2. Introduction
Spectroscopy and Absorption
While defining spectroscopy, we used the word 'absorb' several times, as well as
'emitted.' Absorption refers to how much light (or other waves) can be taken in by the
material being measured. Emission, on the other hand, refers to how much light (or other
waves) can be released by the material being measured - emitted light is usually altered
from its original state by the material, and that altered light is what's measured during
spectroscopy.[1]
Principle
When radiation is passed through a substance under examination, absorption of energy
result in the promotion of electron from the ground state to the excited electronic state.
During the process of absorption, a large number of photon molecule collisions are possible
but only those collision will cause absorption of energy in which the energy of photon
matches the energy difference between the ground and excited electronic state of the
molecule. The absorption of energy is quantised.[2]
It refers to spectroscopic techniques that measure the absorption of radiation, as a function
of frequency or wavelength, due to its interaction with a sample. The sample absorbs
energy, i.e., photons, from the radiating field. The intensity of the absorption varies as a
function of frequency, and this variation is the absorption spectrum. Absorption
spectroscopy is performed across the electromagnetic spectrum.[3]
Absorption lines are typically classified by the nature of the quantum mechanical change
induced in the molecule or atom. Rotational lines are typically found in the microwave
spectral region. Vibrational lines correspond to changes in the vibrational state of the
molecule and are typically found in the infrared region. Electronic lines correspond to a
change in the electronic state of an atom or molecule and are typically found in the visible
and ultraviolet region. X-ray absorptions are associated with the excitation of inner shell
electrons in atoms.
3. There are several example of absorption spectroscopies is available which are given below:
1) UV-VIS Spectroscopy
2) IR Spectroscopy
3) X-Ray Spectroscopy
4) Microwave absorption spectroscopy
5) Electron spin resonance spectroscopy
6) Nuclear magnetic resonance spectroscopy etc. [4]
Here we only can discuss about UV-VIS Spectroscopy.
UV-VIS Spectroscopy
The absorption laws
Beer-Lambert laws govern the absorption of light by the molecule. These laws
are formulated as below:
4. I0-Intensity of incident light, I-Intensity of transmitted light.
Electronic Transitions-
According to molecular orbital theory, when a molecule is excited by the absorption of
energy its electrons are promoted from bonding to an antibonding. Various transitions
involved in UV-VIS Spectroscopy.
Absorption and intensity Shifts-
Bathochromic effect-It is an effect due to which the absorption maximum is shifted towards
longer wavelength due to the presence of auxo chrome or by the change of solvent
increase in conjugation causes bathochromic shift.
Hypsochromic Shifts or effects-absorption maximum is shifted towards shorter wavelength.
The absorption shifted towards shorter wavelength is called blue shift or hypsochromic
shift.
Hyperchromic effects-It is an effect due to which the intensity of absorption maximum
increases.
Hypochromic effects-It is an effect due to which the intensity of absorption maximum
decreases.[5]
5. Application-
Absorption spectroscopy is useful in chemical analysis because of its specificity and its
quantitative nature. Absorption Spectroscopy is used in various purpose like-
1)Remoting Sensing,
2)Astronomy,
3)Atomic and molecular physics,[6]
4)Detection of functional groups,
5)Identification of an unknown compound.[7]
Absorption and Emission Spectroscopy of Carbon nanotubes
• Compared to the vibrational spectroscopy of carbon nanotubes, their absorption and
luminescence spectroscopy kind of lives in the shadows. This is, however, not due to
a lack of information these methods could provide to the understanding of the
nanotubes' electronic structure. There are rather experimental complications that
arise from the inhomogeneity of the available materials.
• Due to the one-dimensionality of nanotubes, absorption and luminescence spectra
can be predicted from theoretical considerations. The extinction should depend on
the structure of the respective tube. Especially in the lower energy range (infrared)
most of the transitions between n-bands are observed.
• The position of absorption maxima consequently depends on the diameter as well as
on the chirality angle of the tube under consideration as both parameters influence
the distance between singularities in the density of electronic states.
• Examining bundles of different tubes hardly provides any information as the
assignment of individual signals is virtually impossible. A strong intratubular
electronic coupling causes a significant mixing of electronic states, and so the fine
structure of the spectra does not allow for data evaluation with regard to individual
tubes.
• Therefore, the fluorescence of nanotubes can at least be taken as an indicator for
successful de bundling of SWNT: Bundled samples do not show infrared fluorescence,
whereas it is easily measured for separated nanotubes.
6. • For nanotubes separated by surfactants or other techniques, absorption or emission
spectra with a distinct structure and coinciding signal positions are obtained. The
characteristic bands are situated at 0.68eV (1823nm), 1.2 eV (1033nm), and 1.7 eV
(729nm). They correspond to the first and second transition in semiconducting tubes
and to the first permitted transition in metallic species. Furthermore, there is the
broad signal at 4.5 eV (275 nm) that represents a n-plasmon band.
(a) Absorption spectra of a single nanotube and of a bundle of tube.
(b) emission spectrum of a CNT-sample at Aexc. = 532 nm in comparison to the
absorption spectrum, (c) excitation spectrum of the same sample at Aexc. = 875 nm
[8]
References
[1] Subscribe to Study.com
[2][5][7] Book-Elementary organic spectroscopy-Y.R. SHARMA
[3][6][4] https://en.wikipedia.org/wiki/Absorption_spectroscopy
[8] https://www.texaspowerfulsmart.com/diamond-films/absorption-and-emission-
spectroscopy-of-carbon-nanotubes.html
![Introduction
Spectroscopy and Absorption
While defining spectroscopy, we used the word 'absorb' several times, as well as
'emitted.' Absorption refers to how much light (or other waves) can be taken in by the
material being measured. Emission, on the other hand, refers to how much light (or other
waves) can be released by the material being measured - emitted light is usually altered
from its original state by the material, and that altered light is what's measured during
spectroscopy.[1]
Principle
When radiation is passed through a substance under examination, absorption of energy
result in the promotion of electron from the ground state to the excited electronic state.
During the process of absorption, a large number of photon molecule collisions are possible
but only those collision will cause absorption of energy in which the energy of photon
matches the energy difference between the ground and excited electronic state of the
molecule. The absorption of energy is quantised.[2]
It refers to spectroscopic techniques that measure the absorption of radiation, as a function
of frequency or wavelength, due to its interaction with a sample. The sample absorbs
energy, i.e., photons, from the radiating field. The intensity of the absorption varies as a
function of frequency, and this variation is the absorption spectrum. Absorption
spectroscopy is performed across the electromagnetic spectrum.[3]
Absorption lines are typically classified by the nature of the quantum mechanical change
induced in the molecule or atom. Rotational lines are typically found in the microwave
spectral region. Vibrational lines correspond to changes in the vibrational state of the
molecule and are typically found in the infrared region. Electronic lines correspond to a
change in the electronic state of an atom or molecule and are typically found in the visible
and ultraviolet region. X-ray absorptions are associated with the excitation of inner shell
electrons in atoms.](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)