Comprehensive Analysis of Absorption Spectrum: A Detailed Overview

This essay provides a comprehensive overview of the absorption spectrum, defining it as the fraction of incident radiation absorbed by a material across a range of frequencies. It explores how the absorption spectrum is determined by a material's molecular and atomic composition and how the absorption lines are classified based on quantum mechanical changes. The essay discusses the relationship between absorption and emission spectra, as well as its connections to reflection and scattering spectra. Furthermore, it highlights the application of absorption spectroscopy in chemical analysis, medical fields, and its use in determining the quantity of a material through the Beer-Lambert law. Various experimental approaches and advantages of absorption spectroscopy are also discussed. The essay covers a wide range of topics related to the absorption spectrum and its applications.

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Blog Writing- Absorption Spectrum

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Absorption Spectrum
July 16th, 2019
What is Absorption Spectrum?
The absorption spectrum of a material can be defined as the fraction of the incident radiation
which is absorbed by that material over a wide range of frequencies. The molecular and
atomic composition of a material is used to determine the absorption spectrum. Fundamental
radiation is generally observed at those frequencies which get mixed with the energy
difference that takes place between two mechanical states of the molecules. The absorption
takes place because of the transition between these two states and it is known as the
absorption line. The spectrum is composed of several absorption lines. The frequencies where
such absorption lines develop along with their relative intensities generally depend on the
molecular structure and electronic structure of the sample. The frequencies also depend on
molecular interactions. In the sample, the crystal structure is found in solids and on different
environmental factors like pressure, temperature, electromagnetic fields, etc. The absorption
lines also possess a definite shape and width which are fundamentally determined by the
density of states for spectral density of the system. Absorption lines are generally classified
by the feature of quantum mechanical change taking place in an atom or molecule. Rotational
states sometimes get changed and give result in the development of rotational lines which are
found in the region of the microwave spectrum. On the other hand, vibrational lines in
correspondence to vibrational state changes in the molecule are found in the area of infrared
region. The electronic lines are composed of several changes taking place in the electronic
state of a molecule or atom which are found in the ultraviolet and visible region.
It can be noticed that there are various dark lines in the sun’s spectrum. These lines are
developed by the atmosphere of the Sun which absorbs light at different wavelengths
resulting in different light intensity at the wavelength to appear dark. The molecules and
atoms present in a gas absorb certain light wavelengths. The pattern of the lines is very
unique with respect to each element which provides us information about the elements which

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help in making the sun's atmosphere. The absorption spectra can be observed from spatial
regions in the presence of a cooler gas line between in a hotter source and the earth. The
absorption spectra can also be observed from the planets with atmospheres, stars, and
galaxies. In analyzing the light of the Sun, a spectrometer is used. The spectrometer is a
device which separates light by color and energy. In separating light by color and energy, the
image of the spectrum of the sun gets created. This is quite similar to the absorption
spectrum. The dark lines are the areas where the light gets absorbed by different elements
present in the Sun's outer layers. The lowest energy is represented by red light and the highest
energy is represented by blue light.
The black gaps or lines in the spectrum of the sun are termed as absorption lines. The gas
present in the sun's outer layers develops the absorption lines by absorbing the light. There
are different elements such as Helium, hydrogen, carbon, and other smaller quantities of
heavy elements in the sun. When the sunlight shines, the elements the energy gets absorbed
by the atoms. The atoms can only absorb the light relevant to the energy the atoms need. The
gaps in the spectrum of the Sun get developed and help in informing the formation of the sun.
The emission spectrum is quite different from the absorption spectrum. In developing an
absorption spectrum, the light needs to shine through a gas but in creating and emission
spectrum a gas needs to be heated up. The atoms present in the gas get absorbed the energy
only for a short tenure. The atoms get energetic and jiggled up by heating the gas because of
the concentration of a high level of energy. The energy is emitted or re-released as light
eventually. Absorption spectrum takes place when the light passes through a dilute and cold
gas and characteristic frequencies get absorbed by the atoms present in the gas. The re-
emitted light cannot be emitted in a similar direction which is followed by absorbed Photon
because of which dark lines in the spectrum are created in the absence of light. Absorption
spectrum is the dark lines. The absorption spectrum is defined as an Electromagnetic
Spectrum in which the radiation intensity at some specific wavelengths gets decreased. An
absorbing substance gets manifested as bands or dark lines. Medically, the absorption
spectrum is also defined as an Electromagnetic Spectrum in which radiation intensity at
specific ranges of wavelength is manifested as dark lines.
X-ray absorptions are highly associated with the excitation taking place in the inner shell
electrons in an atom. These changes generally get combined to develop a new absorption line
which is typically found in the combined energy develop mainly during the changes. The
changes are mainly radiation-vibrations transitions. The energy which is typically found in

