PAH IR Spectral DatabaseDecember 24, 2012 / Posted by: Daniella Scalice
A team of scientists led by Lou Allamandola at NASA Ames Research Center have compiled the world’s largest collection of polycyclic aromatic hydrocarbon (PAH) infrared spectra, and have used them to create a web database to serve a variety of applications.
The web site contains over 800 spectra of polycyclic aromatic hydrocarbons (PAHs) in their neutral and electrically charged states and tools to download PAH spectra ranging in temperature from minus 470 to 2000 degrees Fahrenheit. PAHs are flat, chicken-wire shaped, nano-sized molecules. Thanks to these spectra, PAHs are now known to be abundant throughout the Universe but often in exotic forms not readily available on Earth. They are thought to be produced in the outflows from carbon-rich stars by processes similar to combustion in oxygen poor flames that produces PAH-rich soots on Earth.
To provide these spectra a team of scientists led by Louis Allamandola at NASA Ames Research Center developed a program in the late 1980’s to measure PAH spectra under simulated astronomical conditions experimentally and with computer software. Duplicating the harsh conditions of cold interstellar space in their laboratories and computers, the scientists created a unique collection of PAH spectra primarily to interpret mysterious infrared emission detected by ground, air, and space-based observatories.
The 7 member team is made up of experts in many different fields. “This group has put in a tremendous effort over the past 5 years to create this web accessable database,” said Allamandola. He continued, “There are now about 800 spectra in the database. Six hundred of these have been theoretically computed and two hundred have been measured in the laboratory. The theoretical spectra span the range from 2 to 2000 microns, the experimental spectra cover 2 to 25 microns.”
Co-added (uniformly weighted) spectra produced after querying the PAH spectral database by size and charge. Column 1 shows the spectra produced by co-adding uniformly weighted spectra of all PAHs in the database containing between 16 and 60 carbon atoms broken down by charge. The panels show how each uniformly weighted co-added spectrum depends on PAH charge from neutral (top) to anion (middle) to cation (bottom). Columns 2 and 3 show the corresponding spectra for the PAHs in the database containing between 60 and 90, and more than 90 carbon atoms, respectively.
Besides being of great interest to astronomers, the value of the PAH spectral database extends far beyond the immediate needs of NASA and astronomy. A PAH spectral database has a large and very diverse set of important applications. PAHs are a major product of combustion, they remain in the environment, and they are carcinogenic. Consequently they are important, for example, to scientists, educators, policy makers, and consultants working in the fields of medicine, health, chemistry, fuel composition, engine design, environmental assessment, environmental monitoring, and environmental protection. This PAH database is a new tool for people working in all of these fields.
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