A high-velocity recoil-in-vacuum determination of the g-factor and lifetime of the 1.97 MeV 2⁺ level in ¹⁸O

Using a recoil-distance technique, the g-factor of the short-lived 1.98 MeV 2⁺ level in ¹⁸O has been deduced from the time-differential hyperfine perturbation of the nuclear alignment following the reaction H(¹⁸O,p)¹⁸O* on recoil into vacuum at high velocity. From the observed hyperfine frequency, due to the 1²S_1/2 field in one-electron ions, the value deduced was mod g mod =0.287+or-0.015. A simultaneous time-of-flight determination of the lifetime of the state gave a value for tau _m of 2.99+or-0.12 ps. Interpretation of the present data, combined with the results of earlier experiments of a similar kind, leads to the conclusion that hydrogen-like oxygen ions are formed predominantly in low-lying states, at velocities close to the maximum in the yield of one-electron ions.