Introduction to Spectroscopy

Introduction to Spectroscopy Lecture Date: January 18th, 2007 What is Spectroscopy?  The study of the interaction between radiation and matter  “Analyticalspectroscopy”, as defined in this class, covers applications of spectroscopy to chemical analysis 1 History of Analytical Spectroscopy  1666: Isaac Newton (England) shows that white light can be dispersed into constituentcolors, and coins the term “spectrum” – Newton also produced the first “spectroscope” based on lenses, a prism, and a screen  1800: W.Herschel and J. W.Ritter show that infrared (IR) and ultraviolet(UV) light are part of the spectrum  1814: Joseph Fraunhofer noticed that the sun’s spectrum contains a number of dark lines,developed the diffraction grating  1859: G. Kirchoff obtains spectra of the elements, explains the sun’s spectrum The Visible Spectrum of the Sun (Black lines are absorption by elementsin the cooler outer region of the star) Figurefrom National Optical Astronomy Observatory/Association of Universities for Research in Astronomy/National Science Foundation, http://www.noao.edu/image_gallery/html/im0600.html 2 History of Analytical Spectroscopy  1870: J. C. Maxwell formalizes and combines the laws of electricity and magnetism  1900 to present: More than 25 Nobel prizes awarded to spectroscopists,including: – 1902: H.A. Lorentz and P. Zeeman – 1919: J. Stark – 1933: P.A. M. Dirac and E. Schrodinger – 1945: W.Pauli …. – 1999: A. Zewail Introduction to Spectroscopy  The electromagnetic spectrum  Each color you see is a specific (narrow) range of frequencies in this spectrum Figuresfrom NASA(www.nasa.gov) 3 The Electromagnetic Spectrum  Modern life (not just analytical spectroscopy) revolves around the EM spectrum! Properties of Electromagnetic Radiation  Wave/particleduality  PerpendicularE and B components – E = electric field – B = magnetic field  Waveproperties: Note – this figure shows polarized radiation! 1 – Wavelength(frequency) – Amplitude – Phase 0.5 Long wavelength (low frequency) 1 2 3 4 5 -0.5  = c  -1 1 0.5 Short wavelength (high frequency) 1 2 3 4 5 -0.5 c = the speed of light (~3.00 x 108 m/s)  = the frequency in cycles/second (Hz) -1  = the wavelength in meters/cycle 4 Interference of Radiation  Monochromatic: radiation containing a single frequency  Polychromatic: radiation containing multiple frequencies  Constructive interference: when two waves reinforce each other  Destructive interference: when two waves cancel each other The Interaction of Radiation and Matter  Electromagnetic radiation travels fastest in a vacuum  Whennot travellingin a vacuum, radiation and matter can interactin a number of ways  Some key processes (for spectroscopy): – Diffraction – Refraction – Scattering – Polarization – Absorption 5 ... - tailieumienphi.vn