Optical properties of high-pressure fluid hydrogen across molecular dissociation

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 116; no. 20; pp. 9770 - 9774
• Main Authors: Rillo, Giovanni, Morales, Miguel A., Ceperley, David M., Pierleoni, Carlo
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 14.05.2019; National Academy of Sciences, Washington, DC (United States)
• Subjects: Absorption; Absorptivity; ATOMIC AND MOLECULAR PHYSICS; Diamonds; high pressure; hydrogen; Laser beam heating; metal insulator; Metallizing; Optical properties; Phase transitions; Physical Sciences; quantum Monte Carlo; Reflectance; Thermal conductivity; metal insulator; optical properties; hydrogen; quantum Monte Carlo; high pressure
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1818897116

Optical properties of compressed fluid hydrogen in the region where dissociation and metallization is observed are computed by ab initio methods and compared with recent experimental results. We confirm that at T > 3,000 K, both processes are continuous, while at T < 1,500 K, the first-order phase transition is accompanied by a discontinuity of the dc conductivity and the thermal conductivity, while both the reflectivity and absorption coefficient vary rapidly but continuously. Our results support the recent analysis of National Ignition Facility (NIF) experiments [Celliers PM, et al. (2018) Science 361:677–682], which assigned the inception of metallization to pressures where the reflectivity is ∼0.3. Our results also support the conclusion that the temperature plateau seen in laser-heated diamond-anvil cell (DAC) experiments at temperatures higher than 1,500 K corresponds to the onset of optical absorption, not to the phase transition.