Molecular hydrogen

Double-Resonance Studies in H2

The XUV-laser is employed in double and triple resonance studies of molecular hydrogen. The aim is twofold:

A study of a new class of exotic valence states
Due to adiabatic curve crossings of repulsive states dissociating towards the n=2, and also the n=3 and n=4 states of atomic hydrogen on the one hand, and the ion-pair potential on the other hand, valence states are formed at large internuclear separation. On of these states, the HH-state, calculated by Woniewicz and Dressler, is shown in the figure:


Also shown in the figure is how the XUV-laser is used to prepare an intermediate state, the B-state, which has wave function density at large internuclear separation (8 a.u.) to allow for further excitation into the exotic HH-state. A recorded spectrum is shown in the following figure:


Concurrently work is in progress to study in detail this state in all three isotopes H2, D2 and HD. One of our findings is that in HD the 'u'-'g' symmetry in entirely broken resulting in a coupling of the HH-state with another state, B'B of ungerade symmetry.

Coincidences between inter-Rydberg transitions in H2 with the diffuse interstellar bands
Diffuse interstellar bands are mysterious absorption phenomena observed in the line of sight of many stars of various types. By now over 200 of these absorption features (narrow and broad ones) have been cataloged. Below a reconstructed spectrum of the DIB-phenomena in the entire visible is shown (adapted from the Thesis of P. Jenniskens, Leiden University, 1992):


In a XUV-vis two-colour laser experiment we have found coincidences in the spectrum of H2 and some of the Diffuse Interstellar Bands or DIBs. In the following figure three of such resonances are shown. The level assignement on the left indicates the intermediate (Rydberg states) states prepared with the XUV-laser: