Sum-frequency vibrational spectroscopy at the liquid—air interface of methanol. Water solutions

Wolfrum, K.; Graener, H.; Laubereau, A.

doi:10.1016/0009-2614(93)85415-k

Cited by 132 publications

(164 citation statements)

References 18 publications

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“…However, no such CH 3 -AS mode has ever been observed. 12,26,[47][48][49][50][51][52][53][54] This clearly demonstrates the failure of the bond additivity model in dealing with the CH 3 -AS mode, even though the intensities of the CH 3 -SS and CH 3 -SS Fermi modes can be quantitatively explained as in Fig. 2.…”

Section: B Failure Of the Bond Additivity Modelmentioning

confidence: 95%

An empirical approach to the bond additivity model in quantitative interpretation of sum frequency generation vibrational spectra

Zhang

Gan

et al. 2006

The Journal of Chemical Physics

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Knowledge of the ratios between different polarizability betai'j'k' tensor elements of a chemical group in a molecule is crucial for quantitative interpretation and polarization analysis of its sum frequency generation vibrational spectroscopy (SFG-VS) spectrum at interface. The bond additivity model (BAM) or the hyperpolarizability derivative model along with experimentally obtained Raman depolarization ratios has been widely used to obtain such tensor ratios for the CH3, CH2, and CH groups. Successfully, such treatment can quantitatively reproduce the intensity polarization dependence in SFG-VS spectra for the symmetric (SS) and asymmetric (AS) stretching modes of CH3 and CH2 groups, respectively. However, the relative intensities between the SS and AS modes usually do not agree with each other within this model even for some of the simplest molecular systems, such as the air/methanol interface. This fact certainly has cast uncertainties on the effectiveness and conclusions based on the BAM. One of such examples is that the AS mode of CH3 group has never been observed in SFG-VS spectra from the air/methanol interface, while this AS mode is usually very strong for SFG-VS spectra from the air/ethanol interface, other short chain alcohol, as well as long chain surfactants. In order to answer these questions, an empirical approach from known Raman and IR spectra is used to make corrections to the BAM. With the corrected ratios between the betai'j'k' tensor elements of the SS and AS modes, all features in the SFG-VS spectra of the air/methanol and air/ethanol interfaces can be quantitatively interpreted. This empirical approach not only provides new understandings of the effectiveness and limitations of the bond additivity model but also provides a practical way for its application in SFG-VS studies of molecular interfaces.

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Section: B Failure Of the Bond Additivity Modelmentioning

confidence: 95%

An empirical approach to the bond additivity model in quantitative interpretation of sum frequency generation vibrational spectra

Zhang

Gan

et al. 2006

The Journal of Chemical Physics

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“…The goal of these experiments is to determine the composition of the methanol solution/vapor interface, in particular addressing the possibility of segregation of methanol to the vapor/solution interface, as suggested from Molecular Dynamics simulations 39,40 and SFG measurements. 41,42,43,44 Since the probing depth in XPS depends on the kinetic energy of the photoelectrons, which in turn is determined by the incident photon energy, depth-profiles of the stoichiometry at the solution/vapor interface can be measured, in the case described here up to a depth of about 2 nm.…”

Section: Proof Of Principle Experimentsmentioning

confidence: 99%

A combined droplet train and ambient pressure photoemission spectrometer for the investigation of liquid/vapor interfaces

Starr

Wong

Worsnop

et al. 2008

Phys. Chem. Chem. Phys.

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We describe a combined ambient pressure photoelectron spectroscopy/droplet train apparatus for investigating the nature and heterogeneous chemistry of liquid/vapor interfaces. In this instrument a liquid droplet train with typical droplet diameters from 50…150 µm is produced by a vibrating orifice aerosol generator (VOAG). The droplets are irradiated by soft X-rays (100…1500 eV) in front of the entrance aperture of a differentially pumped electrostatic lens system that transfers the emitted electrons into a conventional hemispherical electron analyzer.The photoemission experiments are performed at background pressures of up to several Torr, which allows the study of environmentally important liquid/vapor interfaces, in particular aqueous solutions, under equilibrium conditions. The exposure time of the droplet surface to the background gases prior to the XPS measurement can be varied, which will allow future kinetic

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“…The surface vibrational spectra of n-alkane show clearly that the monolayer freezing transition is characterized by a conformational change of surface molecules from a configuration of vertically oriented chains with significant defects to a well-ordered nearly all-trans configuration (51). For some liquid mixtures, namely, waterethanol and water-CH3CN, SFG spectra also suggest the occurrence of a phase transition in the surface structure when the bulk composition is varied (55,56). In general, one would hope that through surface vibrational spectroscopy, enough information could be obtained to permit deduction of a general understanding of liquid surfaces and interfaces.…”

mentioning

confidence: 97%

A few selected applications of surface nonlinear optical spectroscopy.

Shen

1996

Proc. Natl. Acad. Sci. U.S.A.

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As a second-order nonlinear optical process, sum-frequency generation is highly surface-specific and accordingly has been developed into a very powerful and versatile surface spectroscopic tool. It has found many unique applications in different disciplines and thus provided many exciting new research opportunities in surface and surfacerelated science. Selected examples are discussed here to illustrate the power of the technique.In recent years, we have been developing and applying modern optical techniques to surface and interface studies. The one that has attracted much attention is surface optical second harmonic generation (SHG) and sum-frequency generation (SFG) (1). This is because the technique has very high surface specificity and wide applicability. SFG is a nonlinear optical process in which two laser beams at frequencies wi and w2 impinging on a medium mix and generate a sum-frequency output at ws = Wl + W2. SHG is a special case of SFG with wi = w2. It is well known that a second-order nonlinear optical process like SHG and SFG is forbidden in a medium with inversion symmetry (2). At a surface or interface, however, the inversion symmetry is necessarily broken. This then leads to the surface specificity of SHG and SFG. More formally, SFG (or SHG) originates from a nonlinear polarization P(2)(ws) induced in a medium by laser wave mixing (2): p(2)(W) = X(2):E()E(W2) [1] where E(wi) is the laser field at wi and X(2) is a tensor describing the nonlinear response of the medium to the fields. Inversion symmetry of the medium yields72) = _.i2), and therefore x (2) must vanish. The SFG Lor SHG) measurement on a surface allows the deduction of X(2)(Ws = Wl + W2), which is a tensor characteristic of the surface (3). For example, the symmetry of 2) provides information about the surface structural symmetry. The spatial variation of x42) over the surface directly reflects the spatial variation of the surface structure. The time variation of 92) indicates how the surface structure changes with time. Of particular importance is that 2) also carries spectroscopic information that enables us to learn microscopic details about the surface. As shown in Fig. 1

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Sum-frequency vibrational spectroscopy at the liquid—air interface of methanol. Water solutions

Cited by 132 publications

References 18 publications

An empirical approach to the bond additivity model in quantitative interpretation of sum frequency generation vibrational spectra

An empirical approach to the bond additivity model in quantitative interpretation of sum frequency generation vibrational spectra

A combined droplet train and ambient pressure photoemission spectrometer for the investigation of liquid/vapor interfaces

A few selected applications of surface nonlinear optical spectroscopy.

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