The CSE and AMA style manuals, which of course don't apply to ACS publications, are more definitive on this question: both recommend using the nonpossessive forms in most cases. That said, until the ACS meets your demand, I suggest that you do a quick Google Scholar search to determine which version of any particular term is used most commonly in the literature, and then use that version consistently in whatever document you're preparing. You can prepare you own personal style sheet listing these kinds of things, so you don't have to look them up repeatedly.
Thanks for your information about the CSE and AMA, Carlotta. A good idea as well.
And what you said about the other two manuals of style convinces me even more that ACS, as the leading society in chemistry, should follow the same path.
Or perhaps, ACS is waiting for an IUPAC recommendation, I don't know. This has to be sorted out.