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# Spectroscopy - Principles,Theory, Techniques and Applications IIT JAM Notes | EduRev

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## IIT JAM : Spectroscopy - Principles,Theory, Techniques and Applications IIT JAM Notes | EduRev

``` Page 1

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Spectroscopy: Principles,
Theory, Techniques and
Applications
Page 2

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PDF generated at: Sat, 30 May 2009 17:33:36 UTC
Spectroscopy: Principles,
Theory, Techniques and
Applications
Spectroscopy
2
Spectroscopy-An Introduction
Spectroscopy
Animation of the dispersion of light as it travels through a
triangular prism
Spectroscopy was originally the
study of the interaction between
radiation and matter as a function
of wavelength (?). In fact,
historically
[1]
, spectroscopy
referred to the use of visible light
dispersed according to its
wavelength, e.g. by a prism. Later
the concept was expanded greatly
to comprise any measurement of a
quantity as function of either
wavelength or frequency. Thus it
also can refer to a response to an
alternating field or varying
frequency (?). A further extension
of the scope of the definition added energy (E) as a variable, once the very close
relationship E = h? for photons was realized (h is the Planck constant). A plot of the
response as a function of wavelengthâ€”or more commonly frequencyâ€”is referred to as a
Spectrometry is the spectroscopic technique used to assess the concentration or amount
of a given species. In those cases, the instrument that performs such measurements is a
spectrometer or spectrograph.
Spectroscopy/spectrometry is often used in physical and analytical chemistry for the
identification of substances through the spectrum emitted from or absorbed by them.
Spectroscopy/spectrometry is also heavily used in astronomy and remote sensing. Most
large telescopes have spectrometers, which are used either to measure the chemical
composition and physical properties of astronomical objects or to measure their velocities
from the Doppler shift of their spectral lines.
Page 3

PDF generated using the open source mwlib toolkit. See http://code.pediapress.com/ for more information.
PDF generated at: Sat, 30 May 2009 17:33:36 UTC
Spectroscopy: Principles,
Theory, Techniques and
Applications
Spectroscopy
2
Spectroscopy-An Introduction
Spectroscopy
Animation of the dispersion of light as it travels through a
triangular prism
Spectroscopy was originally the
study of the interaction between
radiation and matter as a function
of wavelength (?). In fact,
historically
[1]
, spectroscopy
referred to the use of visible light
dispersed according to its
wavelength, e.g. by a prism. Later
the concept was expanded greatly
to comprise any measurement of a
quantity as function of either
wavelength or frequency. Thus it
also can refer to a response to an
alternating field or varying
frequency (?). A further extension
of the scope of the definition added energy (E) as a variable, once the very close
relationship E = h? for photons was realized (h is the Planck constant). A plot of the
response as a function of wavelengthâ€”or more commonly frequencyâ€”is referred to as a
Spectrometry is the spectroscopic technique used to assess the concentration or amount
of a given species. In those cases, the instrument that performs such measurements is a
spectrometer or spectrograph.
Spectroscopy/spectrometry is often used in physical and analytical chemistry for the
identification of substances through the spectrum emitted from or absorbed by them.
Spectroscopy/spectrometry is also heavily used in astronomy and remote sensing. Most
large telescopes have spectrometers, which are used either to measure the chemical
composition and physical properties of astronomical objects or to measure their velocities
from the Doppler shift of their spectral lines.
Spectroscopy
3
Classification of methods
Extremely high resolution spectrum of the Sun showing
thousands of elemental absorption lines (Fraunhofer lines)
Nature of excitation
measured
The type of spectroscopy depends
on the physical quantity measured.
Normally, the quantity that is
measured is an intensity, either of
energy absorbed or produced.
â€¢ Electromagnetic spectroscopy
involves interactions of matter
such as light.
â€¢ ? Electron spectroscopy
involves interactions with
electron beams. Auger
spectroscopy involves inducing the Auger effect with an electron beam. In this case the
measurement typically involves the kinetic energy of the electron as variable.
