High Resolution IR-Cavity Ringdown Spectroscopy on Reactive Gas-phase Species

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There is a surprisingly rich chemistry to be found in different regions in outer space. For example, in the vicinity of dying stars atoms combine to molecules and serve as seed material for dust formation (e.g. silicon carbides). Unlike on earth, interstellar molecules are very often non-saturated compounds that are highly reactive or even of ionic nature (like ionic complexes of hydrogen or noble gases). These species, which are difficult to produce in terrestrial laboratories, are valuable probes to determine the local physical conditions in cosmic environments. Now, with the availability of high-resolution IR instruments on telescopes like EXES/SOFIA and TEXES/N-Gemini a strongly increased demand set in for IR spectroscopic data. In addition, the highly sensitive James Webb space telescope will most likely start already in 2018. Thus, it is now possible to overcome the IR-opaque earthly atmosphere and to view into the mid-IR sky with high resolution astrophysical instruments. It is expected that the already scheduled line surveys will lead to new molecule detections. Specifically species that have no permanent dipole moment and cannot be investigated at radio wavelengths will be new on the list. Many of the expected molecules have characteristic spectra at mid-IR wavelengths. These spectra cannot be calculated by purely theoretical means to the necessary level of precision for astrophysical detections. Without new laboratory measurements the data situation is clearly deficient. The lack of experimental data has several reasons. One difficulty is the production of astrophysically relevant molecules in sufficient abundances, because these species are very reactive and only short-lived. Furthermore, very often adequate light sources for high-resolution mid-IR spectroscopy are missing. The aim of this work is to perform high-resolution and extremely sensitive measurements on astrophysically relevant molecules. Powerful quantum cascade lasers (QCLs) operating above 4.5 mu and OPO systems for the region 2-4.7 mu will be utilized as suitable light sources. These laser systems will be an integral part of the newly to-build highly sensitive cavity-ringdown (CRD) spectrometer. The IR-CRD spectrometer will be combined with special plasma molecule sources (laser ablation/electr. discharge) to produce in-situ high molecule abundances. With the irradiation of microwave radiation double resonance experiments will be feasible which are particularly suitable to investigate molecule plasmas. In practice, it is planned to measure silicon carbides (e.g. Si2C2) and ionic complexes (like [Ar-N2]+).