
^{12}O (1980AJ01)(See the Isobar Diagram for ^{12}O) ^{12}O has been observed in the ^{16}O(α, ^{8}He) reaction at E_{α} = 117.4 MeV. At θ_{lab} = 8°, the differential cross section (lab) = 2 ± 1 nb/sr: Q_{0} = 66.02 ± 0.12 MeV. The width of the ground state is ≈ 400 ± 250 keV. There is some indication of an excited state of ^{12}O at E_{x} = 1.0 ± 0.1 MeV, which would imply an appreciable downward shift from the position of the analog first excited state in ^{12}Be. This would be surprising if the latter is indeed a 2^{+} state (1978KE06), as it appears to be: see ^{12}Be. Q_{0} leads to a mass excess of 32.10 ± 0.12 MeV for ^{12}O: it is thus unstable to decay into ^{10}C + 2p by 1.83 MeV and into ^{11}N* + p by 0.41 [note that ^{11}N* is probably not the ground state of ^{11}N and that it is very broad: see ^{11}N]. The diproton branching ratio of ^{12}O_{g.s.} is estimated to be 60 ± 30%. The dcoefficient in the IMME for A = 12 is calculated to be 0 ± 11 keV. Based on this the first T = 2 state in ^{12}N should occur at E_{x} = 12.29 ± 0.02 MeV (1978KE06). See also (1979NA1E), (1975AJ02, 1977CE05, 1978GU10) and (1975BE31, 1975HU14, 1976IR1B; theor.).
