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Sources of Infrared Radiation
5
Sources of Infrared Spectroscopy
Joanna Choi, April Hyon, Jasleen Singh, and Kelly Yoo
Infrared Radiation Source to Spectra
Silicon Carbide Rod (Globar)
Purpose of
- Most ubiquitous IR source used in FTIR
- Electric current passed through bar, which becomes very hot and produces large amounts of IR radiation
- Obtained from samples in all phases
- Solid: incorporated in a KBr disk, prepared under high pressure, mixed with non-volatile liquid and ground to a paste that is smeared between salt plates
- Liquid: thin film sandwiched between two salt plates
- Gas: a sample cell with a long pathlength required to compensate for diluteness
- Reference
- To identify the molecular structure of a sample (i.e., functional groups) based on the infrared region of the electromagnetic spectrum
- In other words, IR spec measures the vibration of molecules and bonds
Sources
IR Radiation
in Your World
When choosing an IR source, consider:
http://hiq.linde-gas.com/en/analytical_methods/Infrared_spectroscopy/fourier_transform_infrared.html
http://mmrc.caltech.edu/FTIR/FTIRintro.pdf
http://www.rp-photonics.com/mid_infrared_laser_sources.html
http://missionscience.nasa.gov/ems/07_infraredwaves.html
http://www.ipac.caltech.edu/outreach/Edu/Regions/irregions.html
http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Spectrpy/InfraRed/infrared.htm
http://www.interspectrum.ee/ir-sources
http://www.newport.com/Infrared-Elements-for-Light-Sources/376889/1033/info.aspx
Categories of IR Radiation
1. Operating Temperature
2. Color Temperature
3. Radiating Area
...and out of your world
Near-, Mid-, Far-infrared radiation
- Near: 0.75 to 1.4 microns
- Mid: 3 to 8 microns
- Far: 15 to 1000 microns
The Process
FT-IR: Fourier Transform Infrared Spectroscopy
1. Pass a beam of infrared light through the sample
2. When the infrared light interacts with the molecule, it contains sufficient energy to cause vibrational and rotational changes
3. When the frequency of the IR is the same as that of the bond, absorption occurs
i. Specific bonds absorb specific wavelengths
4. Absorption spectra of compounds that is a unique reflection of molecular structure is obtained
- FT-IR vs UV-vis spectroscopy: monochromatic light beam vs broadband
- Glowing black-body source
- Standard sources
- IR source: ceramic sleeve
- retrofit coil
- IR parallel source
- NIR source
What is an Infrared Radiation Source?
When deciding on an IR source, you should consider all of the following except:
- An object that emits radiation of a wavelength between about 0.75 to 1000 µm. A calibrated secondary source usually is a heated cavity (blackbody) or a filament lamp.
- Consists of an inert solid that is electrically heated to a temperature between 1,500 and 2,200 K. The heated material will then emit infrared radiation.
A. Color Temperature
B. Radiating Area
C. Operating Temperature
D. Two of the above
E. All of the above