Neutrality of Molecules by a New Method

We report a new experimental technique for testing the electrical neutrality of molecules. An alternating electric field applied to an acoustic cavity containing S${\mathrm{F}}_6$ gas will generate sound at the electric field frequency if the gas has a charge. With a suitably calibrated microphone in the cavity the sound pressure can be measured yielding an upper limit for the charge per molecule $\epsilon$. Dividing by the mass number of the molecule (146) yields an upper limit for an electron-proton charge difference. (This last result assumes that the electron-proton charge difference equals the neutron charge.) The results: $\left|\epsilon \right|\le 2\times {10}^{-19\mathrm{}}e$ and $\frac{\left|\epsilon \right|}{M}\le 1\times {10}^{-21\mathrm{}}e$, where $e$ is the magnitude of the electronic charge, are consistent with the fundamental belief of zero charge imbalance. The measurement is less affected by the presence of ions than other macroscopic neutrality measurements and has an estimated maximum sensitivity of $\left|\epsilon \right|\le {10}^{-22\mathrm{}}e$.