â€¢ Mass spectrometry involves the interaction of charged species with magnetic and/or
electric fields, giving rise to a mass spectrum. The term "mass spectroscopy" is
deprecated, for the technique is primarily a form of measurement, though it does
produce a spectrum for observation. This spectrum has the mass m as variable, but the
measurement is essentially one of the kinetic energy of the particle.
â€¢ Acoustic spectroscopy involves the frequency of sound.
â€¢ Dielectric spectroscopy involves the frequency of an external electrical field
â€¢ Mechanical spectroscopy involves the frequency of an external mechanical stress, e.g. a
torsion applied to a piece of material.
Measurement process
Most spectroscopic methods are differentiated as either atomic or molecular based on
whether or not they apply to atoms or molecules. Along with that distinction, they can be
classified on the nature of their interaction:
â€¢ Absorption spectroscopy uses the range of the electromagnetic spectra in which a
substance absorbs. This includes ? atomic absorption spectroscopy and various
molecular techniques, such as infrared spectroscopy in that region and nuclear magnetic
resonance (NMR) spectroscopy in the radio region.
â€¢ Emission spectroscopy uses the range of electromagnetic spectra in which a substance
radiates (emits). The substance first must absorb energy. This energy can be from a
variety of sources, which determines the name of the subsequent emission, like
luminescence. Molecular luminescence techniques include spectrofluorimetry.
â€¢ Scattering spectroscopy measures the amount of light that a substance scatters at
certain wavelengths, incident angles, and polarization angles. The scattering process is
much faster than the absorption/emission process. One of the most useful applications of
light scattering spectroscopy is ? Raman spectroscopy.
Page 4

PDF generated using the open source mwlib toolkit. See http://code.pediapress.com/ for more information.
PDF generated at: Sat, 30 May 2009 17:33:36 UTC
Spectroscopy: Principles,
Theory, Techniques and
Applications
Spectroscopy
2
Spectroscopy-An Introduction
Spectroscopy
Animation of the dispersion of light as it travels through a
triangular prism
Spectroscopy was originally the
study of the interaction between
radiation and matter as a function
of wavelength (?). In fact,
historically
[1]
, spectroscopy
referred to the use of visible light
dispersed according to its
wavelength, e.g. by a prism. Later
the concept was expanded greatly
to comprise any measurement of a
quantity as function of either
wavelength or frequency. Thus it
also can refer to a response to an
alternating field or varying
frequency (?). A further extension
of the scope of the definition added energy (E) as a variable, once the very close
relationship E = h? for photons was realized (h is the Planck constant). A plot of the
response as a function of wavelengthâ€”or more commonly frequencyâ€”is referred to as a
Spectrometry is the spectroscopic technique used to assess the concentration or amount
of a given species. In those cases, the instrument that performs such measurements is a
spectrometer or spectrograph.
Spectroscopy/spectrometry is often used in physical and analytical chemistry for the
identification of substances through the spectrum emitted from or absorbed by them.
Spectroscopy/spectrometry is also heavily used in astronomy and remote sensing. Most
large telescopes have spectrometers, which are used either to measure the chemical
composition and physical properties of astronomical objects or to measure their velocities
from the Doppler shift of their spectral lines.
Spectroscopy
3
Classification of methods
Extremely high resolution spectrum of the Sun showing
thousands of elemental absorption lines (Fraunhofer lines)
Nature of excitation
measured
The type of spectroscopy depends
on the physical quantity measured.
Normally, the quantity that is
measured is an intensity, either of
energy absorbed or produced.
â€¢ Electromagnetic spectroscopy
involves interactions of matter
such as light.
â€¢ ? Electron spectroscopy
involves interactions with
electron beams. Auger
spectroscopy involves inducing the Auger effect with an electron beam. In this case the
measurement typically involves the kinetic energy of the electron as variable.
â€¢ Mass spectrometry involves the interaction of charged species with magnetic and/or
electric fields, giving rise to a mass spectrum. The term "mass spectroscopy" is
deprecated, for the technique is primarily a form of measurement, though it does
produce a spectrum for observation. This spectrum has the mass m as variable, but the
measurement is essentially one of the kinetic energy of the particle.
