Final answer:
Metastable states have longer lifetimes and decay through fluorescence or phosphorescence, while virtual intermediate states are short-lived and serve as transitional states in quantum mechanics.
Step-by-step explanation:
Metastable and virtual intermediate states are both states of atoms or molecules that have higher energies than the ground state but are not stable in the long term. The main difference between metastable and virtual intermediate states lies in their lifetimes and the mechanisms through which they decay.
Metastable states have lifetimes that are orders of magnitude longer than the most short-lived states. They can be excited by a suitable energy input and when they decay, they emit light, a process known as fluorescence or phosphorescence.
Virtual intermediate states, on the other hand, are short-lived states that exist only as transitions between other states. They are not directly observed and do not have a significant lifetime. They are useful in explaining certain phenomena in quantum mechanics, such as in the mathematical formulation of scattering processes.