Lecture 8: Volume Interactions Friday, 28 January 2010

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)

Reading

2

LECTURESJan 05 1. IntroJan 07 2. ImagesJan 12 3. PhotointerpretationJan 14 4. Color theoryJan 19 5. Radiative transferJan 21 6. Atmospheric scattering

• Jan 26 7. Lambert’s Law previous• Jan 28 8. Volume interactions today

Feb 02 9. SpectroscopyFeb 04 10. Satellites & ReviewFeb 09 11. MidtermFeb 11 12. Image processingFeb 16 13. Spectral mixture analysisFeb 18 14. ClassificationFeb 23 15. Radar & LidarFeb 25 16. Thermal infraredMar 02 17. Mars spectroscopy (Matt Smith)Mar 04 18. Forest remote sensing (Van Kane)Mar 09 19. Thermal modeling (Iryna Danilina)Mar 11 20. ReviewMar 16 21. Final Exam

Wednesday’s lecture

1) reflection/refraction of light from surfaces(surface interactions)

Today’s lecture:

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

What was covered in the previous lecture

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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 EffectsCharge Transfer AbsorptionsConduction BandsColor 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.

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Electronic Processes

Charge-Transfer Absorptions

Absorption bands can also be caused by charge transfers, or inter-element 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

Electronic transitions (Fe+2, Fe+3), charge transfer (Fe-O)

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Electronic Processes

Conduction Bands

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

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Conduction band processes

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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).

* In general, a molecule with N atoms has 3N-6 normal modes of vibration but linear molecules have only 3N-5 normal modes of vibration as rotation about its molecular axis cannot be observed.

gases

Vibration-higher energy than rotationVibration - harmonic oscillators

stretching, bending

HCl

3.75 µm 3.26 µm

35Cl 37Cl

Molecular vibrations cause the multiple absorption bands

vibrational interactions

Vibration in water molecules

Vibrational - rotational modescombine to produce complexspectra with sharp bands

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Vibrational modes

produce simple spectra

X-OH vibrations in minerals: band position in mica shifts with composition

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Band position in carbonate minerals shifts with composition

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QUARTZ

Si-O bond vibrational resonance

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Thermal infrared

www.pitt.edu/.../Quartz/QuartzCrystal.jpg

SiO2

Examples of mineral spectra

http://www.news.cornell.edu/photos/jarosite300.jpg

Fe2O3

α-FeO(OH)

KFe3(SO4)2(OH)6

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

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