L2 - Biophysical Chemistry Chemistry 24a Winter Term...

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Biophysical Chemistry Chemistry 24a Winter Term 2009-10 Instructor: Sunney I. Chan Lecture 2 January 6, 2010 Classical Description of the Interaction of Light with Matter E + + μ in Note that E is time-dependent (AC). Induced dipole moment A molecule can also have a permanent dipole moment . A molecule will have a permanent dipole moment if the centroid of positive charges and the centroid associated with the distribution of the electron density over the molecule do not coincide (due to different “electronegativity” of the atoms). The effect of an applied E field will be to try to align the permanent dipole with the field. The applied field will also induce changes in the electron distribution and modify the dipole moment of the molecule. Electric dipole moment Definition of dipole moment: μ = Σ q i (r i -r o ) μ -+ Chemists prefer to denote dipole moments as μ chemist +- So μ = - μ chemist
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Interaction between electric dipole and E field μ E θ Energy of interaction = μ E = −⏐ μ ⏐⏐ E cos θ Torque = μ ×E = μ ⏐⏐ E sin θ
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This note was uploaded on 10/27/2010 for the course BI 110 taught by Professor Richards,j during the Winter '08 term at Caltech.

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L2 - Biophysical Chemistry Chemistry 24a Winter Term...

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