Subject: Orbitals and Reality

From: "Phil Hultin" <hultin_at_cc.umanitoba.ca>
Date: Sat, 22 Jan 2005 18:04:20 -0600

I am getting the impression that part of the problem in this discussion is
that people mean different things when they talk about "visualizing an
orbital".

There can be no argument that the mathematical formulation of orbital theory
is a human construct, and hence that orbitals so formulated must be
artificial models.

These models purport to describe the spatial probability density (if that
isn't a redundancy) for a single electron having a particular energy in the
vicinityof a particular nucleus.  Atoms apart from hydrogen have more than
one electron, and our mathematical model is approximate in such cases.
Therefore, it is highly probable that even if a particular application of
the orbital model can give a reasonable agreement with experimental energies
in the aggregate, the individual one-electron wavefunctions will not have
any direct resemblance to the behaviour of any one electron in reality
(whatever that may mean).

 On the other hand, I think it is possible (albeit not probable) that our
orbital model captures some aspect of observable electronic behaviour.
Thus, until someone can explain to me how Villeneuve et al's tomographic
interpretation of their spectroscopic data is fundamentally wrong, I am
prepared to accept that they may have visualized something real, to which
our orbital model roughly corresponds.

Note that I do not say that they have indeed visualized an orbital, because
yes, orbitals are hypothetical objects.  And, I quite agree that you cannot
observe a hypothetical (or perhaps imaginary) object.  So, in the strict
sense there is no way that Villeneuve's claim to have observed an orbital
can be correct.  Is it therefore impossible to observe the spatial
distribution of an electron, and for this distribution to bear some
resemblance to what our theory predicts?

I would welcome any reasoned and referenced rebuttal of my interpretation of
Villeneuve et al's Nature paper.

Dr. Philip G. Hultin

Associate Professor of Chemistry,

University of Manitoba

Winnipeg, MB

R3T 2N2

hultin_at_cc.umanitoba.ca

http://umanitoba.ca/chemistry/people/hultin