Formation of long-lived Rydberg states of H2 at K impregnated surfaces Original Research Article

The formation of Rydberg states of hydrogen molecules H2* at potassium promoted iron oxide surfaces at 900–1000 K is studied using pulsed laser fragmentation neutral time-of-flight measurements. Both neutral Rydberg states H2* and ions H2+ are observed to reach the detector, as well as electronically excited clusters of hydrogen of the Rydberg matter type. The Rydberg states H2* and ions H2+ are not formed by the laser since the fluence is too low, and such particles are not observed from hydrogen molecules in the gas phase. They also carry an excess kinetic energy of <1 eV due to laser fragmentation. This kinetic energy corresponds probably to Coulomb repulsion in the excited clusters with interionic distances of a few nanometers. The size of the signal of H2* varies strongly with the laser fluence at high fluences. The molecular Rydberg states are believed to be formed by transfer of electronic excitation energy from the Rydberg states of the alkali atoms K*, which are formed at the sample surface.