[en] These proceedings are divided into the following sections: Reaction dynamics (6 papers); Laser coherent control I and II (7); Laser diagnostics for combustion (3); Laser spectroscopy of radicals (5); Spectroscopy of clusters (7); and a Poster session (17). Seventeen papers have been processed separately for inclusion on the data base

[en] VUV radiation with a photon energy around 16 eV has been used to study the PFI-ZEKE spectrum and the photoionization mass spectrum following excitation to the ionic ground state of the HF molecule. The radiation is generated by resonantly enhanced sum-frequency mixing of pulsed dye laser radiation in a pulsed beam source, using Kr as the non-linear medium. The resolution of the PFI-ZEKE method is sufficient to resolve the rotational structure in the photoionization process. The large rotational constant and the energetically comparable spin-orbit coupling in the ionic ground state lead to an angular momentum coupling in between Hund's case(a) and (b). Using the well known spectroscopic constants for the HF molecule, all the observed features can be accounted for and the ionization potential (HF ¹Σ⁺, v=0, J=0, → HF⁺²Π_3/2, v=0, J⁺=3/2 ) is determined to be 129420.4±2 cm^-1. Using TOF mass spectroscopy, we observed strong competition between the production of HF⁺ ions due to photoionization and H⁺ ions due to the ion-pair formation process. In the threshold region, the latter dissociative process is as richly structured as the ionization signal

[en] This paper describes a new apparatus which uses coherent vacuum ultraviolet light to photoionize molecules in a supersonic molecular beam, and energy analyzes the resulting photoelectrons by time of flight spectroscopy. The broadly tunable coherent VUV is generated by four wave sum mixing in Hg. Using this apparatus, the authors have studied the dynamics of autoionization for two different systems: spin-orbit autoionization in HI, and vibrational autoionization in NO. In both cases, our recent results have pointed out dramatic new features of the dynamics in these molecules. 24 refs., 9 figs

[en] The results of a pulsed field ionization zero kinetic energy electron spectroscopy (PFI-ZEKE) study of the highly vibrationally excited (v⁺>12) states of the hydrogen ion are reported. The current theoretical understanding of the energy levels of the hydrogen molecular ion provides a unique opportunity for testing the ability of the PFI-ZEKE method to measure ionic energy levels. Depending on current progress the authors may report ongoing experiments on the lifetimes of highly vibrationally excited ion-pair states of molecular hydrogen. These experiments will help determine the viability of a technique analogous to mass analyzed threshold ionization spectroscopy (MATT) for the accurate determination of bond dissociation energies

[en] Pulsed field ionization zero kinetic energy electron spectroscopy (PFI-ZEKE) involves the electric field ionization of high principal quantum number Rydberg states approximately one microsecond after optical excitation. Only recently has it been appreciated that in most cases these Rydberg states should have lifetimes much shorter than one microsecond if purely intramolecular behavior is considered (due to the autoionization and predissociation decay channels). It has been hypothesized that weak electric DC-fields and surrounding ions can stabilize these states against decay. The PFI-ZEKE spectra corresponding to highly vibrationally excited ionic cores of H₂⁺ (v⁺ = 13, 15) have been observed. In this case the Rydberg states responsible for the field ionization signal require some form of stabilization against vibrational autoionization. In this talk it is reported that ion-density influence the H₂ PFI-ZEKE lineshapes in a dramatic manner. This is shown to be consistent with the ion-density stabilization mechanism

[en] The dissociation of glyoxal after excitation to low-lying vibrational levels of the first excited singlet state has been studied by using the method of molecular beam photofragment translational spectroscopy. Detection of products at masses 28, 29, and 30 provides unequivocal proof that the S₁ state of glyoxal predissociates in the absence of collisions. The product time-of-flight (TOF) spectra show the presence of three distinct dissociation channels, the major ones being formation of H₂CO + CO and the triple dissociation forming 2CO + H₂. The third minor channel is attributed to the formation of CO plus an H₂CO isomer, possibly hydroxymethylene. 2 figures

[en] Improved methods of calculating quantum mechanical phase shifts and for performing least-squares fits to scattering cross sections or transport properties, are described. Their use in a five-parameter fit to experimental differential cross sections reduces the computer time by a factor of 4-7. (Auth.)

[en] Reactive scattering cross sections are measured for H(D)+Br₂→HBr(DBr)+Br by crossing a beam of hydrogen atoms with a beam of Br₂

[en] The energetic thresholds for ion-pair photodissociation of diatomic oxygen [O₂ +hν→O⁺+O^-(²P_3/2, ²P_1/2)] were measured using a novel technique. The technique depends on the production and selective detection of highly vibrationally excited ion-pair states which last for at least 5 μs following single photon excitation from the ground electronic state of O₂ . These ion-pair states are analogous to Rydberg states, and they may be dissociated by an electric field in a similar manner to the field ionization of high principal quantum number Rydberg states, allowing for their selective detection. copyright 1997 The American Physical Society

[en] The photoelectron angular distributions from autoionizing ns and nf Rydberg states of NO are presented. A striking dependence of the angular distribution on the rotational level in the excited Rydberg complex is observed: The sign of the asymmetry parameter β alternates for consecutive rotational levels. A multichannel quantum defect calculation shows qualitative agreement with the experimental results and indicates the role of predissociation in the decay of these Rydberg states