Kenshi Takahashi

Observation of the spin‐forbidden O(1D)+O2(X 3Σg−) channel in the 317–327 nm photolysis of ozone

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.

Determination of the heat of formation of O3 using vacuum ultraviolet laser-induced fluorescence spectroscopy and two-dimensional product imaging techniques

Two different techniques, vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy and two-dimensional (2D) ion counting product imaging, have been used to determine the bond energy for the dissociation of jet-cooled O3 into O(1D)+O2(a 1Δg). The photofragment excitation (PHOFEX) spectrum for O(1D) products is recorded by detecting the VUV-LIF signal associated with the 3s 1D0–2p 1D transition at 115.22 nm while scanning the photolysis laser wavelength between 305 and 313 nm. A clear cut-off corresponding to the appearance threshold into O(1D)+O2(a 1Δg) is observed in this PHOFEX spectrum. The 2D image of the O(1D) products from the O3 photolysis near 305 nm is measured using an ion-counting method, with the detection of O(1D) atoms by [2+1] resonance enhanced multiphoton ionization (REMPI) at 205.47 nm. The kinetic-energy distribution obtained from the 2D image shows rotational structure due to the O2(a 1Δg,v″=0) fragment. The bond energy into O(1D)+O2(a 1Δg) has been obtained from the rotatio...

Wavelength and temperature dependence of the absolute O(^1D) production yield from the 305–329 nm photodissociation of ozone

O(1D) and O(3Pj) photofragments produced in the photodissociation of ozone in the wavelength range 305–329 nm both at 295 and 227 K have been detected directly using a technique of laser induced fluorescence (LIF) in the vacuum ultraviolet (vuv). Photofragment excitation (PHOFEX) spectra for both species have been measured by scanning the photodissociation laser wavelength whilst monitoring vuv-LIF at 115 nm [O(1D)] and 130 nm [O(3Pj)]. After applying suitable corrections for the relative detection sensitivities, suitably weighted combinations of these PHOFEX spectra were found to provide a quantitative match to the parent O3 absorption spectrum both at 295 and 227 K, thereby providing a method of determining both the wavelength and temperature dependence of the absolute O(1D) quantum yield, Φ1D(λ,T). Hot band excitation of internally excited O3 molecules and dissociation via the spin-allowed channel yielding O(1D)+O2(a 1Δg) products makes the dominant contribution to the quantum yield Φ1D(λ,T) in the wav...

Stratospheric ozone isotope enrichment studied by submillimeter wave heterodyne radiometry: the observation capabilities of SMILES

The isotopic ratio of molecules often provides valuable information about past or presently occurring processes in the atmosphere because chemical and physical processes may give rise to isotope fractionation of molecular species. However, there are so far no published satellite measurements on the spatial and temporal variations of ozone isotopes in the stratosphere. Spectroscopic remote sensing methods can theoretically be used to observe ozone isotope fractionation on a global scale, but sufficient accuracy has not yet been achieved. A new generation of submillimeter-wave receivers employing sensitive superconductor-insulator-superconductor (SIS) detector technology will provide new opportunities for precise remote sensing measurements of ozone isotopes on a global scale. We have estimated the observation capabilities of two different SIS instruments, namely the space-station-borne Japanese Experimental Module/Sub-Millimeter-wave Limb Emission Sounder (JEM/SMILES) instrument, currently planned for launch in 2008, as well as the airborne Submillimeter wave Atmospheric Sounder/Airborne Submillimeter SIS Radiometer (SUMAS/ASUR) sensor. Measurements of the airborne sensor, conducted in 1996, are presented in order to demonstrate the detection of normal-O/sub 3/ and asymmetric-18-O/sub 3/ in the SMILES frequency bands. In the ideal case, JEM/SMILES has the capability to measure the ozone isotope enrichment (/spl delta//sup M/O/sub 3/) in the middle stratosphere with a precision of /spl sim/12/sup 0///sub 00/, /spl sim/11/sup 0///sub 00/, and /spl sim/9/sup 0///sub 00/, for asymmetric-18-O/sub 3/, symmetric-17-O/sub 3/, asymmetric-17-O/sub 3/, respectively, for a daily zonal mean product with resolution of 10/spl deg/ in latitude. The systematic error, including contributions of all instrumental and spectroscopic uncertainties, is estimated to be of the order of 100/sup 0///sub 00/ to 200/sup 0///sub 00/ and should be reduced by prelaunch laboratory measurements and in-flight calibrations. A remaining bias in the SMILES measurements will have to be quantified by dedicated validation campaigns. JEM/SMILES should then be capable to provide valuable information on the global distribution and seasonal variation of ozone isotope fractionation in the stratosphere. This new technology will allow us to shed new light on this still open issue in atmospheric sciences.

