C566lecture8_000

C566lecture8_000 - C566 Master Lecture Notes Lecture 8...

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Lecture 8 Switching from Cartesian Coordinates to Internal Coordinates V = kl ij kl kl ij ij r r r r V 2 2 1 where kl ij r r V 2 = k ij,kl For a simple triatomic molecule: V = ½ k 12 ( r 12 ) 2 + ½ k 23 ( r 23 ) 2 + ½ k 13 ( r 13 ) 2 + k 12,23 r 12 r 23 + k 23,13 r 23 r 13 + k 120.,13 r 12 r 13 9 total – 3 translational – 3 rotational = 3 vibrational modes Have 6 force constants!! Vibrational modes aren’t actually “normal;” they’re coupled. “Reasonable” Approximations (Hollas, ~p 206): Central Force Field : Only square terms, r ij , are included. V ½ k 12 ( r 12 ) 2 + ½ k 23 ( r 23 ) 2 + ½ k 13 ( r 13 ) 2 This is not practical for describing bend modes in a linear molecule: e . g . , r 13 0 with a bend distortion. 13
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This note was uploaded on 01/18/2012 for the course C 566 taught by Professor Carolinechickjarroll during the Spring '11 term at Indiana.

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C566lecture8_000 - C566 Master Lecture Notes Lecture 8...

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