Search

We report on the development of a low-cost and compact instrument for quantifying atmospheric N[O.sub.2] concentrations by detecting N[O.sub.2] fluorescence using a commercial light-emitting diode around 435 nm as a fluorescence excitation light source. The minimum detectable limit of the N[O.sub.2] instrument developed has been estimated to be 9.8 parts per billion of volume mixing ratio (ppbv) in a 60 s integration time and with a signal-to-noise ratio of 2. [c] 2010 Optical Society of America OCIS codes: 010.0010, 010.1280, 010.7030, 230.3670, 300.6280.

We report on the development of a highly sensitive detection system for measuring atmospheric N[O.sub.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 N[O.sub.2] gas is diluted with synthetic air and is introduced into a fluorescence-detection cell. The N[O.sub.2] LIF signal is detected by a photomultiplier tube and processed by a photon-counting method. The minimum detectable limits of the N[O.sub.2] instrument developed have been estimated to be 0.14 ppbv and 0.39 ppbv (parts per billion, [10.sup.-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 N[O.sub.2] in a suburban area. OCIS codes: 010.0010, 010.1280, 010.7030, 140.0140, 140.2020, 140.3480.

Formation of the ground-state nitrogen atom, N((super 4)S), following 193.3-nm ArF laser irradiation of NO and NO2 is detected directly by a technique of laser-induced fluorescence spectroscopy at 120.07 nm. The rate constants for the reactions of N((super 4)S) with NO and NO2 are determined to be (3.8 plusmn 0.2) x 10(super -11) and (7.3 plusmn 0.9) x 10(super -12) cm(super 3) molecule(super -1)s(super -1), respectively.

Smog chamber/Fourier transform infrared and laser-induced fluorescence spectroscopic techniques are used to study the atmospheric degradation of CH3CHF2. Reaction with Cl atoms gives CH3CF2 radicals in a yield of 99.2 plusmn 0.1% and CH2CHF2 radicals in a yield of 0.8 plusmn 0.1%.

The kinetics of reactions of Cl and Cl* atoms with Ch2OH, C2H5OH, n-C3H7OH, and i-C3H7OH is studied at 295 K using laser flash photolysis/laser-induced-fluorescence techniques. Under ambient conditions spin-orbit excited Cl* atoms are responsible for 0.5%, 0.5%, 0.4%, and 0.7% of the observed reactivity of thermalized chlorine atoms toward Ch3Oh, C2H5OH, n-C3H7OH, and i-C3H7OH.

The formation of O(3P) from N2O photolysis at 193 nm through the direct detection of the O(3P) atoms using a laser-induced fluorescence (LIF) technique is reported. Further study on the impact of the existence of channel 2c on the stratospheric chemistry by atmospheric model calculations with a one-dimensional dynamical and photochemical model is presented.

We report on the development of a high-sensitivity detection system for measuring atmospheric N[O.sub.2] 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 N[O.sub.2] concentration. This procedure can give a good selectivity for N[O.sub.2] and avoid interferences of fluorescent or particulate species other than N[O.sub.2] in the sample air. The N[O.sub.2] 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 measured up to 1000 pptv. A good linear relationship between the LIF measurements and the PF-CL measurements is obtained.

Photodissociation reaction of O3 following ultraviolet photon excitation around the thermodynamic threshold is studied under room temperature and jet-cooled condition and the photoproducts are detected by vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy. This model includes the contributions of the spin-forbidden process and thermal excitation in the vibrational and rotational states of O3 molecules in electronically ground state.

Translational energy relaxation and electronic quenching to O(3P), two processes resulting from the collisions of translationally hot O(1D) with O2, have been investigated using the vacuum ultraviolet laser-induced fluorescence technique. The experimentally obtained collision energy dependence is the result of the centrifugal forces on the entrance attractive potential.

Potential energy curves of triplet states for collinear O-O[sub 2] were calculated by ab initio CASSCF and MRSDCI methods. We found a pseudocrossing between 1 ³Σ[sup -] (6 ³A″) and 2 ³Σ[sup -] (7 ³A″) states at long O-O[sub 2] separation. The electronic quenching reaction, O(¹D)+O[sub 2](X ³Σ[sup -, sub g])→O(³P) + O[sub 2](b ¹&Sigma[sup +, sub g]), is dominated by the nonadiabatic transition via the pseudocrossing. The collision energy dependence of the quenching reaction probability, which is evaluated by Zhu and Nakamura's formula, is found to be in good agreement with experiment. [ABSTRACT FROM AUTHOR]

Cl(2P3/2) and Cl*(2P1/2) atoms produced from the photodissociation of chloroflurocarbons (CFCs) and chlorinated hydrocarbons are detected quantitatively by a technique of vacuum ultraviolet laser-induced fluorescence spectroscopy. The UV photodissociation processes giving rise to formation of Cl(2Pj) atoms from the chlorinated compounds studied are discussed.

An experimental study to determine the absolute O[(super 1)D] quantum yield from ozone photolysis at 308 nm and room temperature by using a technique of vacuum ultraviolet-laser-induced fluorescence is conducted. The O[(super 1)D] quantum yield values at photolysis wavelengths between 307 and 311.5 nm are presented.

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 values for O((super 1)D) production from the photodissociation reaction of O3 between 193and 225 nm at 298 plusmn 2K are reported. It is found that the O((super 1)D) quantum yield values decrease monotonically as the photolysis wavelength become shorter from 0.90 plusmn 0.12 (225nm) to 0.48 plusmn 0.03 (193 nm).

The performance of the effective fragment potential (EFP) method, a quantum mechanical-molecular mechanical (QM-MM) method, to reproduce fully quantum mechanical results is investigated. The findings suggest that reduced variational space analysis can be used to predict which systems may pose problems for the EFPO method.