| MadSci Network: Chemistry |
Tiago, Normally during a combustion process, there is little ultraviolet emission because most of the changes in the atom involve changes in the valence shell of electrons. The energies for changes in this region are normally in the visible or infrared spectral regions. The references for this are very wide--any college level freshman chemistry text will cover these changes. It will also give ionization energies in a table at the back of the book. In order to reach ultraviolet energies, the electron(s) ionized are usually deeper in the electron shell than the valence electrons. Small amounts of UV may be available from high temperature reduction of fluorine or chlorine. UV light is usually generated through gas discharge tubes where an electric current is passed through a low pressure gas in a quartz tube. The mercury gas discharge tube (as well as mercury vapor arc lights used in gyms and outdoors) emits a high amount of UV light. There have been many accidental burns from mercury arc lights or gas discharge tubes. A new method of producing UV is presented in a patent at the following URL: http://www.wipo.int/pctdb/en/wo.jsp?IA=WO2003% 2F049499&WO=2003% 2F049499&DISPLAY=CLAIMS (Paste that into your browser, and you will get the document) The device uses air or oxygen mixed with fluorine or chlorine and undergoing the reaction between two high voltage plates. That is not a device for home or even general use. The mercury vapor gas discharge tube just requires a high voltage transformer (a neon sign transformer will work) to maintain the discharge, and will produce large amounts of UV radiation. The industrial mercury vapor lights REQUIRE shielding. There are cases on record of severe burns and partial or worse blindness from lights with missing or broken UV shields. An example is a news release from OREGON Occupational Safety and Health of an accidental overexposure in Salem, OR. http://www.nietc.org/resources/4/downloads/metal%20halide% 20lamps.pdf Old Coleman Lanterns using mantles containing thorium and cesium which formed oxides when the mantle was ignited after being installed.The light emitted by these oxide mantles is shorter in average wavelength than can be explained simply by the temperature of the burning gases, so it isn't just thermal radiation at the ambient temperature. The mantle's unexpected light emission is called candoluminescence and is thought to involve non-thermal light emitted as the result of chemical reactions and radiative transitions involving the burning gases and the mantle oxides. http://www.howeveryth ingworks.org/prints.php? topic=incandescent_light_bulbs&page=3 You notice that none of the methods produce UV alone; all have a large component of visible radiation. The following is a good introduction to "Black Lights" where a special glass is used to absorb visible light: http://en.wikipedia.org/wi ki/Black_light Black Lights are used extensively in theaters and shows; they produce longer wave UV light, and are safer (not totally safe) than bulbs that produce shorter wavelength (more energetic) UV A and B. Be sure to wear safety goggles that absorb UV-A and UV-B rays when doing any experimentation involving ultraviolet emissions!
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