Observation of a Large Electric Dipole Moment Produced in Electron-Transfer Collisions ofH+on He

The measured intensity and polarization of Balmer-alpha radiation resulting from 40-80-keV collisions of ${\mathrm{H}}^{+}$ on He exhibited a strong dependence on electric fields applied axially along the beam direction. With use of a density matrix formalism the collisionally produced electric dipole moment for the $n=3\mathrm{}$ state was found to be large, reaching $4.4e{a}_0$ at the lowest collision energy. The center of the electron cloud distribution was found to lag behind the proton.