18_562ln08

18_562ln08 - MIT OpenCourseWare http/ocw.mit.edu 5.62 Physical Chemistry II Spring 2008 For information about citing these materials or our Terms

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MIT OpenCourseWare http://ocw.mit.edu 5.62 Physical Chemistry II Spring 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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5.62 Lecture #18: Model Intermolecular Potentials Readings: Hill, pp. 261-274 Intermolecular potentials are interactions between molecules — up to this point, particles are treated as independent, ideal particles that do not interact. Approximation okay for gas molecules at low pressure All atoms and molecules interact with one another, even inert gas atoms. Interaction potential between non-polar atoms Attractive forces: London dispersion or van der Waals force. Induced dipole interaction due to fluctuations in electron distribution: Charge 1 distribution on one atom is “off center” due to fluctuation. The U ( r ) 6 resulting electric dipole induces a temporary dipole on the other can be derived by QM atom. Dipole-dipole attraction. perturbation theory Repulsive forces: Due to electron orbital overlap (“overlap” or “Pauli” repulsion) Difficult to derive explicit distance dependence : usually treated as strongly repulsive, e.g.
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5.62 Spring 2008 Lecture #18, Page 2 U(r) 1 OR U(r) exp[–a(r – R min ) d ] (d is odd integer) r 12 Add attractive and repulsive portions of potential — resulting interaction potential looks like that for a diatomic molecule!! Two Ar atoms form a non-covalent "bond", but the binding
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This note was uploaded on 11/27/2011 for the course CHEM 5.43 taught by Professor Timothyf.jamison during the Spring '07 term at MIT.

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18_562ln08 - MIT OpenCourseWare http/ocw.mit.edu 5.62 Physical Chemistry II Spring 2008 For information about citing these materials or our Terms

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