Spectroscopy Of NO Research Articles

Applications of midinfrared quantum cascade lasers to spectroscopy

We review the use of both pulsed and continuous wave quantum cascade lasers in high-resolution spectroscopic studies of gas phase species. In particular, the application of pulsed systems for probing kinetic processes and the inherent rapid passage structure that accompanies observations of low-pressure samples using these rapidly chirped devices are highlighted. Broadband absorber spectroscopy and time-resolved concentration measurements of short-lived species, respectively exploiting the wide intrapulse tuning range and the pulse temporal resolution, are also mentioned. For comparison, we also present recent sub-Doppler Lamb-dip measurements on a low-pressure sample of NO, using a continuous wave external cavity quantum cascade laser system. Using this methodology the stability and resolution of this source is quantified. We find that the laser linewidth as measured via the Lamb-dip is ca. 2.7 MHz as the laser is tuned at comparably slow rates, but decreases to 1.3 MHz as the laser scan rate is increased such that the transition is observed at 30 kHz. Using this source, wavelength modulation spectroscopy of NO is presented.

ChemInform Abstract: Examination of the 2A′2 and 2E′′ States of NO3 by UV Photoelectron Spectroscopy of NO- 3.

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Possible involvement of NO in the stimulating effect of pifithrins on survival of hemopoietic clonogenic cells

Pifithrin alpha (PFTalpha), one of the first known low molecular weight modulators of activity of tumor suppressor p53, increases survival of hemopoietic clonogenic cells (evaluated by the criterion of formation of endogenous spleen CFU-C8 colonies in irradiated animals). This effect appeared when PFTalpha was administered either before or after irradiation. Increase in CFU-C8 was also observed after administration of two PFTalpha analogs, derivatives of 2-amino-4,5,6,7-tetrahydrobenzothiazole. These included a parent compound, 2-ATBT (2-amino-4,5,6,7-tetrahydrobenzothiazole), which is used for synthesis of PFTalpha, and a product of its intramolecular cyclization under physiological conditions, cyclo-PFT (2-(4-methylphenyl)imidazo[2,1-b]-5,6,7,8-tetrahydrobenzothiazole). Earlier we found that many low molecular weight compounds increasing number of CFU-C8 (e.g. isothiourea derivatives) demonstrate NO inhibitory activity. Such activity was also found in 2-ATBT and cyclo-PFT by means of EPR spectroscopy of NO. These compounds caused more than twofold inhibition of NO production in vivo. Thus, it has been demonstrated that PFTalpha and its structural analogs increase survival of hemopoietic clonogenic cells in vivo, and NO may play a role in the mechanism of this effect.

Pulsed Laval nozzle study of the kinetics of OH with unsaturated hydrocarbons at very low temperatures

The kinetics of reactions of the OH radical with ethene, ethyne (acetylene), propyne (methyl acetylene) and t-butyl-hydroperoxide were studied at temperatures of 69 and 86 K using laser flash-photolysis combined with laser-induced fluorescence spectroscopy. A new pulsed Laval nozzle apparatus is used to provide the low-temperature thermalised environment at a single density of approximately 4x10(16) molecule cm(-3) in N2. The density and temperature within the flow are determined using measurements of impact pressure and rotational populations from laser-induced fluorescence spectroscopy of NO and OH. For ethene, rate coefficients were determined to be k2=(3.22+/-0.46)x10(-11) and (2.12+/-0.12)x10(-11) cm3 molecule(-1) s(-1) at T=69 and 86 K, respectively, in good agreement with a master-equation calculation utilising an ab initio surface recently calculated for this reaction by Cleary et al. (P. A. Cleary, M. T. Baeza Romero, M. A. Blitz, D. E. Heard, M. J. Pilling, P. W. Seakins and L. Wang, Phys. Chem. Chem. Phys., 2006, 8, 5633-5642) For ethyne, no previous data exist below 210 K and a single measurement at 69 K was only able to provide an approximate upper limit for the rate coefficient of k3<1x10(-12) cm3 molecule(-1) s(-1), consistent with the presence of a small activation barrier of approximately 5 kJ mol(-1) between the reagents and the OH-C2H2 adduct. For propyne, there are no previous measurements below 253 K, and rate coefficients of k4=(5.08+/-0.65), (5.02+/-1.11) and (3.11+/-0.09)x10(-12) cm3 molecule(-1) s(-1) were obtained at T=69, 86 and 299 K, indicating a much weaker temperature dependence than for ethene. The rate coefficient k1=(7.8+/-2.5)x10(-11) cm3 molecule(-1) s(-1) was obtained for the reaction of OH with t-butyl-hydroperoxide at T=86 K. Studies of the reaction of OH with benzene and toluene yielded complex kinetic profiles of OH which did not allow the extraction of rate coefficients. Uncertainties are quoted at the 95% confidence limit and include systematic errors.

