What are vibrational levels and energy states?

I know that UV-Vis spectroscopy is based on the principle of electrons jumping to higher energy states but I just read that each energy state has a number of "vibrational energy levels" inside it. Heres a diagram:
photlum1.gif

I'm confused now, what is a vibrational energy level and what is an energy state? The ground state is the state that all electrons are in before excitation and according to that diagram, the ground state has around 20 vibrational energy levels in it. Why would electrons in the ground state molecule be in any of those higher vibrational energy levels, as opposed to being in the lowest vibrational energy level?
 

DrClaude

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The black lines are vibrational energy levels and the different electronic states are represented as the three "columns."

At room temperature, the probability of finding a molecule in an excited vibrational state is generally very close to zero, which is why step one is seen as only taking place from the ground vibrational state of the ground electronic state. I would however quibble about the fact that arrows 2 and 3 only points towards the ground vibrational state. In reality, most of the time de-excitation by photon emission will result in the molecule being in an excited vibrational level.
 

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