CHAPTER THIRTEEN Spectroscopy As diverse as these techniques are, all of them are based on the absorption of energy by a molecule, and all measure how a molecule responds to that absorption. In describing these techniques our emphasis will be on their application to structure determination. We'll start with a brief discussion of electromagnetic radiation, which is the source of the energy that a molecule absorbs in NMR, IR, and UV-VIs spectroscopy 13.1 PRINCIPLES OF MOLECULAR SPECTROSCOPY ELECTROMAGNETIC RADIATION Electromagnetic radiation, of which visible light is but one example, has the properties of both particles and waves. The particles are called photons, and each possesses an " Modern"physics dates from amount of energy referred to as a quantum. In 1900, the German physicist Max Planck proposed that the energy of a photon(E) is directly proportional to its frequency(v) the stage for the develop- Planck received the 1918 No- The SI units of frequency are reciprocal seconds(s ) given the name hertz and the bel Prize in physics symbol Hz in honor of the nineteenth-century physicist Heinrich R. Hertz. The constant of proportionality h is called Plancks constant and has the value h=6.63×10-34J.s Electromagnetic radiation travels at the speed of light(c=3.0 X 10 m/s), which is equal to the product of its frequency v and its wavelength A The range of photon energies is called the electromagnetic spectrum and is shown in Figure 13. 1. Visible light occupies a very small region of the electromagnetic spec- trum. It is characterized by wavelengths of 4 X 10 m(violet)to 8 x 10 m(red) Lowest energy Wavelength(nm) Gamma y X-ray violet nfrared Radio frequency FIGURE 13.1 The electromagnetic spectrum. From M. Silberberg, Chemistry, 2d edition WCB/McGraw-Hill, 2000, p. 260) Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsiteAs diverse as these techniques are, all of them are based on the absorption of energy by a molecule, and all measure how a molecule responds to that absorption. In describing these techniques our emphasis will be on their application to structure determination. We’ll start with a brief discussion of electromagnetic radiation, which is the source of the energy that a molecule absorbs in NMR, IR, and UV-VIS spectroscopy. 13.1 PRINCIPLES OF MOLECULAR SPECTROSCOPY: ELECTROMAGNETIC RADIATION Electromagnetic radiation, of which visible light is but one example, has the properties of both particles and waves. The particles are called photons, and each possesses an amount of energy referred to as a quantum. In 1900, the German physicist Max Planck proposed that the energy of a photon (E) is directly proportional to its frequency (). E hv The SI units of frequency are reciprocal seconds (s1 ), given the name hertz and the symbol Hz in honor of the nineteenth-century physicist Heinrich R. Hertz. The constant of proportionality h is called Planck’s constant and has the value h 6.63  1034 J  s Electromagnetic radiation travels at the speed of light (c 3.0  108 m/s), which is equal to the product of its frequency and its wavelength : c v The range of photon energies is called the electromagnetic spectrum and is shown in Figure 13.1. Visible light occupies a very small region of the electromagnetic spec￾trum. It is characterized by wavelengths of 4  107 m (violet) to 8  107 m (red). 488 CHAPTER THIRTEEN Spectroscopy 100 Infrared Ultra￾violet 10–2 102 104 106 108 1010 1012 1020 1018 108 106 104 Frequency (s–1) Wavelength (nm) 400 500 600 750 nm X-ray Microwave Radio frequency Gamma ray Ultra￾violet 1016 Visible Infrared Visible region 1012 1014 1010 Highest energy Lowest energy 700 “Modern” physics dates from Planck’s proposal that en￾ergy is quantized, which set the stage for the develop￾ment of quantum mechanics. Planck received the 1918 No￾bel Prize in physics. FIGURE 13.1 The electromagnetic spectrum. (From M. Silberberg, Chemistry, 2d edition, WCB/McGraw-Hill, 2000, p. 260.) Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website