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Simple Harmonic Oscillator model for diatomic molecules

Hi i need some help in understanding this question...

"A real diatomic molecule does not behave exactly like a simple harmonic oscillator. The SHO model becomes progressively worse as the vibrational energy is increased.
WHY?"
Original post by franniexo
Hi i need some help in understanding this question...

"A real diatomic molecule does not behave exactly like a simple harmonic oscillator. The SHO model becomes progressively worse as the vibrational energy is increased.
WHY?"





The model closest to what actually is the case is the anharmonic oscillator (in blue)
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franniexo
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Original post by Kamara7


The model closest to what actually is the case is the anharmonic oscillator (in blue)


I understand that bit:h:, but for the Simple H. model the graph doesn't plateau out, what does that mean about the bonds of the vibrating molecule? :/
Original post by franniexo
I understand that bit:h:, but for the Simple H. model the graph doesn't plateau out, what does that mean about the bonds of the vibrating molecule? :/


The simple harmonic model doesn't plateau out, absolutely right.
The plateau you see for an actual diatomic potential energy corresponds to the fact that the bond breaks if it gains too much energy.

In the harmonic model, as you stretch the bond the restoring force gets bigger and bigger, so if a bond were really harmonic you could never actually break it!
Original post by franniexo
I understand that bit:h:, but for the Simple H. model the graph doesn't plateau out, what does that mean about the bonds of the vibrating molecule? :/


The fact that the SHO doesn't plateau out is why it isn't a good model: in reality as the particles get a significant distance apart from each other, the bond breaks, as shown by the other model, but the SHO doesn't really show that very well, which is why is only approximately valid when the bond length is near the equilibrium point (near the rest position). That's my understanding of it at least :smile:
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franniexo
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Thanks guys! :smile:
Original post by franniexo
Thanks guys! :smile:


No problem! :wink:

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