TRICKY IR MONOMER SPECTROSCOPY IN PLANAR MOLECULAR JETS

An experimental technique based on double resonance spectroscopy in th e collisional environment of a seeded molecular jet expansion is descr ibed. Using this technique, hot band spectra of several small hydrocar bons have been investigated as well as the (related) collision-induced relaxational behavior upon vibrational excitation. The collisional re laxation in the jet is of crucial importance to the experiments presen ted here as it distributes the population over many rovibrational stat es after initial excitation by a pump laser. A second IR laser then pr obes the transitions starting from the vibrationally excited state(s), as hot bands. In that way one enters an energy region around 4000 cm( -1), beyond the highest fundamental bands. The possibility to label an individual rovibrational state with the pump laser enables us to obta in reliable initial spectroscopic assignments. In addition, the presen t technique allows one to distinguish the cold bands due to depletion of the vibrational ground state, which may reveal new and surprising s pectral features as well.