important for all the students of bs chemistry this is very important topics for all type of exams

2. • Course#: 620
• By: Dr. Aftab Ahmed Kandhro
• Associate Professor

3. Spectroscopy
The spectroscopy is the study of interaction of
electromagnetic radiation (EMR) with matter and
its applications.
To begin to understand the theory and
instrumental application of spectrometry,
requires an understanding of the interaction of
EMR (i.e. light) with matter.

4. Questions
• What is nature of light?
• Are these different types of light?
– How are they same?
– How are they different?
• How does light propagate?

5. What is Light?
 Light is a form of energy.
 Light energy travels at the universal
speed of light in electric and magnetic
fields.
– The speed of light (c) ~ 3 x 1010 cm/sec or
186,000 miles per second.
 Light is referred to as electromagnetic
radiation.

6. Characteristics of Light
 Light behaves like a wave.
– That is, it can be modeled or characterized with wave
like properties.
 Light also behaves like a particle.
– The photon and photoelectric effect.
 Today, we envision light as a self-contained
packet of energy, a photon, which has both
wave and particle like properties.

7. Radiation is a form of energy. There are two basic
types of radiation. One kind is particulate radiation,
which involves tiny fast-moving particles that have both
energy and mass. Particulate radiation is primarily
produced by disintegration of an unstable atom and
includes Alpha and Beta particles.

8. The second basic type of radiation is electromagnetic
radiation. This kind of radiation is pure energy with no
mass and is like vibrating or pulsating waves of electrical
and magnetic energy.
Electromagnetic waves are produced by a vibrating
electric charge and as such, they consist of both an
electric and a magnetic component. In addition to acting
like waves, electromagnetic radiation acts like a stream of
small "packets" of energy called photons.
Wave Properties of Electromagnetic
Radiation

9.  EMR has both electric (E) and magnetic
(M) components that propagate at right
angles to each other.
EMR can be described as wave with properties
of wavelength, frequency, velocity and amplitude

10. wavelength
• The linear distance between successive maxima or
minima of wave is known as wave length. It is usually
expressed in centimeter cm.
• Each wavelength of light energy is associated with a
unique frequency.
– A nanometer is the measure of wavelength and is equivalent
to 1 x 10-9 meters.

11. Frequency (ν)
The number of cycles occurring per second is called frequency.
OR
• Frequency is a measure of the number of occurrences of a
repeating event per unit time.
Frequency = speed of light cms-1/wavelength
ν= c/λ
ν= frequency
c= speed of light
λ= wavelength
Wavelength is inversely proportional to the frequency (v = c/λ).

12. Wave number ( )
 It is the number of waves spread in a length of 1
centimeter (cm).
 The wave number is direct measure of the energy of
radiation.
 wave number inversely proportional to the wavelength.
 The wave number is the direct measure of the energy of
radiation.
=1/λ
= Wave length cm
λ
= Wave number cm-1

13. Wave number ( )
(cm)

14. Amplitude
• Amplitude: Height of a wave

15. Velocity (V)
• The product of wavelength and frequency
is equal to the velocity of wave in the
medium.
• Velocity has the unit of cms-1 or ms-1.
X λ= V
At a particular frequency, the
relationship of between the
wavelength, frequency and
velocity of light in vacuum is

16. Concepts of Wavelengths
Wavelength (amplitude):
Height of the wave
Frequency: number of
waves occurring per
sec.
Short waves=high frequency
and high energy
Long waves= low frequency,
low energy
–There is an inverse relationship between wavelength, frequency, and energy.

17. • Energy is directly proportional to the frequency
(E = hν).
• The highest energy (E) radiation corresponds to
the X-ray region in the EM spectrum. Energy
may be great enough to break bonds in
molecules.
• On the other hand radiofrequencies have low
energies, only enough to cause nuclear or ES
transition with in molecules (NMR or ESR).

18. The Electromagnetic Spectrum
• The arrangement of all types of EMR in order of increasing wavelength or
decreasing frequency

19. Types of transition in each region of the EM
spectrum
Region of
spectrum Energy transition
a X-rays Bond Breaking
b UV-Visible Electronic
c IR Vibrational
d Microwave Rotational
e
Radio
frequency
Nuclear spin (NMR,
ESR)
Different portions of the EMR spectrum and different types
of spectroscopy involve different parts (quantum states)
of the atom.

