# Isotope pairs in different states at room temperature?

Does any pair of isotopes exist which are in different states at room temperature—either in isolation or as part of an otherwise-identical compound?

• Please Elaborate. – A.K. Sep 28 '16 at 2:19
• I'll try ... two isotopes of some element that exist in different states of matter from each other at room temperature--all other variables being equal as well? – Richard Simões Sep 28 '16 at 2:27
• Typically no, but processes such as the Gridler-Sulfide or COLEX process can greatly enrich an isotope. – A.K. Sep 28 '16 at 2:41
• Ordinary water and heavy water differ in boiling point by $1.4^\circ\,\rm C$. Guess $\ce{HF}$ and $\ce{DF}$ might be the very example you are after (not that it would be of any use for anything, though). – Ivan Neretin Sep 28 '16 at 5:50
• @Ivan Neretin Would $HF$ and $DF$ have different state? I am sorry I cant find any data about b.p. or m.p. of $DF$. – Mockingbird May 5 '17 at 5:24

At very low temperatures (below $1~\mathrm{K}$) liquefied helium will separate into a superfluidic helium-4 phase and a normal liquid phase containing mostly helium-3. The superfluid and the normal liquid can be considered different phases and are immiscible.