NQR - DEFINITION - ELECTRIC FIELD GRADIENT - NUCLEAR QUADRUPOLE MOMENT - NUCLEAR QUADRUPOLE COUPLING CONSTANT - PRINCIPLE OF NQR - ENERGY OF INTERACTION - SELECTION RULE - FREQUENCY OF TRANSITION - APPLICATIONS
Photoelectron spectroscopy
- a single photon in/ electron out process
• X-ray Photoelectron Spectroscopy (XPS)
- using soft x-ray (200-2000 eV) radiation to
examine core-levels.
• Ultraviolet Photoelectron Spectroscopy (UPS)
- using vacuum UV (10-45 eV) radiation to
examine valence levels.
NQR - DEFINITION - ELECTRIC FIELD GRADIENT - NUCLEAR QUADRUPOLE MOMENT - NUCLEAR QUADRUPOLE COUPLING CONSTANT - PRINCIPLE OF NQR - ENERGY OF INTERACTION - SELECTION RULE - FREQUENCY OF TRANSITION - APPLICATIONS
Photoelectron spectroscopy
- a single photon in/ electron out process
• X-ray Photoelectron Spectroscopy (XPS)
- using soft x-ray (200-2000 eV) radiation to
examine core-levels.
• Ultraviolet Photoelectron Spectroscopy (UPS)
- using vacuum UV (10-45 eV) radiation to
examine valence levels.
The postulates of quantum mechanics have been successfully used for deriving exact solutions to Schrodinger equation for problems like A particle in 1 Dimensional box Harmonic oscillator Rigid rotator Hydrogen atom • However for a multielectron system, the SWE cannot be solved exactly due to inter-electronic repulsion terms.
The SWE is solved by method of seperation of variables.
• However, the inter-electronic repulsion term cannot be solved because the variables cannot be seperated and the SWE cannot be solved. • Approximate methods have helped to generate solutions for such and even more complex real quantum systems. • Approximate methods have been developed for solving Schrodinger equation to find wave function and energy of the complex system under consideration. • Two widely used approximate methods are, 1. Perturbation theory 2. Variation method
Perturbation theory is an approximate method that describes a complex quantum system in terms of a simpler system for which the exact solution is known. • Perturbation theory has been categorized into, i. Time independent perturbation theory, proposed by Erwin Schrodinger, where the perturbation Hamiltonian is static. ii. Time dependent perturbation theory, proposed by Paul Dirac, which studies the effect of time dependent perturbation on a time independent Hamiltonian H0.
PERTURBATION THEOREM
FIRST ORDER PERTURBATION THEORY
FIRST ORDER ENERGY CORRECTION
FIRST ORDER WAVE FUNCTION CORRECTION
APPLICATIONS OF PERTURBATION METHOD
SIGNIFICANCE OF PERTURBATION METHOD
It contains the basic principle of Mossbauer Spectroscopy.
Recoil energy, Dopler shift.
The instrumentation of Mossbauer Spectroscopy.
Hyperfine interactions.
This presentation is about Classical theory of Raman Effect. This lecture gives brief explanation about rayleigh scattering and raman scattering and about the classical theory which talks about the polarisation of molecule and how the polarisation relates with raman scattering. Have fun Learning!
Electron Spin Resonance (ESR) SpectroscopyHaris Saleem
Electron Spin Resonance Spectroscopy
Also called EPR Spectroscopy
Electron Paramagnetic Resonance Spectroscopy
Non-destructive technique
Applications
Extensively used in transition metal complexes
Deviated geometries in crystals
The all the content in this profile is completed by the teachers, students as well as other health care peoples.
thank you, all the respected peoples, for giving the information to complete this presentation.
this information is free to use by anyone.
The postulates of quantum mechanics have been successfully used for deriving exact solutions to Schrodinger equation for problems like A particle in 1 Dimensional box Harmonic oscillator Rigid rotator Hydrogen atom • However for a multielectron system, the SWE cannot be solved exactly due to inter-electronic repulsion terms.
The SWE is solved by method of seperation of variables.
