Electron impact excitation of the O I lambda 1172.6 A multiplet

The cross section for the dissociative excitation of the O I 1172.6 A multiplet is measured by the bombardment of O2 by 100 eV electrons. A cross section value of about 1.56 x 10 to the -22nd sq cm + or - 30 percent and an O I 1173 A/O I 989 A branching ratio of about 0.00013 + or - 35 percent are obtained. The branching ratio values are compared to the data of Morrison (1985) and Garstang (1961). The data reveal that the 1173 A branch from the O I (3s prime 3D0) state is not large enough to account for the discrepancy between the predicted and observed O I 989 A intensity in the earth's upper atmosphere.