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We present the first threshold ion-pair production spectrum of a triatomic molecule. We have recorded the ion-pair yield spectrum and TIPP spectrum for the H2S → H⁺+SH^- ion-pair channel using single-photon excitation. From the TIPP spectrum, we have determined the H−SH bond energy (31451 ± 4 cm^-1) to unprecedented accuracy and demonstrated the formation of weakly bound H⁺−SH^- (J‘) ion-pair states, with rotational excitation of the SH^- anion up to J‘ = 4. The bound nature of these states, and the assigned spectrum that results from their field dissociation suggests that this technique can be applied to many other triatomic and larger polyatomic molecules in the future, leading to energetic, spectroscopic, and dynamical information about these species.

A new experimental apparatus is described which permits the determination of binding energetics for metal−ligand complexes. This technique mates laser ablation for the generation of atomic metal ions with the environment of a high-pressure ion source which leads to rapid termolecular stabilization of metal ion-ligand complexes containing one or more ligands. The time resolved capability of the detection system allows equilibrium to be studied quantitatively for binding energies in the range of 5−30 kcal mol^-1. Such measurements of the absolute binding energy of formaldehyde to Al⁺ combined with existing bimolecular Al⁺ exchange equilibrium data leads to an absolute Al⁺ affinity scale. For two ligand complexes an extensive ab initio search of the potential energy surfaces shows that the experimentally observed species involving CH3CN and (CH3)2O involve simple ligand complexation with an acute L-Al−L bond angle (L = ligand) rather than hydrogen bonded or inserted structures. In one instance a third ligand complexation has been experimentally investigated likely leading to a species of pyramidal geometry.

To examine the issues concerning Rydberg-state stabilization in pulsed-field ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectroscopy, spectra at the first and second ionization thresholds of argon have been taken under different ion-density conditions. These provide a contrast between the signals from autoionizing and nonautoionizing Rydberg series. A careful comparison between the PFI-ZEKE spectra and relative partial photoionization cross sections provides the first measurement of the efficiency of stabilization in PFI-ZEKE spectroscopy. This efficiency or quantum yield varies at the second ionization threshold with changing ion density and principal quantum number, introducing ion-density-dependent line-shape distortions. These changes may be ascribed to the competition between stabilization and autoionization of the Rydberg states and its variation with principal quantum number.