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CHAPTER 6 Key 6 1 a Coherent radiation is radiation that is made up of wave trains having identical frequencies or sets of frequencies and phase relationships that are constant with time b Dispersion in a transparent medium is its variation in refractive index as a function of wavelength c Anomalous dispersion is the sharp change in refractive index of a substance in a wavelength region where absorption is occurring d The work function of a substance is a constant that measures the energy required to remove an electron from the surface of the substance e The photoelectric effect involves the emission of electrons from the surface of a substance brought about by a beam of radiation f The ground state of a molecule is its lowest energy state g Electronic excitation is the process by which electrons in a substance are promoted from their ground state to higher electronic states by absorption of energy h Blackbody radiation is the continuum radiation emitted by a solid when it is heated i Fluorescence is a type of emission which is brought about by irradiating atoms ions or molecules with electromagnetic radiation Fluorescence involves a singlet tosinglet transition The lifetime of the excited state in fluorescence is very short 10 5 s or less j Phosphorescence is a type of emission brought about by irradiating a molecular system with electromagnetic radiation Phosphorescence involves a triplet to singlet transition and the excited state lifetime is longer than that of a fluorescing species k Resonance fluorescence is a type of emission in which the radiation produced is of the same wavelength as that used to excite the fluorescence l A photon is a bundle or particle of radiant energy with a magnitude of h where h is Planck s constant and is the frequency of the radiation m Absorptivity a is defined by the equation a A bc where A is the absorbance of a medium contained in a cell length of b and concentration c The path length b is expressed in cm or another specific