Question

Well, reading about "Raman Effect" I saw that when the electron absorb some energy, with frequency $\omega_{abs}$, that is different from $\omega_{n} - \omega_{n-1} \neq \omega_{abs1}$ , it go to an "virtual energy level" that is unstable, but nevertheless we could measure its lifetime. And more, the electron could stay in this unstable level enough time to absorb another electron with frequency $\omega_{abs2}$, such that $\omega_{n} - \omega_{n-1} = \omega_{abs1} + \omega_{abs2}$ , and than finally go to an stable energy level, that is foreseen by the Quantum Mechanics.

My question is: Is this right? An electron could stay a little time in a unstable energy level?

Answer 1

All excited energy levels are unstable to this or that extent. So, yes, it can. If below a given energy level $E_n$there are many lower possible levels $E_{n'} < E_n$, there are usually several channels of transition, each with its own probability and energy difference so we can observe emission of different frequencies.

On the other hand, absorbing two different photons, although possible in an intensive EM wave, normally happens rarely. I think it is one-photon absorption (excitation) and many-photon deactivation of atoms and molecules that normally happen (cascade decay).

If you mean existence of unstable energy levels between two neighboring levels, then no, they do not exist.

EDIT: I remember deriving the atom ionization probability by an intensive EMW of low frequency, following the work by Keldysh. Atom can be excited and even ionized with a strong constant or low-frequency EMF and it is a simultaneous multi-photon process, when a single $\hbar \omega$ is smaller than the energy $E_n - E_{n'}$ required for a given transition.