[seqfan] Re: Chemistry sequence

[David Wilson]

----- Original Message ----- 
From: "Richard Mathar" <mathar at strw.leidenuniv.nl>
To: <seqfan at seqfan.eu>
Sent: Saturday, August 29, 2009 10:08 AM
Subject: [seqfan] Re: Chemistry sequence


>
> http://list.seqfan.eu/pipermail/seqfan/2009-August/002255.html asks
> in addition
>
> dw> I doubt we'll run into these problems for molecules of, say, 10 
> protons or
> dw> fewer.
> dw> I guess I'm curious as to what the problems are at the small-molecule 
> end.
>
>
> The remaining problem is to decide for each partition
> of the total number of protons (say for the 42 possibilities at n=10
> if A000041 is correct), whether a stable molecule with that composition 
> exists:

And there may be isomers, with the same partition of elements accounting for 
more than one molecule.

> n=1: H stable
> n=2: H_2 stable, He stable
> n=3: H_3 (unstable I guess), HeH (?), Li stable
> n=4: H_4 (?), HeH_2 (?), He_2 probably unstable, LiH (likely stable, but 
> don't touch) Be stable
> n=5: H_5 (unstable I guess), HeH_3 (unstable I guess), He_2H probably 
> unstable,
>     LiH_2 (probably unstable) HeBe (probably unstable), BeH (?), B stable
> ....

Yes, it gets interesting. A chemist might be able to help us.

> As long as the number of protons stays low such that the various bending
> structures of carbon rings are not to be decided, this is as close at
> it gets to mathematics as I can imagine. So the sequence that is defined
> above starts as a(1)=1 (the math-oriented people would add a(0)=1, which 
> is
> the vacuum or what they call the empty set), a(2)=2, a(3)>=1, likely 
> a(3)=2.
>
> I am not sure whether the question of stability is an easy one. Marginally
> stable molecules may exist isolated in the ultra-high vacuum in
> the insterstellar medium, but would not be detectable in any laboratory
> because they would immediately collide (=interact and decompose) with the
> surrounding vessel. But if you ask in the associated chemistry related
> news groups (seqfan is not a suitable forum for that), you may find 
> answers to
> those questions.
>
> For the H_3 case see for example the article
> "H_3^{2+} molecular ions can exist in strong magnetic field",
> JETP Lett, vol 69 (11) (1999), p 800-805
> which claims that with magnetic fields larger than 10^11 Gauss
> this can be stabilized. Does this qualify to count H_3 ?
> The article on the Ag-clusters in JCP 118 (2003) 9241 clearly indicates
> that H_3 is unstable with respect to the standard dissociation into the 
> dimer and
> atom.
>
> For HeH see for example Phys Rev Lett 43 (1979) 1719 which
> discusses the infrared spectrum of the singly charged molecule, or the 
> earlier
> article in JCP 23 (1955) 1169. Since the dissociation energy is around 1 
> eV, this
> ionized form is stable under standard conditions.
>
> Richard

The whole idea may be a chimera. It seems like there are two many conditions
(temperature, pressure, magnetic field, etc) that affect the stability of 
molecules,
it would be difficult not to be arbitrary about such conditions.


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