1. This lecture discusses electromagnetic radiation and its interaction with matter, covering atomic and molecular spectroscopy. 2. Electromagnetic radiation exhibits both wave and particle properties and can be modeled as oscillating electric and magnetic fields propagating through space. The energy of photons is directly related to their wavelength and frequency. 3. When radiation interacts with atoms and molecules, it can be absorbed, emitted, or scattered. Absorption and emission spectra provide information about the electronic, vibrational, and rotational energy levels of materials.

1. LECTURE 1
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2. The study of the interaction between
ELECTROMAGNETIC (EM) RADIATION
and MATTER
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3. covers
ATOMIC MOLECULAR
SPECTROSCOPY SPECTROSCOPY
(atomic absorption) (molecular absorption)
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4. What is Electromagnetic Radiation?
 is a form of energy that has both Wave and
Particle Properties.
 For example: Ultraviolet, visible, infrared,
microwave, radio wave.
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5. 5

6. 6

7. 7

8.  EM radiation is conveniently modeled as waves
consisting of perpendicularly oscillating
electric and magnetic fields, as shown below.
Direction of
propagation
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9. o At 90° to the direction of propagation is an
oscillation in the ELECTRIC FIELD.
o At 90° to the direction of propagation and 90°
from the electric field oscillation (orthagonal) is
the MAGNETIC FIELD oscillation.
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10.  Period (p)
the time required for one cycle to pass a fixed
point in space.
 Frequency (V @ f )
the number of cycles which pass a fixed point in space per
second. Unit in Hz or s-1
 Amplitude (A)
The maximum length of the electric vector in the
wave (Maximum height of a wave).
 Wavelength (λ)
The distance between two identical adjacent points in a
wave (usually maxima or minima).
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11.  Wavenumber (ν)
The number of waves per cm in units of cm-1.
 Radiant Power ( P )
The amount of energy reaching a given area per second.
Unit in watts (W)
 Intensity (I)
The radiant power per unit solid angle.
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12. Speed of light = Wavelength x Frequency
Speed of light = Wavelength x Frequency
c = λV
c = λV
Where as
Where as
λ is the wavelength of the waves
λ is the wavelength of the waves
V is the frequency of the waves
V is the frequency of the waves
c is the speed of light
c is the speed of light
c = 3.00 x 1088 m/s = 3.00 x 1010 cm/s
c = 3.00 x 10 m/s = 3.00 x 1010 cm/s
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13. 800 nm
Infrared radiation Ultraviolet radiation
V = 3.75 x 1014 s-1 V = 7.50 x 1014 s-1
Wavelength is inversely proportional to frequency
λ ∝ 1/V
 The Higher the Frequency the Shorter the
Wavelength . The Longer the Wavelength the
Lower the Frequency.
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14. EMR is viewed as a stream of discrete particles of
energy called photons.
We can relate the energy, E of photon to its
wavelength, frequency and wavenumber by
hc
E = hV = = hcν
λ
h = Planck’s constant
h = 6.63 x 10 -34 J.s
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15. hc
E = hV = hcν =
λ
Therefore wavenumber, ν
ν = 1/λ = V/c
Unit of wavenumber is cm-1

16. What is the energy of a 500 nm photon?
V = c/λ
= (3 x 108 m s-1)/(5.0 x 10-7 m)
V = 6 x 1014 s-1 @ Hz
E = hV
= (6.626 x 10-34 J•s)(6 x 1014 s-1)
= 4 x 10-19 J
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17. 17

18. Region Wavelength
Range
UV 180 – 380 nm
Visible 380 – 780 nm
Near-IR 780 – 2500 nm
Mid-IR 2500 – 50000 nm
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19. Region Unit Definition (m)
X-ray Angstrom unit, Å 10-10 m
Ultraviolet/visible Nanometer, nm 10-9 m
Infrared Micrometer, μm 10-6 m
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20. 20

21.  Atoms are the basic blocks of matter.
 They consist of heavy particles (called protons
and neutrons) in the nucleus, surrounded by
lighter particles called electrons.
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22.  An electron will interact with a photon.
 An electron that absorbs a photon will gain
energy.
 An electron that loses energy must emit a
photon.
 For absorption to occur, the energy of the
photon must exactly match an energy level
in the atom (or molecule) it contacts.
◦ Ephoton = Eelectronic transition
 We distinguish two types of absorption
◦ Atomic
◦ Molecular
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23.  Absorption
EMR energy transferred to absorbing molecule
(transition from low energy to high energy state).
 Emission
EMR energy transferred from emitting molecule
to space (transition from high energy to low
energy state).
 Scattering
redirection of light with no energy transfer.

