H3+ laser spectroscopy
H3+ is an important molecule in the chemistry of interstellare clouds and is an simple polyatomic molecule with three protons and two electron. Because it has no permant dipole moment and no excited electronic state, it is hard to spectroscopic experiments. It takes almost 70 years from the discovery of H3+ in 1911 to the first spectra obtained in a labrotary at 1980. The spectrum above an energy of 10000 cm-1 is currently not well understood and gets more worse to the dissociation energy at 35000 cm-1. Using laser spectroscopy at wavelengths of 10000 cm-1 and above the potential of H3+ is measured and can be used as input for theoretical calculations.
The experimental setup consist of a 22 pol trap (http://www.mpi-hd.mpg.de/ion-storage/Trap22/trap22.html) and is similar to the experiment described in (mikosch2004). Also here Ar is used for the chemical probing. The laser diode is replaced by a titanium sapphire laser or a dye laser to reach the desired wavelength. The results with the titanium sapphire laser are published in JCP (kreckel:164312).
Instead of using Ar also Ne or even He could be used for chemical probing, but the energy of the photons must be larger to induce a chemical reaction. If spectroscopy closer to the dissociation limit is carried out, this is already fulfilled.