• However, the inter-electronic repulsion term cannot be solved because the variables cannot be seperated and the SWE cannot be solved. • Approximate methods have helped to generate solutions for such and even more complex real quantum systems. • Approximate methods have been developed for solving Schrodinger equation to find wave function and energy of the complex system under consideration. • Two widely used approximate methods are, 1. Perturbation theory 2. Variation method
Perturbation theory is an approximate method that describes a complex quantum system in terms of a simpler system for which the exact solution is known. • Perturbation theory has been categorized into, i. Time independent perturbation theory, proposed by Erwin Schrodinger, where the perturbation Hamiltonian is static. ii. Time dependent perturbation theory, proposed by Paul Dirac, which studies the effect of time dependent perturbation on a time independent Hamiltonian H0.
PERTURBATION THEOREM
FIRST ORDER PERTURBATION THEORY
FIRST ORDER ENERGY CORRECTION
FIRST ORDER WAVE FUNCTION CORRECTION
APPLICATIONS OF PERTURBATION METHOD
SIGNIFICANCE OF PERTURBATION METHOD
It contains the basic principle of Mossbauer Spectroscopy.
Recoil energy, Dopler shift.
The instrumentation of Mossbauer Spectroscopy.
Hyperfine interactions.
This presentation is about Classical theory of Raman Effect. This lecture gives brief explanation about rayleigh scattering and raman scattering and about the classical theory which talks about the polarisation of molecule and how the polarisation relates with raman scattering. Have fun Learning!
Electron Spin Resonance (ESR) SpectroscopyHaris Saleem
Electron Spin Resonance Spectroscopy
Also called EPR Spectroscopy
Electron Paramagnetic Resonance Spectroscopy
Non-destructive technique
Applications
Extensively used in transition metal complexes
Deviated geometries in crystals
The all the content in this profile is completed by the teachers, students as well as other health care peoples.
thank you, all the respected peoples, for giving the information to complete this presentation.
this information is free to use by anyone.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Done by Group: ABW-Pearls7
School: Amna Bint Wahb Independent School for Girls
Dye-Sensitized Solar Cells (DSSC) Module: The students study the concept of using dyes to plant dyes to capture the solar energy to convert it into electrical energy simulating the natural process “photosynthesis”. They use the workshop-gained knowledge in DSSC to invent new products.
ABW-Pearls7 used Henna to form silver Nano-particles to be used as a dye in DSSC with reference to a research paper in 2013. The results we gained were better than this paper. The application idea is D-SOBATT which is a battery charged with the solar energy through DSSC.
Beyond the Elements XRD Mineralogy & XRF Analysis for Advanced Mud LoggingOlympus IMS
More information on Olympus XRF and XRD solutions: http://bit.ly/1pZ3zBo
A presentation from the webinar Beyond the Elements XRD Mineralogy & XRF Analysis for Advanced Mud Logging.
Learn how XRD and XRF analyzers help maximize the efficiency of drilling operations by quickly finding commercially viable target zones for better production and improved ROI.
Understand rock type indicating oil and gas bearing zones and identify mineralogical trends to keep the drill in the shale pay zone with real-time XRD and XRF analysis.
On-site analysis provides faster results and reduces costs from sending fewer samples to the outside lab. We will review techniques for on-site analysis to make informed geo-steering decisions.
Watch the webinar associated with this presentation: http://bit.ly/1ohxid8
Contact us: http://bit.ly/1rDmq94
Sign up for our newsletter: http://bit.ly/1j5FOTy
Ferrites: Ferrites are mixed metal oxides of magnetic nature in which iron is the main component.
In general, ferrites show four different types of crystal structures namely,
1] Ferrospinel Structure.
2] Hexagonal Structure.
3] Garnet Structure.
4] Orthoferrite structure.
We are going to discuss about spinel structure as Co Ni ferrite is a spinel ferrite.
Ferrospinel Structure.
They have the general formula MeFe2O4, where Me is divalent metal ion or a mixture of ions having average valence of two. The unit cell is cubic. The oxygen ions forms a nearly close-packed face centered cubic structure and the metal ions are distributed over tetrahedral and octahedral holes.
