Photodissociation Of NO Research Articles

Theoretical study of the selective control of photoionization and photodissociation

Present work have investigated the selective control of the optimal path and the population transfer rate for photoionization and photodissociation of CO and NO by using time-dependent wave packet dynamics method. Combing the calculated transition properties, it has determined the optimal route of photoionization that is CO X1Σ+→E1П(v’ = 0)→CO+ X2Σ+ by two-photon, which the laser wavelength corresponds to 110 nm and 202 nm, respectively. By changing the laser parameters, we found that, when the intensity is 6.7 × 1013W/cm2 and duration is 100fs, not only the transfer rate of ionized population reaches maximum 99.1%, but also the purity is very high. For photodissociation of NO molecule, the projection of initial wave function of ground state on the quantum state v’ = 8 of excited state A2Σ+ is calculated. It showed that the yield of photodissociation is about 43% by using guassian pulse with intensity 1 × 1014W/cm2 and duration 56fs. However, not only promoting earlier t = 25fs of reaction time but also making the yield increases up to 57% by the positive chirp pulse. These main information suggest a scheme for the feasibly photochemical reaction and will provide an important reference for further theoretical and experimental researches.

Change in the structure and function of lectin by photodissociation of NO.

We have shown here that the structure and sugar-binding activity of lectin can be changed by the photodissociation of NO. Intramolecular S-S bonds are photogenerated from SNO in the protein, which can be used to photo-control the structure and function of proteins.

Photoacoustic Calorimetry Studies of Ferric Cytochrome-C Folding using an No Photo-Trigger

In this study, NO is utilized as a photo-trigger together with photoacoustic calorimetry to probe the kinetics, enthalpy and molar volume changes associated with the earliest folding events in ferric Cytochrome-c (Cc3+). The ferric heme protein was examined under different denaturing conditions including guanidine hydrochloride (2.8M GdnHCl) and Sodium dodecyl sulfate (SDS 0.4mM) (both in 50 mM Hepes buffer, pH ∼7.5) along with NO resulting in the disruption of the axial heme Methionine-80 heme bond, triggering the partial unfolding of the complex. Under these conditions photo-dissociation of NO leaves the protein in a conformational state that favors refolding of the protein. The PAC data reveals three kinetic phases taking place subsequent to photolysis regardless of the denaturant environment. Specifically, in the presence of 2.8 M GdnHCl photolysis gave rise to kinetic events with lifetimes of <20 ns, ∼860 ns, and ∼6 μs that were associated with ΔH/ΔV = −25 kcal mol-1/-9 mL mol-1, 26 kcal mol-1/15mL mol-1, and 9 kcal mol-1/-26 mL mol-1, respectively. In the presence of 0.4 mM SDS, kinetic events were observed with lifetimes of <20 ns, ∼640 ns, and ∼8 μs with corresponding ΔH/ΔV of −11 kcal mol-1/-1 mL mol-1, 5 kcal mol-1/3 mL mol-1, and 30 kcal mol-1/-9 mL mol-1, respectively. The data suggests a uniform mechanism for the early folding events occurring in the folding of Cc3+ complex subsequent to NO photo-dissociation which are attributed to NO dissociation from the heme, followed by reorganization of the distal pocket (i.e hydrogen bond formation/breakage, NO solvation, etc.) and potentially a intermolecular binding of Methionine (80 or 65) or Histidine (23 or 33) to the heme iron upon folding.

A combined crossed-beam and theoretical study of the reaction dynamics of O(3P) + C2H3 → C2H2 + OH: Analysis of the nascent OH products with the preferential population of the Π(A′) component

The gas-phase reaction dynamics of ground-state atomic oxygen [O((3)P) from the photo-dissociation of NO(2)] with vinyl radicals [C(2)H(3) from the supersonic flash pyrolysis of vinyl iodide, C(2)H(3)I] has been investigated using a combination of high-resolution laser-induced fluorescence spectroscopy in a crossed-beam configuration and ab initio calculations. Unlike the previous gas-phase bulk kinetic experiments by Baulch et al. [J. Phys. Chem. Ref. Data 34, 757 (2005)], a new exothermic channel of O((3)P) + C(2)H(3) → C(2)H(2) + OH (X (2)Π: υ" = 0) has been identified for the first time, and the population analysis shows bimodal nascent rotational distributions of OH products with low- and high-N" components with a ratio of 2.4:1. No spin-orbit propensities were observed, and the averaged ratios of Π(A('))∕Π(A") were determined to be 1.66 ± 0.27. On the basis of computations at the CBS-QB3 theory level and comparison with prior theory, the microscopic mechanisms responsible for the nascent populations can be understood in terms of two competing dynamical pathways: a direct abstraction process in the low-N" regime as the major pathway and an addition-complex forming process in the high-N" regime as the minor pathway. Particularly, during the bond cleavage process of the weakly bound van der Waals complex C(2)H(2)-OH, the characteristic pathway from the low dihedral-angle geometry was consistent with the observed preferential population of the Π(A') component in the nascent OH products. A molecular-level discussion of the reactivity, mechanism, and dynamical features of the title reaction are presented together with a comparison to gas-phase oxidation reactions of a series of prototypical hydrocarbon radicals.

