Stability of the ground state vinylidene anion H2CC-

A technique to measure very low collisionless decay rates of ionic species has been applied at a new electrostatic storage ring to obtain the rate for spontaneous rearrangement of the vinylidene anion to neutral acetylene. The measurement yields a rate of k(0) = (0.009+/-0.006) s(-1), corresponding to a natural lifetime of the vinylidene anion of tau(0) approximately 110 s.