Electronic spectroscopy of NO–(Rg)x complexes (Rg=Ne,Ar) via the 4s and 3d Rydberg states

We have employed (2 + 1) resonance enhanced multiphoton ionization spectroscopy to investigate the 3d and 4s Rydberg states of the NO molecule when bound to the surface of Rg(x) clusters (Rg = rare gas). We observe that the spectra of the NO-Ar(x) species converge in appearance as x increases, and this is discussed in terms of two Rg atoms interacting with the NO+ core, with other Rg atoms being "outside" the Rydberg orbital. We show that the interaction of each of the Rg atoms with the NO is essentially independent for the NO-Rg2 complexes: both by comparing our spectra for Rydberg states of NO-Rg and NO-Rg2, and from the results of ab initio calculations on NO+ - Rg and NO+ - Rg2. In addition, we discuss the disappearance of some electronic bands upon complexation in terms of Franck-Condon factors that are very sensitive to the angular coordinate. We relate our results to those of the bulk by comparing to the previously reported electronic spectroscopy of NO in both Rg matrices and He nanodroplets.

Nature, Density, and Catalytic Role of Exposed Species on Dispersed VOx/CrOx/Al2O3 Catalysts

The structure and surface composition of binary oxides consisting of CrO(x) and VO(x) dispersed on alumina and their effects on the rate and selectivity of oxidative dehydrogenation (ODH) of propane were examined and compared with those for CrO(x) and VO(x) dispersed on alumina. VO(x) deposition on an equivalent CrO(x) monolayer on alumina and deposition of CrO(x) on an equivalent monolayer of VO(x) deposited on alumina led to CrVO(4) species during thermal treatment with concomitant reduction of Cr(6+) to Cr(3+). Autoreduction of Cr(6+) to Cr(3+) is also detected for CrO(x), even without the presence of VO(x). Infrared spectroscopy of NO adsorbed at 153 K probes the relative abundance of alumina and of V(5+), Cr(3+), and Cr(6+) at surfaces. This technique detects differences in the surface composition of VO(x)/CrO(x)()/Al(2)O(3) and CrO(x)/VO(x)/Al(2)O(3). The first of these samples is enriched in VO(x) relative to CrO(x) compared with the second sample. Consistent with this finding, VO(x)/CrO(x)/Al(2)O(3) and CrO(x)/VO(x)/Al(2)O(3) are distinguishable in their ODH activities and propene selectivities. The highest ODH activity and propene selectivity is observed for VO(x)/CrO(x)/Al(2)O(3), which exhibits a surface enriched in VO(x) and having a low surface concentration of Cr(6+).

SERS and infrared reflection‐absorption spectroscopy of NO on cold‐deposited Cu

AbstractSurface enhanced Raman spectroscopy (SERS) of NO on cold‐deposited Cu yields only bands of the dissociation products of NO, but not the stretching bands of NO. In contrast, infrared reflection‐absorption spectroscopy (IRRAS) on similarly prepared samples displays strong NO stretching bands and only a very weak band of N2O from multilayer NO. The differences can be explained neither by thermal or photo‐desorption nor by photochemical effects in the laser focus. Whereas the SERS results may be explained by the action of special sites, it is still unclear why the IRRAS signal from the dissociation products of NO at the ‘catalytically active sites’ is below the noise level. Copyright © 2006 John Wiley &amp; Sons, Ltd.

