Some lines are called resonant

[vladivostok]

some lines are called "resonant"

Hi,

I would like some explanation on a topic for which I do not find detailed literature online or in books.
In photon absorption/emission processes by atoms, some lines are called "resonant" (for example, the 2P_1/2 (or 2P_3/2) to 1S_1/2 transition of hydrogen).
What does it really mean?
In what is it different from other transitions?
What is different in the quantum derivation of cross section between a 'non-resonant' and a 'resonant' transition?

If someone could shed some light on the topic or give good reference to some literature, it would be quite helpful!
Thanks!

 

[vladivostok]

No idea? :)

 

[DrDu]

Could you be more specific on the context of you question? Maybe a citation?

 

[vladivostok]

Yep, sure. Thanks for replying.

The questions would be:

- what is your definition of a resonant transition line?
- what is your definition of resonant scattering?

When you calculate a "resonant scattering" cross section, what differs from a the calculation of a "NON-resonant scattering" cross section?

In the reference below (beginning of page 4), they present the in equation (1) the cross section for the resonant scattering, where Phi is the absorption profile (=convolution of a Lorentzian and a Maxwellian). OK, but what makes this calculation specific of a resonant line ??

http://arxiv.org/abs/1005.0338

Extra-question: what is your favorite reference for the derviation of a scattering cross-section in:
- Quantum Mechanics
- Classical physics

Thanks a lot !
cheers

 

[DrDu]

Ok, now I see. In your first post, you were asking about absorption& emission processes. These processes only happen when the radiation being absorbed or emitted is resonant with the absorbing or emitting system, i.e. if the frequency of the light coincides with the difference of the energy levels of the system.
However, what you really seem to be interested in is not absorption and emission but scattering. In scattering, the photon enters the realm of the system, interacts with it and finally leaves the system. There you can distinguish between resonant and non-resonant scattering. In the first case, the energy of the incident light coincides with the difference of some energy levels of the system, in the second case it doesn't. In the first case, the light can excite the system, the system can stay in that excited state for a long time until it re-emits the light. In the non-resonant case the time the system can interact with the radiation is very short and mainly determined by energy time uncertainty with the mismatch between the energy of the light and the energy level difference of the system playing the role of the energy uncertainty.
My favorite book on scattering is R. Newton, Scattering theory of waves and particles.