

Software for the frontiers of quantum chemistry:An overview of developments in the Q-Chem 5 package

This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange–correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear–electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an “open teamware” model and an increasingly modular design

Microbiological oceanography in the region west of the Antarctic Peninsula: Microbial dynamics, nitrogen cycle and carbon flux

Microorganisms are ubiquitous in Southern Ocean habitats and playa vital role in production and ttans-fcnnation of organic matter. Compared to other coastal and oceanic habitats, however, microbial processes in antarctic marine habitats are poorly understood. One major reason is the spatially and temporally variable nature of the habitat and the general inaccessibility of selected habitats (e.g., multi-year pack ice in austral winter). Despite these limitations, the region west of the Antarctic Peninsula is beginning to provide an op-portunity for yeaHound field investigations. Progress to date has focused on the role of microorganisms in the biogeochemical cycling of carbon and associated elements, the regulation of bacterial populations and the relationships between primary production and particulate matter export from the euphotic zone. 1be emergent patterns of carbon and energy flow and of microbial population inter-actions comprise a prospectus and a challenge for future studies in this region. 1

Sedimentary structures from the Carbondale Formation (Middle Pennsylvanian) of Northern Illinois /

v.33:no.29 (1978