I have a really conceptual question on vibrational partition function for a diatomic molecule.If we consider a diatomic molecule, we write :(adsbygoogle = window.adsbygoogle || []).push({});

Energy of simple harmonic oscillator=[tex]E_{i}=(n + 1/2) h\nu[/tex].We plug this eqn. into

[tex]Z_{vib}=\sum e^{-\beta\epsilon_{i}}[/tex].

Now , my question, is that the energy of harmonic oscillator has been derived for single mass vibrating under harmonic approx., but a diatomic molecule contains "two" atoms or masses.

Somewhere on the Net it was written about considering the center of mass as vibrating...but if the the two masses are vibrating in the normal modes,the center of mass remains constant.

In addition , can anybody tell me why the degrees of freedom for a diatomic molecule for vibration are 2? Shouldn't they be 3?

I have looked in reif and huang for this but I couldn't find anything.Is there good book which explains the vibrational and rotational partition functions for di and polyatomic molecules?

Thanks a lot,

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# Vibrational Partition Function

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