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## Main Question or Discussion Point

I'm confused about infrared spectroscopy. Wikipedia states that "when the frequency of the IR is the same as the vibrational frequency of a bond, absorption occurs." However, if I look at some vibrational transitions of HCl for the anharmonic oscillator, I see:

0-->1 [tex]\omega[/tex] = 2885.7

0-->2 [tex]\omega[/tex] = 5771.8

The observed frequency that you would see on the spectrum is clearly different than the vibrational frequency of the bond. My line of thinking is that in vibration state 0, the bond oscillates with a frequency and that in vibration state 1 it oscillates in a higher frequency. So the frequency absorbed corresponds to the frequency that is appropriate to excite from one energy level to the other, instead of a frequency that matches the vibrational frequency of the lower vibrational state such as 0. Can someone tell me in simple terms where my thinking is wrong?

0-->1 [tex]\omega[/tex] = 2885.7

0-->2 [tex]\omega[/tex] = 5771.8

The observed frequency that you would see on the spectrum is clearly different than the vibrational frequency of the bond. My line of thinking is that in vibration state 0, the bond oscillates with a frequency and that in vibration state 1 it oscillates in a higher frequency. So the frequency absorbed corresponds to the frequency that is appropriate to excite from one energy level to the other, instead of a frequency that matches the vibrational frequency of the lower vibrational state such as 0. Can someone tell me in simple terms where my thinking is wrong?