The doubly excited states of molecular hydrogen have been studied by means of electron-energy-loss spectroscopy in coincidence with the detection of H(2p) formation at 80 eV incident energy and 3 • scattering angle. This is the first observation of doubly excited states of H 2 in electron energy-loss spectra. It is shown that a forbidden doubly excited state makes a large contribution as well as allowed states. The measured spectrum has been analysed by theoretical fits based on the reflection approximation.

The electron energy-loss spectra of H2 have been measured in coincidence with the neutral dissociation leading to H(1s)+H(2p) near the first ionization potential at the electron impact energy of 150 eV and the scattering angles of 2 degrees and 10 degrees , and compared with ordinary electron energy-loss spectra. The two spectra, the coincident and the ordinary ones, are similar to each other in shape below the energy level of H2+(X2 Sigma g+, upsilon i=1), while they are different from each other above this energy level. Such a large change around upsilon i=1 is discussed in terms of the dynamics of superexcited hydrogen molecules, and the availability of this method for such studies is examined.

The state-resolved isotope effect on the cross sections of 2p atom formation via precursor doubly excited states of H 2 and D 2 is obtained at 80 eV incident electron energy and 3 • scattering angle by means of coincident electron-energy-loss spectroscopy as well as theoretical fits based on the reflection approximation and the survival probability. It turns out that the degree of the isotope effect depends strongly on the precursor doubly excited states and hence is a significant character of them. The origin of this dependence is discussed.

The theoretical formulation given in this article allows the vacuum ultraviolet (VUV) production efficiency to be calculated from the electron temperature of the plasma and the gas parameters including gas mixing ratio, excitation energies, and excitation cross sections using the separately determined conversion efficiency of the plasma input power into the electron heating power. The VUV production efficiencies calculated for (Ne+Xe) mixture (neon (Ne) and xenon (Xe) mixture) discharge gases using the formulation show that the efficiency can be increased by decreasing the electron temperature and by increasing the amount of Xe in the gas mixture. A method for determining the electron temperature of the plasma display panel (PDP) plasma from emission intensity measurements was also given, and was used to show that the electron temperature in the ordinary PDP plasma is 3 eV.

A generalized analytical method to determine the density of energy states of electron emission source (EES) is devised by using a thermal excitation and emission model for an exoelectron in the MgO layer and the emission time constants of the exoelectron extracted from experimental stochastic distributions of discharge delay time. When applied to Si-doped MgO, the emission time constant of the exoelectron from the Si EES becomes shorter at high temperature and at short time intervals due to thermal excitation. The density of energy states of the Si EES DSi(E) shows the main peak at 736 meV, a satellite peak at 601 meV, and broad energy structures over the range of 586–896 meV. The effective number of Si EES is 5.5 times larger than that in purified MgO. The excitation energy in a Si-doped MgO cluster with a crystal structure is obtained to be 0.83 eV by using the symmetry-adapted-cluster configuration interaction method and the Si EES contributes to exoelectron emission. The thermal excitation is governed by the transition from the Si–O bound state and the Mg edge state to the antisymmetrical edge states and the extended surface state. The excitation energy in an MgO cluster with a Si-doped atom inside and a nearest oxygen vacancy taking account of structural relaxation is calculated to be 0.75 eV, which shows good agreement with the main peak in DSi(E). The excitation energies of 0.64, 0.73, and 0.78 eV are also obtained in an MgO cluster with a Si-doped atom at the surface and a nearest oxygen vacancy. The first excitation energy corresponds with the satellite peak. The broad energy structures of DSi(E) are caused by the dependence of excitation energy on the position of Si-doped atoms inside and at the surface of the MgO cluster, and on the interatomic distance of Si–O due to structural relaxation. The energy structures can be also attributed to the thermal excitation to the various symmetrical Mg edge states and the surface states. When the number of complex structures of the Si EES with adjacent oxygen vacancies increases, oxygen vacancies are generated from the complex structures and the increase in the electron traps degrades electron emission rate. Therefore, the number of complex structures has an optimum value that leads to the maximum effective number of Si EES.