Vibrational Spectroscopy CHE 626

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Vibrational SpectroscopyCHE 626

• Alex Nazarenko
• nazareay_at_buffalostate.edu

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Energy (kJ/mol)
IR Raman
UV-vis
NMR
Frequency(Hz)
Wavelength (m)
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Only photons of one specified wavelength
are absorbed
Excited state
Ground state
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Width
Velocity of a particle gt1000 m/s
Doppler
Speed of light 300,000,000 m/s
collisions
Approximately as Doppler
Both effects increase with the temperature and
decrease with the size of the molecule/atom
Width is around 0.01-0.001 nm in visible area
Multiple energy levels
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Energy levels of excited state
Energy sublevels
Energy levels of ground state
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A primitive rule
Molecular spectra - wide bands
Atomic spectra - narrow lines
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Frequency
Wavenumber
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Carbon Monoxide in gas
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Rayleigh scattering
No changes!
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Raman scattering
Escaping photon has smaller energy because the
molecule did not return to the ground state
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Raman scattering
Raman scattering
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http//symmetry.otterbein.edu/tutorial/pointgroups
.html
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E The identity transformation (E coming from the German Einheit, meaning unity).
Cn Rotation (clockwise) through an angle of 2p/n radians, where n is an integer. The axis for which n is greatest is termed the principal axis.
Cnk Rotation (clockwise) through an angle of 2kp/n radians. Both n and k are integers.
Sn An improper rotation (clockwise) through an angle of 2p/n radians. Improper rotations are regular rotations followed by a reflection in the plane perpendicular to the axis of rotation. Also known as alternating axis of symmetry and rotation-reflection axis.
i The inversion operator (the same as S2). In Cartesian coordinates, (x, y, z)?(-x, -y, -z). Irreducible representations that are even under this symmetry operation are usually denoted with the subscript g for gerade (germaneven), and those that are odd are denoted with the subscript u for ungerade (germanodd).
s A mirror plane (from the German word for mirror - Spiegel).
sh Horizontal reflection plane - passing through the origin and perpendicular to the axis with the highest symmetry.
sv Vertical reflection plane - passing through the origin and the axis with the highest symmetry.
sd Diagonal or dihedral reflection in a plane through the origin and the axis with the highest symmetry, but also bisecting the angle between the twofold axes perpendicular to the symmetry axis. This is actually a special case of sv.