â€¢ Acoustic spectroscopy involves the frequency of sound.
â€¢ Dielectric spectroscopy involves the frequency of an external electrical field
â€¢ Mechanical spectroscopy involves the frequency of an external mechanical stress, e.g. a
torsion applied to a piece of material.
Measurement process
Most spectroscopic methods are differentiated as either atomic or molecular based on
whether or not they apply to atoms or molecules. Along with that distinction, they can be
classified on the nature of their interaction:
â€¢ Absorption spectroscopy uses the range of the electromagnetic spectra in which a
substance absorbs. This includes ? atomic absorption spectroscopy and various
molecular techniques, such as infrared spectroscopy in that region and nuclear magnetic
resonance (NMR) spectroscopy in the radio region.
â€¢ Emission spectroscopy uses the range of electromagnetic spectra in which a substance
radiates (emits). The substance first must absorb energy. This energy can be from a
variety of sources, which determines the name of the subsequent emission, like
luminescence. Molecular luminescence techniques include spectrofluorimetry.
â€¢ Scattering spectroscopy measures the amount of light that a substance scatters at
certain wavelengths, incident angles, and polarization angles. The scattering process is
much faster than the absorption/emission process. One of the most useful applications of
light scattering spectroscopy is ? Raman spectroscopy.
Spectroscopy
4
Common types
Absorption
Absorption spectroscopy is a technique in which the power of a beam of light measured
before and after interaction with a sample is compared. When performed with tunable
diode laser, it is often referred to as Tunable diode laser absorption spectroscopy (TDLAS).
It is also often combined with a modulation technique, most often wavelength modulation
spectrometry (WMS) and occasionally frequency modulation spectrometry (FMS) in order
to reduce the noise in the system.
Fluorescence
Spectrum of light from a fluorescent lamp showing prominent
mercury peaks
Fluorescence spectroscopy uses
higher energy photons to excite a
sample, which will then emit lower
energy photons. This technique
has become popular for its
biochemical and medical
applications, and can be used for
confocal microscopy, fluorescence
resonance energy transfer, and
X- ray
When X-rays of sufficient
frequency (energy) interact with a
substance, inner shell electrons in the atom are excited to outer empty orbitals, or they may
be removed completely, ionizing the atom. The inner shell "hole" will then be filled by
electrons from outer orbitals. The energy available in this de-excitation process is emitted
as radiation (fluorescence) or will remove other less-bound electrons from the atom (Auger
effect). The absorption or emission frequencies (energies) are characteristic of the specific
atom. In addition, for a specific atom small frequency (energy) variations occur which are
characteristic of the chemical bonding. With a suitable apparatus, these characteristic
X-ray frequencies or Auger electron energies can be measured. X-ray absorption and
emission spectroscopy is used in chemistry and material sciences to determine elemental
composition and chemical bonding.
X-ray crystallography is a scattering process; crystalline materials scatter X-rays at
well-defined angles. If the wavelength of the incident X-rays is known, this allows
calculation of the distances between planes of atoms within the crystal. The intensities of
the scattered X-rays give information about the atomic positions and allow the arrangement
of the atoms within the crystal structure to be calculated.
Page 5

PDF generated using the open source mwlib toolkit. See http://code.pediapress.com/ for more information.
PDF generated at: Sat, 30 May 2009 17:33:36 UTC
Spectroscopy: Principles,
Theory, Techniques and
Applications
Spectroscopy
2
Spectroscopy-An Introduction
Spectroscopy
Animation of the dispersion of light as it travels through a
triangular prism
Spectroscopy was originally the
study of the interaction between
radiation and matter as a function
of wavelength (?). In fact,
historically
[1]
, spectroscopy
referred to the use of visible light
dispersed according to its
wavelength, e.g. by a prism. Later
the concept was expanded greatly
to comprise any measurement of a
quantity as function of either
wavelength or frequency. Thus it
also can refer to a response to an
alternating field or varying
frequency (?). A further extension
of the scope of the definition added energy (E) as a variable, once the very close
relationship E = h? for photons was realized (h is the Planck constant). A plot of the
response as a function of wavelengthâ€”or more commonly frequencyâ€”is referred to as a
Spectrometry is the spectroscopic technique used to assess the concentration or amount
of a given species. In those cases, the instrument that performs such measurements is a
spectrometer or spectrograph.