High-Resolution Spectroscopy of NO in Helium Droplets: A Prototype for Open Shell Molecular Interactions in a Quantum Solvent

We have measured the high-resolution infrared spectrum of the radical NO in the (2)Pi(1/2) state in superfluid helium nanodroplets. The features are attributed to the -doubling splitting and the hyperfine structure. The hyperfine interaction is found to be unaffected by the He solvation. For the Lambda-doubling splitting, we find a considerable increase by 55% compared to the gas phase. This is explained by a confinement of the electronically excited NO states by the surrounding He. The rotational level spacing is decreased to 76% of the gas phase value. The IR transition to the J=1.5 state is found to be homogeneously broadened. We attribute both observations to the coupling between the molecular rotation and phonon/roton excitations in superfluid (4)He droplets.

Low-Temperature Reduction of NO2 on Oxidized Mo(110)

The reactions of nitrogen dioxide (NO(2)) were investigated on oxidized Mo(110) containing both chemisorbed oxygen and a thin film oxide. NO(2) reacts on both oxidized Mo(110) surfaces via a combination of reversible adsorption and reduction to NO, N(2), and trace amounts of N(2)O below 200 K. On the surface containing chemisorbed O, there is some complete dissociation of NO(2) to yield N(a) and O(a). N(2) forms at high temperatures through atom combination. On both surfaces, NO is the predominant product of NO(2) reduction. However, the chemisorbed layer which has a low oxidation state, and hence a greater capacity to accept oxygen, more effectively reduces NO(2). The selectivity for N(2) formation over N(2)O is greater for NO(2) as compared with NO on both surfaces studied. The selectivity changes are largely attributed to an increase in the concentration of Mo=O species and a change in the distribution of oxygen on the surface. Notably, more oxygen, in particular Mo=O moieties, is deposited by NO(2) reaction than by O(2) reaction, indicating that NO(2) is a stronger oxidant. The fact that there are several N-containing species on the surface at low temperatures may also affect the product distribution. On both surfaces, N(2)O(4), NO(2), and NO are identified by infrared spectroscopy upon adsorption at 100 K. All N(2)O(4) desorbs by 200 K, leaving only NO(2) and NO on the surface. Infrared spectroscopy of NO(2) on (18)O-labeled surfaces provides evidence for oxygen transfer or exchange between different types of sites even at low temperatures.

Multiwavelength ultraviolet absorption spectroscopy of NO and OH radical concentration applied to a high-swirl diesel-like system

Ultraviolet absorption measurements were carried out in an optical research engine by exploiting the emitted plasma kernel of laser-induced breakdown. Temporal evolution and spatial distribution of OH radical and NO absolute concentrations were evaluated by a numerical procedure for retrieving optical data. Spectral measurements were made in an optically accessible external combustion chamber obtained by modifying a single cylinder, four-stroke diesel engine. The experiments were performed using a commercial diesel fuel at two engine speeds varying the ignition delay and fixing the injected fuel amount. In-chamber NO concentrations for each engine operating condition were correlated with those measured at the exhaust by a conventional method.

Photoelectron–photofragment coincidence spectroscopy of NO 2−(NO) 1,2: solvation effects of NO on NO 2−

A study of the dissociative photodetachment dynamics of N 2O 3 − and N 3O 4 − at 258 nm is reported. Using photoelectron–photofragment coincidence (PPC) spectroscopy, information on the energetics and dissociation dynamics is recorded for both N x O y − species. The results indicate that these anions exist as NO 2 −(NO) 1,2 clusters, and dissociation occurs to form NO and NO 2 products upon photodetachment of the extra electron. It is shown that the energy released in the solvation of NO 2 − with one and two NO molecules is 0.23±0.05 and 0.38±0.05 eV, respectively. The photoelectron spectra show that solvation of NO 2 − by one NO does not significantly affect the electronic structure of the anion. The addition of a second NO to NO 2 −(NO), however, leads to a suppression of photodetachment to the A ̃ 2 B 2 excited state of NO 2 in the NO 2(NO) 2 cluster. The data also suggests that the three-body dissociation process of the larger cluster may occur via a sequential decay mechanism.

