18029
Examples of sigma - bonds made of a single electron delocalized over two neighboring atoms were until recently found only in gas - phase cations such as H2 ( + ) and Li2 ( + ) and in highly unstable species generated in solid matrices .
 Chemical: H2 ( + ); Chemical: Li2 ( + )
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: H2 ( + ); Chemical: Li2 ( + )