One of the electrodes includes {HEAD ~ openings} for allowing {TAIL ~ the vapor} to enter the space 
for allowing
One of the electrodes includes { HEAD ~ openings } for allowing { TAIL ~ the vapor } to enter the space
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH