Showing papers by "Yutaka Matsumi published in 2004"

Formation of O(3P) atoms in the photolysis of N2O at 193 nm and O(3P) + N2O product channel in the reaction of O(1D) + N2O

Abstract: The O(3P) atom produced in the 193 nm photolysis of N2O has been detected by a technique of vacuum-ultraviolet laser-induced fluorescence spectroscopy around 130 nm. The quantum yield value of the O(3P) atoms produced directly in the photolysis of N2O at 193 nm at room temperature has been determined to be 0.005 ± 0.002. The O(3P) atom formation process in the reaction of O(1D) + N2O is also studied, and the channel branching ratio of O(3P) + N2O has been determined to be 0.04 ± 0.02 among the product channels, 2NO, N2 + O2, and O(3P) + N2O. Photodissociation processes of N2O at 193 nm and reaction processes of O(1D) + N2O system have been discussed on the basis of the experimental results. Because of importance of the O(1D) + N2O reaction in the stratosphere, impact of the experimental result of O(3P) formation from the O(1D) + N2O reaction on the stratospheric chemistry is also studied by one-dimensional atmospheric model calculations.

Secondary Organic Aerosol Formation during the Photo-Oxidation of Toluene : Dependence on Initial Hydrocarbon Concentration

Abstract: Aerosol formation in toluene–NOx–air–photoirradiation systems was examined in a 6-m3 photochemical reaction chamber. The initial toluene concentration was varied between 2 and 16 ppmv, whereas the ...

Equilibrium Constants of the Reaction of Cl with O2 in the Formation of ClOO

Abstract: The equilibrium constants for the formation of ClOO from Cl and O2 are experimentally measured at 212−245 K using cavity ring-down spectroscopy. A van't Hoff plot analysis yields ΔHr = 4.8 ± 1.5 kcal mol-1. The Cl−OO bond dissociation energy is determined to be 4.69 ± 0.10 kcal mol-1 from the present and previously reported temperature dependences of the equilibrium constant by the third-law analysis utilizing our recent accurate rotational spectroscopic data. High level ab initio calculations using MRSDCI+Q with the complete basis set extrapolation are also performed. The present ab initio calculations yield the Cl−OO bond dissociation energy to be 4.56 kcal mol-1.

Photodissociation of water dimer at 205 nm

Abstract: A deuterated water dimer, (D 2 O) 2 , absorbs a photon at 205 nm releasing a fragment D atom. The negative angular anisotropy parameters are observed experimentally with photofragment imaging spectroscopy. In this dissociation, one of the translational energy distributions obtained for the fragment D atoms peaks at around 1 kcal mol - 1 , which is much smaller than the maximum available energy, 16.2 kcal mol - 1 . These results suggest an energy loss process of the fragment D atom, which is induced by a collision with the oxygen atom in the dimer before it leaves the parent molecule. A direct ab initio trajectory calculation for the internal collision process of the D atom in the dimer has been performed. The obtained energy loss is in good agreement with the present experimental results.

Atmospheric Chemistry of Pivalaldehyde and Isobutyraldehyde: Kinetics and Mechanisms of Reactions with Cl Atoms, Fate of (CH3)3CC(O) and (CH3)2CHC(O) Radicals, and Self-Reaction Kinetics of (CH3)3CC(O)O2 and (CH3)2CHC(O)O2 Radicals

Abstract: The kinetics and mechanism of the reactions Cl + (CH3)3CCHO and Cl + (CH3)2CHCHO were investigated at room temperature using two complementary techniques: flash photolysis/UV absorption and continuous photolysis/Fourier transform infrared (FTIR) smog chamber. Reactions proceed predominantly by abstraction of the aldehydic H atom to form acyl radicals. FTIR measurements indicated that the acyl-forming channel accounts for 81% ± 8% and 85% ± 10% of the reaction of Cl atoms with (CH3)3CCHO and (CH3)2CHCHO. UV measurements indicated that the acyl-forming channel accounts for 88% ± 6% and 85% ± 5% of the reaction of Cl atoms with (CH3)3CCHO and (CH3)2CHCHO. The atmospheric fate (>98%) of the resulting (CH3)3CC(O) and (CH3)2CHC(O) radicals is an addition of O2 to give the corresponding acylperoxy radical. In 700 Torr of N2/O2 mixtures at a temperature of 296 K, the decomposition of (CH3)3CC(O) and (CH3)2CHC(O) radicals via CO elimination occurs at rates of ∼1 × 105 and ∼4 × 103 s-1, respectively. Relative rate...

Quantum Yield for O(1D) Production from Ozone Photolysis in the Wavelength Range of 193−225 nm

Abstract: The quantum yield values for O(1D) production from the photodissociation reaction of O3 between 193 and 225 nm at 298 ± 2 K are reported. The O(1D) photofragments have been detected directly using a technique of vacuum ultraviolet laser-induced fluorescence spectroscopy at 115.22 nm which is associated with the electronic transition of O(3s1D° − 2p1D). It has been found that the O(1D) quantum yield values decrease monotonically as the photolysis wavelength becomes shorter from 0.90 ± 0.12 (225 nm) to 0.48 ± 0.03 (193 nm). Photodissociation processes of O3 around 210 nm and its atmospheric implications have been discussed.

Hydrogen Atom Formation in the Photolysis of Acetone at 193 nm

Abstract: An experimental and theoretical study of the formation of hydrogen atom in the photolysis of acetone at 193 nm is reported. The H atom photofragments are detected by the technique of vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy at 121.6 nm. The quantum yield for H atom formation from acetone photolysis at 193 nm is determined to be 0.039 ′ 0.006. The Doppler profiles of the H atom photofragments are measured by scanning the probe laser wavelength around the resonance frequency of the H atom at 121.6 nm. The nascent kinetic energy distribution of the H atom fragments is found to be characterized by a Maxwell-Boltzmann function with the temperature of 5000 K. The spatially isotropic recoil distribution in the H atom photofragmentation is observed. The potential energy surfaces for the H atom formation processes from acetone photolysis are examined using molecular orbital calculation methods. Atmospheric implications of the present result are briefly discussed.

Accurate Determination of the Absolute Quantum Yield for O(1D) Formation in the Photolysis of Ozone at 308 nm

Abstract: Absolute O('D) quantum yield from the photodissociation reaction of O 3 at 308 nm should be determined accurately with high precision for its atmospheric significance. This is because it has been used as a reference in previous relative measurements to obtain the O( 1 D) quantum yields as a function of photolysis wavelength in the near-UV region. In this study, the near-UV pulsed-laser photolysis of O 3 with the direct detection of the O( 1 D) and O( 3 P) photofragments using a technique of vacuum UV laser-induced fluorescence has been applied to determine the absolute O('D) quantum yield from O 3 photolysis. The absolute O( 1 D) quantum yield at 308.0 nm at room temperature (298 ′ 2 K) is determined to be 0.804 ′ 0.048 (95% confidence interval), in which the uncertainty is much smaller than the values recommended for use in atmospheric studies. The O( 1 D) quantum yield values at photolysis wavelengths between 307 and 311.5 nm are also presented.