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Unformatted text preview: Chem 120A Why Chemistry needs QM (cont.) 08/30/2010 Fall 2010 Lecture 2 Reading • Engel Ch. 1, 2 • Atkins Ch. 0, 2.1-2.15, 3.1-3.4 • McQuarie ch. 1 The de Broglie relation As we saw last time photons are particle-like and carry momentum. If we take the relativistic expression for the energy of a particle, E 2 = m 2 c 4 + p 2 c 2 and set the mass to 0 (photons have no mass) and plug in the expression for the energy of a photon from last time E = h ν we arrive at h ν = pc (1) p = h ν c = h λ (2) which is the expression for the momentum carried by a photon. This momentum can be probed through the measurement of scattering of light from electrons (measuring the change in λ due to momentum transfer) which is called compton scattering. In 1924 de Broglie suggested that the same relation holds for particles. Specifically a particle with momen- tum p has a wavelength given by λ = h p (3) which has since been validated through the observation of e- , He, H 2 , He n (cluster), C 60 (large molecule),...
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This note was uploaded on 10/31/2010 for the course PHYSICAL C 11209 taught by Professor Whaley during the Fall '10 term at University of California, Berkeley.
- Fall '10