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the quantum mechanical change fundamentally determines the absorption line frequency. The
frequency can get shifted because of several interactions. The magnetic and electric fields can
give result in a shift. The interactions with some of the neighboring molecules can also cause
shifts. Absorption lines of any gas-phase molecule can get shifted typically when the
molecule is present in either solid or liquid phase and involves in interacting with
neighboring molecules strongly. The shape and width of the absorption lines are generally
determined by the observation instrument. The physical environment radiation and material
absorbing of that material also determine the shape and width of absorption lines.
The relation between Transmission and absorption spectra
Transmission and absorption spectra are interconnected. Transmission and absorption spectra
are found to represent similar information. Transmission spectrum can be calculated from the
absorption spectrum only. Absorption spectrum can also be calculated from transmission
spectra. Mathematical transformation is used in calculating either the absorption spectrum or
transmission spectrum. It has been observed that a transmission spectrum has maximum
intensities where the wavelengths of the absorption spectrum are quite weak because of the
transmission of more light through the sample takes place. Similarly, an absorption spectrum
is found to have maximum intensities at its wavelengths where the absorption rate is quite
stronger. The absorption spectrum is also related to any emission spectrum. Now, it is
important to understand the concept of the emission spectrum. The process by which a
substance can release energy is known as emission process. The energy which is released
from a substance through any emission process can be found in an electromagnetic radiation
form. Emission can take at any frequency of absorption which makes the absorption lines to
gets determined from the emission spectrum. But it is to be remembered that the emission
spectrum will always have different intensity pattern where it becomes distinguished from
that of the absorption spectrum. Hence, it can be said that the absorption spectrum and
emission spectrum can never be equivalent. The emission spectrum can be used to calculate
the absorption spectrum with the application of effective theoretical models and other
relevant information from where quantum mechanical states of a substance can be
understood.
Relationship between Absorption spectrum and reflection and scattering spectra
The absorption spectrum is also related to reflection and scattering spectra. The scattering and
reflection spectra of any material get influenced by the absorption spectrum and index of

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refraction of that material. Extinction coefficient quantifies the absorption spectrum and
index coefficients along with extinction coefficients which are related through Kramers-
Kroing relation quantitatively. Therefore, it can be said that reflection or scattering spectrum
standardize absorption spectrum can give rise to absorption spectrum. Reflection or scattering
spectrum assumptions or models need to be simplified so that it can lead to effect an
approximation of the derivation of absorption spectra. In the domain of chemical analysis, we
can find the use of absorption spectroscopy because of the quantitative nature and specificity
of the absorption spectrum. The specificity enables the compounds to get distinguished from
each other in a mixture which makes absorption spectroscopy to be highly useful in different
applications. For example, the presence of any pollutant in the air can be identified by the use
of infrared gas analyzers. These analyses are also used to distinguish the air pollutant from
oxygen, water, nitrogen, and other constituents. The specificity is also helpful in allowing
several unknown samples to get rightly identified. It can be done by comparing the measured
spectrum with the findings of reference spectra. It has been found that qualitative information
of any sample can also be determined even if the information is not present in a library. For
example, infrared spectra have several characteristics absorption bands which help in
indicating the presence of carbon-oxygen bond or Carbon hydrogen bonds. Absorption
spectrum can also be related to the quantity of material present with the use of Beer-Lambert
law. This relationship is established quantitatively. In determining the typical compound
concentration, it needs knowledge of the absorption coefficient of the compound. The
absorption coefficient can be known from several reference sources and can be measured by
accessing caliber standard spectrum with an available target concentration.

