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The dissociation of aligned, electronically excited H₂(E,F ¹Σ_g⁺), followed by ionization of the produced H atom, is analyzed via the velocity mapped imaging technique. The dissociation and ionization processes are accomplished, respectively, by a two- and a onephoton absorption from a single 532-nm laser pulse, while the alignment is induced by a separate 1064-nm laser pulse. The velocity of the produced H⁺ photofragments shows a weak perpendicular alignment at low alignment laser field values, evolving to strongly parallel for larger fields. We modeled this alignment behavior with a simple two-state model involving the Stark mixing of the initially-prepared J =more » 0 with the J = 2 rotational state. This model is able to reproduce all of the observed angular distribution, and permits us to extract from the fit the polarizability anisotropy of H₂(E,F) electronic state. We determine this value to be (3.7 ± 1.2) x 10³ a.u. As this value is extremely large in comparison to what one would expect from the pure H₂(E,F) electronic state, we hypothesize that this value comes from the 1064-nm laser beam mixing nearby electronic states with the initially laser prepared (E,F) state generating a mixed state (EF**) with an extremely large polarizability anisotropy.« less

Alignment, dissociation and ionization of H₂ molecules in the ground or the electronically excited E,F state of the H₂ molecule are studied and contrasted using the Velocity Mapping Imaging (VMI) technique. Photoelectron images from nonresonant 7-, 8- and 9-photon radiation ionization of H₂ show that the intense laser fields create ponderomotive shifts in the potential energy surfaces and distort the velocity of the emitted electrons that are produced from ionization. Photofragment images of H+ due to the dissociation mechanism that follows the 2-photon excitation into the (E,F; v = 0, J = 0, 1) electronic state show a strong dependencemore » on laser intensity, which is attributed to the high polarizability of the H₂ (E,F) state. For transitions from the J = 0 state, particularly, we observe marked structure in the angular distribution, which we explain as the interference between the prepared J = 0 and Stark-mixed J = 2 rovibrational states of H₂, as the laser intensity increases. Quantification of these effects allows us to extract the molecular polarizability of the H₂ (E,F) state, and yields a value of 103 ± 37 A.U.« less

The observation of the gaseous UFO^– anion is reported, which is investigated using photoelectron spectroscopy and relativisitic ab initio calculations. Two strong photoelectron bands are observed at low binding energies due to electron detachment from the U-7sσ orbital. Numerous weak detachment bands are also observed due to the strongly correlated U-5f electrons. The electron affinity of UFO is measured to be 1.27(3) eV. High-level relativistic quantum chemical calculations have been carried out on the ground state and many low-lying excited states of UFO to help interpret the photoelectron spectra and understand the electronic structure of UFO. The ground state ofmore » UFO^– is linear with an O–U–F structure and a ³H₄ spectral term derived from a U 7sσ²5fφ¹5fδ¹ electron configuration, whereas the ground state of neutral UFO has a ⁴H_7/2 spectral term with a U 7sσ¹5fφ¹5fδ¹ electron configuration. Strong electron correlation effects are found in both the anionic and neutral electronic configurations. In the UFO neutral, a high density of electronic states with strong configuration mixing is observed in most of the scalar relativistic and spin-orbit coupled states. In conclusion, the strong electron correlation, state mixing, and spin-orbit coupling of the electronic states make the excited states of UFO very challenging for accurate quantum chemical calculations.« less