Specialising in custom-designed, precision scientific instruments, built, programmed and calibrated to the most exacting standards. The range includes precision dataloging barographs, with built-in statistical analysis, Barographic Transient Event Recorders and computer-interfaced detectors and sensors for environmental monitoring & process control.
A site dedicated to scientific techniques, experimental methods, & investigative tools for the inventor, researcher and laboratory pioneer. Articles on glassblowing, electronics, metalcasting, magnetic measurements with new material added continually. Check it out! www.drkfs.net
click on any item in the list for its wikipedia entry if available.
When an electron is raised to a higher orbital the direction of the electron spin is not changed. As most molecules have an even number of electrons and these are arranged in pairs having opposite spin, the elevation of one electron to a higher orbit does not disturb this balance. However, it is possible for the spin of an electron to change direction on excitation and, as a consequence will then not be paired. Thus, the molecule will have two independent electrons of the same spin in different orbits.
Quantum theory predicts that such a molecule can exist in three forms, each form having very slightly different energy; a molecule in this condition is said to be in a triplet state. The change of singlet state to a triplet state is called intersystem crossing and can occur when the lowest vibrational level of the excited single state has the same energy level as an upper vibrational level of the triplet state.
The transition of an electron from an excited singlet state to a ground state occurs readily (usually within 10-9-10-6 sec) with emission of a photon of light and this, as already defined, is called Fluorescence. However, the transition of an electron from a triplet state to a ground state is much more difficult and may take a much longer time (ca 10-4-102sec). Thus, light may be emitted long after the excitation light has been removed. This persistent emission of light is called Phosphorescence. The relative position of the adsorption, Fluorescence and Phosphorescence bands for Chrysene are shown in figure 3. A molecule in a triple state has a lower energy than it would have in its singlet state, thus when returning to its ground state there is a lower energy change and light is emitted at a lower energy (longer wavelength) than it would from the singlet state.
About the Author
RAYMOND PETER WILLIAM SCOTT was born on June 20 1924 in Erith, Kent, UK. He studied at the University of London, obtaining his B.Sc. degree in 1946 and his D.Sc. degree in 1960. After spending more than a decade at Benzole Producers, Ltd. Where he became head of the Physical Chemistry Laboratory, he moved to Unilever Research Laboratories as Manager of their Physical Chemistry department. In 1969 he became Director of Physical Chemistry at Hoffmann-La Roche, Nutley, NJ, U.S.A. and subsequently accepted the position of Director of the Applied Research Department at the Perkin-Elmer Corporation, Norwalk, CT, U.S.A.
In 1986 he became an independent consultant and was appointed Visiting Professor at Georgetown
University, Washington, DC, U.S.A. and at Berkbeck College of the University of London; in 1986 he retired but continues to write technical books dealing with various aspects of physical chemistry and physical chemical techniques. Dr. Scott has authored or co-authored over 200 peer reviewed scientific papers and authored, co-authored or edited over thirty books on various aspects of physical and analytical chemistry. Dr. Scott was a founding member of the British chromatography Society and received the American Chemical society Award in chromatography (1977), the M. S. Tswett chromatography Medal (1978), the Tswett chromatography Medal U.S.S.R., (1979), the A. J. P. Martin chromatography Award (1982) and the Royal Society of Chemistry Award in Analysis and Instrumentation (1988).
Dr. Scott’s activities in gas chromatography started at the inception of the technique, inventing the Heat of Combustion Detector (the precursor of the Flame Ionization Detector), pioneered work on high sensitivity detectors, high efficiency columns and presented fundamental treatments of the relationship between the theory and practice of the technique. He established the viability of the moving bed continuous preparative gas chromatography, examined both theoretically and experimentally those factors that controlled dispersion in packed beds and helped establish the gas chromatograph as a process monitoring instrument. Dr. Scott took and active part in the renaissance of liquid chromatography, was involved in the development of high performance liquid chromatography and invented the wire transport detector. He invented the liquid chromatography mass spectrometry transport interface, introduced micro-bore liquid chromatography columns and used them to provide columns of 750,000 theoretical plates and liquid chromatography separations in less than a second. Dr. Scott has always been a “hands-on” scientist with a remarkable record of accomplishments in chromatography ranging from hardware design to the development of fundamental theory. He has never shied away from questioning “conventional wisdom” and his original approach to problems has often produced significant breakthroughs.