Tatsuo Arikawa

Formation of O(3Pj) photofragments from the Hartley band photodissociation of ozone at 226 nm

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.

Mechanism of the ultraviolet photodissociation of chloroethylenes determined from the Doppler profiles, spatial anisotropy, and power dependence of the photofragments

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 ...

Three-dimensional velocity analysis combining ion imaging with Doppler spectroscopy : application to photodissociation of HBr at 243 nm

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.

Photodissociation of chlorine molecule in the UV region

Abstract Chlorine molecules are photodissociated at 308 and 351 nm, in the first UV absorption band that peaks at 335 nm. The resulting chlorine atoms are solely in the 2P 3 2 state. Doppler line shapes provide information about the angular distribution of the chlorine atoms, which show the distribution of a totally perpendicular transition.

Angular distributions of photofragments from NO2 photodissociation

The angular distributions of recoil of NO molecules from the photodissociation of NO2 near the dissociation threshold of 397.86 nm are presented and analyzed to obtain information about the effect of molecular rotation of parent molecules on the angular distribution. For the one‐photon dissociation process, as laser wavelengths become closer to the dissociation threshold, the anisotropy of the angular distribution is reduced. When laser wavelengths become larger than the threshold, NO2 dissociates via two‐photon absorption, and the photofragment angular distribution again becomes anisotropic reflecting the second photon absorption.

Angular distributions of CH+3 photofragments from CH3I+ prepared by multiphoton ionization

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+.

Angular distributions of photofragments generated in the two‐photon dissociation of nitrogen dioxide and carbon disulfide

Two‐photon dissociation of nitrogen dioxide and carbon disulfide at 308 nm has been studied by means of multiphoton ionization of photofragments. The angular distributions of fragments are well represented by a form of 1+β2P2(cos θ)+β4P4(cos θ). Because the intermediate state of NO2 (2B2) generated by the first one‐photon process is dissociative, the coefficient β4 for the fourth degree Legendre polynomial is appreciable. The coefficient β4 for CS2 is, however, not appreciable because the intermediate CS2 (1B2) state has a long fluorescence lifetime. The angular distributions not only reveal the symmetry and lifetimes of the two‐photon excited states of NO2 and CS2 but also information on the two‐photon excitation process of these molecules.

Photodissociation of methyl nitrite: Angular distributions in one‐ and two‐photon dissociations

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.

Angular distributions of sulfur atoms in the 3p 3PJ and 3p 1D states from two-photon dissociation of carbon disulfide

Abstract A molecular beam of carbon disulfide was photodissociated at 288–292 and 308–309 nm (a one-color, multiphoton dissociation). The angular distributions of sulfur atoms were measured in the S (3p 3 P J ) and (3p 1 D 2 ) states. Both S ( 1 D) and ( 3 P J fragments have anisotropic distributions for the two-photon dissociation.

Perfect Focusing Mass Spectrometer

A perfect focusing mass spectrometer has been investigated and the tests were carried out with electrons in the energy range up to 1 KeV concerning both properties of the perfect velocity focusing and of the perfect direction focusing. A luminous intensity of more than 95 percents was obtained experimentally for s=1, where s is a field parameter connecting the electric and the magnetic fields. In addition, the resolving power of this spectrometer was experimentally studied and compared with theoretical results.