Dissociative photoionization of H2 at high photon energies: uncovering new series of doubly excited states

Formation of hot hydrogen atoms from superexcited states of acetylene

The cross sections for the formation of the H(2p) and H(2s) atoms, σ _2p and σ _2s , respectively, in photoexcitation of C₂H₂ were obtained in an absolute scale for studying formation and decay of superexcited states in the extreme ultraviolet range. Several superexcited states of C₂H₂ including multiply excited states were found in the curve of the σ _2p cross sections as a function of the incident photon energy. The same states seem to contribute to the variation in the σ _2s cross sections as well, which can be ascribed to the non-adiabatic transitions between the 2p and 2s channels. The Σ/Π symmetry-resolved cross sections for the H(2s) atom formation, σ 2 s Σ and σ 2 s Π , were also obtained on an absolute scale. The coupling between the Σ u + 1 and ¹Π _u states was found to be small.

Time-resolved momentum imaging system for molecular dynamics studies using a tabletop ultrafast extreme-ultraviolet light source

We describe a momentum imaging setup for direct time-resolved studies of ionization-induced molecular dynamics. This system uses a tabletop ultrafast extreme-ultraviolet (EUV) light source based on high harmonic upconversion of a femtosecond laser. The high photon energy (around 42 eV) allows access to inner-valence states of a variety of small molecules via single photon excitation, while the sub--10-fs pulse duration makes it possible to follow the resulting dynamics in real time. To obtain a complete picture of molecular dynamics following EUV induced photofragmentation, we apply the versatile cold target recoil ion momentum spectroscopy reaction microscope technique, which makes use of coincident three-dimensional momentum imaging of fragments resulting from photoexcitation. This system is capable of pump-probe spectroscopy by using a combination of EUV and IR laser pulses with either beam as a pump or probe pulse. We report several experiments performed using this system.