Normal ferrites:In which all-divalent metal ions occupy A sites and all the Fe3+ occupy B sites.
e.x. Zn 2+ [Fe23+] O4
Zn 2+ ions have a very low octahedral preference; therefore they enter the A-sites of the lattice, resulting in normal ferrites.
Inverse ferrites:In which all divalent metal ions and half the Fe3+ ions occupy B sites while remaining Fe3+ occupy A sites.
e.x. Fe3+[ Fe3+ Ni2+] O4
Mixed ferrites:In which all divalent metal ions and Fe3+ ions are uniformly distributed over the tetrahedral and octahedral sites.
Co - Ni ferrite is a mixed spinel ferrite, which has general formulae
AII x BII 1-x Fe2O4
ir spectroscopy: introduction modes of vibration, selection rule, factor, influcing of vibration, scaning of ir spectroscopy(instrumentation) vibration frequency of organic and inorganic compound
Ultraviolet spetroscopy by Dr. Monika Singh part-1 as per PCI syllabusMonika Singh
UV Visible spectroscopy as per PCI syllabus: Electronic transitions, chromophores, auxochromes, spectral shifts, solvent effect on absorption spectra, Beer and Lambert’s law, Derivation and deviations.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
The use of Nauplii and metanauplii artemia in aquaculture (brine shrimp).pptxMAGOTI ERNEST
Although Artemia has been known to man for centuries, its use as a food for the culture of larval organisms apparently began only in the 1930s, when several investigators found that it made an excellent food for newly hatched fish larvae (Litvinenko et al., 2023). As aquaculture developed in the 1960s and ‘70s, the use of Artemia also became more widespread, due both to its convenience and to its nutritional value for larval organisms (Arenas-Pardo et al., 2024). The fact that Artemia dormant cysts can be stored for long periods in cans, and then used as an off-the-shelf food requiring only 24 h of incubation makes them the most convenient, least labor-intensive, live food available for aquaculture (Sorgeloos & Roubach, 2021). The nutritional value of Artemia, especially for marine organisms, is not constant, but varies both geographically and temporally. During the last decade, however, both the causes of Artemia nutritional variability and methods to improve poorquality Artemia have been identified (Loufi et al., 2024).
Brine shrimp (Artemia spp.) are used in marine aquaculture worldwide. Annually, more than 2,000 metric tons of dry cysts are used for cultivation of fish, crustacean, and shellfish larva. Brine shrimp are important to aquaculture because newly hatched brine shrimp nauplii (larvae) provide a food source for many fish fry (Mozanzadeh et al., 2021). Culture and harvesting of brine shrimp eggs represents another aspect of the aquaculture industry. Nauplii and metanauplii of Artemia, commonly known as brine shrimp, play a crucial role in aquaculture due to their nutritional value and suitability as live feed for many aquatic species, particularly in larval stages (Sorgeloos & Roubach, 2021).
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
Phenomics assisted breeding in crop improvementIshaGoswami9
As the population is increasing and will reach about 9 billion upto 2050. Also due to climate change, it is difficult to meet the food requirement of such a large population. Facing the challenges presented by resource shortages, climate
change, and increasing global population, crop yield and quality need to be improved in a sustainable way over the coming decades. Genetic improvement by breeding is the best way to increase crop productivity. With the rapid progression of functional
genomics, an increasing number of crop genomes have been sequenced and dozens of genes influencing key agronomic traits have been identified. However, current genome sequence information has not been adequately exploited for understanding
the complex characteristics of multiple gene, owing to a lack of crop phenotypic data. Efficient, automatic, and accurate technologies and platforms that can capture phenotypic data that can
be linked to genomics information for crop improvement at all growth stages have become as important as genotyping. Thus,
high-throughput phenotyping has become the major bottleneck restricting crop breeding. Plant phenomics has been defined as the high-throughput, accurate acquisition and analysis of multi-dimensional phenotypes
during crop growing stages at the organism level, including the cell, tissue, organ, individual plant, plot, and field levels. With the rapid development of novel sensors, imaging technology,
and analysis methods, numerous infrastructure platforms have been developed for phenotyping.
