Re: a question from an AP Chem student...

[Michael Burns-Kaurin <mburns-k@spelman.edu>]

For a student in an introductory course, it might help to model the
electron in the atom as a harmonic oscillator with a resonance frequency
corresponding to the energy difference between the levels.  The
oscillator is driven at the frequency of the light (i.e. the frequency
of the oscillating electric field).  Far from resonance, the atom
oscillates weakly at the driving frequency, producing scattered light. 
Being near resonance corresponds to a strong response and absorption of
the photon.  Far from resonance, this model is actually reasonable; near
resonance, you should look at the electric field as coupling the two
levels--I think there can actually be oscillation between the levels.

Michael Burns-Kaurin
Physics Department
Spelman College
mburns-k@spelman.edu

Donald E. Simanek wrote:
> On Tue, 6 Oct 1998, Jerome Epstein wrote:
>
> > It is perhaps a little better to think of the photon as interacting with
> > the atom, rather than the elctron. The "how does the electron know"
> > question implies the view of an electgron as a point particle that
> > begins travelling to a higher orbit (like a planet getting kicked), and
> > how does it know the end point of the trip. But that view is just not
> > tenable.
> >
> > The atom is in an energy state, it has other possible states. If the
> > right amouint of energy is available, a transition can take place. If
> > the energy of the photon does not correspond to an energy transition of
> > the atom, and is insufficient to remove an electron from the atom, the
> > electron will either scatter off the atom or simply pass through
> > unaffected.
> >       Jerry Epstein
>
> Correct, of course. But it begs the question asked. How does either
> particle receive information that the interaction is a "go"? If the
> energies aren't matched, the interaction doesn't happen. Presumably the
> interaction is a substantial "event". What mechanism of interaction
> between the approaching particles sets the stage for the even to happen.
> An event can't happen until the participating entities "know" (receive
> physical stimuli/information) from each other.
>
> What is wanted (by the student with the inquiring mind) is the detailed
> mechanism of the interaction from the first stage to the last. To say "it
> happens or it doesn't depending on the energies" is a cop-out. At least
> we'd like to know where the explanation must lie, and if that involves
> physics or math beyond the introductory level, we should simply say so and
> defer the question till later, when one takes quantum mechanics.
>
>         -- Donald