Re: questions about electrons and photons

Steve,

Excellent question. It's taken me a bit of time to formulate an answer that "feels" right. It is not rigorous and it might not be completely satisfying to you, but it's hard for me to do much better at a lay level.

Quantum mechanics describes particles like electrons by their "wavefunction". This is a function of space and time that, when squared, gives the probability that you will observe the electron at a given point in space and time. The different-shaped atomic and molecular orbitals are simply derived from the time-independent components of these functions.

Notice that I wrote time independent. These orbital functions assume that the electron is sitting in one particular orbital and not changing energy. If you are now talking about an energy transition through absorption or emission of a photon, you have to consider a time dependent solution involving both the electron and the photon.

Remember that the photon is also described by a time-dependent wavefunction, with a probability distribution roughly the size of the classical wavelength. This means that you don't have a precise "moment" of interaction. Rather, the wavefunctions "evolve" over time.

Consider the case of photon absorption. Before the photon arrives at the atom, the electron is in the ground state, so its wavefunction is described by a single orbital. As the photon approaches the atom, the time-dependent wavefunctions of the electron and photon begin to "interact", so the electron could be either in the ground state or the excited state. At an early stage, it is most likely that the electron is still in the ground state. As time progresses, the probability of measuring the electron in the excited state increases, with a proportionate decrease in the probability the electron is still in the ground state. Later, the photon wavefunction has collapsed and the electron is in the excited state.

Everyone has a different way of "visualizing" these processes, and all ways have limitations. I personally like to think of those "morphing" programs where you gradually go from one image to another. The electron is not instantly transitioning from one energy level to another. Rather, its wavefunction is "morphed" from one orbital to another over a (short) period of time as it interacts with the photon's wavefunction. I see it as a gradual process, rather than an instantaneous one.

I hope this helps.

Cheers, Sam