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Absorption spectroscopy and its application
Absorption spectroscopy is one of the methods with the help of which a substance can get
characterized by the support of wavelengths at which the spectrum of color gets absorbed
during the passage of light through a substance solution. It is one of the fundamentally used
methods used in assessing the chromospheres concentrations in the solutions. Absorption
spectroscopy can also be explained as a non-destructive technique which is widely used by
biochemists and biologists to assess the characteristic parameters and cellular components of
functional molecules. This quantification is highly important in the domain of systems
biology. In developing metabolic pathway quantitative depiction, various variables and
parameters are needed which are to be assessed experimentally. Ultraviolet-visible absorption
spectroscopy is used in producing experimental data which help in modeling techniques of
system biology. These techniques use kinetic parameters and concentrations of enzymes of
signaling on metabolic pathways, fluxes, and intercellular metabolic concentrations.
Absorption spectroscopy also describes the usage of the technique in quantifying bio-
molecules and investigating bio-molecular interactions.
Absorption spectroscopy is a significant technique which is used in chemistry to study simple
inorganic species. It refers to spectroscopic techniques which are used in measuring radiation
absorption as a function of wavelength or frequency when the interaction between absorption
radiation and sample takes place. Photons are absorbed by the samples from the field of
radiation. The absorption intensity varies as a frequency function and this absorption intensity
is the absorption spectrum. Absorption spectroscopy is fundamentally performed across an
absorption spectrum or electromagnetic spectrum. In the domain of analytical chemistry,
absorption spectroscopy is used to assess the presence of any specific substance in a sample.
In several cases, absorption spectroscopy is also used to quantify the quantity of a substance.
In the domain of analytical applications, ultraviolet-visible and infrared spectroscopy is
commonly observed. In the study of atomic physics, remote sensing, molecular physics, and
astronomical spectroscopy, the use of absorption spectroscopy are widely observed. There are
various experimental approaches which are used to measure the absorption spectrum. The
most commonly used arrangement is to guide the regenerated radiation beam at the sample in
detecting the radiation intensity passing through it. The transmitted energy can be applied in
calculating the absorption. The sample arrangement source and detection technique are also
very used quite significantly depending on the objective of the experiment and that of the
frequency range.

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Advantages of absorption spectroscopy
There can be several advantages of absorption spectroscopy because it can be used as an
analytical method where measurements can be accomplished without any contact between the
sample and the instrument. Radiation which travels between an instrument and a sample
contains some important spectral information and measurement which is done remotely.
Remote spectral sensing is quite significant in different situations. For example, hazardous
and toxic environments can be measured without risking any instrument or operator. The
material of the sample needs not to be brought into direct contact with any instrument which
can prevent cross-contamination at a possible rate. Remote spectral measurements have
certain challenges as compared to that of the laboratory measurements. To reduce such
challenges, differential optical absorption spectroscopy has become quite popular because it
mainly emphasizes on the features of differential absorption and erasers broadband
absorption like the extinction of aerosol extinction because of Rayleigh scattering. This
technique is used in airborne, ground-based, and satellite-based measuring actions. There are
certain ground-based techniques which profile the possibilities of retrieving stratospheric and
tropospheric trace gas profiles.
Absorption spectrum and photosynthesis
Absorption spectrum generally defines the electromagnetic radiation spectrum or the visible
light spectrum. The graphic representation of various wavelengths of the light which gets
absorbed by pigments of a leaf during the process of photosynthesis is also an absorption
spectrum. The region which depicts the intensity of the absorbed light is relatively connected
to its wavelength. Absorption spectrum explains the fundamental relationship between
pigments’ absorbing capacity and light quality. In the process of photosynthesis, chlorophyll
generally absorbs red and blue light. One the other hand, carotenoids absorb blue and violet
lights. The pigments of a leaf absorb different wavelengths of light which can be measured by
the use of a spectrophotometer. During the process of photosynthesis, absorption spectrum
portrays the light which is typically absorbed by the leaves. The green pigments of the plants
absorb the energy of the light. When the energy of the light of photons coincides with the
molecules of chlorophyll an electron gets excited which puts that electron into a state of
higher energy. This excited electron sets off the process of photosynthesis which converts the
light energy present in the electron into sugar or stored energy. When the green pigments of
the plants absorb light energy, either heat is given off as energy or the light energy changes

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into longer wavelength. Chemical reaction or photosynthesis also takes place during the
process of absorbing energy by the green pigments of the plants. The absorption spectrum is
the graph or the plot which shows absorption of light at various wavelengths.
The plants are generally green in color because green light gets reflected by them. They are
more effective in absorbing blue and red light. Absorption spectrum shows the light which a
leaf absorbs. On the other hand, the action spectrum shows the light which is typically used
for the process of photosynthesis. Sometimes, the action spectrum gets confused with
absorption spectrum but both are highly different from each other. An action spectrum is a
plot or the graph which shows the effectiveness of various wavelengths involved in the
process of photosynthesis. It ratifies the actual pigments involved in the process of
photosynthesis. An action spectrum is also known as the visible spectrum which depicts the
efficiency of various wavelengths of light in the process of photosynthesis. The
photosynthesis rate is assessed ion action spectrum as an amount of oxygen production,
carbon dioxide fixation, reduction, etc. On the other hand, the absorption spectrum is the
ability of the green pigments of the plants in absorbing light at some specific wavelengths.
Maximum photosynthesis takes place in red and blue light which is absorbed by chlorophyll
present in the plants.