Photodissociation Of NO Research Articles

On the origins of night-time NO at a rural measurement site

Mixing ratios for NO and NO 2 were measured during 1980/1981 at Deuselbach, a rural site in Germany. The data are analyzed with regard to the occurrence of nocturnal NO signals and their origins. Anthropogenic influences arising from road traffic and home heating activities are identified by their dependence on wind direction. An additional non-directional component is found to exist. It shows up most frequently in summer and when it occurs, the NO mixing ratio increases with rising temperature indicating a biological origin of night-time NO. The temporal behavior of night-time NO is usually correlated with that of CO 2 but anticorrelated to that of O 3. This shows that NO is brought upwards to the air intake of the NO x monitor from lower levels and that the source of the non-directional component of nocturnal NO is the earth's surface. The release of NO from soils is known from other work and this process is probably also responsible for the present observations. A flux estimate agrees with soil fluxes reported by other authors. The accumulation of NO in the surface air layer under stagnant conditions leads to the appearance of a morning peak of NO after sunrise when increased vertical mixing brings NO rich air up to the monitoring level. During summer, the morning peak may override the NO peak expected to occur at noon due to the photodissociation of NO 2.

The troposphere-stratosphere radiation field at twilight: A spherical model

Time-dependent calculations of trace constituent distributions require as input the dissociating radiation field as a function of altitude and solar zenith angle. An isotropic, spherical, multiple scattering model of the radiation field has been developed to determine the radiation field at twilight. Comparison of the spherical model with a plane parallel model at twilight shows that: (1) for solar zenith angles less than 92°, plane parallel solutions for the source function are suitable if the initial deposition of solar energy is calculated for a spherical atmosphere; (2) for solar zenith angles greater than 92°, the plane parallel radiation field can be several orders of magnitude smaller than that calculated with the spherical model; (3) at altitudes above 40 km and at all solar zenith angles, the spherical model predicts 10–20% less radiation than the radiation field calculated with the plane parallel model. Calculations of the rate of photodissociation of NO 2 in the troposphere and stratosphere show that the spherical model yields significantly higher values at solar zenith angles greater than 92°.

XPS, ESR and resistivity measurements on amorphous silicon oxynitride films (a-SiO xN y) prepared by reactive evaporation of Si in presence of NO 2

Silicon oxynitride films (SiO x N y ) are prepared by reactive, electron gun evaporation of Si at nitrogen dioxide pressures ranging from 10 −6 T to 5 × 10 −5 T. In this way the brightness of W-filament of the electron gun probably contributes to the photodissociation of NO 2 and favours the introduction of oxygen. The oxygen composition, determined by XPS analysis, may be varied nearly over the entire range between Si and SiO 2 (O < x < 2), that of the nitrogen remaining limited (y < 0.4) Starting from pure a-Si, with rising NO 2 pressures and oxygen content, the resistivity and the optical transmission vary gradually — as for a-SiO x samples — to insulating and transparent samples. The XPS Si 2p electron energy shift and the ESR g-value shift are also well connected with the composition and the local surroundings of the Si atoms. The behaviour of thse spectra versus the composition provides arguments for a description of the structure of the SiO x N y films with a ternary random bonding model and local bondings of the kind |Si-(Si 4− X− Y O X N Y )| ( X or Y = 0, 1, 2, 3, but Y is generally less than X, X + Y ⩽ 4). On the other hand the ESR spin density remains high (10 18–10 19 cm −3) if care is taken in its determination, and is not related to the conduction and the sample composition for high x values, but seems to be connected with the method of preparation.

Laser photodissociation of NO 2 at 248 nm and production of NO(A 2Σ + → X 2Π) fluorescence

Laser photodissociation of NO 2 at 248 nm and production of NO(A 2Σ + → X 2Π) fluorescence

Variations of NO, NO 2 and O 3 concentrations downwind of a Los Angeles freeway

A sampling study was conducted to quantify the relationships of NO, NO 2 and O 3 concentrations with distance downwind of the San Diego freeway in Los Angeles. By continuously, monitoring at a site upwind (background) of the freeway and at selected downwind sites, patterns of NO, NO 2 and O 3 concentrations were detailed. Minimal separation distances of the samplers from the roadway to eliminate measurable influence were estimated to be approx 400–500 m for NO, NO 2 and O 3. A spatial model was fitted to the empirical NO and NO 2 data, which incorporated the effects of dilution, reaction and background level on measured downwind concentration. This model fit the experimental data closely and indicated that: 1. (1) the decrease of NO x downwind of the freeway can be expressed by a simple exponential dilution, 2. (2) the reaction of NO and O 3 downwind of the freeway is not well mixed and deviates from the ideal photostationary state, and 3. (3) the simple rate equations for the reaction of NO with O 3 and the photodissociation of NO 2 could be combined with a simple exponential dilution term to define the measured concentrations of NO 2.

Photodissociation of cytochrome oxidase-nitric oxide at low temperatures.

