Photodissociation Of NO2 Research Articles

Detection of “ended” NO recoil in the 355 nm NO2 photodissociation mechanism

Circularly polarized 1+1′ REMPI with ion imaging detection was used to probe μ–v–j angular correlations of the NO (X 2Π1/2,3/2, v=0) photoproduct from linearly polarized 355 nm photodissociation of NO2 in a molecular beam. Rotational angular momentum orientation was measured for the NO product, with the sense and magnitude of the orientation depending upon the direction of the NO recoil velocity with respect to the polarization vector of the photolysis light. The rotational orientation is shown to originate from the directionality of the torque responsible for NO rotational motion. The experimentally observed sense of rotation in the plane of the NO2 parent molecule is consistent with an effective recoil impulse force applied to the N end of the NO product. A preliminary measure of the bipolar moment associated with this orientation for the j=21.5 and j=36.5 rotational levels gives a value of approximately β02(21)=0.2.

Comparison of observed and simulated NO2 photodissociation rates using measured aerosol and drop size distributions

Comparison of observed and simulated NO2 photodissociation rates using measured aerosol and drop size distributions

Quantum fluid dynamics in the Lagrangian representation and applications to photodissociation problems

This paper considers the practical utility of quantum fluid dynamics (QFD) whereby the time-dependent Schrödinger’s equation is transformed to observing the dynamics of an equivalent “gas continuum.” The density and velocity of this equivalent gas continuum are respectively the probability density and the gradient of the phase of the wave function. The numerical implementation of the QFD equations is carried out within the Lagrangian approach, which transforms the solution of Schrödinger’s equation into following the trajectories of a set of mass points, i.e., subparticles, obtained by discretization of the continuum equations. The quantum dynamics of the subparticles which arise in the present formalism through numerical discretization are coupled by the density and the quantum potential. Numerical illustrations are performed for photodissociation of NOCl and NO2 treated as two-dimensional models. The dissociation cross sections σ(ω) are evaluated in the dramatically short CPU times of 33 s for NOCl and 40 s for NO2 on a Pentium-200 MHz PC machine. The computational efficiency comes from a combination of (a) the QFD representation dealing with the near monotonic amplitude and phase as dependent variables, (b) the Lagrangian description concentrating the computation effort at all times into regions of highest probability as an optimal adaptive grid, and (c) the use of an explicit time integrator whereby the computational effort grows only linearly with the number of discrete points.

Ab initio ground potential energy surface, VTST and QCT study of the O(3P)+CH4(X 1A1)→OH(X 2Π)+CH3(X 2A2″) reaction

An ab initio study of the ground potential energy surface (PES) of the O(3P)+CH4→OH+CH3 reaction has been performed using the second- and fourth-order Mo/ller–Plesset methods with a large basis set. A triatomic analytical ground PES with the methyl group treated as an atom of 15.0 a.m.u. has been derived. This PES has been employed to study the kinetics [variational transition state theory (VTST) and quasiclassical trajectory (QCT) rate constants] and dynamics (QCT method) of the reaction. The ab initio points have also been used directly to calculate the VTST rate constant considering all atoms of the system. The best VTST methods used lead to a good agreement with the experimental rate constant for 1000–2500 K, but QCT rate constant values are about one-third the experimental ones for 1500–2500 K. The cold QCT OH(v=0) rotational distribution arising from the simulation of the reaction with O(3P) atoms produced in the photodissociation of NO2 at 248 nm is in good agreement with experiment, while the very small QCT OH(v=1) population obtained is consistent with measurements. The triatomic PES model derived in this work may be used in studies of the kinetics and dynamics under conditions where the methyl group motions are not strongly coupled to the motions leading to reaction.

Coherence in polyatomic photodissociation: Aligned O(3P) from photodissociation of NO2 at 212.8 nm

Strong orbital alignment is observed in the ground-state oxygen atom following photodissociation of NO2 at 212.8 nm using ion imaging. The imaging method allows for investigation of the angular distribution of this alignment, providing insight into the dynamics in the frame of the molecule. The results are analyzed using a rigorous quantum mechanical theory yielding alignment parameters having direct physical significance. This alignment is dominated by a strong incoherent parallel contribution. In addition, the results reveal direct evidence of coherence between parallel and perpendicular contributions to the excitation of a polyatomic molecule, showing that the electron cloud in the recoiling atom “remembers” the original molecular plane.

