20866
In order to investigate outer valence ionic states of open - shell metallocenes , we have applied two - dimensional collision - energy / electron - energy - resolved Penning ionization electron spectroscopy ( 2D - PIES ) upon collision with metastable He * ( 2 ( 3 ) S ) excited atoms as well as a high level ab initio molecular orbital calculation ( the partial third - order quasiparticle theory of the electron propagator ( P3 ) ) to ionization from neutral ground states of vanadocene ( ( 4 ) A2g ) and nickelocene ( ( 3 ) A2g ) .
 Chemical: metallocenes; Chemical: He; Chemical: vanadocene; Chemical: nickelocene
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: metallocenes; Chemical: He; Chemical: vanadocene; Chemical: nickelocene