light by the species adsorbed on the mirror surface is related to the absorption
coefficient of Lambert-Beer law, which describes the attenuation of the intensity
of light propagating through the absorbing medium,
I ¼ I i exp À
4πk
λ
d 2
ð2:19Þ
where I i is the intensity of the incoming radiation and d 2 is the thickness of the
adsorbed film. According to Eq. (2.19) the beam reflected from the metal surface IR
beam is attenuated by the absorption of the light by the film adsorbed on the metal
surface. However, for a few nm thick film adsorbed on the gold surface the
attenuation of the intensity of the reflected beam is very small. In addition, due to
the constructive interference taking place on the gold surface (Fig. 2.2a) the normal
component of the electric field vector of the p-polarized IR light is enhanced. The
intensity of the IR light is proportional to E
2 (Eq. 2.5). Thus, the enhancement of E p
on the metal surface gives higher intensity of the IR absorption modes which are
measured in reflection mode. This measuring technique is called infrared reflection
absorption spectroscopy (IRRAS). IRRAS was expanded to study thin molecular
films adsorbed on the metal|gas interface [1], gas|liquid [6–8], and the metal|liquid
interfaces [9–12].
The applicability of IRRAS to investigate films adsorbed on the metal|liquid
interface is very attractive for its applications in electrochemistry. It opens possibilities of in situ studies of electric potential-dependent structural changes occurring in
molecular films adsorbed on electrode surfaces. Application of IRRAS to the
electrochemical interface requires:
(i) Use of smooth reflecting surfaces in order to obey the laws of light reflection;
(ii) Use of monocrystalline or polycrystalline metal electrodes;
(iii) Use of a thin electrolyte layer cell in order to reduce the absorption of the IR
radiation by the solvent [13].
2.2 Application of IRRAS to the Electrochemical Interface
When IRRAS is combined with electrochemical experiments, an IR incoming beam
has to travel through few phases, before it is reflected from the metal (electrode and
mirror) surface. In in situ spectroelectrochemical experiments, the following considerations have to be taken into account:
(i) Selection of a mirror for the IR radiation which simultaneously serves as a
working electrode;
(ii) Absorption of the IR radiation by the electrolyte (usually aqueous solution)
which attenuates the intensity of the measured signal and
(iii) Use of an IR optical window which prevents the electrolyte leakage.
2.2 Application of IRRAS to the Electrochemical Interface
13
coefficient of Lambert-Beer law, which describes the attenuation of the intensity
of light propagating through the absorbing medium,
I ¼ I i exp À
4πk
λ
d 2
ð2:19Þ
where I i is the intensity of the incoming radiation and d 2 is the thickness of the
adsorbed film. According to Eq. (2.19) the beam reflected from the metal surface IR
beam is attenuated by the absorption of the light by the film adsorbed on the metal
surface. However, for a few nm thick film adsorbed on the gold surface the
attenuation of the intensity of the reflected beam is very small. In addition, due to
the constructive interference taking place on the gold surface (Fig. 2.2a) the normal
component of the electric field vector of the p-polarized IR light is enhanced. The
intensity of the IR light is proportional to E
2 (Eq. 2.5). Thus, the enhancement of E p
on the metal surface gives higher intensity of the IR absorption modes which are
measured in reflection mode. This measuring technique is called infrared reflection
absorption spectroscopy (IRRAS). IRRAS was expanded to study thin molecular
films adsorbed on the metal|gas interface [1], gas|liquid [6–8], and the metal|liquid
interfaces [9–12].
The applicability of IRRAS to investigate films adsorbed on the metal|liquid
interface is very attractive for its applications in electrochemistry. It opens possibilities of in situ studies of electric potential-dependent structural changes occurring in
molecular films adsorbed on electrode surfaces. Application of IRRAS to the
electrochemical interface requires:
(i) Use of smooth reflecting surfaces in order to obey the laws of light reflection;
(ii) Use of monocrystalline or polycrystalline metal electrodes;
(iii) Use of a thin electrolyte layer cell in order to reduce the absorption of the IR
radiation by the solvent [13].
2.2 Application of IRRAS to the Electrochemical Interface
When IRRAS is combined with electrochemical experiments, an IR incoming beam
has to travel through few phases, before it is reflected from the metal (electrode and
mirror) surface. In in situ spectroelectrochemical experiments, the following considerations have to be taken into account:
(i) Selection of a mirror for the IR radiation which simultaneously serves as a
working electrode;
(ii) Absorption of the IR radiation by the electrolyte (usually aqueous solution)
which attenuates the intensity of the measured signal and
(iii) Use of an IR optical window which prevents the electrolyte leakage.
2.2 Application of IRRAS to the Electrochemical Interface
13