[Doctor Stochastic]

One could take the carbon monoxide down to (absolute) zero in a magnetic field. Then the entropy should be Sqrt(2) smaller than that of field free frozen CO. Melting of the crystals could be used to measure this difference.

[Right Wing Professor]

Last time I checked, nobody had figured out how to make CO order. I don't think a magnetic field would work; I doubt the diamagnetic suceptibility anisotropy is large enough, and the barrier to rotation is too large.

The molecule I really like, though, it CH₂D₂. Even though the only departure from tetrahedral symmetry is isotopic, the molecules align at about 1 K. In this case, tunneling through the rotational barrier is fast enough to allow the disorder to anneal out.