Photodissociation of N2O: J-dependent anisotropy revealed in N2 photofragment images

Photofragment imaging is used to measure the state-specific angular distributions of N2 produced in the ultraviolet photodissociation of N2O. 2+1 REMPI (resonance enhanced multiphoton ionization) through the a″(1Σg+) state is used to ionize individual rotational states of N2(ν=0) between J=40 and J=90 produced when N2O is dissociated by light of approximately 203 nm. The anisotropy parameter, β, used to characterize the angular distributions of the N2 ion images, is greater than one for the lower rotational levels probed, and decreases to approximately zero for the highest rotational levels of N2. The positive beta parameter indicates that the products arise primarily from a parallel transition to the 2 1A′(1Δ) state in the parent molecule, and the decrease in β with increasing J of N2 is due to increased bending in the parent N2O during dissociation. The ion images also allow us to assign transitions in a spectroscopically perturbed region of the N2 photofragment REMPI spectrum and to reveal the production of N2 products in the first vibrationally excited state.

Probing the alignment of NO(X 2Π) by [2+1] resonance-enhanced multiphoton ionization via the C 2Π state: A test of semiclassical theory in 355 nm photodissociation of NO2

A theoretical method to analyze the two- and three-dimensional imaging data of photofragments with polarized angular momentum was tested by comparing with the experimental data on NO from 355 nm photodissociation of NO2. The alignment of NO(X 2Π) was detected by [2+1] resonance-enhanced multiphoton ionization via the C 2Π state. The data were analyzed by assuming the μ–ν–J triple vector correlation described by semiclassical multipole moments in the velocity-fixed frame. The geometrical factors for the two-photon absorption were derived rigorously for the intermediate coupling between Hund’s cases (a) and (b). It was also shown, however, that the geometrical factors for high J are independent of the coupling case and can be approximated by simple formulas. Excellent agreement between the simulation and the experimental data proved the validity of the semiclassical treatment.

Atomic orbital alignment and coherence in N2O photodissociation at 193.3 nm

Download options Please wait... Article information DOI https://doi.org/10.1039/A902626F Article type Paper Download Citation Faraday Discuss., 1999,113, 425-436 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Atomic orbital alignment and coherence in N2O photodissociation at 193.3 nm M. Ahmed, E. R. Wouters, D. S. Peterka, O. S. Vasyutinskii and A. G. Suits, Faraday Discuss., 1999, 113, 425 DOI: 10.1039/A902626F To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Musahid Ahmed Eloy R. Wouters Darcy S. Peterka Oleg S. Vasyutinskii Arthur G. Suits

Multidimensional wave packet dynamics within the fluid dynamical formulation of the Schrödinger equation

This paper explores the quantum fluid dynamical (QFD) representation of the time-dependent Schrödinger equation for the motion of a wave packet in a high dimensional space. A novel alternating direction technique is utilized to single out each of the many dimensions in the QFD equations. This technique is used to solve the continuity equation for the density and the equation for the convection of the flux for the quantum particle. The ability of the present scheme to efficiently and accurately describe the dynamics of a quantum particle is demonstrated in four dimensions where analytical results are known. We also apply the technique to the photodissociation of NOCl and NO2 where the systems are reduced to two coordinates by freezing the angular variable at its equilibrium value.

Zero Kinetic Energy Photofragment Spectroscopy: The Threshold Dissociation of NO2

A new type of photofragment spectroscopy has been developed and applied to the photodissociation of NO2. Photofragments with zero recoil kinetic energy are selectively detected as the total energy of the dissociating system is varied. The resulting spectra provide information about the transitions that occur between energy levels of the transition state and energy levels of the final products. With proper calibration of the laser wavelength, the method may be useful in the accurate identification of the dissociation threshold. The technique is demonstrated by the detection of O atoms from the near-threshold photodissociation of NO2. A sharp onset of signal occurs at the dissociation threshold of, while for higher energies, a new peak occurs as the energy threshold is reached for each possible NO internal state. An analysis of the intensity distribution of the spectral peaks suggests that the maximum orbital angular momentum allowed by the 0.5 cm-1 resolution of the instrument is near 5ℏ, implying that the...

Bimolecular Reaction Dynamics of Thiophosgene with O(3P) Atoms

The nascent vibrational and the near-nascent rotational state distributions for the SO(X3Σ-) product following the oxidation reaction of thiophosgene (CSCl2) with O(3P) have been studied by laser-induced fluorescence (LIF) spectroscopy on the (B3Σ-−X3Σ-) transition. O(3P) atoms are produced from the 355 nm photodissociation of NO2. The measured SO(X3Σ-) product vibrational state distribution can be characterized as Boltzmann with a vibrational temperature Tvib = 1150 ± 55 K corresponding to 8% of the available energy for the reaction. The statistical nature of the SO(X3Σ-) vibrational state distribution suggests a stable intermediate for this reaction, and ab initio calculations confirm a triplet dichlorosulfine (Cl2CSO(3A‘‘)) as a minimum on the excited triplet state potential energy surface. Statistical modeling of the observed SO(X3Σ-) vibrational state distribution results in an available energy E = 18 kcal/mol, which is 1.6 kcal/mol more than the exoergicity of this reaction. On the basis of ab initi...

