Chemical promenades: Exploring potential-energy surfaces with immersive virtual reality

The virtual-reality framework AVATAR (Advanced Virtual Approach to Topological Analysis of Reactivity) for the immersive exploration of potential-energy landscapes is presented. AVATAR is based on modern consumer-grade virtual-reality technology and builds on two key concepts: (a) the reduction of the dimensionality of the potential-energy surface to two process-tailored, physically meaningful generalized coordinates, and (b) the analogy between the evolution of a chemical process and a pathway through valleys (potential wells) and mountain passes (saddle points) of the associated potential energy landscape. Examples including the discovery of competitive reaction paths in simple A + BC collisional systems and the interconversion between conformers in ring-puckering motions of flexible rings highlight the innovation potential that augmented and virtual reality convey for teaching, training, and supporting research in chemistry.

Plasma Processes in the Inner Coma

The solar wind interaction with comets is characterized by the mass-loading of the solar wind with heavy cometary ions that are produced by the ionization of neutrals in the extensive cometary coma. This mass-loading slows down the solar wind and ultimately leads to the formation of a magnetic barrier and a magnetotail. Solar wind protons disappear in the vicinity of the cometopause due to charge-exchange collisions with neutrals. The plasma and fields inside the cometopause of comets Halley and Giacobini-Zinner were observed by instruments on board several spacecraft. Several plasma populations were detected in the inner coma, including cold (less than 1 eV) and energetic (several keV or more) ions, and cold and hot electrons. The Giotto magnetometer observed a diamagnetic cavity surrounding the nucleus, which is a consequence of an outward ion-neutral drag associated with the flow of cometary neutrals past plasma frozen onto field lines in the magnetic barrier. In addition to large-scale structures, many small-scale structures in the plasma and fields have been observed in comets, including tail rays and kinks, and plasma pile-ups and depletions in the barrier. Theoretically, the existence of a very narrow layer of enhanced plasma density just inside the diamagnetic cavity boundary has been predicted. The behavior of plasma in the inner coma (within the cometopause) of an active comet is determined both by plasma processes, such as magnetohydrodynamics, and by collisional processes such as ion-neutral friction, resistivity, electron and ion thermal cooling, ion-neutral chemical reactions, and electron-ion recombination.

High-resolution spectroscopy of the 22Πu←X4Σg− forbidden transitions of C2+

The electronic absorption spectrum of the (0,2), (1,3), and (6,9) bands of the B4Sigmau(-)-X4Sigmag- system of C2+ was obtained using the velocity modulation technique in conjunction with heterodyne detection. The rotationally resolved spectrum shows perturbations, which are attributed to the 2(2)Piu state. The mixing between the B4Sigmau- state and the 2(2)Piu state for nearly degenerate levels generated enough intensity borrowing to observe twenty 2(2)Piu<--X4Sigmag- forbidden transitions. The parameters of a model Hamiltonian were fit to the bands and their corresponding forbidden transitions. Line position measurements, line strength factors, and expectation values for the orbital angular momentum Lambda' for the forbidden transitions are reported. Molecular parameters from the global fit of each band, including their corresponding forbidden transitions, are reported.