( ( Single ( electron atom-ion ) ) ( collisions . ) )
(ROOT (S (NP (JJ Single) (NN electron) (NN atom-ion)) (VP (VBZ collisions)) (. .)))
Single electron atom-ion collisions .
(ROOT (S (NP (JJ Monatomic) (NNS ions)) (VP (VBP form) (SBAR (WHADVP (WRB when)) (S (NP (DT a) (JJ single) (NN atom)) (VP (VBZ gains) (CC or) (VBZ loses) (NP (NNS electrons)))))) (. .)))