Degrees of Freedom

Rotational Spectroscopy

Electronic Transitions

Vibrational Spectroscopy

microwave infrared

Interaction with matter Energy levels

Spectroscopy

Absorption Spectroscopy Emission Spectroscopy

Introduction to Matters

Rotational Spectroscopy

Vibrational Spectroscopy

Absorption and emission Spectroscopy

Lakowicz, “Principles of Fluorescence Spectroscopy”, Springer Publishers, 3rd Edition, 2011

Atkins, Physical Chemistry, 9th edition, 2009

Banwell & McCash, Fundamentals of Molecular Spectroscopy, 4th edition, 1996

Moog, Spencer and farrell, Physical Chemistry: A Guided Inquiry: Atoms, Molecules,

and Spectroscopy, 2003

• The sun produces a full spectrum of electromagnetic

radiation

http://csep10.phys.utk.edu/astr162/lect/light/spectrum.html

http://kr.blog.yahoo.com/bmw26z/2188

Components of Electro Magnetic

Radiation

v

Two Components of EM

Radiation • Electrical field (E): varies in magnitude in a direction

perpendicular to the direction of propagation

• Magnetic field (M): at right angle to the electrical

field, is propagated in phase with the electrical field

• Wavelength (l), distance from one wave crest to another

• Frequency (n), No. of crests passing a fixed point/ given time

• Amplitude, height of each peak (watts/sq. meter

• The speed of EM energy “c” 300,000km/second,

c = nl where l and n are inversely related

Interaction of radiation with matter

• If there are no available quantized energy levels matching the quantum

energy of the incident radiation, then the material will be transparent to that

radiation

Wavelength

Molecular Transitions

for UV-Visible Absorptions

• What electrons can we use for these

transitions?

Nature of Shift Descriptive Term

To Longer

Wavelength Bathochromic

To Shorter

Wavelength Hypsochromic

To Greater

Absorbance Hyperchromic

To Lower

Absorbance Hypochromic

Absorption and Emission Spectroscopy

Reflection and Scattering Losses

Introduction to Absorption

LAMBERT-BEER LAW

ionconcentrat

pathlength

tyabsorptivi

loglog0

0

c

b

a

kcabcA

P

PTA

P

P

P

PT

solvent

solution

Power of

radiation after

passing through

the solvent

Power of radiation

after passing

through the sample

solution

Problems

23 CY 515 (Spectroscopic Method of Analysis)

Dr. Priyabrat Dash

NIT Rourkela, India

Beer’s law and mixtures • Each analyte present in the solution absorbs light!

• The magnitude of the absorption depends on its e

• A total = A1+A2+…+An

• A total = e1bc1+e2bc2+…+enbcn

• If e1 = e2 = en then simultaneous determination is

impossible

• Need nl’s where e’s are different to solve the mixture

Spectral nomenclature of shifts

Electronic Transitions in Molecules

Molecular Orbital (MO) Theory

for C2H4 molecule,

UV or Visible

spectral region

Department of Chemistry, KAIST

Fate of Excited Electronic States

Molecular Motion and Spectroscopy

Study of Interaction of Matter and Light (Photon)

• Molecular Spectroscopy

Information about molecules such as geometry and energy

levels are obtained by the interaction of molecules and photons

• Molecular motions: Translation, Rotation, Vibration

determines the energy levels for the absorption or emission of

photons

Electronic, Vibrational, and Rotational Energy Levels

of a Diatomic Molecule

Exercise: Indicate the

molecular state in which it is

electronically in the ground

state, vibrationally in the first

excited state, and rotationally

in the ground state.