Lecture 25 - Spectroscopy

Lecture 25 - Spectroscopy - Chapter 14: Spectroscopy...

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Unformatted text preview: Chapter 14: Spectroscopy Homework: 2, 4, 6, 8, 10, 12, 24, 26, 28, 30, 32, 34, 36, 38, 39, 42, 47, 60, 67, 68, 74, 76, 80, 82, 84 h * Spectral Line Width Gas phase Solution * 1 1 Z t = = t h E 4 Z 1 10 8 s-1 (gas) = 10 ns Z 1 10 12 s-1 (soln) = 1 ps 4 h t E Excited State Lifetime vs h E E E m n = = W mn = aborption rate A nm = excited state lifetime B mn = Einstein coefficient N m = # molecules in m ( ) = radiation density ) ( m mn mn N B = nm n A N ) ( n nm nm N B W = absorption stimulated emission spontaneous emission nm n nm n mn m A N B N B N + = ) ( ) ( 1 1 ) ( / = kT h nm nm e B A 1 1 8 ) ( / 3 3 = kT h e c h 3 3 8 c h B A nm nm = kT h m n e N N / = 1 1 ) ( ) ( = = n m nm nm n m n nm nm N N B A N N N B A rate prob rate prob Intensity rate probability 1 Selection Rules Selection rules determine which quantum transitions are allowed: spin-forbidden and symmetry-forbidden 1. Spin-forbidden transitions : change in spin multiplicity not allowed! Allowed transitions follow S = 0 multiplicity = 2S + 1 where S is spin quantum number 1s 1s H 2 1s * 1s H 2 h not allowed 2. Symmetry-forbidden transitions : charge cancellation during transition. Allowed transitions follow = 1 h Symmetry-Forbidden Transitions Some transitions are forbidden due to charge cancellation during transition. = 1 are allowed ( is angular momentum quantum number). = 0 forbidden! = 1 allowed 1s 2s 1s 2p = dt j i ij j i is even f(x) odd ) ( ) ( ) ( ) ( x x x x j i j i = Transition dipole 2 1 2 1 =...
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This note was uploaded on 04/06/2011 for the course CHEM 107B taught by Professor Jamesames during the Winter '09 term at UC Davis.

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Lecture 25 - Spectroscopy - Chapter 14: Spectroscopy...

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