( ( When ( ( F 2 ) ( collides ( with silicon ) ) ) ) ( , ( ( one ( F atom ) ) ( ( can ( chemisorb ( while ( ( the other ) ( is ( ejected ( into ( the ( gas phase ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NN F) (CD 2)) (VP (VBZ collides) (PP (IN with) (NP (NN silicon)))))) (, ,) (NP (CD one) (NN F) (NN atom)) (VP (MD can) (VP (VB chemisorb) (SBAR (IN while) (S (NP (DT the) (JJ other)) (VP (VBZ is) (VP (VBN ejected) (PP (IN into) (NP (DT the) (NN gas) (NN phase))))))))) (. .)))
When F 2 collides with silicon, one F atom can chemisorb while the other is ejected into the gas phase.
(ROOT (S (PP (IN Within) (NP (DT a) (NN substance))) (, ,) (NP (NP (NNS atoms)) (SBAR (WHNP (WDT that)) (S (VP (VP (VBP collide) (ADVP (RB frequently))) (CC and) (VP (VBP move) (ADVP (RB independently)) (PP (IN of) (NP (CD one) (DT another)))))))) (VP (VBP are) (ADJP (ADJP (RBS most) (JJ likely)) (PP (IN in) (NP (DT a) (NN gas)))))))