Yes, I agree, but ... > Probably not that long, uranocene (a comparatively heavy molecule of similar structure) apparently has an appreciable vapor pressure of

Yes, I agree, but ... > Probably not that long, uranocene (a comparatively heavy molecule of similar structure) apparently has an appreciable vapor pressure of 10^-3 torr or so at 200C. 200°C(392°F) is hotter than boiling cooking oil (it's a hot oven to cook, but far from red hot) vapor pressure of water at 0°C(32°F) is 5 torr i.e. almost frozen water has 5000x the vapor pressure of very hot uranocele. Let's replace "forever" with "extremely slowly". > Weight does matter of course, but intermolecular bonding/affinity is generally the more important consideration. I agree, so I choose a non-polar material to compare. (i.e. petrol instead of water). Probably petrol and parafin are very saturated and linear, and both change the properties of the molecules a lot. I'd better have choose something with more double bounds, but I don't have a very good example at hand.