# I Solid diprotium saturated vapour density

1. May 29, 2018

### snorkack

What precisely is the equilibrium vapour density of bulk solid diprotium surface now, at 2,7 K?

The density of the world falls with some power of temperature (which one?). The density of saturated vapour falls exponentially.
At which temperature shall the world saturate with respect to bulk solid diprotium?

2. May 30, 2018

### BvU

What has your research brought you so far ? Any reason you don't like hydrogen and focus on the isotope that's overwhelmingly dominant anyway ?
http://www.tvu.com/PEngPropsSH2Web.htm
https://www1.eere.energy.gov/hydrogenandfuelcells/tech_validation/pdfs/fcm01r0.pdf
https://en.wikipedia.org/wiki/Solid_hydrogen
https://nvlpubs.nist.gov/nistpubs/jres/47/jresv47n2p63_a1b.pdf

Can you give some more context ? What are you trying to find ? What, for example is the reason you want it 'precisely' (without giving a definition) ? In an age of global warming it might be good enough to use approximate values from physical property approximation expressions and equations of state ?

Anyway, why look at solid hydrogen when first the oceans freeze, then O2 and N2 condense etc etc ?
The temperature of the earth, of course
But if the 'which' refers to the power, then I'd start with 1 (see iron/nickel or rock)

Last edited: May 30, 2018
3. May 30, 2018

### snorkack

Tables tend to break off at temperatures far above 2,7 K.
That one was useful.
For 2,7 K, I get log P at about -13.
Hydrogen and helium are as yet gases, even in molecular clouds.
How does that present equilibrium vapour pressure, of 10-13 mm Hg, compare with pressure in molecular clouds?

4. May 30, 2018

### BvU

Dunno, but outer space is different from 'the world' . With a few H atoms per m3 there's no chance of solid formation.

wouldn't trust those numbers: with those values in the Antoine eqn I can't even reproduce the pressures they mention ! and 2.7 K is extrapolating way out...

Those guys have funny 'standard units' P/kB of 104 to 107 cm-3 K, it seems (nice exercise: convert to mm Hg -- I get 10-15 to 10-12 , so perhaps a case of oops! -- but I may well be mistaken. It's past bedtime here )

But then again, when you google 'interstellar ice' or 'volatiles' ...

Let me know if and how you find inroads for this diprotonium ice !

Last edited: May 31, 2018
5. May 31, 2018

### snorkack

Sure, but I could not find actual measurements for 2,7 K.
Do you expect that the pressure would be subject to some sort of Antoine equation?

6. May 31, 2018

### BvU

Here's another (table 6) with eqn $A + B/T + B'\ln T$
Perhaps you can sort out he references mentioned here (section 2.2.30) ; data are on P 6-288

7. Dec 1, 2018

### snorkack

Page 17. For eH2, it gives A as 2,5 (for Torr), B as -85,3, B' as 2,9.
For 2,7 K, that would mean B/T=-31,6, ln T=1, B´/ln T=2,9
then ln Q=2,5-31,6+2,9=5,4-31,6=-26,2
log Q=ln Q/2,303=-11,5

Thus, two sources give P as 10-13 and 10-11,5 mm Hg respectively. Appreciable divergence, but not unreasonably big seeing how these are extrapolated out of the measurable range. Same ballpark.
How do these numbers - 10-13...10-11 mm Hg - compare to the present pressures in molecular clouds?