Results from the Intergovernmental Panel on Climatic Change Photochemical Model Intercomparison (PhotoComp)

Results from the Intergovernmental Panel on Climatic Change (IPCC) tropospheric photochemical model intercomparison (PhotoComp) are presented with a brief discussion of the factors that may contribute to differences in the modeled behaviors of HOx cycling and the accompanying O3 tendencies. PhotoComp was a tightly controlled model experiment in which the IPCC 1994 assessment sought to determine the consistency among models that are used to predict changes in tropospheric ozone, an important greenhouse gas. Calculated tropospheric photodissociation rates displayed significant differences, with a root‐mean‐square (rms) error of the reported model results ranging from about ±6–9% of the mean (for O3 and NO2) to up to ±15% (H2O2 and CH2O). Models using multistream methods in radiative transfer calculations showed distinctly higher rates for photodissociation of NO2 and CH2O compared to models using two‐stream methods, and this difference accounted for up to one third of the rms error for these two rates. In general, some small but systematic differences between models were noted for the predicted chemical tendencies in cases that did not include reactions of nomnethane hydrocarbons (NMHC). These differences in modeled O3 tendencies in some cases could be identified, for example, as being due to differences in photodissociation rates, but in others they could not and must be ascribed to unidentified errors. O3 tendencies showed rms errors of about ±10% in the moist, surface level cases with NOx concentrations equal to a few tens of parts per trillion by volume. Most of these model to model differences can be traced to differences in the destruction of O3 due to reaction with HO2. Differences in HO2, in turn, are likely due to (1) inconsistent reaction rates used by the models for the conversion of HO2 to H2O2 and (2) differences in the model‐calculated photolysis of H2O2 and CH2O. In the middle tropospheric “polluted” scenario with NOx concentrations larger than a few parts per billion by volume, O3 tendencies showed rms errors of ±10–30%. These model to model differences most likely stem from differences in the calculated rates of O3 photolysis to O(1D), which provides about 80% of the HOx source under these conditions. The introduction of hydrocarbons dramatically increased both the rate of NOx loss and its model to model differences, which, in turn, are reflected in an increased spread of predicted O3. Including NMHC in the simulation approximately doubled the rms error for O3 concentration.

Detection of O(3P2) by Vacuum Ultraviolet Laser Spectroscopy

O atoms in the 3P2 state were detected by vacuum ultraviolet laser-induced fluorescence (VUV LIF) technique. The O(3P2) atoms were produced by the collision between the O atoms in the 1D excited state and collision partner N2. O atoms in the 1D excited state were obtained by photodissociation of N2O at 193 nm laser light. As O(3P2) species has their first transition in the VUV region, the probe laser was used to excite O(2p3Pj) atoms to the O(3s3So) state at 130.212 nm. A four wave difference frequency mixing (2ω1−ω2) process using Kr as nonlinear media was employed to generate 130.212 nm probe laser light.

Global inventory of NO x sources

Nitrogen oxides are key compounds for the oxidation capacity of the troposphere. NOx concentrations depend on the proximity of sources because of their short atmospheric lifetime. An accurate knowledge of the distribution of their sources and sinks is therefore crucial. At global scale, the dominant sources of nitrogen oxides - combustions of fossil fuel (∼50%) and biomass burning (∼20%) - are basically anthropogenic. Natural sources, including lightning and microbial activity in soils, represent therefore less than 30% of total emissions. Fertilizer use in agriculture constitutes an anthropogenic perturbation to the microbial source. The methods to estimate the magnitude and distribution of these dominant sources of nitrogen oxides are discussed. Some minor sources which may play a specific role in tropospheric chemistry such as NOx emission from aircraft in the upper troposphere or input from production in the stratosphere from N2O photodissociation are also considered.

State‐Resolved Stereodynamics of an Insertion Reaction O(1D2) + H2(v = 0, j) → OH(X2Πi; v′, N′, f′) + H

AbstractThe product state‐resolved stereodynamics of the reaction of O(1D2) with H2 have been studied at 300 K at a mean collision energy of ca. 12 kJ mol−1, using polarized, Doppler‐resolved laser‐induced fluorescence to probe the scattered products, OH(X2Πi; v′ = 0, N′, f′), and polarized photodissociation of N2O to provide the reagent O(1D2) atoms. Product state‐resolved differential cross sections, rotational polarizations, and excitation functions are in very good qualitative agreement with the results of quasi‐classical trajectory (QCT) calculations, conducted on the Schinke‐Lester, SL1 ab initio potential energy surface (PES) for the ground electronic state of the collision complex. The experimental and computational results are compared with those obtained in a complementary study of the reaction of O(1D2) with CH4 and remarkable parallels have been exposed. The linear and angular momentum vector correlations are all consistent with an “insertion” mechanism, proceeding over an attractive PES, which presents no entrance barrier.

