The electron impact excitation of the n=2 states of atomic hydrogen has been investigated using the electron-photon coincidence technique.
The parameters λ and R have been determined at incident electron energies of 100eV and 350eV for a small range of scattering angles about the forward direction
A coincidence apparatus capable of time resolution of the order of half a nanosecond has been developed, permitting the study of the time evolution of the 2S and 2P states results in experimental observables which depend on the relative phase of the f00 and f10 scattering amplitudes. Such quantities have been determined for an incident electron energy of 350eV over a small range of scattering angles about the forward direction.
In addition, a quantum beat pattern, resulting from the interference between the decays of the Stark mixed states, has been observed.
These measurements represent the first attempt to investigate the coherent excitation of states of opposite parity using the coincidence technique.