The techniques of electron-electron and electron-ion covariance mapping have been used to confirm that a laser of modest rise time (∼1 ps) and focused intensity (∼${10}^{15}$ W/${\mathrm{cm}}^2$) will doubly ionize ${\mathit{H}}_2$ molecules in a sequential manner. This stepwise behavior manifests itself in structureless features on the electron-electron maps. However, the technique can be employed to search for correlated emission of two or more electrons in more complex systems. Electron-ion maps, on the other hand, can apportion the electrons in a typical photoelectron spectrum to the parent ions and to fragment ions of all energies.

• Received 12 June 1992

DOI:https://doi.org/10.1103/PhysRevA.46.R6789