Spectroscopy Absoption
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Transcript of Spectroscopy Absoption
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Degrees of Freedom
Rotational Spectroscopy
Electronic Transitions
Vibrational Spectroscopy
microwave infrared
Interaction with matter Energy levels
Spectroscopy
Absorption Spectroscopy Emission Spectroscopy
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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
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• 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
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Components of Electro Magnetic
Radiation
v
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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
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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
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Molecular Transitions
for UV-Visible Absorptions
• What electrons can we use for these
transitions?
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Nature of Shift Descriptive Term
To Longer
Wavelength Bathochromic
To Shorter
Wavelength Hypsochromic
To Greater
Absorbance Hyperchromic
To Lower
Absorbance Hypochromic
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Absorption and Emission Spectroscopy
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Reflection and Scattering Losses
Introduction to Absorption
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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
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Problems
23 CY 515 (Spectroscopic Method of Analysis)
Dr. Priyabrat Dash
NIT Rourkela, India
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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
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Spectral nomenclature of shifts
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Electronic Transitions in Molecules
Molecular Orbital (MO) Theory
for C2H4 molecule,
UV or Visible
spectral region
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Department of Chemistry, KAIST
Fate of Excited Electronic States
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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
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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.