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25.  Electrons bound to
atoms have discrete
energies (i.e. not all
energies are allowed).
 Thus, only photons of
certain energy can
interact with the
electrons in a given
atom.
 Transitions between
electronic levels of the
electrons produce line
spectra.
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26.  Consider hydrogen, the
simplest atom.
 Hydrogen has a specific
line spectrum.
 Each atom has its
own specific line
spectrum (atomic
fingerprint).
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27. The energy of photon that can promote electrons
to excite/jump to a higher energy level depends
on the energy difference between the electronic
levels.
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28. Each atom has a specific set of energy levels, and
thus a unique set of photon wavelengths with which
it can interact.
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29.  Absorption and emission
for the sodium atom in the
gas phase.
 The diagram illustrate the
transitions (excitation and
emission) of electrons
between different energy
levels in sodium atom.
ΔEtransition = E1 - E0 = hv = hc/λ
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30.  The energy, E, associated with the molecular bands:
Etotal = Eelectronic + Evibrational + Erotational
 In general, a molecule may absorb energy in 3 ways:
1. By raising an electron (or electrons) to a higher
energy level. (electronic)
2. By increasing the vibration of the constituent nuclei.
(vibrational)
3. By increasing the rotation of the molecule about the
axis. (rotational)

31. hν
En En
hν hν
Eo Eo
Absorption Emission

32. Rotational
absorption
Vibrational
absorption

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34.  Absorption spectrum
◦ A plot of the absorbance as a function of
wavelength or frequency.
 Emission spectrum
◦ A plot of the relative power of the emitted
radiation as a function of wavelength or
frequency.
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35. Absorption Spectrum of Na
 The two peaks arise from the promotion of
a 3s electron to the two 3p states
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36. Electronic Transition Vibrational Transition
Superimposed on the
Electronic Transition
Absorption Band –
A series of closely
shaped peaks
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37.  In solvents the rotational
and vibrational
transitions are highly
restricted resulting in
broad band
absorption spectra.
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38.  Three types of
spectra:
◦ Lines
◦ Bands
◦ Continuum
spectra
Emission spectrum of a brine sample
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39. 39

40. Absorption Spectroscopy
Emission Spectroscopy
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41. 1. Source
A stable source of radiant energy at the
desired wavelength (or λ range).
2. Sample Holder
A transparent container used to hold the
sample (cells, cuvettes, etc.).
3. Wavelength Selector
A device that isolates a restricted region
of the EM spectrum used for measurement
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(monochromators, prisms, & filters).

42. 4. Photoelectric Transducer (Detector)
Converts the radiant energy into a useable
signal (usually electrical).
5. Signal Processor & Readout
Amplifies or attenuates the transduced
signal and sends it to a readout device such as
a meter, digital readout, chart recorder,
computer, etc.
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43. Generate a beam of radiation that is stable and has sufficient
power.
A. Continuum Sources
emit radiation over a broad
wavelength range and the intensity of the radiation
changes slowly as a function of wavelength.
This type of source is commonly
used optical instruments.
Deuterium lamp is the most
common UV source.
Tungsten lamp is the most 43
common Visible source.

44. B. Line Sources
Emit a limited number lines or bands of radiation
at specific wavelengths. Used in atomic absorption
spectroscopy.
Types of line sources:
1.Hollow cathode lamps
2.Electrodeless discharge lamps
3.Lasers (Light­amplification by stimulated
emission of radiation)
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45. Sample containers usually is called cells or
cuvettes, must have side/windows that are
transparent in the spectral region of interest.
There are few types of cuvettes
1. quartz or fused silica (below 350nm)
required for UV & VIS region
2. silicate glass (350 – 2000nm)
cheaper compared to quartz. Used in VIS
3. crystalline sodium chloride
used in IR 45

46. Wavelength selectors provides a limited, narrow,
continuous group of wavelengths called a band.
Two types of wavelength selectors:
A) Filters
B) Monochromators
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47. 47

48. Early detectors in spectroscopic instruments were
the human eye, photographic plates or films.
Modern instruments contain devices that convert
the radiation to an electrical signal.
Two general types of radiation transducers:
a. Photon detectors
b.Thermal detectors
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49. A. Photon Detectors
Commonly useful in ultraviolet, visible and near
infrared instruments.
Several types of photon detectors are available:
1. Vacuum phototubes
2.Photomultiplier tubes
3.Photovoltaic cells
4. Silicon photodiodes
5.Diode array transducers
6. Photoconductivity transducers
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50. B. Thermal Detectors
Used for infrared spectroscopy because photons in
the IR region lack the energy to cause
photoemission of electrons.
Three types of thermal detectors:
1. Thermocouples
2. Bolometers
3. Pyroelectric transducers
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51. SPECTROMETER
is an instrument that provides information about
the intensity of radiation as a function of
wavelength or frequency.
SPECTROPHOTOMETER
is a spectrometer equipped with one or more exit
slits and photoelectric transducers that permits
the determination of the ratio of the radiant
power of two beams as a function of wavelength
as in absorption spectroscopy.
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52. REGION SOURCE SAMPLE DETECTOR
HOLDER
Ultraviolet Deuterium lamp Quartz /fused Phototube,
silica Photo Multiplier
tube, diode
array
Visible Tungsten lamp Silicate Glass Phototube,
/Quartz Photo Multiplier
tube, diode
array
Infrared Nernst glower (rare Salt crystals Thermocouples,
earth oxides or silicon (crystalline bolometers
carbide glowers) sodium chloride)
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