Dipole Moment ofPH+and the Atomic Masses ofSi28,P31by Comparing Cyclotron Frequencies of Two Ions Simultaneously Trapped in a Penning Trap

Abstract

By trapping pairs of ions in a Penning trap, alternating each ion between large and small cyclotron orbits, we have measured the cyclotron frequency ratios ${}^{12}\mathrm{C}_2\mathrm{H}_4{}^{+}/{}^{28}\mathrm{Si}^{+}$, ${}^{13}\mathrm{C}_2\mathrm{H}_2{}^{+}/{}^{28}\mathrm{Si}^{+}$, ${}^{28}\mathrm{SiH}_3{}^{+}/{}^{31}\mathrm{P}^{+}$, and ${}^{16}\mathrm{O}_2{}^{+}{/}^{31}{\mathrm{PH}}^{+}$, all to $<30\mathrm{ppt}$ precision. The ${}^{16}\mathrm{O}_2{}^{+}{/}^{31}{\mathrm{PH}}^{+}$ data exhibit a bimodal distribution due to the polarizability of the $\Lambda$-doubling components of the ${\mathrm{PH}}^{+}$ ground state, from which we obtain the electric dipole moment of ${}^{31}\mathrm{PH}^{+}$, 0.331(8) $e{a}_0$. Combined with other atomic mass measurements we also obtain improved values for $m({}^{28}\mathrm{Si})$, 27.976 926 535 0(6) u, and $m({}^{31}\mathrm{P})$, 30.973 761 998 9(9) u.