This document provides an overview of spectroscopy. It begins by defining spectroscopy as the study of the interaction between matter and radiated energy. It then discusses the history and development of spectroscopy. The document classifies different types of spectroscopy based on the type of radiative energy and nature of interaction. It provides examples of various spectroscopic techniques including electromagnetic spectroscopy, nuclear magnetic resonance spectroscopy, mass spectrometry, and fluorescence. Key terms related to spectroscopy are defined.

1. SPECTROSCOPY :-
Spectroscopy is the study of the interaction between matter and radiated
energy.Historically, spectroscopyoriginated through the study of visible light dispersed
according to its wavelength, by a prism. Later the conceptwas expanded greatlyto
comprise anyinteraction with radiative energyas a function of its wavelength or frequency.
Spectroscopic data is often represented by a spectrum, a plot of the response ofinterest as
a function of wavelength or frequency.
 Spectroscopy-the study of the light from an object.
 Spectrometer- an instrumentwhich spreads outlight making a
spectra.
 Spectra- range of electromagnetic energyseparated by wavelength.
History
The history of spectroscopybegan with Isaac Newton's optics experiments (1666–1672).
Newton applied the word "spectrum" to describe the rainbowof colors that combine to form
white light and that are revealed when the white light is passed through a prism. During the
early 1800s, Joseph von Fraunhofermade experimentaladvances with dispersive
spectrometers that enabled spectroscopyto become a more precise and quantitative
scientific technique.Since then, spectroscopyhas played and continues to play a significant
role in chemistry, physics and astronomy.
Spectroscopyand spectrographyare terms used to refer to the measurementof radiation
intensity as a function of wavelength and are often used to
describe experimentalspectroscopic methods.Spectralmeasurementdevices are referred
to as spectrometers,spectrophotometers,spectrographs orspectralanalyzers.
Daily observations of color can be related to spectroscopy. Neon lighting is a direct
application of atomic spectroscopy.Neon and othernoble gases have characteristic
emission frequencies (colors).Neon lamps use collision of electrons with the gas to excite
these emissions. Inks, dyes and paints include chemicalcompoundsselected for their
spectral characteristics in orderto generate specific colors and hues.A commonly
encountered molecularspectrum is that of nitrogen dioxide.Gaseous nitrogen dioxide has a
characteristic red absorption feature, and this gives air polluted with nitrogen dioxide a

2. reddish brown color. Rayleigh scattering is a spectroscopic scattering phenomenon that
accounts for the color of the sky.
Classification of methods
Spectroscopyis a sufficiently broad field that manysub-disciplines exist, each with
numerous implementations ofspecific spectroscopic techniques.The various
implementations and techniques can be classified in severalways.
Type of radiative energy
Types of spectroscopyare distinguished by the type of radiative energyinvolved in the
interaction. In many applications,the spectrum is determined by measuring changes in the
intensity or frequency of this energy.The types of radiative energystudied include:
 Electromagnetic radiation was the first source ofenergyused for spectroscopic studies.
Techniques thatemploy electromagnetic radiation are typically classified by the
wavelength region of the spectrum and include microwave, , infrared ,visible and
ultraviolet, x-ray and gamma spectroscopy.
Nature of the interaction
Types of spectroscopycan also be distinguished by the nature of the interaction between
the energyand the material. These interactions include:[1]
 Absorption occurs when energyfrom the radiative source is absorbed bythe material.
Absorption is often determined by measuring the fraction of energytransmitted through
the material; absorption will decrease the transmitted portion.
 Emission indicates that radiative energyis released by the material. A
material's blackbodyspectrum is a spontaneous emission spectrum determined byits
temperature. Emission can also be induced byother sources ofenergysuch
as flames or sparks orelectromagnetic radiation in the case of fluorescence.
Electromagnetic Radiation
Electromagnetic radiation—light—is a form of energywhose behavioris described by the
properties of both waves and particles. Some properties of electromagnetic radiation, such
as its refraction when it passes from one medium to another , are explained bestby
describing lightas a wave. Other properties, such as absorption and emission,are better

3. described bytreating light as a particle. he exactnature of electromagnetic radiation
remains unclear,as it has since the developmentof quantum mechanics in the first quarter
of the 20th century.
WAVE PROPERTIES OF
ELECTROMAGNETIC RADIATION
Electromagnetic radiation consists of oscillating electric and magnetic fields that propagate
through space along a linear path and with a constantvelocity. In a vacuum electromagnetic
radiation travels at the speed oflight, c, which is 2.997 92 × 108 m/s. When
electromagnetic radiation moves through a medium other than a vacuum its velocity, v, is
less than the speed oflight in a vacuum. he difference between v and c is sufficiently small
(<0.1%) that the speed oflight to three significantfigures,3.00 × 108 m/s, is accurate
enough formost purposes.
An electromagnetic wave is characterized byseveral fundamental properties,including its
velocity, amplitude, frequency,phase angle,polarization,and direction of propagation.
PARTICLE PROPERTIES OF
ELECTROMAGNETIC RADIATION
When matter absorbs electromagnetic radiation it undergoes a change in energy.
He interaction between matter and electromagnetic radiation is easiestto
understand if we assume thatradiation consists of a beam ofenergetic particles
called photons.When a photon is absorbed bya sample it is “destroyed,” and its
energyacquired by the sample.
t he energyof a photon,in joules, is related to its frequency, wavelength, and
wavenumber
by the following equalities
E=hv=hc/λ=hcν
where h is Planck’s constant, which has a value of 6.626 × 10–34 J . s.
Photons as a Signal Source

