Vibrational spectroscopy is one of the most important among spectroscopic
methods, which probes a sample with photons. Infrared spectroscopy (IRS) is an
attractive analytical method for the analysis of the electrochemical interface because:
(i) It is a powerful method for the identification of the molecular structure
(in particular of organic molecules);
(ii) Since different functional groups absorb the IR light at various frequencies, a
simultaneous analysis of each kind of species present on the electrode surface is
possible;
(iii) A complex sample composition limits neither the spectral resolution nor the
sensitivity of the IRS;
(iv) No labelling with any molecular probes is required;
(v) Reflection based techniques are applicable to studies of molecular films present
at the electrified interface.
Transmission IRS measurements are not applicable for studies of potentialdependent structural changes in molecules present on the electrode surfaces, because
the IR radiation does not pass through most of the electrode materials. Internal and
external infrared reflection spectroscopy techniques have been successfully applied
to probe the electrode|electrolyte interface. Reflection-based IRS techniques enable
the measurement of very small absorptions originating usually from 1 to100 nm
thick molecular films, which are imposed on a large background reflection spectrum.
The large advantage of IR reflection based techniques arises from the polarization
selectivity of the surface absorption [1]. When parallel polarized to the plane of
incidence IR radiation encounters a molecular film adsorbed on the metallic electrode surface at large angles of incidence the reflected beam interacts strongly with
the molecules present in the film, resulting in the absorption of the radiation by the
surface species. Under the same experimental conditions, perpendicular polarized to
the plane of incidence IR light does not interact with the species adsorbed on the
metal surface. This radiation is not absorbed by the molecules present on the surface.
The method of measuring the IR absorption spectra of a thin film on metallic
surfaces at grazing angles of incidence is called infrared reflection absorption
spectroscopy (IRRAS). [1] The difference in the interaction of linearly polarized
IR light with molecules adsorbed on a reflecting surface results in surface selection
rule of IRRAS [2]. Thanks to the surface selection rule the quantitative analysis
(conformation and orientation) of the species adsorbed on the reflecting surface is
possible.
In 1979 Hipps and Crosby showed that the modulation of the polarization state of
the incoming electromagnetic radiation during a measurement gives a double modulated differential reflectance spectrum [3]. It has the advantage of the cancellation
of the strong background signal from the sample environment versus the weak signal
of the adsorbed species. Few years later polarization modulation infrared reflection
absorption spectroscopy (PM IRRAS) was introduced to probe species adsorbed on
the air|metal interface [4, 5]. The PM IRRA spectra enable both the qualitative
(composition) and quantitative (orientation, conformation) analysis of the species
adsorbed on interfaces reflecting the IR radiation. The immunity of PM IRRAS to
2
1 Introduction
methods, which probes a sample with photons. Infrared spectroscopy (IRS) is an
attractive analytical method for the analysis of the electrochemical interface because:
(i) It is a powerful method for the identification of the molecular structure
(in particular of organic molecules);
(ii) Since different functional groups absorb the IR light at various frequencies, a
simultaneous analysis of each kind of species present on the electrode surface is
possible;
(iii) A complex sample composition limits neither the spectral resolution nor the
sensitivity of the IRS;
(iv) No labelling with any molecular probes is required;
(v) Reflection based techniques are applicable to studies of molecular films present
at the electrified interface.
Transmission IRS measurements are not applicable for studies of potentialdependent structural changes in molecules present on the electrode surfaces, because
the IR radiation does not pass through most of the electrode materials. Internal and
external infrared reflection spectroscopy techniques have been successfully applied
to probe the electrode|electrolyte interface. Reflection-based IRS techniques enable
the measurement of very small absorptions originating usually from 1 to100 nm
thick molecular films, which are imposed on a large background reflection spectrum.
The large advantage of IR reflection based techniques arises from the polarization
selectivity of the surface absorption [1]. When parallel polarized to the plane of
incidence IR radiation encounters a molecular film adsorbed on the metallic electrode surface at large angles of incidence the reflected beam interacts strongly with
the molecules present in the film, resulting in the absorption of the radiation by the
surface species. Under the same experimental conditions, perpendicular polarized to
the plane of incidence IR light does not interact with the species adsorbed on the
metal surface. This radiation is not absorbed by the molecules present on the surface.
The method of measuring the IR absorption spectra of a thin film on metallic
surfaces at grazing angles of incidence is called infrared reflection absorption
spectroscopy (IRRAS). [1] The difference in the interaction of linearly polarized
IR light with molecules adsorbed on a reflecting surface results in surface selection
rule of IRRAS [2]. Thanks to the surface selection rule the quantitative analysis
(conformation and orientation) of the species adsorbed on the reflecting surface is
possible.
In 1979 Hipps and Crosby showed that the modulation of the polarization state of
the incoming electromagnetic radiation during a measurement gives a double modulated differential reflectance spectrum [3]. It has the advantage of the cancellation
of the strong background signal from the sample environment versus the weak signal
of the adsorbed species. Few years later polarization modulation infrared reflection
absorption spectroscopy (PM IRRAS) was introduced to probe species adsorbed on
the air|metal interface [4, 5]. The PM IRRA spectra enable both the qualitative
(composition) and quantitative (orientation, conformation) analysis of the species
adsorbed on interfaces reflecting the IR radiation. The immunity of PM IRRAS to
2
1 Introduction