Trace detection of atmospheric NO2 by laser-induced fluorescence using a GaN diode laser and a diode-pumped YAG laser.

We report on the development of a highly sensitive detection system for measuring atmospheric NO(2) by means of a laser-induced fluorescence (LIF) technique at 473 nm using a diode-pumped Nd:YAG laser. A GaN-based laser diode emitting at 410 nm is also used as an alternative fluorescence-excitation source. For laboratory calibrations, standard NO(2) gas is diluted with synthetic air and is introduced into a fluorescence-detection cell. The NO(2) LIF signal is detected by a photomultiplier tube and processed by a photon-counting method. The minimum detectable limits of the NO(2) instrument developed have been estimated to be 0.14 ppbv and 0.39 ppbv (parts per billion, 10(-9), by volume) in 60 s integration time (signal-to-noise ratio of 2) for 473 and 410 nm excitation systems, respectively. Practical performance of the instrument has been demonstrated by the 24 hour continuous measurements of ambient NO(2) in a suburban area.

TRANSLATIONAL ENERGY AND ANGULAR DISTRIBUTIONS OF O(1D) AND O(3PJ) FRAGMENTS IN THE UV PHOTODISSOCIATION OF OZONE

Abstract Nascent O( 1 D ) and O( 3 P ) photoproducts from the photodissociation of O 3 are state-selectively detected in a flow cell, using a technique of vacuum-ultraviolet laser-induced fluorescence. Doppler profiles of the O( 1 D ) atoms are measured in the photodissociation of O 3 at 193, 230, and 266 nm, and those of the O( 3 P ) atoms at 193, 266 and 308 nm. The translational energy and the speed-resolved spatial angular distributions are derived from the Doppler profiles, from which photodissociation dynamics at each wavelength is discussed. The photodissociation dynamics in the Hartley band is characterized by the spin-allowed photodissociation processes from the O 3 ( 1 B 2 ) state. Below the blue end of the Hartley band, the photoexcitation process is mainly perpendicular transition. Multiple peaks observed in the translational energy distribution of O( 1 D ) and O( 3 P ) photoproducts from the photodissociation of O 3 at 193 nm are attributed to multiple dissociation processes accessible energetically.

Kinetics and mechanism of chlorine-atom-initiated oxidation of allyl alcohol, 3-buten-2-ol, and 2-methyl-3-buten-2-ol.

The gas-phase reactions of Cl atoms with allyl alcohol (k(1)), 3-buten-2-ol (k(2)), and 2-methyl-3-buten-2-ol (k(3)) at 296 +/- 2 K have been investigated using absolute and relative rate methods in 1-700 Torr of N(2) diluent. Absolute rate studies were performed using pulsed laser photolysis/vacuum ultraviolet laser-induced fluorescence spectroscopy techniques. Relative rate studies were performed using smog chamber/Fourier transform infrared spectroscopy techniques. The absolute and relative rate studies gave consistent results. The kinetics of the reactions are dependent on pressure over the range studied. Molar yields for HCl production in 700 Torr of N(2) for reactions of chlorine atoms with allyl alcohol, 3-buten-2-ol, and 2-methyl-3-buten-2-ol were measured to be 0.26 +/- 0.03, 0.23 +/- 0.03, and 0.12 +/- 0.02, respectively. The chlorine-atom-initiated oxidation of 2-methyl-3-buten-2-ol in 700 Torr of air gave the following products (molar yields): acetone (47 +/- 4%), chloroacetaldehyde (47 +/- 5%), and HCHO (7.2 +/- 0.6%). The observation of substantial and indistinguishable yields of acetone and chloroacetaldehyde products indicates that a major fraction of the reaction proceeds via addition of chlorine atoms to the terminal carbon atom. The results are discussed with respect to the literature data.

