Electric Field Quenching of Metastable2S01Helium

We have measured the transition rate of the normally metastable helium $2{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ state in the presence of a uniform electric field by observing the attenuation of a metastable beam of helium passing between parallel electric field plates. This attenuation, when combined with our measurement of the velocity distribution of the beam, yields a transition rate of $(0.926\mathrm{}\pm 0.020)F^2$ ${\sec }^{-1\mathrm{}}$, where $F$ is the field strength in kV/cm. This agrees well with our calculated value of $(0.920\mathrm{}\pm 0.030)F^2$ ${\sec }^{-1\mathrm{}}$ which is derived from a sum of oscillator strengths published by various workers.