Transcript No Slide Title

Thursday, 28 January 2010
Lecture 8: Volume Interactions
Reading
Ch 1.8
http://speclib.jpl.nasa.gov/
Major spectral features of minerals (p. xiii-xv), from Infrared
(2.1-25 mm) Spectra of Minerals, J W Salisbury et al., 1991 –
( class website)
Optional reference reading: Roger Clark’s tutorial on
spectroscopy (class website)
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Wavelength (nm)
Spectral radiance (W/m2/nm/str)
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Last lecture
1) reflection/refraction of light from surfaces
(surface interactions)
2) volume interactions
- resonance
- electronic interactions
- vibrational interactions
3) spectroscopy
- continuum vs. resonance bands
- spectral “mining”
- continuum analysis
4) spectra of common Earth-surface materials
Today
1) reflection/refraction of light from surfaces
(surface interactions)
2) volume interactions
- resonance
- electronic interactions
- vibrational interactions
3) spectroscopy
- continuum vs. resonance bands
- spectral “mining”
- continuum analysis
4) spectra of common Earth-surface materials
Interaction of Energy and Matter
What causes absorption features in spectra?
Three effects of radiant energy on matter:
1) Rotational absorption (gases)
2) Electronic absorption
3) Vibrational absorption
Rotational Processes
Photons striking free molecules can cause them to rotate. The
rotational states are quantized, and therefore there are
discrete photon energies that absorbed to cause the molecules
to spin.
Rotational interactions are low-energy interactions and the
absorption features are at long infrared wavelengths.
Electronic Processes
Isolated atoms and ions have discrete energy states. Absorption of
photons of a specific wavelength causes a change from one
energy state to a higher one. Emission of a photon occurs as a
result of a change in an energy state to a lower one. When a
photon is absorbed it is usually not emitted at the same
wavelength. The difference is expressed as heat.
Four types:
Crystal Field Effects
Charge Transfer Absorptions
Conduction Bands
Color Centers
Electronic Processes
Crystal Field Effects
The electronic energy levels of an isolated ion are usually split and
displaced when located in a solid. Unfilled d orbitals are split
by interaction with surrounding ions and assume new energy
values. These new energy values (transitions between them
and consequently their spectra) are primarily determined by
the valence state of the ion (Fe 2+, Fe3+), coordination number,
and site symmetry.
http://img.alibaba.com/photo/50502613/Europium_Oxide.jpg
Electronic transitions, crystal field effects
Electronic Processes
Charge-Transfer Absorptions
Absorption bands can also be caused by charge transfers, or interelement transitions where the absorption of a photon causes
an electron to move between ions. The transition can also
occur between the same metal in different valence states, such
as between Fe2+ and Fe3+. Absorptions are typically strong.
A common example is Fe-O band in the uv, causing iron
oxides to be red.
http://en.wikipedia.org/wiki/Image:Hematite.jpg
http://www.galleries.com/minerals/silicate/olivine/olivine.jpg
Diopside
Fe
(Mg,Fe)2SiO4
MgCaSi2O6
Electronic transitions
(Fe+2, Fe+3), charge
transfer (Fe-O)
(Mg,Fe)SiO3
http://www.gemstone.org/images/01/Stones_Diopside.jpg
Mg
Electronic Processes
Conduction Bands
Gold
Sulfur
In metals and some minerals, there are two energy levels in which
electrons may reside: a higher level called the "conduction
band," where electrons move freely throughout the lattice,
and a lower energy region called the "valence band," where
electrons are attached to individual atoms. The yellow color
of gold and sulfur is caused by conduction-band absorption.
www.egyptcollections.com
web.syr.edu/~iotz/Gallery.htm
HgS
http://www.mii.org/Minerals/Minpics1/Cinnabar.jpg
Conduction band processes
Vibrational Processes
The bonds in a molecule or crystal lattice are like springs with
attached weights: the whole system can vibrate. The
frequency of vibration depends on the strength of each spring
(the bond in a molecule) and their masses (the mass of each
element in a molecule). For a molecule with N atoms, there
are 3N-6 normal modes of vibrations called fundamentals.
Each vibration can also occur at multiples of the original
fundamental frequency (overtones) or involve different modes
of vibrations (combinations).
vibrational
interactions
gases
Vibration-higher energy than rotation
Vibration - harmonic oscillators
stretching, bending
Molecular vibrations cause the
multiple absorption bands
HCl
3.75 µm
35Cl
37Cl
3.26 µm
n3
n1
n2
Vibrational modes
produce simple spectra
Vibrational - rotational modes
combine to produce complex
spectra with sharp bands
Vibration in water molecules
www.pitt.edu/.../1IgneousMineralz/Micas.html
X-OH vibrations in minerals: band
position in mica shifts with composition
KAl2(AlSi3O10)(F,OH)2
MgCO3
CaCO3
www.galleries.com/.../calcite/calcite.htm
Band position in carbonate minerals shifts with composition
Si-O bond vibrational resonance
O
QUARTZ
SiO2
O Si
O
O
www.pitt.edu/.../Quartz/QuartzCrystal.jpg
Thermal infrared
Examples of mineral spectra
Fe2O3
α-FeO(OH)
KFe3(SO4)2(OH)6
http://www.news.cornell.edu/photos/jarosite300.jpg
Spectra of common Earth-surface materials
www.gfmer.ch/.../Papaver_somniferum.htm
www.oznet.ksu.edu/fieldday/kids/soil_pit/soil.htm
www.bigwhiteguy.com/photos/images/814.jpg
Next lecture: more on spectroscopy