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Unformatted text preview: 1 Physical Chemistry Lecture 22 Diatomic Molecules Geometry of dihydrogen Dihydrogen Two nuclear centers Two electrons Focus on translation and Coulombic interactions Nuclear translation Electronic translation Nuclear repulsion Nuclear-electron attraction Electron-electron repulsion Spin-orbit coupling SO ee ne nn e n H V V V T T H Center of mass Treat the system as if electrons were massless for purposes of determining the center of mass m e = m p /1836 Good approximation Center of mass determined by the positions of the nuclei Center-of-mass problem is again a particle in a box 2 2 2 2 2 2 CM CM n n M T T M m m m m M B A B A Relative problem Nuclei and electrons move relative to the center of mass Cannot readily use prior techniques to separate electron and nuclear motions because of the Coulomb potentials Born-Oppenheimer approximation Solve problem in steps...
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