I am told that carbon dioxide is IR inactive.
This somehow strikes me as untrue or at best oversimplified, because yes, it is overall symmetrical, but can't CO2CO2 be induced to show asymmetric stretching patterns?
So this leads me to the question: in a simplified presentation of IR, why might someone present symmetrical, non-polar molecules as IR "inactive"? Could we be relying on a simpler definition of IR inactive?