Sentence:  Some 80 reaction tubes from 13 manifold fillings were illuminated in the temperature range from 40 to 85 ` in a further endeavor to determine the cause of the irreproducibility and to obtain information on the <WSD>activation</WSD> energy and the effect of light intensity . 
Meaning of the word marked with <WSD> tags:  the energy that an atomic system must acquire before a process (such as an emission or reaction) can occur