Electronic spectroscopy of transient species in plasma discharges

The work was focused on the spectroscopic study of carbon chain species as well as small boron clusters in the gas phase. The experimental apparatus was built before, however, in order to produce boron species. The source had to be modified as in this case a solid sample of precursor had to be used. Up to now the apparatus could be used to study the electronic transitions of variety of the species producing only by discharging a suitable gas precursor. The heating system built for this purpose worked flawlessly and the first gas-phase electronic spectrum of B3 could be obtained. This experiment showed that solid-state precursors can be also used for the production of the exotic species in the gas phase, which increases significantly the potential of the CRD experiment. The heated source can be promising for further studies of the bare carbon chains C6+, C7+ and C9+. Their spectra were already measured in the neon matrix and solid precursor (perchloronaphtalene) was used in this case. Since C10Cl8 worked very well in the matrix experiment, it seems reasonable to assume that in the CRD experiment this precursor could work as well. As mentioned before, cavity ringdown spectroscopy combined with a supersonic slit jet plasma have been applied to obtain gas-phase spectra of the variety of carbon chain species. They ranged from rather short ones like HC4H+, to relatively long such as HC10H+. Most of them are linear, however, spectra of the nonlinear carbon chains were also measured (C4H4+, C6H4+ and C8H4+). High sensitivity of the cavity ringdown method and low temperature attained in a jet, in many cases allowed to obtain and analyze rotationally resolved electronic spectra. One of the main results of the work was obtaining the electronic spectrum of the pentaacetylene cation. It turned out to be the largest polyacetylene cation measured in the gas phase so far. Astrophysical relevance of the HC10H+ was considered, however, the work showed that HC10H+ can not be a carrier of the DIBs. There was no match with the hitherto reported diffuse interstellar bands in the near infrared. Apart from carbon chain species, the spectrum of the cyclic B3 molecule was also measured. It was the first detection of this molecule in the gas phase. The analysis of the rotational structure of the spectrum allowed the geometry of the molecule to be inferred, which turned out to be the first structural information on cyclic boron trimer in the gas phase.