Quantum yields of O(1D) formation in the photolysis of ozone between 230 and 308 nm

[1] Ozone molecules are photolyzed in the strong photoabsorption band of the Hartley band at 230-308 nm, and the O( 3 P j ) photofragments produced by the photolysis are detected directly by a technique of laser-induced fluorescence around 130 nm. The quantum yield values for O( 1 D) formation in the photolysis of ozone at 297 ± 2 K are determined as a function of the photolysis wavelength, using the O( 1 D) quantum yield value of 0.79 at 308 nm as a reference. The O( 1 D) quantum yield values obtained are found to be almost independent of the photolysis wavelength over the Hartley band (∼0.91). The results are compared with the values measured previously using various experimental techniques and also with the recommendation values for use in atmospheric modeling. The effects of the present yield data on the O( 1 D) production rates from ozone photolysis in the stratosphere are evaluated. Impact of our new O( 1 D) quantum yield values on the stratospheric chemistry has also been explored using a one-dimensional photochemical model. The smaller O( 1 D) production rates as compared to the latest NASA/JPL recommendation values are followed by changes in the efficiency of the chemical chain reactions involving HO x , NO x , and ClO x and result in the higher O 3 concentrations throughout the stratosphere.

Characterization of Aerosol Particles in the Tokyo Metropolitan Area using Two Different Particle Mass Spectrometers

Particle mass spectrometers of two types—a time-of-flight aerosol mass spectrometer (AMS) of Aerodyne Research Inc. and a laser desorption/ionization single particle aerosol mass spectrometer (LISPA-MS) developed at Nagoya University—were deployed to characterize aerosol particles in the Tokyo metropolitan area during the summer of 2008. Based on the ensemble measurements by AMS, equivalent mass concentration of organic aerosol, traced by mass-to-charge ratio (m/z) 44, showed a closer correlation with particulate nitrate and gas-phase odd oxygen, [O 3 +NO 2 ], whereas equivalent mass concentration of organic aerosol, traced by m/z 57, did not. On a particle-by-particle basis, the relative signal peak area of various target species in the LISPA-MS spectra, which was calculated as the ion-signal fraction of the species relative to the total signal peak area summed over all the ion peaks in each spectrum, was used as a measure of the relative amount of the species. A rough qualitative agreement was obtained between the temporal variation observed in the LISPA-MS RCOO– signal and that in the AMS m/z 44, but not the AMS m/z 57, in which the LISPA-MS RCOO– signal was defined as the sum of the relative signal peak areas of 17 different negative-ion mass peaks used as markers of oxygenated organics. Analysis of the LISPA-MS spectra also showed that approximately 95% of the oxygen-containing organic particles contained nitrate, which is expected to be responsible in part for the correlation between AMS m/z 44 and AMS nitrate.

Atmospheric chemistry of BrO radicals: kinetics of the reaction with C2H5O2 radicals at 233-333 K.

Cavity ring-down spectroscopy was used to study the title reaction in 50-200 Torr of O2 diluent at 233-333 K. There was no discernible effect of total pressure, and a rate constant of k(BrO + C2H5O2) = (3.8 +/- 1.7) x 10(-12) cm3 molecule(-1) s(-1) was determined at 293 K in 150 Torr total pressure of O2 diluent. The addition of 1.4 x 10(17) molecules cm(-3) of H2O vapor had no measurable impact on k(BrO + C2H5O2) at 293 K and 150 Torr. The rate constant exhibited a negative temperature dependence and was described by k(BrO + C2H5O2) = 6.5 x 10(-13) exp((505 +/- 570)/T) cm3 molecule(-1) s(-1). Results are discussed with respect to the atmospheric chemistry of BrO radicals.