Vibrational Spectra in Liquids

What Does Vibrational Spectrum Tell Us

Vibrational, e.g., infrared, Raman, and nonlinear IR, spectroscopies are frequently used to characterize liquids due to the close relationship between a mode's vibrational frequency and its environment. Because the vibrational spectrum is intrinsically quantum mechanical, it is challenging to simulate from classical molecular dynamics. We are working on new approaches to simulate vibrational spectra while also developing models within the empirical (electrostatic) mapping technique. We are primarily interested in applying these methods in protic liquids like water and alcohols and in environments like nanoscale silica pores. We particularly focus on the questions

• What does a vibrational spectrum tell us (or not tell us!) about the liquid structure and dynamics?
• How does the vibrational spectrum of a nanoconfined liquid differ from that of the bulk liquid?

Thus, we spend significant effort in developing an accurate, detailed picture of the molecular-level liquid properties and see if and how they are manifested in the vibrational spectra. Further, our current work also explores what nonlinear vibrational spectroscopies can reveal about the structure and dynamics of nanoconfined liquids. One of the issues there is that the dynamics is quite slow and the long timescales are not always accessible due to short vibrational lifetimes of the typical modes of interest. For example, the OH stretching mode in water has a vibrational lifetime of less than 1 ps so that its dynamics can only be probed for 8-10 ps. Other molecules, like SeCN-, that can act as probes have much longer lifetimes (>35 ps) enabling examination of the slow dynamics.

Relevant References

Steven A .Yamada, Jae Yoon Shin, Ward H. Thompson, and Michael D. Fayer, Journal of Physical Chemistry C 123, 5790-5803 (2019). "Water Dynamics in Nanoporous Silica: Ultrafast Vibrational Spectroscopy and Molecular Dynamics Simulations"

Steven A .Yamada, Ward H. Thompson, and Michael D. Fayer, Journal of Chemical Physics 147, 234501 (2017). "Water-Anion Hydrogen Bonding Dynamics: Ultrafast IR Experiments and Simulations"

Oluwaseun O. Mesele and Ward H. Thompson, Journal of Physical Chemistry A121, 5823-5833 (2017). "A ``Universal'' Spectroscopic Map for the OH Stretching Mode in Alcohols"

Stephane Abel, Nuno Galamba, Esra Karakas, Massimo Marchi, Ward H. Thompson, and Damien Laage,  Langmuir 32, 10610-10620 (2016). “On the Structural and Dynamical Properties of DOPC Reverse Micelles”

Paul C. Burris, Damien Laage, and Ward H. Thompson,  Journal of Chemical Physics 144, 194709 (2016). "Simulations of the Infrared, Raman, and 2D-IR Photon Echo Spectra of Water in Nanoscale Silica Pores"

Tatsuya Joutsuka, Ward H. Thompson, and Damien Laage, Journal of Physical Chemistry Letters7, 616-621 (2016). "Vibrational Quantum Decoherence in Liquid Water"

Christine M. Morales and Ward H. Thompson, Journal of Physical Chemistry B115, 7597-7605 (2011). "Molecular-Level Mechanisms of Vibrational Frequency Shifts in a Polar Liquid"

Christine M. Morales and Ward H. Thompson, Journal of Physical Chemistry A113, 1922-1933 (2009). "Simulations of Infrared Spectra of Nanoconfined Liquids: Acetonitrile Confined in Nanoscale, Hydrophilic Silica Pores"

Katie R. Mitchell-Koch and Ward H. Thompson, Journal of Physical Chemistry B113=2, 7448-7459 (2008). "Infrared Spectroscopy of a Model Phenol-Amine Proton Transfer Complex in Nanoconfined CH₃Cl"