Showing papers by "Yutaka Matsumi published in 1996"

Translational relaxation and electronic quenching of hot O(1D) by collisions with N2

Abstract: Translational relaxation and electronic quenching processes of translationally hot O(1D) atoms by collisions with N2 in a gas cell at room temperature are studied using a vacuum ultraviolet laser induced fluorescence technique. The initial hot O(1D) atoms which have translational energies of 18.2 and 9.8 kcal mol−1 are produced by the photodissociation of N2O at 193 nm and O2 at 157 nm, respectively. The translational relaxation processes are investigated by time resolved measurements of the Doppler profiles for the O(1D) atoms, while the quenching processes are studied by measuring both the decrease of the O(1D) concentration and the increase of the product O(3P) concentration after the photochemical formation of the hot O(1D) atoms. When the initial translational energy of O(1D) is 9.8 kcal mol−1, about 40% of the O(1D) atoms are electronically quenched before the entire thermalization of the hot O(1D) atoms takes place in a gaseous mixture with N2. This indicates that the translational relaxation rate ...

Observation of the spin-forbidden O(1D) + O2(X3Σg-) channel in the 317-327 nm photolysis of ozone

Abstract: The photofragment excitation spectra for O(1D) production from the 317–327 nm photolysis of ozone under supersonic free‐jet and low‐temperature flow conditions show structure superimposed on an underlying continuum. Doppler profiles of the nascent O(1D) photofragments confirm that the O(1D) formed by photolysis at the wavelengths of the peaks in the photofragment excitation spectrum arises from the hitherto unobserved spin‐forbidden predissociation to O(1D)+O2(X 3Σg−) products.

Ion imaging of the photodissociation of chlorine-containing molecules

Abstract: The photodissociation dynamics of four chlorine-containing compounds was studied by the ion imaging technique. Two compounds, ClNO and (CH3)3COCl, exhibited strong anisotropy, and the kinetic energy distributions for Cl(2P3/2) and Cl*(2P1/2) were indistinguishable. For CCl4 and SOCl2 the kinetic energy distributions of Cl and Cl* were very different. In all cases most of the chlorine atoms were released in their ground 2P3/2 state. A general explanation is given based on these data and those of others. The process is described in terms of three states whose energies are in the following order: the ground state, a state correlating with Cl*, and a state correlating with Cl. Sooner or later the Cl state must cross the Cl* state. If the crossing is sooner, i.e. in the Franck−Condon region, Cl and Cl* will have different translational energy distributions. If the crossing is later, i.e. at long distances, Cl and Cl* will have descended a repulsive surface and reached their asymptotic and nearly equal kinetic...

Chemical dry etching mechanisms of GaAs surface by HCl and Cl2

Abstract: Dry etching mechanisms of thermal and photochemical reactions with Cl2 and HCl on GaAs(100) Ga‐rich c(8×2) surfaces were investigated, using x‐ray and ultraviolet photoelectron spectroscopy. At a substrate temperature of −100 °C, the etchant gases are chemisorbed on the GaAs surface. Cl2 deposition on GaAs produces about five times more Cl‐containing species than HCl deposition. The GaAs surface is disrupted with Cl2 when the substrate temperature is increased to 250 °C after the saturated deposition of Cl2 at −100 °C. A similar etching procedure with HCl forms an ordered surface of GaAs with As atoms on the top layer. After desorption of the etchant gases, the photoirradiation effect at room temperature was investigated by pulsed laser irradiation with excimer (193 and 248 nm) and YAG (266, 355, and 532 nm) lasers at an intensity of 2–10 mJ/cm2. Only the 193 nm irradiation removes Cl‐containing species from the surface. With cw laser irradiation at 488 nm (60 mW/cm2), photochemical reactions take place on the GaAs substrate on which Cl2 has been deposited.

Photolysis of ch3sh and h2s at 243.1 nm studied by photofragment ion imaging

Abstract: The near-UV photolyses of hydrogen sulfide and methanethiol following excitation at 243.1 nm have been investigated further using ion-imaging methods to monitor the nascent H atom photofragments. The angular distributions of these H atoms are found to be well described by anisotropy parameters, β=– 0.9 ± 0.2 (for CH3SH photolysis) and – 1.0 ± 0.2 (for H2S), consistent with the fact that the near-UV photodissociation of these parent molecules involves a perpendicular photoexcitation process followed by prompt S—H bond rupture. Analysis of the radial form of the ion images also serves to highlight the strong similarities between the primary photochemistry of these two thiols following excitation to their respective dissociative first excited singlet states and to confirm previous reports that the bulk of the excess energy in these two photodissociation processes appears in the form of product recoil.

Vibrational Distribution of ClO Radicals Produced in the Reaction Cl + O3 → ClO + O2

Abstract: The nascent vibrational distribution of ClO(X2Π) radicals produced in the ozone destruction reaction Cl + O3 → ClO + O2 has been measured, using vacuum-ultraviolet laser-induced fluorescence of the ClO(C2Σ-−X2Π) transition. The nascent vibrational distribution of the ClO radicals is shown to be strongly inverted, with the relative ratio (v=0):(v=1):(v=2):(v=3):(v=4):(v=5) = 0.8:1:1.3:2.4:2.9:2.7. The slope of the surprisal plots for the vibrational distribution of the product ClO is found to be (−8 ± 2). Vibrational relaxation processes for the ClO radicals in the X2Σ state by collisions are also studied. The upper limit values of the vibrational relaxation rate constants for ClO (v=1→0) by collisions with N2 and Ar molecules are estimated to be both 5 × 10-14 cm3 molecule-1 s-1.