Question

What is a Virtual state?

Short answer

Part a: The virtual state is the term used to describe the intermediate state produced in the Raman process

Part b: A virtual state is an intermediate state sometimes described as imaginary in a multi step process that mediates otherwise forbidden transitions.

Step-by-step solution

Background

In most Raman experiments, the incident radiation is not near( or at) an absorbing wavelength , and so you will never access a real, honest to god excited state ( stationary state). ( If it was close to an absorbing wavelength, we would be talking about a resonance Raman experiment.)

Explanation

Now obviously something is going on between the molecule and the incident light. what you are really doing ia preparing a superposition of real excited states, or stationary states, of your hamiltonian, so its energy is undefined. ( you are free to compute an expectation value though.)

Step:3  Conclusion

The virtual state doesn't last forever, and when it decays, scatters radiation in some direction ( it doesn't matter where, unless you are doing an angle resolved Raman experiment.)