of the six optical transitions expected between the three upper states at 4 to 4.5 electron volts and the two lowest states , five have been observed in the afterglow of a conventional helium-oxygen microwave discharge in both 16o ( 2 ) and ( 18 ) o ( 2 ) , three of them for the first time in gas-phase spectra .
C1875235
helium-oxygen
C0030054
o ( 2