crazyboy
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Determining bond lengths and atomic size
I want some data comparing uranyl ions of U-235 and U-238. Wikipedia says the U-O bond is about 180pm but it doesn't specify an isotope. Are they much
different? How much larger is the U-238 than U-235? Is there a good program for this kind of thing?
[Edited on 10-4-2015 by crazyboy]
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annaandherdad
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Bond lengths are quite insensitive to the nuclear isotope. The electrons move in the field of the nuclei, which depends on the nuclear charges and
positions but not their masses. Hence the Born-Oppenheimer potentials do not depend on the nuclear masses. The kinetic energy term in the
Born-Oppenheimer Hamiltonian for the nuclear motion does contain the nuclear masses, and this affects the vibrational frequencies. It also affects
the size of the (approximately Gaussian) wave function for the ground state, but since this wave function is to a good approximation centered at the
minimum of the potential, which as just mentioned doesn't depend on the nuclear masses, the average bond length of a diatomic also does not depend
strongly on the nuclear masses. The Born-Oppenheimer potential is not exactly symmetric about the minimum, so changing the width of the ground state
wave function does cause a shift in the average position, but the effect is small.
Any other SF Bay chemists?
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crazyboy
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OK that makes sense. The reason I ask is I am in a protein engineering class and we have to think of a novel protein to design. I thought that perhaps
a protein could be made to selectively bind certain isotopes but that may not be the case. Are there any elements that are that are hard to separate
that are in the same group or maybe have similar properties? For example palladium and platinum. The ions could be separated by a selectivity filter
or if they are complexed then perhaps stabilized by different sized binding pockets... Any thoughts?
Selectivity filter 1
Selectivity filter 2
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