Spectroscopy/spectrometry is often used in physical and analytical chemistry for the
identification of substances through the spectrum emitted from or absorbed by them.
Spectroscopy/spectrometry is also heavily used in astronomy and remote sensing. Most
large telescopes have spectrometers, which are used either to measure the chemical
composition and physical properties of astronomical objects or to measure their velocities
from the Doppler shift of their spectral lines.
Spectroscopy
3
Classification of methods
Extremely high resolution spectrum of the Sun showing
thousands of elemental absorption lines (Fraunhofer lines)
Nature of excitation
measured
The type of spectroscopy depends
on the physical quantity measured.
Normally, the quantity that is
measured is an intensity, either of
energy absorbed or produced.
â€¢ Electromagnetic spectroscopy
involves interactions of matter
such as light.
â€¢ ? Electron spectroscopy
involves interactions with
electron beams. Auger
spectroscopy involves inducing the Auger effect with an electron beam. In this case the
measurement typically involves the kinetic energy of the electron as variable.
â€¢ Mass spectrometry involves the interaction of charged species with magnetic and/or
electric fields, giving rise to a mass spectrum. The term "mass spectroscopy" is
deprecated, for the technique is primarily a form of measurement, though it does
produce a spectrum for observation. This spectrum has the mass m as variable, but the
measurement is essentially one of the kinetic energy of the particle.
â€¢ Acoustic spectroscopy involves the frequency of sound.
â€¢ Dielectric spectroscopy involves the frequency of an external electrical field
â€¢ Mechanical spectroscopy involves the frequency of an external mechanical stress, e.g. a
torsion applied to a piece of material.
Measurement process
Most spectroscopic methods are differentiated as either atomic or molecular based on
whether or not they apply to atoms or molecules. Along with that distinction, they can be
classified on the nature of their interaction:
â€¢ Absorption spectroscopy uses the range of the electromagnetic spectra in which a
substance absorbs. This includes ? atomic absorption spectroscopy and various
molecular techniques, such as infrared spectroscopy in that region and nuclear magnetic
resonance (NMR) spectroscopy in the radio region.
â€¢ Emission spectroscopy uses the range of electromagnetic spectra in which a substance
radiates (emits). The substance first must absorb energy. This energy can be from a
variety of sources, which determines the name of the subsequent emission, like
luminescence. Molecular luminescence techniques include spectrofluorimetry.
â€¢ Scattering spectroscopy measures the amount of light that a substance scatters at
certain wavelengths, incident angles, and polarization angles. The scattering process is
much faster than the absorption/emission process. One of the most useful applications of
light scattering spectroscopy is ? Raman spectroscopy.
Spectroscopy
4
Common types
Absorption
Absorption spectroscopy is a technique in which the power of a beam of light measured
before and after interaction with a sample is compared. When performed with tunable
diode laser, it is often referred to as Tunable diode laser absorption spectroscopy (TDLAS).
It is also often combined with a modulation technique, most often wavelength modulation
spectrometry (WMS) and occasionally frequency modulation spectrometry (FMS) in order
to reduce the noise in the system.
