Question

hello,

I didn't understant a passage of this text, from Optics Hecht, in the second sentence , it says the molecules haven't resonance in the visible so they can't absorb quanta and in the third sentence , the molecules can absorb an incoming photon. I'm confused . Thanks a lot !

,, " Now, suppose we mix a wisp of air into the void—some molecules of nitrogen, oxygen, and so forth. These molecules have no resonances in the visible, no one of them can be raised into an excited state by absorbing a quantum of light, and the gas is therefore transparent. Instead, each molecule behaves as a little oscillator whose electron cloud can be driven into a ground-state vibration by an incoming photon. Immediately upon being set vibrating, the molecule initiates the re-emission of light ",,

Answer 1