I was thinking about stuff like beryllium sulphide, which should be
extremely plentiful in the universe, but which I couldn't find on
google. At least, that's my guess: it can be made in an autoclave, but
I couldn't find a record of a temperature at which it broke-down. That
set me to wondering wether there are compounds that should be very
common, but aren't out there. Proof of extraterrestrials?

Probably a rather complex subject to which I am sure modern day
astronomy has no definive answer.

A good book on this subject (although a little outdated) is 
Ken Croswell's The Alchemy of the Heavens (Doubleday/Anchor, 1995)
(See http://www.ccnet.com/~galaxy)
 
Only the cooler (spectral types M,N,R and S) stars will harbour
chemical compounds. The detection of these compounds would depend on a
number of factors such as:
- Are there individual elements present in the first place to create the compound?
- What is the stability of the compounds?
- Is the compound located in the atmosphere of the star at a point 
   where its spectra can be detected from Earth?
- Does the compound have a strong enough spectral signature that it will 
  be detected and distinguished from other stronger spectra?    
DPRK007

Thanks very much dprk007-ga:

It's nice when there's a comment on something technical.

Hmmm. Well first, *why* ought certain compounds be present? You only
specified one, beryllium sulphide. What are the others? Why would you
expect compounds to exist stably in the hot atmospheres of stars? Why
would their absence be evidence of extraterrestrials in particular?
Why wouldn't it just mean that we on Earth don't understand enough
about nature to know why such materials are scarce?

scotttygett-ga 

You are very welcome!
DPRK007

I heard that they found aromatic hydrocarbons in the outer regions of
the milky way, i couldnt find an article on that but i did find this
which has stuff to do with extraterrestrials and compounds found in
space
http://www.newscientistspace.com/article.ns?id=dn7754
actually this might have been it
http://www.newscientist.com/article.ns?id=dn4552
or this
http://www.newscientist.com/article.ns?id=dn2703
but they're all pretty interesting.
I never actually understood the whole chemical formation thing in
cosmology, i vaguely understood the idea of different atomic
abundancies after the big bang, ie why there was more hydrogen than
helium, and more lithium than helium or less i cant remember, but
chemical formation was a big mystery to me.  I think it is to a lot of
real scientists too though which makes me feel better!

The two main factors affecting it, I?d imagine, are the abundance of
the atomic components of the molecule and the highest temperature it
can withstand.  Beryllium is high up on the periodic table (atomic
weight of 9) and sulphur is on the second row (32).  I don?t know but
would sulphur atoms form at the same point in a stars life as
beryllium?  That would affect their abundances in the locality of the
star, as they'd be in different regions of the star system, or
possibly ejected from it at different times.  Could they hang around
in star birthing clouds long enough to react?  If hydrocarbons can
hang around the edges for ages then maybe, I don?t know.
The abundance of hydrocarbons would defiantly give some idea to the
abundance of life, especially as water is already known to be such a
common compound in the universe.
Intelligent life though, the only way abundances being affected by
specifically intelligent life would be harvesting for some reason (I
reckon), but surely if they could harvest on a scale that was
noticeable to us we'd have seen such a massive force of aliens, and
probably been enslaved by them, beaten with whips and made to mine for
gold or something out of that crap battlefield earth series of books,
wouldn't we?

I did come across a URL a few days back that said that gamma radiation
was supposed to dissociate beryllium sulfide. That alone would be the
sort of thing that I think would prompt the "A Beautiful Mind" guy to
calculate the probability of God's existence once again. I wasn't
looking for it, and there it was.

It remains an interesting chemical phenomenon, that certain compounds
that can stand very high heat yet cannot stand gamma radiation. It
makes one wonder if it should play a role in ceramics fabrication or
evaluation.

I also don't know if star sprectra tend to have a lot of gamma
radiation past their photospheres, which are hot enough to re-compound
beryllium sulfide. It may still be an interesting hypotheis.