Self-consistent dielectric functions of materials: Toward accurate computation of Casimir-van der Waals forces.

From Europe PMC via Jisc Publications RouterHistory: ppub 2021-05-01, epub 2021-05-26Publication status: PublishedFunder: Swiss National Science Foundation; Grant(s): 186747Research on theoretical calculation of Casimir-van der Waals (vdW) forces is characterized by a great number of inconsistencies and conflicting reports with widely differing results for many known materials, including water, contradicting experimental measurements. Despite its importance for conceptual advances in both fundamental aspects and practical applications, a universal framework for the accurate determination of Casimir-vdW forces is lacking. Here, we propose a universal theoretical platform for computing Casimir-vdW forces, accounting for the electronic dielectric constant, optical bandgap, density, and chemical composition. Using this methodology, we determine the dielectric function for 55 materials, over a wide range of photon energies, covering an extensive list of common metals, organic and inorganic semiconductors, and insulators. Internal consistency of the compiled data is validated using optical sum rules and Kramers-Kronig relations. We demonstrate that the calculated vdW forces based on these data match remarkably well with the experimentally measured vdW forces

Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies Evaluation Number 15

This is the fifteenth in a series of evaluated sets of rate constants and photochemical cross sections compiled by the NASA Panel for Data Evaluation. The data are used primarily to model stratospheric and upper tropospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena. Copies of this evaluation are available in electronic form and may be printed from the following Internet URL: http://jpldataeval.jpl.nasa.gov/

Mars Thermospheric Variability Revealed by MAVEN EUVM Solar Occultations: Structure at Aphelion and Perihelion, and Response to EUV Forcing

The Mars thermosphere holds clues to the evolution of the Martian climate, and has practical implications for spacecraft visiting Mars, which often use it for aerobraking upon arrival, or for landers, which must pass through it. Nevertheless, it has been sparsely characterized, even when past accelerometer measurements and remote observations are taken into account. The Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter, which includes a number of instruments designed to characterize the thermosphere, has greatly expanded the available thermospheric observations. This paper presents new and unanticipated measurements of density and temperature profiles (120-200 km) derived from solar occultations using the MAVEN Extreme Ultraviolet (EUV) Monitor. These new measurements complement and expand MAVEN's intended thermospheric measurement capacity. In particular, because the local-time is inherently fixed to the terminator, solar occultations are ideally suited for characterizing long-term and latitudinal variability. Occultation measurements are made during approximately half of all orbits, resulting in thousands of new thermospheric profiles. The density retrieval method is presented in detail, including an uncertainty analysis. Altitude-latitude maps of thermospheric density and temperature at perihelion and aphelion are presented, revealing structures that have not been previously observed. Tracers of atmospheric dynamics are also observed, including a high altitude polar warming feature at intermediate latitudes, and an apparent thermostatic response to solar EUV heating during a solar rotation, which shows heating at high altitudes that is accompanied by cooling at lower altitudes.Comment: Submitted to JGR: Planet

The MPI-Mainz UV/VIS spectral atlas of gaseous molecules of atmospheric interest

We present the MPI-Mainz UV/VIS Spectral Atlas of Gaseous Molecules, which is a large collection of absorption cross sections and quantum yields in the ultraviolet and visible (UV/VIS) wavelength region for gaseous molecules and radicals primarily of atmospheric interest. The data files contain results of individual measurements, covering research of almost a whole century. To compare and visualize the data sets, multicoloured graphical representations have been created. The MPI-Mainz UV/VIS Spectral Atlas is available on the Internet at <a href="http://www.uv-vis-spectral-atlas-mainz.org"target="_blank">http://www.uv-vis-spectral-atlas-mainz.org</a>. It now appears with improved browse and search options, based on new database software. In addition to the Web pages, which are continuously updated, a frozen version of the data is available under the <a href="http://dx.doi.org/10.5281/zenodo.6951"target="_blank">doi:10.5281/zenodo.6951</a>

Understanding the kinetics of the ClO-Dimer cycle

International audienceAmong the major factors controlling ozone loss in the polar winter is the kinetics of the ClO dimer catalytic cycle. The most important issues are the thermal equilibrium between ClO and Cl2O2, the rate of Cl2O2 formation, and the Cl2O2 photolysis rate. All these issues have been addressed in a large number of laboratory, field and theoretical studies, but large discrepancies between individual results exist and a self-consistent set of parameters compatible with field observations of ClO and Cl2O2 has not been identified. Here, we use thermodynamic calculations and unimolecular rate theory to constrain the ClO/Cl2O2 equilibrium constant and the rate constants for Cl2O2 formation and dissociation. This information is used together with available atmospheric data to examine Cl2O2 photolysis rates based on different Cl2O2 absorption cross sections. Good overall consistency is achieved using a ClO/Cl2O2 equilibrium constant recently suggested by Plenge et al. (2005), the Cl2O2 recombination rate constant reported by Nickolaisen et al. (1994) and Cl2O2 photolysis rates based on averaged absorption cross sections that are roughly intermediate between the JPL 2002 assessment and a laboratory study by Burkholder et al. (1990)