18244
These are identified as the [ 20 . 2 ] a 1 <-- X ( 1 ) Sigma ( + ) , the [ 23 . 1 ] A ( 1 ) Sigma ( + ) <-- X ( 1 ) Sigma ( + ) , and the [ 24 . 7 ] B ( 1 ) Pi <-- X ( 1 ) Sigma ( + ) systems , although only the first two have been rotationally resolved .
 None
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None