24692
Molecular dynamics calculations on the ultraviolet photodissociation of different kinds of CO - H2O ice systems have been performed at 10 K in order to demonstrate that the reaction between CO and an OH molecule resulting from H2O photodissociation through the first excited state is a possible route to form CO2 ice .
 CO, H2O, CO, OH, H2O, CO2
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 CO, H2O, CO, OH, H2O, CO2