21686
Here we use vibrational sum frequency spectroscopy ( SF ) to study the origin of the opposite Delta V signs of Langmuir films of CH3 ( CH2 ) 20COCH2CH3 ( ethyl ether , EE ) and CH3 ( CH2 ) 20COCH2CF3 ( fluorinated ethyl ether , FEE ) .
 Chemical: CH3 ( CH2 ) 20COCH2CH3; Chemical: ethyl ether; Chemical: CH3 ( CH2 ) 20COCH2CF3; Chemical: fluorinated ethyl ether; Chemical: FEE
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: CH3 ( CH2 ) 20COCH2CH3; Chemical: ethyl ether; Chemical: CH3 ( CH2 ) 20COCH2CF3; Chemical: fluorinated ethyl ether; Chemical: FEE