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Metastable matter

  1. Dec 2, 2004 #1
    I understand that some atoms have somewhat stable states at states other than the ground state. What I don't understand is how are compounds able to be made with these metastable atoms? Wouldn't the energy released uppon forming the compound or the increased energy needed just immediately disrupt the metastable. If you had a metastable helium ion floating around it could never combine and form a diatomic helium molecule and still have its electrons in their metastable shells right?

    Well other than the fact that heluim isn't diatomic except at millikelvin temps.
    Last edited: Dec 2, 2004
  2. jcsd
  3. Dec 24, 2004 #2


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    Metastable states

    A metastable state in an atom (i.e. excited electron) is not really stable in the sense that it has indefinite lifetime, but it simply means that the lifetime is longer than a normal transition to ground state. The life time can be on the order of microseconds or even milliseconds.

    Much of the recent work regarding metastable states is in the area of noble gases (He, Ne, Ar, Kr, Xe) and has applications in lithography and etching of semiconductors. Noble gases do not necessarily form compounds. Other metastable states have been explored in alkali and alkali earth metals, and these would form compounds. Certainly in compounds, the molecular orbitals would prevent atomic metastable states.

    However, there are certainly solid state materials, like Ti-doped sapphire (Al2O3) in which meta-stable states are exploited for production of laser.

    Here are some references. The Nobel Lecture by Willis Lamb is particularly noteworthy for its historical significance. Enjoy.


    Lithography with metastable rare gas atoms

    Atoms join in the race for lithography in the next century

    Towards Bose-Einstein Condensation of Neon

    A discrete time-dependent method for metastable atoms in intense fields

    http://www.icpig.uni-greifswald.de/proceedings/data/Baguer_1 (pdf file)
    Role of the fast atoms, ions and metastable Ar atoms in a HCD by ...

    Optical production of metastable rare gases (abstract)

    Willis E. Lamb, Jr Nobel Lecture (1955) - impressive history
    Fine structure of the hydrogen atom

    Quenching of resonant laser-driven ionisation at high buffer gas pressures

  4. Dec 25, 2004 #3


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    Astronuc's covered this very nicely, but let me add one little thing here : a simplified picture to help understand the why and how of metastable systems.

    When a system is at Potential Energy minimum, it's in a stable state. If the walls surrounding this local minimum are large compared to perturbations (eg :thermal fluctuations, fluctuations in chemical potential), the stability is high. If the walls are comparable to the size of thermal fluctuations, you have a metastable state.

    The lifetime of this metastable state depends on the height of these walls (activation energy) compared to the magnitude of thermal fluctuations at the ambient temperature. So, you can have metastable states that live for nanoseconds (eg: excited electronic states in fluorescent materials) or for years (eg : high temperature phases in quenched steels).
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