10:00 AM - 10:15 AM
[PCG21-05] Theoretical calculation for optical constants of condensed-phase water using a mixed quantum/classical approach
Keywords:ISM, Water, Optical constants, Spectral simulation
Water ice is a ubiquitous component of interstellar environments, predominantly coating dust grains in metastable, porous, amorphous forms. Despite its prevalence, the detailed structure of amorphous water ice remains poorly characterized, limiting our understanding of its role in interstellar chemical evolution. Moreover, interactions between water ice and other volatile species, such as CO, CO2, NH3, and CH4 are thought to play a crucial role in the formation of complex organic molecules (COMs) on dust grain surfaces.
Observational advances in the vibrational (infrared) region, particularly with the James Webb Space Telescope (JWST) [1], have significantly enriched our understanding of interstellar ices. However, interpreting these observations requires precise experimental data, such as the optical constants of icy materials, which remain insufficient due to experimental challenges. In order to gain the most out of observational data, such experimental data are much desired.
To adress this challenge, we present a novel theoretical framework inspired by methods from condensed-phase chemistry. By extending the mixed quantum/classical approach initially developed by Skinner and his co-workers [2-4], we have developed a technique capable of yielding absolute spectral properties, including optical constants and absorption cross-sections, for condensed-phase materials, such as liquids and ices. Validation against experimental data for liquid water at 298 K was conducted, with discrepancies between experimental and theoretical results (water model: TIP4P/2005, number of molecules: 512, spectroscopic maps are taken from Refs. [3, 4]) being around 10% at most, demonstrating the accuracy and robustness of this method.
Further advancement of this method towards water ice will enable detailed characterization of amorphous water ice under interstellar conditions through molecular dynamics simulations. Moreover, it is expected that the presented approach can be extended to other astrophysically relevant species, yielding crucial information that is difficult to obtain experimentally with high accuracy, thereby aiding observational studies.
[1] McClure, M. K., W. R. M. Rocha, K. M. Pontoppidan, N. Crouzet, L. E. U. Chu, E. Dartois, T. Lamberts, et al. 2023. "An Ice Age JWST Inventory of Dense Molecular Cloud Ices." Nature Astronomy 7 (4): 431–43.
[2] Auer, B. M., and J. L. Skinner. 2008. "IR and Raman Spectra of Liquid Water: Theory and Interpretation." The Journal of Chemical Physics 128 (22): 224511.
[3] Gruenbaum, S. M., C. J. Tainter, L. Shi, Y. Ni, and J. L. Skinner. 2013. “Robustness of Frequency, Transition Dipole, and Coupling Maps for Water Vibrational Spectroscopy.” Journal of Chemical Theory and Computation 9 (7): 3109–17.
[4] Kananenka, Alexei A., and J. L. Skinner. 2018. “Fermi Resonance in OH-Stretch Vibrational Spectroscopy of Liquid Water and the Water Hexamer.” The Journal of Chemical Physics 148 (24): 244107.
Observational advances in the vibrational (infrared) region, particularly with the James Webb Space Telescope (JWST) [1], have significantly enriched our understanding of interstellar ices. However, interpreting these observations requires precise experimental data, such as the optical constants of icy materials, which remain insufficient due to experimental challenges. In order to gain the most out of observational data, such experimental data are much desired.
To adress this challenge, we present a novel theoretical framework inspired by methods from condensed-phase chemistry. By extending the mixed quantum/classical approach initially developed by Skinner and his co-workers [2-4], we have developed a technique capable of yielding absolute spectral properties, including optical constants and absorption cross-sections, for condensed-phase materials, such as liquids and ices. Validation against experimental data for liquid water at 298 K was conducted, with discrepancies between experimental and theoretical results (water model: TIP4P/2005, number of molecules: 512, spectroscopic maps are taken from Refs. [3, 4]) being around 10% at most, demonstrating the accuracy and robustness of this method.
Further advancement of this method towards water ice will enable detailed characterization of amorphous water ice under interstellar conditions through molecular dynamics simulations. Moreover, it is expected that the presented approach can be extended to other astrophysically relevant species, yielding crucial information that is difficult to obtain experimentally with high accuracy, thereby aiding observational studies.
[1] McClure, M. K., W. R. M. Rocha, K. M. Pontoppidan, N. Crouzet, L. E. U. Chu, E. Dartois, T. Lamberts, et al. 2023. "An Ice Age JWST Inventory of Dense Molecular Cloud Ices." Nature Astronomy 7 (4): 431–43.
[2] Auer, B. M., and J. L. Skinner. 2008. "IR and Raman Spectra of Liquid Water: Theory and Interpretation." The Journal of Chemical Physics 128 (22): 224511.
[3] Gruenbaum, S. M., C. J. Tainter, L. Shi, Y. Ni, and J. L. Skinner. 2013. “Robustness of Frequency, Transition Dipole, and Coupling Maps for Water Vibrational Spectroscopy.” Journal of Chemical Theory and Computation 9 (7): 3109–17.
[4] Kananenka, Alexei A., and J. L. Skinner. 2018. “Fermi Resonance in OH-Stretch Vibrational Spectroscopy of Liquid Water and the Water Hexamer.” The Journal of Chemical Physics 148 (24): 244107.