( ( ( The ( orbit ( and ( energy levels ) ) ) ) ( of ( the ( two particles ) ) ) ) ( ( are ( similar ( to ( that ( of ( ( the ( hydrogen atom ) ) ( -LRB- ( ( ( electron and ) proton ) -RRB- ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN orbit) (CC and) (NN energy) (NNS levels)) (PP (IN of) (NP (DT the) (CD two) (NNS particles)))) (VP (VBP are) (ADJP (JJ similar) (PP (TO to) (NP (NP (DT that)) (PP (IN of) (NP (NP (DT the) (NN hydrogen) (NN atom)) (PRN (-LRB- -LRB-) (NP (NN electron) (CC and) (NNS proton)) (-RRB- -RRB-)))))))) (. .)))
The orbit and energy levels of the two particles are similar to that of the hydrogen atom (electron and proton).
(ROOT (S (NP (DT The) (NN spectrum)) (VP (VBZ is) (VP (VBN made) (PRT (RP up)) (PP (IN of) (NP (NP (JJ discrete) (NNS lines)) (VP (VBG representing) (NP (NP (NNS transitions)) (PP (IN of) (NP (NP (DT the) (NN hydrogen) (NN electron)) (PP (IN between) (NP (JJ specific) (NN energy) (NNS levels)))))) (PP (IN within) (NP (DT the) (NN atom)))))))) (. .)))