Excited-Ion Lifetimes Using Penning-Ionizing Collisions

Abstract

We show that in the Penning-ionizing collision $\mathrm{He}\left(2^3{S}_1\right)+X\to \mathrm{He}\left(1^1{S}_0\right)+{\left(X^{+}\right)}^{*}+e$ the precession of the ${\mathrm{He}}^m$ spin at its Larmor frequency forces the $J$ polarization of the Penning ion to rotate at the same frequency but shifted in phase. The tangent of the phase shift is proportional to the lifetime of the ionic state and presents a unique method for measuring excited-ion lifetimes.