Showing papers by "Yutaka Matsumi published in 2001"

Kinetics of the Reactions of Cl(2P1/2) and Cl(2P3/2) Atoms with C2H6, C2D6, CH3F, C2H5F, and CH3CF3 at 298 K

Abstract: The title reactions were studied using laser flash photolysis in conjunction with laser-induced fluorescence techniques. Separate monitoring of the two spin−orbit states, Cl(2P1/2) and Cl(2P3/2), was used to measure the kinetics of the reactions of Cl(2P3/2) with C2H6, C2D6, CH3F, C2H5F, and CH3CF3, the reaction of Cl(2P1/2) with C2H6, and the relaxation of Cl(2P1/2) by collisions with C2H6, C2D6, CH3F, C2H5F, and CH3CF3. Measured reaction rate constants were (units of cm3 molecule-1 s-1): k(Cl(2P3/2) + C2H6) = (5.85 ± 0.55) × 10-11, k(Cl(2P3/2) + C2D6) = (1.87 ± 0.12) × 10-11, k(Cl(2P3/2)+ CH3F) = (2.7 ± 0.2) × 10-13, k(Cl(2P3/2) + CH3CH2F) = (6.8 ± 0.5) × 10-12, and k(Cl(2P3/2) + CH3CF3) < 1 × 10-14 cm3 molecule-1 s-1. Measured relaxation rate constants for deactivation of Cl(2P1/2) to Cl(2P3/2) via collisions with C2H6, C2D6, CH3F, C2H5F, CH3CF3, and CF4 were (1.22 ± 0.09) × 10-10, (2.4 ± 0.2) × 10-10, (6.4 ± 0.5) × 10-11, (1.9 ± 0.2) × 10-10, (2.0 ± 0.2) × 10-10, and (2.3 ± 0.4) × 10-11, respectively...

High-sensitivity instrument for measuring atmospheric NO2.

Abstract: We report on the development of a high-sensitivity detection system for measuring atmospheric NO2 using a laser-induced fluorescence (LIF) technique around 440 nm. A tunable broad-band optical parametric oscillator laser pumped by the third harmonic of a Nd:YAG laser is used as a fluorescence excitation source. The laser wavelength is tuned at peak and bottom wavelengths around 440 nm alternatively, and the difference signal at the two wavelengths is used to extract the NO2 concentration. This procedure can give a good selectivity for NO2 and avoid interferences of fluorescent or particulate species other than NO2 in the sample air. The NO2 instrument developed has a sensitivity of 30 pptv in 10 s and S/N = 2. The practical performance of the detection system is tested in the suburban area for 24 h. The intercomparisons between the LIF instrument and a photofragmentation chemiluminescence (PF-CL) instrument have been performed under laboratory conditions. The correlation between the two instruments is mea...

Above-Threshold Effects in the Photodissociation and Photoionization of Iodobenzene†

Abstract: The method of velocity map imaging is used to investigate the photoinduced dynamics of iodobenzene in weak laser fields as well as in fields of sufficient intensity to produce multiphoton excitation without dressing the potential energy surfaces. The speed and angular distributions of the recoiling iodine atoms observed with weak fields at 266 and 304 nm are in good agreement with previous studies, showing evidence of dissociation via n,σ* and π,π* states. Density functional theory calculations are used to determine the energies of the excited states. Ion and electron images produced with intense visible radiation (532−609 nm, 3 × 1010 to 5 × 1012 W/cm2) show both two-photon threshold dissociation and higher order (four- to seven-photon) ionization processes. A unique characteristic of the I+ images obtained with intense visible radiation is a continuous, hourglass-shaped feature peaked at zero kinetic energy, displaying highly nonstatistical speed and angular distributions. A mechanism that is consistent...

Airborne vacuum ultraviolet resonance fluorescence instrument for in situ measurement of CO

Abstract: An airborne instrument for fast-response, high-precision measurement of tropospheric carbon monoxide (CO) was developed using a vacuum ultraviolet (VUV) resonance fluorescence technique. The excitation radiation is obtained by a DC discharge CO resonance lamp combined with an optical filter for the CO fourth positive band emission around 150 nm. The optical filter consists of a VUV monochromator and a crystalline quartz window (<147-nm cutoff). The crystalline quartz window ensures a sharp discrimination against wavelengths below 135.7 nm that yield a positive interference from water vapor. Laboratory tests showed that the optical system achieved a precision of 1. 1 parts per billion by volume (ppbv) at a CO concentration of 100 ppbv for a 1-s integration period, and the flow system provided a response time (1/e time constant) of ∼2 s. The aircraft measurement campaign Biomass Burning and Lightning Experiment-phase B (BIBLE-B) was conducted between August and September 1999 over the western Pacific and Australia. The flight data obtained during this campaign were used to demonstrate the high precision and fast response of the instrument. An intercomparison of the VUV CO measurement and a gas chromatographic CO measurement was conducted during BIBLE-B. Overall, these two independent measurements showed good agreement, within the experimental uncertainties.

Reaction Processes of O( 1 D) with fluoroethane compounds

Abstract: Product branching ratios and rate constants for the O(3P) atom and OH radical formation processes in the reaction of electronically excited oxygen O(1D) atoms with fluoroethanes were measured at room temperature. The reactions of CHF2−CF3 (HFC-125), CH2F−CF3 (HFC-134a), CHF2−CHF2 (HFC-134), CH3−CF3 (HFC-143a), CH2F−CHF2 (HFC-143), and CH3−CHF2 (HFC-152a) were studied. Laser-induced fluorescence techniques using vacuum and near-ultraviolet lasers are applied to the detection of O(1D, 3P2) atoms and OH radicals, respectively. The results are compared with previous investigations, and reaction mechanisms are discussed on the basis of the present results. The rate constants for the OH radical production were proportional to the total number of H atoms included in the fluoroethane reactants, and those for the reaction processes are interpreted with the molecular structures of fluoroethane reactants.

Above-Threshold Dissociative Ionization in the Intermediate Intensity Regime

Abstract: The problem of dissociative ionization at intermediate intensities ( ${10}^{10}--{10}^{12}\mathrm{W}{\mathrm{cm}}^{\ensuremath{-}2}$) was studied using the example of ${\mathrm{I}}_{2}$ and the technique of velocity map imaging. Several new phenomena were observed, including a continuous distribution of recoil energies peaked at zero-kinetic energy, a set of constant dissociative ionic states, and strong anisotropy of the fragment velocity distribution that is diminished by intermediate resonances.

Doppler Profiles of the Distribution of O( 1 D) Relaxing in Ne

Abstract: The relaxation of hot atoms in a gaseous moderator remains a fundamental problem in rarefied gas dynamics [1, 2]. The rate of relaxation of energetic particles to equilibrium has important applications in diverse fields. In addition to the calculation and measurement of relaxation times, in recent years there have been numerous measurements of the details of the relaxing velocity distribution functions by Doppler spectroscopy [3, 4]. For example, Park et al [5] have investigated the relaxation of H atoms produced in laser dissociation of H2S at 193 nm. They measured the Doppler profiles of the H atoms at the Lyman-α line during the relaxation by collisions with the rare gases and some molecular moderators. Nan and Houston [6] monitered the velocity relaxation of S(1D) by He, Ar and Xe by measuring the Doppler profile of S(1D) created by pulsed laser photolysis of OCS at 222 nm. Cline et al [7] reported the relaxation of hot I(2 P 1/2) that was produced from photodissociation of of n-C3F7I at 266 nm in a background of He.