4. A spectroscopic measurementis possible only if the photon’s interaction with the
sample leads to a change in one or more of these characteristic properties.
Whatare the different types of Spectrophotometers?
There are 2 major classifications of spectrophotometer. They are single beam and
double beam.
 A double beam spectrophotometer compares the light intensity between 2 light paths, one
path containing the reference sample and the other the test sample.
 A single beam spectrophotometer measures the relative light intensity of the beam before
and after the test sample is introduced.
Even though, double beam instruments are easierand more stable for comparison
measurements,single beaminstruments can have a large dynamic range and is also simple
to handle and more compact.
How does a spectrophotometerwork?
Lightsource, diffraction grating, filter, photo detector, signal processor and display are the
various parts of thespectrophotometer. The lightsource provides all the wavelengths of

5. visible lightwhile also providing wavelengths in ultraviolet and infra red range. The filters
and diffraction grating separate the lightinto its component wavelengths so that very small
range ofwavelength can be directed through the sample. The sample compartmentpermits
the entry of no stray lightwhile at the same time without blocking any lightfrom the source.
The photo detector converts the amountof lightwhich ithad received into a currentwhich is
then sent to the signal processor which is the soul of the machine. The signal processor
converts the simple current it receives into absorbance, transmittance and concentration
values which are then sentto the display.
PRINCIPLE OF FLUORESENCE
Fluorescence is the emission of light by a substance that has absorbed lightor
other electromagnetic radiation. It is a form of luminescence.In mostcases,the emitted
light has a longer wavelength, and therefore lower energy,than the absorbed radiation.The
moststriking examples offluorescence occurwhen the absorbed radiation is in
the ultraviolet region of the spectrum,and thus invisible to the human eye,and the emitted
light is in the visible region.
Fluorescence has manypracticalapplications, including mineralogy,gemology,chemical
sensors (fluorescence spectroscopy),fluorescentlabelling, dyes, biologicaldetectors,
cosmic-raydetection, and,mostcommonly, fluorescentlamps.Fluorescence also occurs
frequently in nature in some minerals.
Fluorescence occurs whenan orbital electron of a molecule,atom or nanostructure relaxes
to its ground state by emitting a photon of light after being excited to a higherquantum state
by some type of energy:

6. Excitation:
Fluorescence (emission):
here is a generic term for photon energywith h = Planck's constant and
= frequency of light. (The specific frequencies of exciting and emitted light are dependent
on the particular system.)
State S0 is called the ground state of the fluorophore (fluorescentmolecule)and S1 is its first
(electronically) excited state.
A molecule,S1, can relax by various competing pathways. It can undergo non-
radiative relaxation in which the excitation energyis dissipated asheat(vibrations) to the
solvent. Excited organic molecules can also relax via conversion to a triplet state, which
may subsequently relax via phosphorescence orbya secondarynon-radiative relaxation
step.
Relaxation of an S1 state can also occurthrough interaction with a second molecule
through fluorescence quenching.Molecular oxygen (O2)is an extremely efficient quencher
of fluorescence justbecause ofits unusualtriplet ground state.
In mostcases,the emitted light has a longerwavelength, and therefore lower energy, than
the absorbed radiation.However,when the absorbed electromagnetic radiation is intense, it
is possible for one electron to absorb two photons;this two-photon absorption can lead to
emission of radiation having a shorter wavelength than the absorbed radiation.The emitted
radiation may also be of the same wavelength as the absorbed radiation,termed
"resonance fluorescence".
OTHER TYPES OF
SPECTROSCOPY:-

7.  Nuclear magnetic resonance
spectroscopy
Nuclearmagnetic resonance spectroscopy,mostcommonlyknown as NMR spectroscopy,
is a research technique thatexploits the magnetic properties of certain atomic nuclei.It
determines the physicaland chemicalproperties of atoms or the molecules in which they
are contained.It relies on the phenomenonof nuclearmagnetic resonance and can provide
detailed information aboutthe structure, dynamics,reaction state, and chemical
environmentof molecules.The intramolecularmagnetic field around an atom in a molecule
changes the resonancefrequency,thus giving access to details of the electronic structure of
a molecule.
Mostfrequently, NMR spectroscopyis used by chemists and biochemists to investigate the
properties of organic molecules,although it is applicable to any kind of sample that contains
nucleipossessing spin.Suitable samples range from small compounds analyzed with 1-
dimensionalprotonorcarbon-13NMRspectroscopyto large proteins or nucleic acids using
3 or 4-dimensionaltechniques.The impactof NMR spectroscopyon the sciences has been
substantial because ofthe range of information and the diversity of samples,
including solutions and solids.

