( Ozone ( ( is ( produced ( by ( ( the photolysis ) ( of ( ( molecular oxygen ) ( followed ( by ( reaction ( of ( ( the ( resulting ( oxygen atom ) ) ) ( with ( another ( oxygen molecule ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NN Ozone)) (VP (VBZ is) (VP (VBN produced) (PP (IN by) (NP (NP (DT the) (NNS photolysis)) (PP (IN of) (NP (NP (JJ molecular) (NN oxygen)) (VP (VBN followed) (PP (IN by) (NP (NP (NN reaction)) (PP (IN of) (NP (NP (DT the) (VBG resulting) (NN oxygen) (NN atom)) (PP (IN with) (NP (DT another) (NN oxygen) (NN molecule)))))))))))))) (. .)))
Ozone is produced by the photolysis of molecular oxygen followed by reaction of the resulting oxygen atom with another oxygen molecule.
(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.