4
H. Kaur et al.
1 Introduction
Infrared (IR) spectroscopy is a well-recognized fundamental spectroscopic tool that
involves the analytical processing of atomic and molecular vibrations of the molecule
upon resonantly associating with an incident IR radiation source. It is employed as
one of the most convenient tools to selectively probe the molecular functional groups
through their distinct IR absorption bands, which are greatly influenced by the molecular composition, conformation, and the condition of the surrounding medium [1–3].
These properties directly influence the associated vibrational transitions. Established
by Coblentz in the early twentieth century [1], IR spectroscopic techniques have
been revamped since then and revolutionized the modern molecular spectroscopic
methods. Improvements at the instrumental level have led to the evolution of sensitivity and efficiency of probing by IR spectroscopic techniques that could be applied
for exploring the properties of any sample with an effective polarity in any of its
morphological states (liquid, powder, films, gases, etc.) [1–4]. The advancements
have further provided precedence in the requirement of less sample amount for a
cost-effective spectroscopic analysis. These include the designing of Fourier transform infrared (FTIR) spectrometer in the 1980s, which aimed to improve the performance of IR spectrometer by collecting the data at a faster pace with an enhanced
signal to noise ratio [1, 2, 5].
Among the other IR based spectroscopic techniques, attenuated total reflectance
Fourier transform infrared (ATR-FTIR) spectroscopy is the most promising tool that
works on the amalgamation of the biochemical and biophysical properties of the
system [3–5]. The concept of the ATR technique was first suggested by N. J. Harrick
in 1960 and J. Fahrenfort in 1961 [6, 7]. Both of them advocated the possible working
model of the ATR technique with multiple and single reflection ATR geometries,
respectively. The ATR mode of IR spectroscopy allows the evaluation of waterbased samples known to be strong absorber of IR radiation which makes experiments
very difficult to conduct by conventional FTIR experiments. The ATR-FTIR tool
addresses the issues of absorption by acquiring the molecular vibrations through
reduced pathlength of the probing beam across the sample. With the ATR mode
configuration, the molecular structural information in terms of vibrational modes of
the molecules can be extracted from the probing depth of a few micrometers via
evanescent wave generated at the interface between ATR crystal and the sample
medium. The IR beam strikes the crystal-sample interface at an angle greater than
the critical angle of incidence (θ c ) then undergoes total internal reflection (TIR)
as a result of refractive index differences, with the ATR crystal having a higher
refractive index value than the sample. The ATR-FTIR configuration provides the
right platform to investigate solid-aqueous interfaces effectively [1, 2, 5, 8, 9]. The
ATR-FTIR spectroscopic technique has been further advanced to provide a detailed
assessment of the molecular bonding, surface adsorption, interactions, molecular
orientation, and kinetics, as well as the structural parameter of the sample [8–12].
H. Kaur et al.
1 Introduction
Infrared (IR) spectroscopy is a well-recognized fundamental spectroscopic tool that
involves the analytical processing of atomic and molecular vibrations of the molecule
upon resonantly associating with an incident IR radiation source. It is employed as
one of the most convenient tools to selectively probe the molecular functional groups
through their distinct IR absorption bands, which are greatly influenced by the molecular composition, conformation, and the condition of the surrounding medium [1–3].
These properties directly influence the associated vibrational transitions. Established
by Coblentz in the early twentieth century [1], IR spectroscopic techniques have
been revamped since then and revolutionized the modern molecular spectroscopic
methods. Improvements at the instrumental level have led to the evolution of sensitivity and efficiency of probing by IR spectroscopic techniques that could be applied
for exploring the properties of any sample with an effective polarity in any of its
morphological states (liquid, powder, films, gases, etc.) [1–4]. The advancements
have further provided precedence in the requirement of less sample amount for a
cost-effective spectroscopic analysis. These include the designing of Fourier transform infrared (FTIR) spectrometer in the 1980s, which aimed to improve the performance of IR spectrometer by collecting the data at a faster pace with an enhanced
signal to noise ratio [1, 2, 5].
Among the other IR based spectroscopic techniques, attenuated total reflectance
Fourier transform infrared (ATR-FTIR) spectroscopy is the most promising tool that
works on the amalgamation of the biochemical and biophysical properties of the
system [3–5]. The concept of the ATR technique was first suggested by N. J. Harrick
in 1960 and J. Fahrenfort in 1961 [6, 7]. Both of them advocated the possible working
model of the ATR technique with multiple and single reflection ATR geometries,
respectively. The ATR mode of IR spectroscopy allows the evaluation of waterbased samples known to be strong absorber of IR radiation which makes experiments
very difficult to conduct by conventional FTIR experiments. The ATR-FTIR tool
addresses the issues of absorption by acquiring the molecular vibrations through
reduced pathlength of the probing beam across the sample. With the ATR mode
configuration, the molecular structural information in terms of vibrational modes of
the molecules can be extracted from the probing depth of a few micrometers via
evanescent wave generated at the interface between ATR crystal and the sample
medium. The IR beam strikes the crystal-sample interface at an angle greater than
the critical angle of incidence (θ c ) then undergoes total internal reflection (TIR)
as a result of refractive index differences, with the ATR crystal having a higher
refractive index value than the sample. The ATR-FTIR configuration provides the
right platform to investigate solid-aqueous interfaces effectively [1, 2, 5, 8, 9]. The
ATR-FTIR spectroscopic technique has been further advanced to provide a detailed
assessment of the molecular bonding, surface adsorption, interactions, molecular
orientation, and kinetics, as well as the structural parameter of the sample [8–12].