8.  Mass spectrometry
Mass spectrometry (MS) is an analytical chemistry technique that helps identify the amount
and type of chemicals presentin a sample by measuring the mass-to-charge ratio and
abundance ofgas-phase ions.[1]
A mass spectrum (pluralspectra)is a plot of the ion signal as a function of the mass-to-
charge ratio. The spectra are used to determine the elemental or isotopic signature of a
sample,the masses of particles and of molecules,and to elucidate the chemicalstructures
of molecules,such as peptides and other chemicalcompounds.Mass spectrometryworks
by ionizing chemicalcompounds to generate charged molecules ormolecule fragments and
measuring their mass-to-charge ratios.
In a typical MS procedure,a sample,which maybe solid, liquid, or gas,is ionized,for
example by bombarding itwith electrons. This may cause some ofthe sample's molecules
to break into charged fragments.These ions are then separated according to their mass-to-
charge ratio, typically by accelerating them and subjecting them to an electric or magnetic
field: ions of the same mass-to-charge ratio will undergo the same amountof
deflection.[1] The ions are detected by a mechanism capable ofdetecting charged particles,
such as an electron multiplier. Results are displayed as spectra of the relative abundance of
detected ions as a function of the mass-to-charge ratio. The atoms or molecules in the
sample can be identified by correlating known masses to the identified masses orthrough a
characteristic fragmentation pattern.
VOCABULARY WORDS:-
WAVELENGTH = the distance between successive crests of a wave
FREQUENCY = the rate persecond ofa vibration constituting a wave
SPECTRUM = a band ofcolours,as seen in a rainbow,produced by
separation of the components of light by their different degrees ofrefraction according to
wavelength.
RADIATIVE ENERGY = The emission and propagation of energyin the form of
rays or waves. Theenergyradiated or transmitted in the form of rays, waves, or particles. A
stream of particles or electromagnetic waves that is emitted by the atoms and molecules of
a radioactive substance as a result of nucleardecay.
GAMMA RAY =
A photon of electromagnetic radiation of very short wavelength, less than about0.01 nanom
eter,and very high energy,greater than about100,000 electron volts. Gamma rays are emitt
ed in thedecay of certain radioactive nuclei and in electron-positron annihilation.

9. X RAY = an electromagnetic wave of high energyand very short
wavelength, which is able to pass through manymaterials opaque to light.
ULTRA VOILET = (of electromagnetic radiation) having a wavelength
shorter than that of the violet end of the visible spectrum butlongerthan that of X-rays.
VISIBLE LIGHT = Visible light waves are the only electromagnetic waves
we can see.We see these waves as the colors of the rainbow.Each colorhas a different
wavelength. Red has the longestwavelength and violet has the shortestwavelength.
INFRARED RADIATION = (of electromagnetic radiation) having a wavelength just
greater than that of the red end ofthe visible light spectrum but less than that of
microwaves.Infrared radiation has a wavelength from about800 nm to 1 mm, and is
emitted particularly by heated objects.
RADIOWAVES = an electromagnetic wave of a frequency between about
104 and 1011 or1012 Hz,as used for long-distance communication.
LUMINESCENCE = the emission oflight by a substance that has notbeen
heated,as in fluorescence.
PHOSPHORESCENCE= the emission of radiation in a similar mannerto
fluorescence buton a longertimescale, so that emission continues after excitation ceases.
PHOTON = a particle representing a quantum of light or other
electromagnetic radiation. A photon carries energy proportionalto the radiation frequency
but has zero restmass.
QUESTIONS
Q1 Whatis spectrophotometer?

10. ANS An apparatus for measuring the intensity of light in a part of the spectrum,especially
as transmitted or emitted by particular substances.
Q2 Whatis Spectroscopy?
ANS the branch of science concernedwith the investigation and measurementof spectra
produced when matter interacts with or emits electromagnetic radiation.
Q3 Whatis Rayleigh scattering?
ANS The scattering of light by particles in a medium,without change in wavelength. It
accounts,for example,for the blue colourof the sky, since blue light is scattered slightly
more efficiently than red.
Q4 Whatis planck’s constant?
ANS A fundamentalconstant, equalto the energyof a quantum of electromagnetic radiation
divided by its frequency, with a value of 6.626 × 10−34 joules.
Q5 Whatis blackbody?
ANS A black body (also,blackbody)is an idealized physical bodythat absorbs allincident
electromagnetic radiation, regardless offrequency or angle of incidence.
Q6 Whatis florophore?
ANS A fluorophore is a fluorescentchemicalcompound thatcan re-emit light upon light
excitation. Fluorophores typically contain several combined aromatic groups,orplane or
cyclic molecules.
Q7 Whatis fluorescence?
Ans the visible or invisible radiation produced from certain substances as a result of
incidentradiation of a shorter wavelength such as X-rays or ultraviolet light.
the property of absorbing lightof shortwavelength and emitting light of longerwavelength.