Optical Electronic Spectroscopy 1. Lecture Date: January 23 rd , 2008. The Electromagnetic Spectrum. UV-Visible X-ray. What is Electronic Spectroscopy?. Spectroscopy of the electrons surrounding an atom or a molecule: electron energy-level transitions.
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Lecture Date: January 23rd, 2008
Atoms: electrons are in hydrogen-like orbitals (s, p, d, f)
Molecules: electrons are in molecular orbitals (HOMO, LUMO, …)
(The LUMO of benzene)
(The Bohr model for nitrogen)
M + heat M*
E = hn
M* M + heat
c = the speed of light (~3.00 x 108 m/s)
i = the velocity of the radiation in the medium in m/s
ni = the refractive index at the frequency i
Where the absorbance A has no units, since A = log10 P0 / P
e is the molar absorbtivity with units of L mol-1 cm-1
b is the path length of the sample in cm
c is the concentration of the compound in solution, expressed in mol L-1 (or M, molarity)
For an alternative view, see: Bare, William D. A More Pedagogically Sound Treatment of Beer's Law:
A Derivation Based on a Corpuscular-Probability Model, J. Chem. Educ.2000,77, 929.
Figure from Chapter 5 of Cazes, Analytical Instrumentation Handbook 3rd Ed. Marcel-Dekker 2005.
= 1000, 1000
= 1500, 500
= 1750, 250
Diagrams from http://csep10.phys.utk.edu/astr162/lect/light/absorption.html
s = total spin quantum number
j = total angular momentum quantum number
l = orbital quantum number (s,p,d,f…)
Figure from the Sapphire Electronic Spectroscopy Software Package, Cavendish Instruments Limited.
Figure from H. A. Strobel and W. R Heineman, Chemical Instrumentation: A Systematic Approach, Wiley, 1989.
E = energy of state
P = number of states having equal energy at each level
N = number of atoms in state
(Values from Cazes pg 79, Table 1)
The simulated spectrum for the sodium atom
Photo by Steve Kvech, http://www.cee.vt.edu/program_areas/environmental/teach/smprimer/icpms/icpms.htm#Argon%20Plasma/Sample%20Ionization
Diagram from Lagalante, Appl. Spect. Reviews. 34, 191 (1999)
m = d(sin i + sin r)
Varian Vista PRO
1. Axial flame view
2. Echelle grating polychromator
3. CCD detector
Figure from Varian Vista PRO sales literature.
Images are of Aurora AI1200, http://www.spectronic.co.uk
Figure from T. Wang, in J. Cazes, ed, “Ewing’s Analytical Instrumentation Handbook”
Picture from Perkin-Elmer
Figure from US Army/Ames
Review Skoog et al. Chapters 6-10
Review Cazes Chapters 3-4
Optical Electronic Spectroscopy
H. A. Strobel and W. R. Heineman, “Chemical Instrumentation: A Systematic Approach”, 3rd Ed., Wiley (1989).