Pulsed cavity ring-down spectroscopy of NO and NO 2 in the exhaust of a diesel engine

The application of pulsed cavity ring-down spectroscopy has been demonstrated for the in situ quantitative determination of NO and NO2 in the exhaust of a diesel engine. NO absorption has been monitored at the transition from the Χ2Π ground state to the A2Σ+ state at 226 nm. For NO2, absorption bands in the spectral region from 438 nm to 450 nm were used. At the selected engine conditions, concentrations of 212±22 ppm and 29±4 ppm have been measured for NO and NO2, respectively, in good agreement with separate chemical exhaust gas analysis. The method is sensitive enough to meet the European Euro V standard directive on NOx emissions. This communication discusses the relatively simple setup needed for this type of measurement, the problems encountered, as well as the prospects for single-stroke, simultaneous measurements of both NO and NO2 at the sub-ppm level.

Sub-Doppler resolution limited Lamb-dip spectroscopy of NO with a quantum cascade distributed feedback laser

A quantum cascade distributed feedback laser operating at 5.2 microm is used to obtain sub-Doppler resolution limited saturation features in a Lamb-dip experiment on the R(13.5)1/2 and R(13.5)3/2 transitions of NO. The dips appear as transmission spikes with full widths of ~ 4.3 MHz. At this resolution the 73 MHz _-doubling of the R(13.5)3/2 line, which is normally obscured by the 130 MHz Doppler broadening, is easily resolved.

A pseudopotential study of molecular spectroscopy in rare gas matrices: absorption of NO in argon

We present a pseudopotential method to study the absorption spectroscopy of NO in an argon matrix modeled by a large albeit finite cluster. The excited states of NO are described with the virtual orbitals of a NO+ Hartree-Fock calculation plus a core-polarization operator to account for the electron-NO+ correlation. The argon atoms of the matrix are replaced by pseudopotentials for the repulsive contributions and core-polarization operators to account for matrix polarization and correlation with the excited electron. The model is shown to account for the matrix-induced transition shifts and also for the cut-off of the Rydberg series for n >3 reported in absorption experiments from the ground state.

Two-photon spectroscopy of the low lying Rydberg states of NO. I. The 3p and 3d complexes

The rotational structure and polarization dependence of two-photon spectra of aligned ensembles of open shell diatomics is investigated in terms of the spherical tensor components of the two-photon absorption operator. The formalism allows the straightforward incorporation of state interactions and perturbations. It is applied to the two-photon spectroscopy of NO, in particular to the excitation of the Rydberg states derived from the 3p and 3d complexes. All states investigated show a nearly quadratic power dependence indicating the saturation of the ionization step. Transitions dominated by a zeroth rank tensor component (e.g., C 2Π–X 2Π or H 2Σ, H′ 2Π–X 2Π) are insensitive to a possible angular momentum alignment in the ensemble. These transitions are ideally suited to determine degeneracy averaged observables, e.g., collision cross sections in a molecular beam scattering experiment or product velocity anisotropies in a single color photodissociation experiment. Rotational alignment data must be determined using two-photon transitions which are carried by a second rank tensor component (e.g., D 2Σ–X 2Π or F 2Δ–X 2Π).

High-resolution bolometric spectroscopy of NO 2 in the region of 13352 cm −1

The vibronic band at 13352 cm −1 of NO 2 is measured up to the hyperfine structure by bolometric detection. The excited vibronic state involved is a hybrid state having a major contribution from electronic ground state. This follows from the hyperfine splitting of the K_=0 and K_=1 stacks as well as from the value of the rotational constant A′. The anomalous intensity distribution induced by rovibrational interactions is not observed in the vibronic band analysis here. Although we suggest the absence of rovibronic interactions of significant strength, we underline the presence of vibronic interactions in the vibronic band analysed here.

