( ( ( ( Stratospheric O ) ( 3 Ozone ) ) ( -LRB- ( ( O 3 ) -RRB- ) ) ) ( ( is ( ( ( produced ( by ( reactions ( between ( ( ( molecular oxygen ) and ) ( atomic oxygen ) ) ) ) ) ) , ) ( in ( ( the presence ) ( of ( another ( molecule ( to ( serve ( as ( a catalyst ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NP (NNP Stratospheric) (NNP O)) (NP (CD 3) (NN Ozone))) (PRN (-LRB- -LRB-) (NP (NNP O) (CD 3)) (-RRB- -RRB-))) (VP (VBZ is) (VP (VBN produced) (PP (IN by) (NP (NP (NNS reactions)) (PP (IN between) (NP (NP (JJ molecular) (NN oxygen)) (CC and) (NP (JJ atomic) (NN oxygen)))))) (, ,) (PP (IN in) (NP (NP (DT the) (NN presence)) (PP (IN of) (NP (DT another) (NN molecule) (S (VP (TO to) (VP (VB serve) (PP (IN as) (NP (DT a) (NN catalyst)))))))))))) (. .)))
Stratospheric O 3 Ozone (O 3 ) is produced by reactions between molecular oxygen and atomic oxygen, in the presence of another molecule to serve as a catalyst.
(ROOT (S (ADVP (RB Replace)) (NP (NP (DT another)) (PP (IN in) (NP (DT a) (NN molecule)))) (VP (VBZ happens) (PP (TO to) (NP (NNS atoms))) (PP (IN during) (NP (DT a) (NN substitution) (NN reaction)))) (. .)))
Replace another in a molecule happens to atoms during a substitution reaction.