The photodissociation threshold of NO2: Precise determination of its energy and density of states

The NO2 photodissociation threshold has been observed by laser induced fluorescence in a jet at 25 128.57±0.05 cm−1. The unexpected high vibronic level density of 2.7 levels/cm−1 is tentatively attributed to long range interactions between the NO (2Π1/2) and O(3P2) products. The energy spacing and intensity distributions indicate rovibronic chaos.

Observed and model‐calculated photostationary state at Mauna Loa Observatory during MLOPEX 2

During the Mauna Loa Observatory Photochemistry Experiment (MLOPEX 2), simultaneous clear sky measurements of [NO2], [NO], [O3], and NO2 photodissociation rate were collected during autumn 1991, winter, spring, and summer 1992 intensive measurement periods at Mauna Loa Observatory (MLO), Hawaii. These measurements were used to assess the O3‐NO‐NO2 photostationary state, and to infer peroxy radical concentration, ozone photochemical production and destruction rates, as well as the relationship between the deviation of the photostationary state parameter, ϕ = j2[NO2]/k1[O3][NO], from unity and environmental variables. In addition, a photochemical box model was used for the purpose of comparison with observations and interpretation of the results. A systematic deviation of ϕ from unity was determined from measurements, this parameter reached values of 1.5–2 for high‐sun conditions depending on the season. The inferred total peroxy radical concentrations were generally larger (25–70 pptv for high‐sun conditions depending on the season) than those directly measured (20–25 pptv during noontime). Model results seem generally to underestimate the value of ϕ and to overpredict the hydroxyl and total peroxy radical concentrations, suggesting loss processes not accounted for in the model for these species. Analysis of the contributions to the net ozone photochemical production indicates total production and destruction terms reaching 10–15 ppbv/day which tend to nearly cancel on a daily average basis. High‐sun values of ϕ − 1 were shown to be independent of NOx (= NO + NO2) for NOx concentrations above about 50 pptv. However, below this level, observations show that ϕ − 1 generally decreases with increasing nitrogen oxide concentrations. Furthermore, the measured ϕ − 1 correlation with suggests the existence of NO to NO2 oxidants not accounted for in a simplified HOx chemistry.

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

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 of O(1D) by collisions with N2 is not fast enough compared with the electronic quenching by N2. It is found that the steady state distribution of the O(1D) translational energy in the upper stratosphere is superthermal and that the populations at high translational energies are higher than that estimated from an equilibrated condition with the ambient air. The cross section of the electronic quenching by N2 at the high collision energy of (8±6) kcal mol−1 is found to be (0.7±0.1) Å2, which is about 5 times smaller than that at thermal collision energy at 298 K.

Nascent rotational and vibrational distributions in 16OH and 18OH produced in the reaction of O(1D) with H218O

Rotational and vibrational state distributions of the OH radicals produced in the reaction 16O(1D) +H218O → 16OH+ 18OH have been determined using a laser-induced fluorescence technique. 16O(1D) was prepared by the 193 nm photodissociation of N2O. The rotational distributions for 16OH and 18OH in the v = 0 level are characterized by the Boltzmann temperatures of 6000 and 2600 K, respectively. A considerable amount of 16OH exists in the v = 1 state while18OH was produced predominantly in the v = 0 state.

A Study on the Reaction of O(1D) and N2O by Trajectory Calculation and Time‐Resolved FTIR Spectroscopy

AbstractO(1D) atoms, generated via the laser photodissociation of N2O at 193 nm, reacting with N2O was studied by Time‐Resolved Fourier Transform Infrared (TR‐FTIR) Spectroscopy. The IR emission from NO(v1–11.) was collected at 30 μs after the laser was fired. Several instrumental corrections were made to obtain reliable experimental results. The vibrational temperature of the nearly‐nascent NO product was estimated to be Tv  9,000 K. A Quasi‐Classical Trajectory (QCT) calculation of the reaction was performed. The calculated results, corresponding to a head‐on attack mechanism, agree with the experimental data. Additional reaction channel with side‐on attack producing N2 and O2 was also studied by QCT, where vibrationally hot O2(a 1 Δg) and cold N2(X1∑g+) products are predicted.