Search

A simple and sensitive method combining ion imaging with Doppler spectroscopy has been developed to measure full three-dimensional velocity distributions of low energy scattering particles. This technique was applied to the photolysis study of an HBr molecular beam at 243 nm. [ABSTRACT FROM AUTHOR]

Doppler profiles of chlorine and hydrogen atomic fragments produced in the photodissociation of mono- and dichloroethylenes at 193 nm have been measured in a pump-and-probe experiment using 2+1 resonance-enhanced multiphoton ionization. In a second experiment, the angular distributions of the Cl fragments produced from chloroethylenes at 235 and 238 nm were measured using a perfect-focusing mass spectrometer. In a third experiment, we measured the power dependence of the relative yields of H, Cl, HCl, and HCl+ produced from vinyl chloride at 193 nm. For Cl detachment, two primary processes have been confirmed. One produces an isotropic angular distribution of photofragments, while the other produces an anisotropic distribution. For H atom detachment, an isotropic angular distribution and a Boltzmann velocity distribution were found. The ratio of yields of the Cl and H fragments was found to be 4±1 for CH2CCl2 and higher than 10 for t-CHClCHCl and CCl2CClH. The H, Cl, and HCl yields were found to be first order in laser intensity, while the HCl+ yield was found to be third order. Saturation measurements of the ion yield indicate that the latter results from a 1+1+1 resonance-enhanced process involving a bound state of the parent molecule. This intermediate state may also be responsible for producing the statistical component of the Cl atom product. [ABSTRACT FROM AUTHOR]

The photodissociation of ozone at 226 nm is studied for O3→O2(X3 Σ-g)+O(2p3Pj) by probing O(3Pj) atomic photofragments with a resonance-enhanced multiphoton ionization method. Angular and kinetic energy distributions are determined by measuring time-of-flight spectra as a function of the angle between the polarization vector of the dissociation laser and the detector axis. The Doppler width of O(3Pj) photofragments is also measured. The translational energy distribution is well represented by assuming the formation of vibrationally excited O2 molecules with an average vibrational quantum number of 12. The anisotropy parameter β for the angular distribution is found to be 0.7±0.1. The predissociation dynamics from the photoprepared O3(1B2) state to the repulsive potential surface is discussed. [ABSTRACT FROM AUTHOR]

The photodissociation of methyl nitrite in the molecular beam has been studied by laser irradiation at 348–364 nm. The NO photofragments were analyzed by MPI analysis in a one-color experiment. The translational energy distribution for the photofragment indicates that there are two distinct paths by which CH3O and NO radicals are produced; one is a one-photon dissociation, and the other is a two-photon dissociation. The angular distribution of fragment intensities peaks in a direction orthogonal to the electric vector of the photolysis light indicating that the transition moments for both the first and the second one-photon absorptions lie perpendicular to the O–N bond that breaks. [ABSTRACT FROM AUTHOR]

Methyl iodide ions prepared by two-photon resonant three-photon ionization via Rydberg states are photodissociated by a one-photon process to result in the formation of methyl fragment ions by laser irradiation at 335–403 nm. The parallel angular distributions of these fragment ions have rather small anisotropy parameters, suggesting that dissociation is predissociative via the A(2E1/2) state of CH3I+. [ABSTRACT FROM AUTHOR]