20. Particle Properties of EMR
• The energy of a photon depends on its
frequency (v).
E = hν eq (i)
• h = Planck’s constant (6.63 x 10-34 Js)
• The wavelength λ, of a photon is related to its
frequency by
v = c/λ eq (ii)
Combination of eq (i) and eq (ii) yields
E = hc / λ ( = 1/ λ)
or E = hc

21. How Light Interacts with Matter
 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.
 The total energy (electron plus photon)
remains constant during this process.

22. Characteristics of Absorption
• Absorption is defined as the process by
which EMR is transferred, in the form of
energy, to the medium (Solid, Liquid, or
gas) through which it is traveling involves
discrete energy transfers.
• Transitions from ground state energy
levels to “excited” states.
– The reverse process is called emission.

23. Characteristics of Absorption
 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

24. Instrumentation
• All instruments involved in the
measurement of light intensity will use one
of the following principles:
– Absorption
– Reflectance
– Emission
– Scatter

25. Absorption
• The concentration of a sample in solution
is determined by measuring the amount of
light transmitted through the sample; as
the concentration of the sample increases
the amount of transmitted light decreases
logarithmically.

26. Reflectance
• The concentration of a sample in solution
is determined by measuring the amount of
light reflected; the concentration is
inversely proportional to the amount of
light reflected by the sample

27. Emission
• The concentration of a sample in solution
is determined by measuring the amount of
light emitted or given off by the sample;
the concentration of the sample and the
amount of light emitted are directly
proportional.

28. Scatter
• The concentration of a sample in solution
is determined by measuring the amount of
light scattered by the solution; light scatter
is proportional to sample concentration.

29. Electromagnetic Radiation &
Electromagnetic Spectrum
• The word light usually makes one think of the colors of the rainbow
or light from the Sun or a lamp. This light, however, is only one type
of electromagnetic radiation. Electromagnetic radiation comes in a
range of energies, known as the electromagnetic spectrum. The
spectrum consists of radiation such as gamma rays, x-rays,
ultraviolet, visible, infrared and radio.

32. Types of Spectroscopy
• Infrared (IR) spectroscopy measures the bond
vibration frequencies in a molecule and is used
to determine the functional group.
• Mass spectrometry (MS) fragments the molecule
and measures the masses.
• Nuclear magnetic resonance (NMR)
spectroscopy detects signals from hydrogen
atoms and can be used to distinguish isomers.
• Ultraviolet (UV) spectroscopy uses electron
transitions to determine bonding patterns.

34. • BS 4th Year, Semester-VII/ M.Sc.(Pass) Final, Semester-III
• Paper-I
• Title of the Course : Instrumental Methods of Analysis Course # CHEM: 620
• 1. Infrared spectroscopy.
• 2. Ultra violet spectroscopy
• 3. Nuclear Magnetic Resonance Spectroscopy
• 4. Mass Spectrometry
• 5. Thermal Analysis
• Recommended Books
• 1. Daniels, T., “Thermal Analysis” (Latest Edition)
• 2. Pavia, D. L., Lampman, G. M. and Kriz, G.S., “Introduction to Spectroscopy”,
Saunders College Publishing, (Latest Edition).
• 3.Silverstein, R. M., Barler, C. G. and Mogrill, T. C., “Spectrometric Identification of
OrganicCompounds”,
• 4. Kemp, W., “NMR in Chemistry A Multi Nuclear Introduction”, McMillan Press Ltd.,
(Latest Edition)
• 5. Drago, R. S., “Physical Method in Inorganic Chemistry”, W.B. Saunders Company,
(LatestEdition)
• 6. Douglas, A. Skoog, F. James Holler, Trmothy, A., “Principles of Instrumental
Analysis”,Saunders College Publishing, New York, (Latest Edition).
• 7. Ewing, G.W., “Instrumental Methods of Chemical Analysis”, McGraw Hill, New
York, (Latest Edition).