Electronic spectroscopy of astrophysically relevant species
Molecular Physics seminar
Monday 22 February 2010
to 11:00 at
Prof. John Paul Maier (University of Basel)
The focus of our research is the first time measurement of the electronic spectra of carbon containing chains, rings and ions, and their simpler derivatives with hydrogen, nitrogen and metals. Such transient species chosen for the investigations are of astrophysical relevance and of chemical interest in their electronic structure. We have been using and developing a number of approaches to observe the electronic transitions. The recent studies of new radicals and ions will be discussed. Initial information on the systems is often obtained by measuring the electronic spectra in absorption in 6 K neon matrices using mass-selected ion beams. In the gas-phase the transient molecules are produced in discharges and laser vaporization sources coupled with supersonic free jets. The transitions are searched for with laser-based approaches including cavity ring-down, degenerate four-wave mixing and resonant multiphoton spectroscopies. The availability of the laboratory gas-phase spectra enables a direct comparison with astronomical observations to be made and the implications for the potential carriers of the diffuse interstellar absorptions discussed. The use of the non-linear degenerate four-wave technique enables the disentanglement of overlapping electronic transitions of different molecules made in the plasma discharge. The double resonance nature of the two color variants of the method is exploited to obtain unambiguous assignments. Specific for the studies of cations is an instrument using ion trapping technology. Mass-selected ions are constrained in a 22-pole radio-frequency trap where they are cooled by collisions to around 20 K. The electronic transitions are measured by two color two photon approaches whereby the first photon induces the transition of interest whereas the second UV photon produces a fragment ion which is detected following its mass-selection.