Deuterated molecules, especially D_2O (heavy water) are used to moderate neutron
ID: 1073030 • Letter: D
Question
Deuterated molecules, especially D_2O (heavy water) are used to moderate neutrons in nuclear reactors. In the presence of H_2O, the following equilibrium takes place in solution: D_2O + H_2O doubleheadarrow 2HOD Can you use IR spectroscopy to distinguish between the D_2O, H_2O and HOD species in solution? You are freezing the solution and assume you get crystals of pure D_2O, pure H_2O and pure HOD, all colorless. You are able to orient the crystals in space such that you can align the molecules along chosen Cartesian coordinates. Can you use IR spectroscopy to distinguish between the D_2O, H_2O and HOD species in crystals?Explanation / Answer
1) In the reaction,
we get formation of HOD species which has an O-H and an O-D bond. the O-D bonds are stringer than the O-H bonds and thus, of greater energy. The frequency we would observed in the IR would also be higher than the ones we see for typical O-H bonds.
a) We can distinguish between D2O (with two O-D bonds), H2O (with two O-H bonds) and HOD (with one O-H and one O-D bonds). H2O will give lowest frequency for streching of O-H bond. D2O would give highest bond strtching frequency for the molecule. Whereas, HOD would give somewhere, in between these two values.
b) When freezing of the three solutions H2O, D2O and HOD is done, the H2O and D2O would give more symmetrical strechings whereas, HOD would give nonsymmetrical orientation of crystals and mixed stretching frequencies due to irregular crystals formed.
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