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Mance, Jason G.

Publications and source records attributed to Mance, Jason G..

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Real-time latent heat emission during dynamic-compression freezing of water

Abstract Dynamic compression studies have been used to study the nucleation kinetics of water to ice VII for decades. Diagnostics such as photon Doppler velocimetry, transmission loss, and imaging have been used to measure pressure/density, and phase fraction, while temperature has remained the difficult thermodynamic property to quantify. In this work, we measured pressure/density and implemented a diagnostic to measure the temperature. In doing so the temperature shows quasi-isentropically compressed liquid water forms ice at pressures below the previously defined metastable limit, and the liquid phase is not hypercoooled as previously thought above that limit. Instead, the latent heat raises the temperature to the liquid-ice-VII melt line, where it remains with increasing pressure. We propose a hypothesis to corroborate these results with previous work on dynamic compression freezing. These results provide constraints for nucleation models, and suggest this technique be used to investigate phase transitions in other materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

X-ray Transient Absorption Studies of Exciton Self-Trapping

Here, we present optical pump/X-ray absorption probe studies to probe changes in electronic distribution and local structure upon formation of a self-trapped exciton. The experiments were carried out on the mixed-valence halide-bridged transition metal linear chain charge density wave material [Pt(en 2 )][Pt(en 2 )Cl 2 ]·(ClO 4 ) 4 . Photoinduced changes in the Pt L III XANES spectrum were measured on a picosecond time scale following generation of excitons via optical excitation of the intervalence charge transfer transition. Ab initio FEFF9 modeling of the spectra and the associated angular momentum projected density of states was used to interpret the response. We find photoinduced changes reflecting electronic redistribution and local lattice distortions that correspond to strong localization of the self-trapped state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