A time correlation function theory describing static field enhanced third order optical effects at interfaces

Abstract

Sum vibrational frequency spectroscopy, a second order optical process, is interface specific in the dipole approximation. At charged interfaces, there exists a static field, and as a direct consequence, the experimentally detected signal is a combination of enhanced second and static field induced third order contributions. There is significant evidence in the literature of the importance/relative magnitude of this third order contribution, but no previous molecularly detailed approach existed to separately calculate the second and third order contributions. Thus, for the first time, a molecularly detailed time correlation function theory is derived here that allows for the second and third order contributions to sum frequency vibrational spectra to be individually determined. Further, a practical, molecular dynamics based, implementation procedure for the derived correlation functions that describe the third order phenomenon is also presented. This approach includes a novel generalization of point atomic polarizability models to calculate the hyperpolarizability of a molecular system. The full system hyperpolarizability appears in the time correlation functions responsible for third order contributions in the presence of a static field.

Molecular Restructuring of Water and Lipids upon the Interaction of DNA with Lipid Monolayers

“…Much prior work has demonstrated that sum frequency intensities decrease with decreasing surface potentials either as a result of the decreasing surface field orienting interfacial liquid molecules less strongly, a decreasing χ (3) contribution to the sum frequency signal or both. − McLoughlin et al have shown that adsorption of DNA to the cationic lipid DODAB (dioctadecyldimethylammonium bromide) leads to a decrease in surface potential of ≈0.3 V while adsorption of DNA to the zwitterionic lipid DSPC (distearoyl- sn -glycero-3-phosphocholine) in the presence of Ca 2+ (the change in surface potential for the bare DSPC monolayer in the presence of DNA was not measured) leads to a decrease in surface potential of less than 0.1 V. If we assume that DPTAP and diC14-amidine behave similarly to DODAB and DPPC similarly to DSPC, the change in spectral response with DNA adsorption appears to map qualitatively to the potential decrease: DNA adsorbed to a cationic lipid leads to a larger surface potential decrease than that adsorbed to a zwitterionic and the former system shows a larger decrease in hydrogen bonded OH stretch intensity than the latter.…”

Recent progress in theoretical analysis of vibrational sum frequency generation spectroscopy

“…The effects of the higherorder polarization and quantum correction should be further studied. [53][54][55]…”

An Optical Voltmeter for Studying Cetyltrimethylammonium Interacting with Fused Silica/Aqueous Interfaces at High Ionic Strength

“… χ R ν ( 2 ) ∝ N normal a d s false⟨ β ν false⟩ The value of β ν increases when the frequency of the incoming IR pulse matches a vibrational transition of the adsorbate or interface leading to resonance enhancement of the SFG signal. As demonstrated by Eliel et al with a free electron laser and Richter et al with a tabletop solid state laser, IR fields that are broad in the frequency domain allow for collection of broadband SFG spectra within a single laser pulse, this approach can be utilized to monitor multiple vibrational modes during the adsorption/desorption process providing information about both the surface coverage and orientation of adsorbates. ,− Lastly, for the silica/aqueous interface the nonresonant contribution to the SFG signal has, on the molecular level, the same origins as the nonresonant SHG signal used in the χ (3) technique . Therefore, the nonresonant SFG signal can be modeled following the same theory described for the χ (3) technique in the previous section.…”

“…51,[53][54][55][56][57][58][59] Lastly, for the silica/aqueous interface the nonresonant contribution to the SFG signal has, on the molecular level, the same origins as the nonresonant SHG signal used in the χ (3) technique. 60 Therefore, the nonresonant SFG signal can be modeled following the same theory described for the χ (3) technique in the previous section.…”