Spectrum analysis

Spectrum, also known as emission spectrochemical analysis, is the original scientific method of charting and analyzing the chemical properties of matter and gases by looking at the bands in their optical spectrum. The empirical laws of spectrum analysis are commonly known as Kirchhoff's Three Laws of Spectroscopy as follows:

1. An incandescent solid, liquid, or gas under high pressure emits a continuous spectrum.
2. A hot gas under low pressure emits a "bright-line" or emission-line spectrum.
3. A continuous spectrum source viewed through a cool, low-density gas produces an absorption-line spectrum.

Origins

Light can be separated into a spectrum by a prism. The resulting spectrum can then be analyzed

Anders Jonas Ångström, Charles Wheatstone, Gustav Kirchhoff, Robert Bunsen, William Crookes, and others contributed to early spectroscopy through the discovery and exploitation of spectral emission lines.

In 1835, Charles Wheatstone reported that different metals could be easily distinguished by the different bright lines in the emission spectra of their sparks, thereby launching the science of spectrum analysis.

In 1854, David Alter, a scientist of Freeport, Pennsylvania, published a work that included the spectral radiance properties for twelve metals, titled On Certain Physical Properties of Light Produced by the Combustion of Different Metals in an Electric Spark Refracted by a Prism. Dr. Alter began studying the optical properties of matter ever since finding a piece of melted, prismatic glass in the debris of the great Pittsburgh fire of 1845. By 1855, Alter published another article that expanded his original theory by including six gases, including the first discovery of what came to be named the Balmer lines of hydrogen. Alter's article contains a paragraph where he visualized the application of spectrum analysis to astronomy, mentioning the study and detection of elements in the combustion of shooting stars or luminous meteors, and daguerreotyped the dark lines of the solar spectrum. Alter's spectral discoveries were noted in various scientific publications in France, Germany, and Switzerland from 1854 to 1860.

In 1853, the Swedish physisist Anders Jonas Ångström presented similar theories about gases having spectra in his work: Optiska Undersökningar to the Royal Swedish Academy of Sciences—pointing out that the electric spark yields two superposed spectra. Ångström postulated that an incandescent gas emits luminous rays of the same refrangibility as those it can absorb—a fundamental principle of spectrum analysis.

In 1860, German physicist Gustav Kirchhoff and chemist Robert Bunsen published their own findings on the spectra of eight metals and identified these metals in natural elements. Kirchoff went on to contribute fundamental research on the nature of spectral absorption. Spectrum analysis was then grouped by Kirchhoff into the three fundamental laws commonly called Kirchoff's Laws, these laws integrated both Alter and Ångström's discoveries of radiance and emission with Kirchhoff's fundamental discoveries of absorption.

Johann Balmer discovered in 1885 that the four visible lines of hydrogen were part of a series that could be expressed in terms of integers. This was followed a few years later by the Rydberg formula, which described additional series of lines.

In the 1860's William Huggins and his wife Margaret used spectroscopy to determine that the stars were composed of the same elements as found on earth. They also used the non-relativistic Doppler shift (redshift) equation on the spectrum of the star Sirius in 1868 to determine its axial speed. They were the first to take a spectrum of a planetary nebula when the Cat's Eye Nebula (NGC 6543) was analyzed. Using spectral techniques, they were able to distinguish nebulae from galaxies.

In the early twentieth century, spectrum analysis led to "atomic spectroscopy" and quantum mechanics.

See also

• Alpha-particle spectroscopy
• Electromagnetic spectrum
• Fast Fourier transform
• Fraunhofer Lines
• Mass spectrometry
• Optical spectrum
• Spectroscopy
• Spectrum
• Quantum mechanics

References

• Alter, David. On Certain Physical Properties of Light Produced by the Combustion of Different Metals in an Electric Spark Refracted by a Prism. Am. J. Sci. Arts 18 (1854): pages 55-57.
• Alter, David. On Certain Physical Properties of the Light of the Electric Spark, Within Certain Gases, as Seen Through a Prism. Am. J. Sci. Arts 19 (1855): pages 213-214.
• Ann. Sci. Phys. Nat. (1856): page 151.
• Bloomfield, P. (1976). Fourier analysis of time series: An introduction. New York: Wiley.
• Brillinger, D. R. (1975). Time series: Data analysis and theory. New York: Holt, Rinehart. & Winston.
• Brace, D. B. (Ed. and translator). The Laws of Radiation and Absorption: Memoirs by Prévost, Stewart, Kirchhoff, and Kirchhoff and Bunsen. New York, NY: American Book Company, 1901, pages 100-125.
• Jenkins, G. M., & Watts, D. G. (1968). Spectral analysis and its applications. San Francisco: Holden-Day.
• Johnson, Allen, ed.; Garraty, John and James, Edward, Eds. Dictionary of American Biography; Supplement Four. New York, NY: Charles Scribner’s Sons, 1974, page 230.
• Kirchhoff, G. R.; Bunsen, R. Ann. Phys. (1860): pages 110, 160.
• Liebig and Kopp, Jahresber. Chem, (1854): page 118; (1855): page 107.
• L’Institut, Paris (1855): 156.
• Retcofsky, H. L. Spectrum Analysis Discoverer, Spectroscopy Society of Pittsburgh, PA 80 (2003): 1003
• Shumway, R. H. (1988). Applied statistical time series analysis. Englewood Cliffs, NJ: Prentice Hall.