Fluorescence
Spectrum of light from a fluorescent lamp showing prominent
mercury peaks
Fluorescence spectroscopy uses
higher energy photons to excite a
sample, which will then emit lower
energy photons. This technique
has become popular for its
biochemical and medical
applications, and can be used for
confocal microscopy, fluorescence
resonance energy transfer, and
X- ray
When X-rays of sufficient
frequency (energy) interact with a
substance, inner shell electrons in the atom are excited to outer empty orbitals, or they may
be removed completely, ionizing the atom. The inner shell "hole" will then be filled by
electrons from outer orbitals. The energy available in this de-excitation process is emitted
as radiation (fluorescence) or will remove other less-bound electrons from the atom (Auger
effect). The absorption or emission frequencies (energies) are characteristic of the specific
atom. In addition, for a specific atom small frequency (energy) variations occur which are
characteristic of the chemical bonding. With a suitable apparatus, these characteristic
X-ray frequencies or Auger electron energies can be measured. X-ray absorption and
emission spectroscopy is used in chemistry and material sciences to determine elemental
composition and chemical bonding.
X-ray crystallography is a scattering process; crystalline materials scatter X-rays at
well-defined angles. If the wavelength of the incident X-rays is known, this allows
calculation of the distances between planes of atoms within the crystal. The intensities of
the scattered X-rays give information about the atomic positions and allow the arrangement
of the atoms within the crystal structure to be calculated.
Spectroscopy
5
Flame
Liquid solution samples are aspirated into a burner or nebulizer/burner combination,
desolvated, atomized, and sometimes excited to a higher energy electronic state. The use of
a flame during analysis requires fuel and oxidant, typically in the form of gases. Common
fuel gases used are acetylene (ethyne) or hydrogen. Common oxidant gases used are
oxygen, air, or nitrous oxide. These methods are often capable of analyzing metallic
element analytes in the part per million, billion, or possibly lower concentration ranges.
Light detectors are needed to detect light with the analysis information coming from the
flame.
â€¢ Atomic Emission Spectroscopy - This method uses flame excitation; atoms are excited
from the heat of the flame to emit light. This method commonly uses a total consumption
burner with a round burning outlet. A higher temperature flame than atomic absorption
spectroscopy (AA) is typically used to produce excitation of analyte atoms. Since analyte
atoms are excited by the heat of the flame, no special elemental lamps to shine into the
flame are needed. A high resolution polychromator can be used to produce an emission
intensity vs. wavelength spectrum over a range of wavelengths showing multiple element
excitation lines, meaning multiple elements can be detected in one run. Alternatively, a
monochromator can be set at one wavelength to concentrate on analysis of a single
element at a certain emission line. Plasma emission spectroscopy is a more modern
version of this method. See Flame emission spectroscopy for more details.
â€¢ ? Atomic absorption spectroscopy (often called AA) - This method commonly uses a
pre-burner nebulizer (or nebulizing chamber) to create a sample mist and a slot-shaped
burner which gives a longer pathlength flame. The temperature of the flame is low
enough that the flame itself does not excite sample atoms from their ground state. The
nebulizer and flame are used to desolvate and atomize the sample, but the excitation of
the analyte atoms is done by the use of lamps shining through the flame at various
wavelengths for each type of analyte. In AA, the amount of light absorbed after going
through the flame determines the amount of analyte in the sample. A graphite furnace for
heating the sample to desolvate and atomize is commonly used for greater sensitivity.
The graphite furnace method can also analyze some solid or slurry samples. Because of
its good sensitivity and selectivity, it is still a commonly used method of analysis for
certain trace elements in aqueous (and other liquid) samples.
â€¢ Atomic Fluorescence Spectroscopy - This method commonly uses a burner with a
round burning outlet. The flame is used to solvate and atomize the sample, but a lamp
shines light at a specific wavelength into the flame to excite the analyte atoms in the
flame. The atoms of certain elements can then fluoresce emitting light in a different
direction. The intensity of this fluorescing light is used for quantifying the amount of
analyte element in the sample. A graphite furnace can also be used for atomic
fluorescence spectroscopy. This method is not as commonly used as atomic absorption or
plasma emission spectroscopy.
Plasma Emission Spectroscopy In some ways similar to flame atomic emission
spectroscopy, it has largely replaced it.
â€¢ Direct-current plasma (DCP)
A direct-current plasma (DCP) is created by an electrical discharge between two electrodes.
A plasma support gas is necessary, and Ar is common. Samples can be deposited on one of
the electrodes, or if conducting can make up one electrode.
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