Transcript Basis of Raman spectroscopy

Vlasta Mohaček Grošev
Training School on Raman Spectroscopy,
COST Action MP 1302 “Nanospectroscopy”,
Zagreb 23.-25. 09. 2015.
1863. book
“Heat Considered as a Mode of Motion”
I ∝ ω4
• differing types of molecules have
differing absorptions of infrared radiation
because their molecular structures give
them differing oscillating resonances
scattering on particles
d≳λ
• used Maxwell’s theory of radiation to explain plasmon
resonances in colloid suspensions of metal particles
Tcherniak et al.:
Probing a Century Old Prediction One Plasmonic Particle at a
Time. Nano Letters 10 (4) (2010) 1398–1404.
John William Strutt, 3rd Baron Rayleigh
I ∝ ω4
scattering on particles
d << λ
• searched for “optical analogue of the
Compton effect”
• 1924. met Compton at a meeting of British
Association in Toronto
• performed measurements on
liquids usig focused sunlight
K. S. Krishnan
On 7th July 1928. published the article
in Nature with K. S. Krishnan in which
explicitly they attributed the newly
found spectral lines to molecular
vibrations.
NOBEL PRIZE FOR PHYSICS FOR 1930.
WENT TO RAMAN.
laser light:
hν0
scattered light: hν
wavenumber is defined as 1/ λ
measured in cm-1
H. J. Galla, Spectroscopische Methoden in der Biochemie, Georg
Thieme Verlag 1988.
H. J. Galla, Spectroscopische Methoden in
der Biochemie, Georg Thieme Verlag 1988.
H. J. Galla, Spectroscopische Methoden in der Biochemie, Georg
Thieme Verlag 1988.
Intensity of the oscillating dipole p0
νS frequency of the dipole oscillation
is the wavenumber of the oscillations
linear Raman effect
Time dependent wave functions of the initial and
final states are approximated with the unperturbed
functions and corrections:
H. J. Galla, Spectroscopische Methoden in
der Biochemie, Georg Thieme Verlag 1988.
H. J. Galla, Spectroscopische Methoden in der Biochemie, Georg
Thieme Verlag 1988.
ωfi = ωf – ωi > 0
ωfi = ωf – ωi = 0
ωfi = ωf – ωi < 0
The selection rules for the i ⤍ f transition require
that both the
and the
be different from zero.
• symmetry of the tensor αρσ is given for each point
group
• symmetry of Qk and the nature of Qk one finds via
normal coordinate analysis
ξ represents all nuclear coordinates
x represents all electronic coordinates
Full line - probability density of finding a particle in the
oscillator quantum state with n =1 (left) and n = 10 (right).
Dashed line – classical probability.
From Pauling&Wilson: “Introduction to Quantum Mechanics”, Dover 1963.
Normal coordinates Qk are defined as
in such a way so that kinetic and potential energy
have DIAGONAL form:
Atoms vibrate in normal modes in such a
way that each atom reaches maximum
amplitude at the same time.
trans
C2h
gauche
C2
Technische Universitaet Darmstadt, dr.Stefan Immel
Tutorials
Symmetry
Point groups
(COOH)2 oxalic acid tTt conformer
V. Mohaček Grošev et al. J. Raman Spectrosc. J. Raman
Spectrosc. 2009, 40, 1605–1614.
Γvib = 7 Ag + 2 Bg + 3 Au + 6 Bu
Ag and Bg modes are RAMAN active
Vibrations are calculated numerically,
e.g. via Gaussian.
Removing the acoustic modes
Matrix of the polarisability tensor
in the crystal has components of
Ag
and Bg
symmetry.
Symmetry elements are now CRYSTAL SYMMETRY elements.
T64000 HORIBA Jobin Yvon
Raman spectrometer
514.5 nm (green) laser line
CCS 350 Janis Research
cryostat
XXI International Conference on Horizons in Hydrogen Bond Research
single crystal was placed in the capillary and mounted inside the cryostat
figure by K. Furić, V. Volovšek: J. Mol. Struct. 976 (2010) 174–180.
XXI International Conference on Horizons in Hydrogen Bond Research
Spectra of powder sample exhibit the same behaviour found
in z(yy)x +z(yz)x spectra:
Low frequency Raman spectra do not show any change that
would indicate phase change:
z(yy)x + z(yz)x
However, when the polarization of the electric field is along
a crystal axis (here z), significant increase of hydrogen bond
modes is observed: