The role of resonant coupling in vibrational sum-frequency-generation spectroscopy: Liquid acetonitrile at the silica interface

TY - JOUR

T1 - The role of resonant coupling in vibrational sum-frequency-generation spectroscopy

T2 - Liquid acetonitrile at the silica interface

AU - Souna, Amanda J.

AU - Cohen, Samuel R.

AU - Rivera, Christopher A.

AU - Manfred, Katherine

AU - Coasne, Benoit

AU - Fourkas, John T.

N1 - Funding Information: This work was supported by the National Science Foundation, grant CHE-1800491. AJS was supported in part by a Millard and Lee Alexander Fellowship and a Department of Education Graduate Assistance in Areas of National Need Fellowship through the University of Maryland Department of Chemistry & Biochemistry. SRC was supported in part by a Chateaubriand Fellowship from the Office for Science & Technology of the Embassy of France in the United States. Some of the computations presented in this paper were performed using the Froggy platform of the GRICAD infrastructure (https://gricad.univ-grenoble-alpes.fr), which is supported by the Rhône-Alpes region (Grant CPER07 13 CIRA) and the Equip@Meso project (reference ANR-10-EQPX-29-01) of the Programme Investissements d’Avenir supervised by the Agence Nationale pour le Recherche. We thank Dr. Shule Liu for providing us with the coordinates for the silica surface used in our simulations. Publisher Copyright: © 2023 Elsevier B.V.

PY - 2023/4/1

Y1 - 2023/4/1

N2 - Vibrational sum-frequency-generation (VSFG) spectroscopy is a versatile technique for probing molecular organization at interfaces. There is a growing recognition that dynamic phenomena, such as reorientation and intermolecular vibrational coupling, can also influence VSFG spectra. The silica/liquid acetonitrile interface is a useful system for exploring these effects in more detail. The organization of acetonitrile at this interface has been well studied, and is known to resemble that of a supported lipid bilayer in many ways. Here isotopic dilution is used to explore the influence of resonant intermolecular coupling of methyl symmetric stretches on the VSFG spectroscopy of this system. VSFG spectra in the methyl stretching region at this interface show a blue shift, a decrease in linewidth, and a higher-than-expected intensity upon dilution in deuterated acetonitrile. We demonstrate that resonant coupling influences VSFG spectral shifts through the infrared transition. Using molecular simulations, we show that our experimental observations are consistent with resonant coupling between methyl transition dipoles being a significant, but not the dominant, contribution to the observed spectral shift upon isotopic dilution. Furthermore, our molecular simulations demonstrate that resonant coupling accounts partially for changes in linewidth and intensity. These classical molecular dynamics simulations also elucidate the behavior of the isotropic Raman spectrum in the bulk liquid upon isotopic dilution. We further simulate the resonant coupling among cyano stretches in this system. These simulations match the experimental shift due to the Raman non-coincidence effect shift of the CN stretch in the bulk liquid, but suggest that the corresponding resonant-coupling-induced shift in the VSFG spectrum at the silica interface is minimal. Our experimental and simulation results indicate that proximity to an interface can cause substantial changes in the resonant coupling of vibrations in a liquid.

AB - Vibrational sum-frequency-generation (VSFG) spectroscopy is a versatile technique for probing molecular organization at interfaces. There is a growing recognition that dynamic phenomena, such as reorientation and intermolecular vibrational coupling, can also influence VSFG spectra. The silica/liquid acetonitrile interface is a useful system for exploring these effects in more detail. The organization of acetonitrile at this interface has been well studied, and is known to resemble that of a supported lipid bilayer in many ways. Here isotopic dilution is used to explore the influence of resonant intermolecular coupling of methyl symmetric stretches on the VSFG spectroscopy of this system. VSFG spectra in the methyl stretching region at this interface show a blue shift, a decrease in linewidth, and a higher-than-expected intensity upon dilution in deuterated acetonitrile. We demonstrate that resonant coupling influences VSFG spectral shifts through the infrared transition. Using molecular simulations, we show that our experimental observations are consistent with resonant coupling between methyl transition dipoles being a significant, but not the dominant, contribution to the observed spectral shift upon isotopic dilution. Furthermore, our molecular simulations demonstrate that resonant coupling accounts partially for changes in linewidth and intensity. These classical molecular dynamics simulations also elucidate the behavior of the isotropic Raman spectrum in the bulk liquid upon isotopic dilution. We further simulate the resonant coupling among cyano stretches in this system. These simulations match the experimental shift due to the Raman non-coincidence effect shift of the CN stretch in the bulk liquid, but suggest that the corresponding resonant-coupling-induced shift in the VSFG spectrum at the silica interface is minimal. Our experimental and simulation results indicate that proximity to an interface can cause substantial changes in the resonant coupling of vibrations in a liquid.

UR - http://www.scopus.com/inward/record.url?scp=85147551484&partnerID=8YFLogxK

U2 - 10.1016/j.molliq.2023.121315

DO - 10.1016/j.molliq.2023.121315

M3 - Article

AN - SCOPUS:85147551484

SN - 0167-7322

VL - 375

JO - JOURNAL OF MOLECULAR LIQUIDS

JF - JOURNAL OF MOLECULAR LIQUIDS

M1 - 121315

ER -