Single-ion cyclotron resonance measurement of M(${\mathrm{CO}}^{+}$)/M(${\mathrm{N}}_2^{+}$)

We have trapped single molecular ions in a precision Penning trap and, using cyclotron resonance techniques, have measured the mass ratio M(${\mathrm{CO}}^{+}$)/M(${\mathrm{N}}_2^{+}$) to be 0.999 598 8876(4). Accuracy is limited at 4×${10}^{\mathrm{-}10}$ predominantly by temporal instability in the magnetic field. All other systematic sources of error are ΔM/M≲${10}^{\mathrm{-}10}$. .AE