Deep Behavioral Phenotyping in Systems Neuroscience for Functional Atlasing a...Ana Luísa Pinho
Functional Magnetic Resonance Imaging (fMRI) provides means to characterize brain activations in response to behavior. However, cognitive neuroscience has been limited to group-level effects referring to the performance of specific tasks. To obtain the functional profile of elementary cognitive mechanisms, the combination of brain responses to many tasks is required. Yet, to date, both structural atlases and parcellation-based activations do not fully account for cognitive function and still present several limitations. Further, they do not adapt overall to individual characteristics. In this talk, I will give an account of deep-behavioral phenotyping strategies, namely data-driven methods in large task-fMRI datasets, to optimize functional brain-data collection and improve inference of effects-of-interest related to mental processes. Key to this approach is the employment of fast multi-functional paradigms rich on features that can be well parametrized and, consequently, facilitate the creation of psycho-physiological constructs to be modelled with imaging data. Particular emphasis will be given to music stimuli when studying high-order cognitive mechanisms, due to their ecological nature and quality to enable complex behavior compounded by discrete entities. I will also discuss how deep-behavioral phenotyping and individualized models applied to neuroimaging data can better account for the subject-specific organization of domain-general cognitive systems in the human brain. Finally, the accumulation of functional brain signatures brings the possibility to clarify relationships among tasks and create a univocal link between brain systems and mental functions through: (1) the development of ontologies proposing an organization of cognitive processes; and (2) brain-network taxonomies describing functional specialization. To this end, tools to improve commensurability in cognitive science are necessary, such as public repositories, ontology-based platforms and automated meta-analysis tools. I will thus discuss some brain-atlasing resources currently under development, and their applicability in cognitive as well as clinical neuroscience.
DERIVATION OF MODIFIED BERNOULLI EQUATION WITH VISCOUS EFFECTS AND TERMINAL V...Wasswaderrick3
In this book, we use conservation of energy techniques on a fluid element to derive the Modified Bernoulli equation of flow with viscous or friction effects. We derive the general equation of flow/ velocity and then from this we derive the Pouiselle flow equation, the transition flow equation and the turbulent flow equation. In the situations where there are no viscous effects , the equation reduces to the Bernoulli equation. From experimental results, we are able to include other terms in the Bernoulli equation. We also look at cases where pressure gradients exist. We use the Modified Bernoulli equation to derive equations of flow rate for pipes of different cross sectional areas connected together. We also extend our techniques of energy conservation to a sphere falling in a viscous medium under the effect of gravity. We demonstrate Stokes equation of terminal velocity and turbulent flow equation. We look at a way of calculating the time taken for a body to fall in a viscous medium. We also look at the general equation of terminal velocity.
Travis Hills' Endeavors in Minnesota: Fostering Environmental and Economic Pr...Travis Hills MN
Travis Hills of Minnesota developed a method to convert waste into high-value dry fertilizer, significantly enriching soil quality. By providing farmers with a valuable resource derived from waste, Travis Hills helps enhance farm profitability while promoting environmental stewardship. Travis Hills' sustainable practices lead to cost savings and increased revenue for farmers by improving resource efficiency and reducing waste.
ANAMOLOUS SECONDARY GROWTH IN DICOT ROOTS.pptxRASHMI M G
Abnormal or anomalous secondary growth in plants. It defines secondary growth as an increase in plant girth due to vascular cambium or cork cambium. Anomalous secondary growth does not follow the normal pattern of a single vascular cambium producing xylem internally and phloem externally.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
2. Vibrational Spectroscopy
• A key experimental technique use to probe the vibrational
modes (normal modes) of a material.
• Raman spectroscopy is commonly used in chemistry to provide
a fingerprint by which molecules can be identified.
• Can be used to explore relative composition of a material (i.e.
relative concentration of a known compound in solution).
• Widely used in industry and quality assurance.
• Key technique in condensed matter research.
