Electronic spectroscopy of unsaturated hydrocarbons and sulfur-terminated carbon chains by cavity ringdown

Unsaturated hydrocarbons are highly reactive species that are found in flames and plasma discharges being important intermediates in the formation of polyaromatic hydrocarbons (PAHs) and in the processes of chemical vapor deposition (CVD). Some particular unsaturated hydrocarbons have been identified in the interstellar medium where their role is not yet fully understood. Linear carbon chains are one of the simplest rigid nanostructures that can potentially conduct electron current. Most of the unsaturated hydrocarbons are highly reactive species and for this reason they can only be studied in situ during the short time after their formation. The species are generated in the gas phase through an electrical discharge of a precursor gas and cooled in the supersonic expansion. High-resolution optical absorption spectra are recorded using a tunable dye laser. Because the concentrations of the reactive species studied are generally low, highly sensitive detection technique has to be used. This work presents a study of highly unsaturated hydrocarbons by cavity ringdown spectroscopy (CRDS). High-resolution electronic spectra of ions and radicals allow identifying them in remote environments such as interstellar medium and providing information about the physical conditions of the environment. It is shown how the information about the structure of the unknown absorbing species can be deduced from its rotationally resolved spectrum.