Ph.D Thesis

Ph.D StudentAharon Bar-David
SubjectInvestigation of the Structure, Dissociaction Energy
and Mean Lifetime of Diatomic Molecular Ions
DepartmentDepartment of Physics
Supervisors Mr. Gertner Isak
Professor Emeritus Rosner Baruch


In this research we investigated the population of rotational and vibrational quantum level present in a beam of the exotic homonuclear molecular ion 4He2+2. Especially we were interested in the presence of high L rotational levels.

The research was done in the Van-De-Graaff Accelerator Laboratory at the Technion.

The technique was based on singly ionized He2+ molecular ions, which were created in the accelerator and then brought to collide with a gas target, which consisted of Argon gas, where a small fraction of this collision resulted in a second ionization of the Helium molecular ions into 4He2+2. These doubly ionized molecular ions of Helium, were then directed to our measuring apparatus. On their way these molecular ions dissociated according to their lifetimes and flew away from the center of the beam.

We used an MCP detector system together with a video camera and a special designed fast timing system to measure the 3 dimensional distances between the dissociated fragments of the molecular ion 4He2+2. Then we analyzed the statistics of the 3 dimensional distances between the fragments to identify the quantum levels they occupy.

Until now this technique could be used only on heteronuclear diatomic molecular ions for technical reasons.

In this research we developed a technique to overcome these problems, and for the first time this kind of technique was used on homonuclear diatomic molecular ions.

The result of the research is very clear. There is a clear preference of the high L quantum levels over the low L levels. This gives some unique answers to until now open questions of the formation of molecular Helium ions, which plays an important role in processes related to astrophysics.