It's been well-known that the potential of staggered ethane is 2.9kcal/mol lower than that of eclipsed ethane. It should be straightforward to calculate this with Gaussian. The eclipsed ethane is not possible to isolate to perform physical measurements, how to measure this with experiments?
It's fine. Everyone know this, but few people know how to get this.
Dear Xiaoquan,
That is really a difficult question! It is connected with the measurements on the separate molecules themselves and belongs to the Nanotechnology area...
I would suggest that you have a detailed look at this writing - it is freely available in Internet:
Physical Methods in Chemistry and Nano Science by Andrew R. Barron, Published 2012:
https://archive.org/download/ost-chemistry-col10699/col10699.djvu
Besides, there is a freely available in Internet copy of the pertinent PhD thesis on the topic:
CONTROLLING MOLECULAR ASSEMBLIES
A Thesis in Chemistry by Arrelaine A. Dameron (2006)
https://etda.libraries.psu.edu/paper/6894/2162
... I hope all this could be helpful in perfectly answering your question ...
Respectfully yours,
Evgeni
Directly, I'm not sure if that is particularly possible. The transition for internal rotation of ethane lacks good optical activity.
Your best bet would be high powered, high resolution, low temperature laser Raman spectroscopy. It would require you to deconvolute a rather large amount of information from the combination and difference overtones of the Raman spectrum which overlap with and exist in combination with the desired torsional (internal rotational) energies. It would then be a matter of theoretically relating the torsional energies to the rotational barrier to obtain a derived energy measurement. Such a proposition seems quite difficult but I don't know if it is impossible.
Check out some of the references mentioned in this article for a better idea of the relationship between Raman / IR measurements and internal rotation in ethane gas.
http://digital.csic.es/bitstream/10261/8922/1/JCP118-2657.pdf
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