Chapter 10
Applications: Organic Interfaces
Abstract Interfaces of organic species offer enormous opportunities to be studied
by SFG spectroscopy. In this chapter we introduce recent advances of computational
analysis of SFG in the organic interfaces. Here we mainly deal with the C–
H vibrations, as they are ubiquitously seen in organic species and have been
most widely investigated by the SFG spectroscopy to date. We discuss molecular
modeling of organic species, and then unified assignment method of alkyl C–
H stretching of SFG spectra in comparison with IR and Raman spectra. Related
topics revealed by the SFG analysis are also discussed, including SFG from
centrosymmetric molecules, quadrupole contribution, and polarization analysis of
molecular orientation.
Keywords C–H stretching · Alkyl groups · Polarization analysis
Interfaces of organic molecules include surfaces of various organic solvents, films
and polymers. These interfaces are relevant to many applications, such as membranes, batteries, adhesion, wetting, tribology, etc. The organic interfaces are often
buried to form liquid-liquid or solid-liquid interfaces. The SFG spectroscopy has
large potential to selectively investigate various chemical species and their structure
at those interfaces. Among various vibrational bands of organic molecules, the C–H
stretching vibrations have been most intensively measured by SFG spectroscopy to
date, since the first vibrational SFG measurement in 1987 [14]. This is because the
C–H stretching vibrations show generally strong intensity and are technically easy
to measure, in addition to that they are ubiquitously included in organic species.
Besides the C–H stretching, other vibrations have been investigated, such as C=O
and C ≡ N stretching bands, by SFG spectroscopy [3, 20, 27, 30, 33, 37, 40].
The SFG spectra of organic interfaces have their own challenge to theoretical
analysis, which is different from that of O–H band of aqueous systems in Chap. 9.
First, the organic interfaces include variety of chemical species and vibrations,
and the theoretical analysis has to accurately describe these variety of species
and interfaces. Reliability of MD calculations capable of reproducing the various
SFG spectra is an integral requisite of the theoretical analysis. This requirement is
© Springer Nature Singapore Pte Ltd. 2018
A. Morita, Theory of Sum Frequency Generation Spectroscopy,
Lecture Notes in Chemistry 97, https://doi.org/10.1007/978-981-13-1607-4_10
247
Applications: Organic Interfaces
Abstract Interfaces of organic species offer enormous opportunities to be studied
by SFG spectroscopy. In this chapter we introduce recent advances of computational
analysis of SFG in the organic interfaces. Here we mainly deal with the C–
H vibrations, as they are ubiquitously seen in organic species and have been
most widely investigated by the SFG spectroscopy to date. We discuss molecular
modeling of organic species, and then unified assignment method of alkyl C–
H stretching of SFG spectra in comparison with IR and Raman spectra. Related
topics revealed by the SFG analysis are also discussed, including SFG from
centrosymmetric molecules, quadrupole contribution, and polarization analysis of
molecular orientation.
Keywords C–H stretching · Alkyl groups · Polarization analysis
Interfaces of organic molecules include surfaces of various organic solvents, films
and polymers. These interfaces are relevant to many applications, such as membranes, batteries, adhesion, wetting, tribology, etc. The organic interfaces are often
buried to form liquid-liquid or solid-liquid interfaces. The SFG spectroscopy has
large potential to selectively investigate various chemical species and their structure
at those interfaces. Among various vibrational bands of organic molecules, the C–H
stretching vibrations have been most intensively measured by SFG spectroscopy to
date, since the first vibrational SFG measurement in 1987 [14]. This is because the
C–H stretching vibrations show generally strong intensity and are technically easy
to measure, in addition to that they are ubiquitously included in organic species.
Besides the C–H stretching, other vibrations have been investigated, such as C=O
and C ≡ N stretching bands, by SFG spectroscopy [3, 20, 27, 30, 33, 37, 40].
The SFG spectra of organic interfaces have their own challenge to theoretical
analysis, which is different from that of O–H band of aqueous systems in Chap. 9.
First, the organic interfaces include variety of chemical species and vibrations,
and the theoretical analysis has to accurately describe these variety of species
and interfaces. Reliability of MD calculations capable of reproducing the various
SFG spectra is an integral requisite of the theoretical analysis. This requirement is
© Springer Nature Singapore Pte Ltd. 2018
A. Morita, Theory of Sum Frequency Generation Spectroscopy,
Lecture Notes in Chemistry 97, https://doi.org/10.1007/978-981-13-1607-4_10
247