07_580ln_fa08

07_580ln_fa08 - MIT OpenCourseWare http:/ocw.mit.edu 5.80...

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MIT OpenCourseWare http://ocw.mit.edu 5.80 Small-Molecule Spectroscopy and Dynamics Fall 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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5.80 Lecture #7 Fall, 2008 Page 1 Lecture #7: How to Assign an Atomic Spectrum Finding lists “sensitive lines” all lines in order of cm –1 high accuracy helps! No prior information? predict what you expect * never trivial * always know when it’s right Carrier which atom? which ionization state? experimental conditions how violent? absorption vs. emission Getting Started list all expected lowest-lying configurations, ~ two for each parity ( 1 i ) e.g. Ti 4s 2 3d 2 even parity 4s 3d 3 even parity 4s 3d 2 4p odd parity 3d 3 4p odd parity list the L–S–J or (j 1 , j 2 ) J terms that arise from each configuration and estimate their energies based on estimates of ζ (n ), F k (n ,n ), G k (n ,n ) values from isoelectronic comparisons or shrewd guesses set up Grotrian diagram organized according to rigorous (parity) and approximate symmetries e.g (L,S) 1 i e.g. odd parity even parity odd etc. singlet singlet triplet 1 1 P°… 1 S 1 P… 3 3 P° … SEE GROTRIAN DIAGRAM FOR Ca (next page) only can see odd even transitions between configurations (entire configuration is odd or even) mostly S = 0 = ±1 (single orbital promotion) L = 0, ±1 J = 0, ±1 J = L strongest in a multiplet (after correcting for 2J + 1 degeneracy of initial state) Key features (intensity provides clues to both J and J assignments) Rydberg series — nearly constant δ (quantum defect) cluster of lines — multiplets — repeated intervals and Landé Interval rule extremely strong lines — “resonance lines” see Grotrian “population funnels” in emission diagram excitation out of lowest state again (ground state or a metastable state) See Herzberg “Atoms” pages 177-181 The Interval Rule; Analysis of Multiplets
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5.80 Lecture #7 Fall, 2008 Page 2 Figure removed due to copyright restrictions. Please see: Fig. 31 in Herzberg, G.
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07_580ln_fa08 - MIT OpenCourseWare http:/ocw.mit.edu 5.80...

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