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Water in BEC form

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  1. Oct 7, 2015 #1
    Is it possible for a molecule like water to exist in BEC form?
     
  2. jcsd
  3. Oct 7, 2015 #2

    DaveC426913

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    Can't see any reason why not.

    There are multiple articles on BECs of molecules.
     
  4. Oct 9, 2015 #3

    Daz

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    I don’t think water would form a Bode-Einstein condensate. A BEC occurs when all “particles” in the system condense into the same ground state - i.e. they all have the same energy. This is only possible if the particles have integral spin. I haven’t checked whether that is the case for water but let’s assume, for the sake of argument, that it is.

    Virtually all substances have a neat trick for finding an even lower energy configuration than the B-E condensate would have. Taking water as an example, H2O is a polar molecule; that is to say parts of the molecule are more positively or negatively charged. So, if you were to try to form a B-E condensate by lowering the temperature, the molecules clump together and wedge themselves into a crystal such that the most positively charged part on one molecule sits next to the most negatively charged parts of its neighbours.

    Water condenses into the solid phase. The binding energy released - the latent heat of crystallisation - gives the ground state of a perfect ice crystal a lower energy configuration than the BEC would have and so that is the configuration the system preferentially adopts.

    The only substance I know of that forms a macroscopic BEC is helium. There may be others but I’m ignoring quasiparticles, Cooper pairs and dilute atomic gasses in ion traps. That’s because He atoms are so weakly interacting that He can remain liquid right down to 0K (over a wide range of pressure.)

    If you look up the phase diagram of helium, you’ll see that at high enough pressure (above about 3MPa) and low enough temperature (below about 0.1K) even helium will crystallise into a BCC lattice. And when it does so, it forms a normal solid, not some kind of “super-BEC”.

    B-E Condensation has been observed in molecules such as Li2 under quite exotic conditions, such as laser ion traps but I’m doubtful whether a polar molecule could undergo BEC. (Happy to be proved wrong, however.)
     
  5. Oct 9, 2015 #4

    Daz

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    Oops - that should have been Bose- Einstein, not "Bode".
     
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