M. Baranska et al.
4
has lead to the following criteria: a given normal vibration of a molecule may appear in the IR spectrum if at least one component of the electric dipole moment
of the molecule changes during the vibration whereas respectively for the Raman
spectrum: at least one component of the polarizability tensor changes. however
according to quantum theory, oscillation of a permanent or induced dipole does not
produce any radiation. For radiation to be emitted or absorbed, a transition should
occur between different vibrational energy levels of the molecule which may be
concomitant with loss or gain of energy in the form of electromagnetic radiations.
the classical analogue of excitation of a molecule to a higher energy level is vibration with increased amplitude [1].
Also a spatial resolution of both vibrational methods is different. According to the
Rayleigh criterion, which defines the resolution obtained from the diffraction limited
grating spectrometers and also by a Fourier transform spectrometer that uses triangular apodization, IR spectroscopy is at the limit of 10–12 microns whereas for Raman
scattering it is 0.3 microns (for the excitation of 488 nm). various sampling technique can improve a spatial resolution, however their employment is also limited.
IR and Raman spectroscopy are complimentary methods. Among 3N-6 vibrational modes (N—the number of atoms in a molecule), for some specific functional
groups a characteristic frequency can be used for their identification, quantification
or conformational study.
Both methods in practice are used as individual techniques, sometimes restricted
only to special applications but also providing unusual possibilities and advantages.
For the purpose of this book the results of Raman and IR imaging, Surface-Enhanced Raman Spectroscopy (SERS), Raman optical Activity (RoA), vibrational
Circular dichroism (vCd), and matrix isolation spectroscopy are presented. Additionally to dichroism and optical activity in vibrational spectroscopy, Electronic
Circular dichroism (ECd) is introduced.
vibrational spectroscopic imaging greatly extend the possibilities of the conventional IR and Raman spectroscopy. Spectral data can be represented as a picture, presenting chemical information simultaneously from thousands of pixels.
the pixel brightness or colour can be derived from any number of spectral parameters, ranging from simple vibrational peak intensities to multivariate parameters.
the ability to explore spectral information in a spatially resolve manner can give
significant insight into organisational motifs and aid the prediction of molecular
functional behaviour. hopefully the usefulness of an integrated spectral and spatial
techniques will result in their application to routine analysis, with a special focus on
biological samples and medical diagnosis [1].
Surface Enhanced Raman Spectroscopy (SERS) is a useful analytical technique
employed for the identification accompanied by investigation of the most probable orientation of molecules adsorbed on the metal surface [2]. Although SERS
spectroscopy is widely applied, the mechanism leading to the surface enhancement
is not completely understood yet. three possible contributions to the enhancement factor have been identified: (i) the surface plasmons resonance in the metal
nanoparticles, (ii) a charge-transfer resonance involving shift of electrons between
4
has lead to the following criteria: a given normal vibration of a molecule may appear in the IR spectrum if at least one component of the electric dipole moment
of the molecule changes during the vibration whereas respectively for the Raman
spectrum: at least one component of the polarizability tensor changes. however
according to quantum theory, oscillation of a permanent or induced dipole does not
produce any radiation. For radiation to be emitted or absorbed, a transition should
occur between different vibrational energy levels of the molecule which may be
concomitant with loss or gain of energy in the form of electromagnetic radiations.
the classical analogue of excitation of a molecule to a higher energy level is vibration with increased amplitude [1].
Also a spatial resolution of both vibrational methods is different. According to the
Rayleigh criterion, which defines the resolution obtained from the diffraction limited
grating spectrometers and also by a Fourier transform spectrometer that uses triangular apodization, IR spectroscopy is at the limit of 10–12 microns whereas for Raman
scattering it is 0.3 microns (for the excitation of 488 nm). various sampling technique can improve a spatial resolution, however their employment is also limited.
IR and Raman spectroscopy are complimentary methods. Among 3N-6 vibrational modes (N—the number of atoms in a molecule), for some specific functional
groups a characteristic frequency can be used for their identification, quantification
or conformational study.
Both methods in practice are used as individual techniques, sometimes restricted
only to special applications but also providing unusual possibilities and advantages.
For the purpose of this book the results of Raman and IR imaging, Surface-Enhanced Raman Spectroscopy (SERS), Raman optical Activity (RoA), vibrational
Circular dichroism (vCd), and matrix isolation spectroscopy are presented. Additionally to dichroism and optical activity in vibrational spectroscopy, Electronic
Circular dichroism (ECd) is introduced.
vibrational spectroscopic imaging greatly extend the possibilities of the conventional IR and Raman spectroscopy. Spectral data can be represented as a picture, presenting chemical information simultaneously from thousands of pixels.
the pixel brightness or colour can be derived from any number of spectral parameters, ranging from simple vibrational peak intensities to multivariate parameters.
the ability to explore spectral information in a spatially resolve manner can give
significant insight into organisational motifs and aid the prediction of molecular
functional behaviour. hopefully the usefulness of an integrated spectral and spatial
techniques will result in their application to routine analysis, with a special focus on
biological samples and medical diagnosis [1].
Surface Enhanced Raman Spectroscopy (SERS) is a useful analytical technique
employed for the identification accompanied by investigation of the most probable orientation of molecules adsorbed on the metal surface [2]. Although SERS
spectroscopy is widely applied, the mechanism leading to the surface enhancement
is not completely understood yet. three possible contributions to the enhancement factor have been identified: (i) the surface plasmons resonance in the metal
nanoparticles, (ii) a charge-transfer resonance involving shift of electrons between