[seqfan] Re: Chemistry sequence

Jonathan Post jvospost3 at gmail.com
Sat Aug 29 18:42:27 CEST 2009

I have a draft paper written to explore what molecular weights are NOT
found in the human Metabolome.

There is a Human Metabolome Data Base online, and I searched it
carefully by molecular weight, sorted, anayzed, cited, and otherwise
massaged the data.

Hence the type of question addressed in this hypothetical sequence is
quite interesting to me. But slippery and definitionally tricky.  I'd
authored at least one Chemistry seq before, which commented on some
caveats, including that there are different isotopic ratios on
different planets.

Cf. A121291, A121818

On Sat, Aug 29, 2009 at 7:57 AM, David Wilson<davidwwilson at comcast.net> wrote:
> ----- 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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