Newsgroups: sci.physics,sci.electronics.basics
From: Peter Berdeklis <peter@atmosp.physics.utoronto.ca>
Subject: Re: [QUESTION] Why negative ground?
Date: Fri, 17 Jan 1997 16:56:30 GMT

On Wed, 15 Jan 1997, Ken wrote:

> Doug Jones said:
>
> >In ice, protons and negative holes are mobile.
>
> Please tell me where you got this interesting tidbit.  Any ice, or
> just water ice?  Why does it behave in a manner different from
> other solids?  If the protons are in motion, what supports the
> crystal lattice?  Why is a proton, which is 2000 times more massive
> than an electron, moving instead of the electron?

This is true of water ice definitely.  I don't know about other forms.

Remember that water is H2O, and in the molecule the electrons of the
hydrogens fill the outer shells of the oxygen molecule (this causes the
dipole of H2O).  Therefore the electrons are tightly bound to the oxygen
and are not free to move as charge carriers as they are in metals.

As to why the hydrogen ions (protons) move as charge carriers, that is
still a matter of some debate.  From Hobbs, _Ice Physics_:

"It is believed that the movement of a proton along a hydrogen bond
occurs by quantum mechanical tunnelling (with virtually zero activation
energy) through the potential barrier of the double-minimum potential of
the hydrogen bond which links the oxygen of a H3O+ ion with neighbouring
oxygen atom. ... the mobility of the proton is determined by a complex
realaxation process involving the absorption of one proton and the
emission of another.  During this process one proton of the ion undergoes
a transition from the ground state to the excited vibational state in the
hydrogen bond."

Basically one proton pushes the next out of the way, and so on down the
line.  The crystal lattice is never broken because the whole line of
protons move together.

Hobbs goes on to point out that not everyone agrees with this theory, but
it is accepted that protons are the charge carriers in ice.

---------------
Peter Berdeklis
Dept. of Physics, Univ. of Toronto