Spectrophotometric studies revealed the irreversible photodissociation of reduced cytochrome oxidase-nitric oxide (NO) at 5 K. The dissociated NO recombined as the sample temperature was raised, and the half-recombination temperature was 65 K. The photodissociation at 5K was also confirmed by a change in the EPR spectrum; that is, ferroheme a-NO signals at gx=2.09 and gm=2.006 were replaced by a new signal at gm=2.03, and this change was reversed at the temperature of liquid nitrogen. Comparison of such behavior with that of cytochrome oxidase-carbon monoxide led us to propose that on photodissociation of NO from heme iron, the NO was trapped specifically at a site near the heme iron producing a new paramagnetic species. Its identification will require further studies.

Sensitivity of the photodissociation of NO 2, NO 3, HNO 3 and H 2O 2 to the solar radiation diffused by the ground and by atmospheric particles

The diffusion of solar radiation by atmospheric molecules and aerosols and by ground albedo affects the photodissociation rates of atmospheric species relevant to the ozone chemistry. In this paper, a previous investigation on the photodissociation of O 3 by Fiocco et. al., (1978) is extended to NO 2, NO 3, HNO 3, H 2O 2. Because of the different character of the absorption spectra of these species, the behaviour of photodissociation profiles with height and their sensitivity to such factors as ground albedo, aerosol loads, solar zenith angle are somewhat different. The results show that the presence of the aerosols usually enhances the photodissociation in the upper troposphere and in the stratosphere, because of scattering, but tends to reduce it at low heights because of the increased extinction. Enhancements in the photodissociation coefficients are as high as 20–40% for low values of the albedo and large aerosol loads such as those obtained after a volcanic eruption. On the other hand, at large values of the albedo, the effect of aerosols is mainly in attenuating the radiation going into and coming from the ground and their presence can lead to reduced photolysis even in the stratosphere.

Dependence of the NO 2 photodissociation rate constant on altitude

An important parameter of photochemical diffusion models is the rate constant ( k) for the photodissociation of NO 2. Theoretical values of k were determined as a function of altitude (surface to 4.2 km) and solar zenith angle (0°–86°), based on calculations of solar actinic flux for average atmospheric conditions. Between the surface and an altitude of 1.0 km, for example, k increases by 21%–70%, depending on solar zenith angle. The effect of greater than average aerosol loadings on the change of k with height was also estimated. As low-level aerosol concentrations increase, so does the vertical gradient of k. The theoretical calculations were compared to measurements of incident ultraviolet radiation made at an urban and at a nearby mountain-top (1.82 km) site near Los Angeles. For similar aerosol optical thicknesses, the changes with altitude of empirical and theoretical downward radiative fluxes were similar.

The formation of O(3s 3S 0) and N(3s 4P) by photodissociation of NO

The dissociation of NO molecules to excited atomic states by dispersed synchrotron radiation (700 Å – 800 Å) is investigated by observing vuv-fluorescence (1050 Å – 1400 Å) of the fragments. The atomic levels are populated by predissociation of high-lying molecular states.

Formation of N2(A3Σu+) and N(2D, 2P) by Photodissociation of HN3 and N2O and Their Reactions with NO and N2O

The formation of NO (A 2Σ+) and NO (B 2II) in the photolysis of N2O at 1236 and 1470 Å was investigated by observing the fluorescence of the γ and β bands. The β-band fluorescence is obtained when pure N2O is photolyzed at 1236 and 1470 Å in a flow system. The β bands are observed with vibrational excitation up to v′=3. The β bands disappear with the addition of small amounts of NO, whereas the emission of rotationally hot γ bands is obtained. The γ bands are observed with vibrational excitation up to v′=2. According to the energetics, NO (A 2Σ+) and NO (B 2II) are formed at 1470 Å as well as at 1236 Å not by direct photodissociation of N2O but by secondary reactions. No fluorescence is obtained when N2O or N2O/NO mixtures are irradiated at wavelengths ≧1600 Å, i.e., within the long-wavelength absorption band of N2O. The roles of N2 (A 3Σu+), N (2D), N (2P) are evaluated and discussed. The emission of γ bands is also obtained in the photolysis of HN3/NO mixtures at 1470 and 1236 Å. This observation is explained by the photodissociationHN3→N2(A Σu+)+NH(X 3Σ−)followed by the reaction between N2 (A 3Σu+) and NO, yielding NO (A 2Σ+). The other possibility, that O atoms which are formed by photodissociation of NO react with HN3 to form excited NO—as in the O/N2H4 atomic flame—is excluded.

The spectrum of no: rotational analysis of epsilon bands and new observations on the beta and delta band-systems

A rotational analysis has been made for the (0,4) and (0,3) bands of the system of nitric oxide. Rotational constants have been evaluated and it has been shown from consideration of the defect (due to A doubling) between P, Q and R combinations that the initial electronic state is of type 2Σ+. Potential-energy curves for the known electronic states of NO are shown. Some observations have also been made on the excitation of the β and δ systems of NO in the nitrogen afterglow. Bands of the β system with ν'=5 and 6 have been obtained in emission. The energy of dissociation of NO and supposed predissociations in the spectrum are discussed. Flory and Johnston's interpretation of the photodissociation of NO by Hg 1832 A. appears to be incompatible with the present observations on the spectrum.