# Effing Virtual States - How do they work?

1. Sep 2, 2010

### WarPhalange

Effing Virtual States -- How do they work?

I want to talk to a scientist cuz this is pissing me off. >:-(

So, I'm learning about CARS and Raman spectroscopy. Since Day 1 of Modern Physics I've been told that atoms have discrete energy levels and only the only way to get an electron from n = 1 to n = 2 is by giving it energy equal to n1 - n2.

Now I get told that there are "virtual states" that an electron can use as a middle man between two eigenstates. It's never actually in the virtual states, it just uses it to hop to an allowed state.

So for example, in Raman spectroscopy you hit the atom with some frequency w > n1 - n2, an electron jumps to some virtual state, then goes back down to some other state, and releases a photon of frequency w - n1 + n2. What exactly is happening here?

I know that without virtual states it would be mathematically impossible for the electron to do that, so I'm not questioning whether they are a hoax or whatever, but I don't get the details.

2. Sep 3, 2010

### alxm

Re: Effing Virtual States -- How do they work?

Well that was a simplified description. You also have selection rules governing the transition probabilities, Raman/Rayleigh/Compton scattering, two-photon emissions, and quite a few other processes.

If you want the simplified rationale usually given when first introducing Raman, this is one case where "time-energy uncertainty" can be applied. The electron can be in a 'virtual' energy state, if only for a very short amount of time.

For a more rigorous description, you need quantum field theory. See e.g. http://quantummechanics.ucsd.edu/ph130a/130_notes/node472.html" [Broken]

Last edited by a moderator: May 4, 2017