Adsorption and reactivity of NO on Cu(111): a synchrotron infrared reflection absorption spectroscopic study

Infrared reflection absorption spectroscopy of NO adsorbed on Cu(111) has been performed in the frequency range 200–2500 cm −1. At low temperatures ( T < 120 K), two different states were identified with increasing coverage: adsorption followed by dissociation. At coverages up to one monolayer, NO molecules adsorb on identical sites, which are suggested to be of threefold symmetry, with an upright geometry. Two ordered overlayers are formed in turn: p(3 × 3) and (√7 × √7)R19.1°. The infrared spectra show two absorption bands: the internal stretching mode of NO, which shifts upwards in frequency with increasing coverage, and a low frequency anti-absorption band. The anti-absorption band is assigned, based on its isotopic frequency dependence, to the hindered rotation of the NO molecules. After completion of the monolayer, the NO molecules react and adsorbed N 2O molecules are found on the surface bound through the oxygen atom (CuON 2 stretching mode at 352 cm −1) with their molecular axis (ONN) parallel to the surface plane. Desorption of the adsorbed N 2O occurs at 120 K. No dimers, which are the reaction intermediates in the formation of N 2O from NO, have been clearly identified.

Activity of PNiW/Al 2O 3 catalysts with varying phosphorus content in the hydrogenation of naphthalene

A series of co-impregnated (pH 1) PNiW/Al 2O 3 catalysts of low tungsten content (1.6 W atoms/nm 2) and varying phosphorus concentration (0–5.9 wt.−% P 2O 5) have been studied in the reaction of hydrogenation of naphthalene in a batch Parr reactor at 573 K and P = 44 atm. In addition to a previous characterization by XRD, DRS and XPS, the catalysts have been characterized here by DRS, FTIR spectroscopy in their oxide state and by FTIR spectroscopy of NO chemisorbed on the sulphided catalysts. A promoting effect of phosphorus is observed in all phosphorus containing samples. The catalytic activity vs. phosphorus content curve has a complex behavior passing through a maximum and a minimum. Phase transitions are observed in the samples with the change of the phosphorus content. The form of the catalytic activity curve is discussed in the light of these phase transitions and the structure and properties of the different phases. The highest catalytic activity is observed for the sample with 0.6% P 2O 5. This sample is also characterized by the highest amount of chemisorbed NO and by a local maximum in the relative number of terminal WO bonds. When strong overlapping of the bands is observed, the NO adsorption technique should be applied with care. Also, NO might adsorb on sites which are not active in the corresponding hydrotreatment reaction and the trend predicted by the total amount of chemisorbed NO should not necessarily coincide with the form of the catalytic activity curve. The catalytic activity curves indicate that during the reaction changes in the number of active sites or the formation of new active sites are possible.

Observation of hyperfine quantum beats in two-color laser-induced grating spectroscopy of nitric oxide

Two-color laser-induced grating spectroscopy of NO via the A 2Σ +, v′=0 state has been used to study the time evolution of population gratings produced in a supersonic molecular beam. For a specific polarization configuration of the input laser beams, quantum beats due to the hyperfine structure of the A 2Σ +, v′=0 state have been observed by varying the delay between the grating-forming laser pulses and the grating-probing laser pulse. This form of quantum beat spectroscopy has the advantages of background-free detection, two-color state selectivity, a quadratic dependence on the level population, and a beat signal independent of the decay mode.

Vibrational spectroscopy of NO and (NO)2 isolated in solid neon

By highly resolved infrared absorption spectra the dependence of aggregation of NO in neon on concentration, annealing, and deposition temperature is studied in recording the intensities of monomers in two sites (1874.54 and 1877.56 cm−1), of cis-(NO)2 dimers in the symmetrical (around 1866 cm−1) and antisymmetrical (around 1780 cm−1) mode, of a special dimer around 1858 cm−1 and a series of monomer side bands shifted by about 0.3, 0.6, and 1.8 cm−1 due to coupling of molecules at different lattice sites. The dimer bands also exhibit a fine structure and a broad background caused by larger aggregates. The almost statistical size distribution at low concentration and condensation temperature changes to a preferential aggregation at higher concentration (≳2×10−3) and condensation temperature (≥7 K) and the irreversible aggregation by diffusion at elevated temperatures is followed on a time scale of hours. A reversible conversion of special dimers at 1778.67 and 1865.48 cm−1 to a dimer at 1857.93 cm−1 is accelerated by lowering the temperature and attributed to a martensitic hcp to fcc phase transition.