3. Simple harmonic motion
Atoms connected via chemical bonds are equivalent to masses
connected by springs. We can describe these using Hooke’s
law (Q is a displacement of an atom away from eqn position)
From Newton’s second law
Where m is the reduced mass
Thus
Find a general solution
where
F = -kQ
F = m
d2
Q
dt2
m
d2
Q
dt2
+kQ = 0
Q(t)= Acos(wvibt)
wvib =
k
m
4. Insert potential into time independent Schrodinger equation:
To find quantized solutions
V(x) =
1
2
kx2
k =
d2
V
dx2
æ
è
ç
ö
ø
÷
From classical to quantum
V(x) = V(0) + x
dV
dx
æ
è
ç
ö
ø
÷+
1
2
x2 d2
V
dx2
æ
è
ç
ö
ø
÷ +
1
3!
x3 d3
V
dx3
æ
è
ç
ö
ø
÷ + ...
If two nuclei are slightly displaced from equilibrium positions (x = R - Re),
can express their potential energy in a Taylor series:
Not interested in absolute potential, so set V(0) = 0.
At equilibrium, dV/dx = 0 (a potential minimum). Providing displacement is small, third
order term can be neglected. We can therefore write:
EY(x) = -
2
2m
Ñ2
+V(x)
é
ë
ê
ù
û
úY(x)
En = wvib (n+
1
2
)
5. This creates a ladder of vibrational modes
This is well-known case of a harmonic oscillator.
The energy of a quantum-mechanical harmonic
oscillator is quantized and limited to the
values.
Selection rules dictate that harmonic
Oscillator transitions are only allowed for
Dn = ± 1
En = (n+
1
2
) wvib
0
1
2
3
4
5
6
7
8
Displacement (x)
Energy
Potential energy V
wvib
V(x) =
1
2
kx2
6. Molecules have many different vibrational modes
O C O
O C O
Asymmetric stretch mode
O
C
O
Bending mode
CO O
Symmetric stretch mode
(100)
(010)
(020)
(030)
(001)
Symmetric
stretch
mode
Bending
mode
Asymmetric
stretch
mode
171 meV
82 meV
290 meV
Example: CO2
Mode frequency dependent on mass of
Atoms, bond stiffness and type of
vibration involved (stretching, rocking,
breathing etc)
7. Light-molecule interactions
During the interaction between light and a molecule, the incident wave induces a
dipole P, given by
Where a is the polarizability of the molecule, and E is the strength of the EM wave.
(Polarisability is the tendency of an electron cloud to be distorted by a field)
The EM field of an incident wave at angular frequency wo can be expressed using.
So the time-dependent induced dipole moment is
P =aE
E = E0 cos(w0t)
P =aE0 cos(w0t)
8. When a molecular bond undergoes vibration at its characteristic frequency
wvib, the atoms undergo a displacement dQ around their equilibrium position
Q0
For small displacements, we can express the change in the polarisability
using a Taylor series.
Here, a0 is the polarizability at the equilibrium position. Substituting, we have
dQ =Q0 cos(wvibt)
Q0
Q0+dQ
a =a0 +
¶a
¶Q
dQ+...
a =a0 +
¶a
¶Q
Q0 cos(wvibt)
9. From our expression for P, we then find
Using the trig identity
It is easy to show
This tells us that dipole moments are created at 3 different frequencies:
P =a0E0 cos(w0t)+
¶a
¶Q
Q0E0 cos(w0t)cos(wvibt)
cos(a)cos(b) =
1
2
cos(a-b)+cos(a+b)[ ]
P =a0E0 cos(w0t)+
¶a
¶Q
Q0E0
2
cos((w0 -wvib )t)+cos((w0 +wvib )t)[ ]
w0 w0 +wvibw0 -wvib
10. Results in a processes called Raman scattering
• Raman-spectroscopy is a form of inelastic
light-scattering.
• Photon interacts with a molecule in its ground
vibronic state or an excited vibronic state.
• Molecule makes a brief transition to a virtual
energy state.
