[seqfan] Re: Chemistry sequence

[Richard Mathar]

http://list.seqfan.eu/pipermail/seqfan/2009-August/002237.html

dw> How many molecules have total atomic number n?
dw> 
dw> There are clearly issues with this question, such as counting 
dw> low-temperature helium compounds. Another problem arises from trying to 
dw> count, say, all the molecular configurations that could be formed from, 
dw> say, 10 carbon atoms. Still, I wonder how far we could go with any 
dw> degree of confidence.

To answer such a question, one would be forced to fix a definition:

What is a molecule?
Does this refer to some sort of stability of the compound at some temperature?

Do we count all different ionized forms individually?

It there a cut with respect to the semi-stable isotopes/isotopomers that may be
employed (see in particular A007656 on which follow-up issues arise)?
Would for example matter-antimatter states (nowadays created in collider
experiments at least in the form of anti-Hydrogen) already qualify as
individual candidates? Is TNT stable? Is the proton stable? would Tritium
be admitted or Deuterium? More generally, do we count baryonic excited states
(or, beware, those with quarks not just of the up-down variety) of the
nucleus(i)?

Is a solid with cracks in it also a "large" molecule if it has a finite edge
length? (That is: where is the transition from a gaseous molecule to the
liquid?) Is a cluster of 11 Gold atoms or are these Buckminsterfullerens
molecules? Do we count them differently if they form a cage around some
big other atom or ion?

Is the DNA a molecule and how many cloned versions of these may exist in real
(and future) life forms on this planet, laboratory glass tubes and elsewhere,
in the frozen ice on Mars?

Richard