Identical atoms work in different sites capturing oxygen (8)
I believe the answer is:
isotopes
'identical atoms' is the definition.
'isotopes' can be an answer for 'atoms' (isotope is a kind of atom). I am not certain of the 'identical' bit.
'work in different sites capturing oxygen' is the wordplay.
'work' becomes 'op' (operation, work done in an operating theatre).
'in' indicates putting letters inside.
'different' is an anagram indicator (letters placed in a different order).
'capturing' is an insertion indicator.
'oxygen' becomes 'O' (atomic symbol for oxygen).
'sites' is an anagram of 'istes'.
'op' placed within 'istes' is 'istopes'.
'istopes' placed around 'o' is 'ISOTOPES'.
Can you help me to learn more?
(Other definitions for isotopes that I've seen before include "Variant forms of element" , "what may be used for diagnostic purposes" , "Stoops, i.e. to become odd types of atoms" , "atomic elements" , "things that may be radioactive" .)