• (Virtual state is an ‘imaginary’ intermediate
state. Lifetime of such states dictated by
uncertainty principle)
• The “scattered” (emitted) photon can be of
lower energy (Stokes shifted) than the
incoming photon, leaving the molecule in an
excited vibrational state.
Ground state
0
1
2
3
4
Virtual state
hn hn '
11. Anti-stokes scattering.
• Can also have a transition from a
vibrationally excited state to the
virtual state.
• The molecule will then return to its
ground-state, with the scattered
photon carrying away more energy
than the incident photon.
• This is called anti-Stokes scattering.
• Raman scattering should not be
confused with the emission of
fluorescence.
Ground state
0
1
2
3
4
Virtual state
hn hn '
12. Raman ‘selection rules’.
A necessity for Raman scattering is that
i.e., as the bond vibrates, there is a change in its polarizability. Why does this
happen?
At max compression, electrons ‘feel’ effects of other nucleus, and are less
purturbed by EM field. At max elongation, electrons feel less interaction with
other atom, and are more perturbed by the EM field. We thus have a change
in polarisability as a function of displacement.
¶a
¶Q
¹ 0
Q0-DQ
Q0 Q0+DQ
Max compression Equilibrium Max elongation
13. Raman spectroscopy: practicalities
Raman signal is often orders of magnitude
weaker than elastic scattering, so we need
A laser and rejection of stray light.
Use an ‘edge filter’ to reject the
Laser light.
Raman scattered cross section given
By
Where
and
Can use shorter wavelengths (higher frequencies), but this can excite fluorescence
that often swamps the weak Raman signal.
Spectroscopists most often express wavenumber of vibrational mode in units of
cm-1 (which is a unit of energy). Typically goes from 200 to 4000 cm-1.
s µ(n0 -nvib )
n0 =1/ l0
nvib = 2pwvib /c
nvib
nvib
14. Example: acetone
394 492 532
789
899
1068
1220
1353
1427 1711
1746
(C=O stretch)
(CC2 symmetric stretch)
(CH3 deformation)
(CH3
rock)
(identification based on Harris et al, Journal of molecular spectroscopy, 43 (1972) 117)
16. Kishan Dholakia and colleagues:
University of St. Andrews
Raman used in
chemical analysis
Quality assurance and
Substance identification
Detecting counterfeits
Mapping drug dispersion
in pharmaceuticals
17. Coupling electronic and vibronic transitions
• We have seen that we can directly measure
the vibrational modes of a material using
Raman spectroscopy.
• Molecules typically vibrate as the make
transitions between electronic states.
• So how does the vibration of a bond affect the
fluorescence of a molecule?
18. Molecular transitions
The ground state and the excited states
of molecules can be represented by
harmonic oscillators with quantized
vibrational modes.
Electronic transitions are allowed between
these modes.
Mass of an electron is very different from
the nuclei. Thus electronic transitions occur
in a stationary nuclear framework (Franck
Condon Principle).
We plot electronic transitions as vertical
lines, representing the same nuclear
distribution in ground and excited states.
Nuclear Displacement
Energy
hn
19. Molecular absorption and emission spectra contain ‘vibrational replicas’.
In ideal case, the excited and ground states have an identical harmonic
potential, and thus absorption spectrum is the mirror image of emission.
Stokes shift measure of energetic relaxation between ground and excited states.
Stokes shift
20. Example: Absorption and PL of diphenyl anthracene
DE ~162 meV
(~1309 cm-1)
Probably a C-C
Stretch mode.
DE
21. The effects of disorder
See strongly broadened transitions
caused by inhomogeneous broadening.
Polymers can be very disordered materials
F8BT
S0 S1 S1 S0S0 S2
22. Vibrational spectroscopy
• In many molecular systems, the harmonic potential results in
quantized vibrational modes.
• Raman spectroscopy allows you to identify and characterize
these vibrational modes.
• We can see fingerprinits of certain vibrational modes when we
measure absorption and fluorescence emission.
• Raman spectroscopy is highly useful in materials research and
is widely used as a routine characterization technique.