Time-slice velocity-map ion imaging studies of the photodissociation of NO in the vacuum ultraviolet region

The time-slice velocity-map ion imaging and the resonant four-wave mixing techniques are combined to study the photodissociation of NO in the vacuum ultraviolet (VUV) region around 13.5 eV above the ionization potential. The neutral atoms, i.e., N((2)D(o)), O((3)P(2)), O((3)P(1)), O((3)P(0)), and O((1)D(2)), are probed by exciting an autoionization line of O((1)D(2)) or N((2)D(o)), or an intermediate Rydberg state of O((3)P(0,1,2)). Old and new autoionization lines of O((1)D(2)) and N((2)D(o)) in this region have been measured and newer frequencies are given for them. The photodissociation channels producing N((2)D(o)) + O((3)P), N((2)D(o)) + O((1)D(2)), N((2)D(o)) + O((1)S(0)), and N((2)P(o)) + O((3)P) have all been identified. This is the first time that a single VUV photon has been used to study the photodissociation of NO in this energy region. Our measurements of the angular distributions show that the recoil anisotropy parameters (β) for all the dissociation channels except for the N((2)D(o)) + O((1)S(0)) channel are minus at each of the wavelengths used in the present study. Thus direct excitation of NO by a single VUV photon in this energy region leads to excitation of states with Σ or Δ symmetry (ΔΩ = ±1), explaining the observed perpendicular transition.

Analysis of Nascent Rotational Energy Distributions and Reaction Mechanisms of the Gas-Phase Radical-Radical Reaction O(3P)+(CH3)2CH→C3H6+OH

This paper reports on the gas-phase radical-radical dynamics of the reaction of ground-state atomic oxygen [O((3)P), from the photodissociation of NO(2)] with secondary isopropyl radicals [(CH(3))(2)CH, from the supersonic flash pyrolysis of isopropyl bromide]. The major reaction channel, O((3)P)+(CH(3))(2)CH→C(3)H(6) (propene)+OH, is examined by high-resolution laser-induced fluorescence spectroscopy in crossed-beam configuration. Population analysis shows bimodal nascent rotational distributions of OH (X(2)Π) products with low- and high-N'' components in a ratio of 1.25:1. No significant spin-orbit or Λ-doublet propensities are exhibited in the ground vibrational state. Ab initio computations at the CBS-QB3 theory level and comparison with prior theory show that the statistical method is not suitable for describing the main reaction channel at the molecular level. Two competing mechanisms are predicted to exist on the lowest doublet potential-energy surface: direct abstraction, giving the dominant low-N'' components, and formation of short-lived addition complexes that result in hot rotational distributions, giving the high-N'' components. The observed competing mechanisms contrast with previous bulk kinetic experiments conducted in a fast-flow system with photoionization mass spectrometry, which suggested a single abstraction pathway. In addition, comparison of the reactions of O((3)P) with primary and tertiary hydrocarbon radicals allows molecular-level discussion of the reactivity and mechanism of the title reaction.

Synthesis, spectroscopic analysis and photolabilization of water-soluble ruthenium(iii)–nitrosyl complexes

In this paper, the synthesis, structural and spectroscopic characterization of a series of new Ru(III)-nitrosyls of {RuNO}(6) type with the coligand TPA (tris(2-pyridylmethyl)amine) are presented. The complex [Ru(TPA)Cl(2)(NO)]ClO(4) (2) was prepared from the Ru(III) precursor [Ru(TPA)Cl(2)]ClO(4) (1) by simple reaction with NO gas. This led to the surprising displacement of one of the pyridine (py) arms of TPA by NO (instead of the substitution of a chloride anion by NO), as confirmed by X-ray crystallography. NO complexes where TPA serves as a tetradentate ligand were obtained by reacting the new Ru(II) precursor [Ru(TPA)(NO(2))(2)] (3) with a strong acid. This leads to the dehydration of nitrite to NO(+), and the formation of the {RuNO}(6) complex [Ru(TPA)(ONO)(NO)](PF(6))(2) (4), which was also structurally characterized. Derivatives of 4 where nitrite is replaced by urea (5) or water (6) were also obtained. The nitrosyl complexes obtained this way were then further investigated using IR and FT-Raman spectroscopy. Complex 2 with the two anionic chloride coligands shows the lowest N-O and highest Ru-NO stretching frequencies of 1903 and 619 cm(-1) of all the complexes investigated here. Complexes 5 and 6 where TPA serves as a tetradentate ligand show ν(N-O) at higher energy, 1930 and 1917 cm(-1), respectively, and ν(Ru-NO) at lower energy, 577 and 579 cm(-1), respectively, compared to 2. These vibrational energies, as well as the inverse correlation of ν(N-O) and ν(Ru-NO) observed along this series of complexes, again support the Ru(II)-NO(+) type electronic structure previously proposed for {RuNO}(6) complexes. Finally, we investigated the photolability of the Ru-NO bond upon irradiation with UV light to determine the quantum yields (φ) for NO photorelease in complexes 2, 4, 5, and additional water-soluble complexes [Ru(H(2)edta)(Cl)(NO)] (7) and [Ru(Hedta)(NO)] (8). Although {RuNO}(6) complexes are frequently proposed as NO delivery agents in vivo, studies that investigate how φ is affected by the solvent water are lacking. Our results indicate that neutral water is not a solvent that promotes the photodissociation of NO, which would present a major obstacle to the goal of designing {RuNO}(6) complexes as photolabile NO delivery agents in vivo.

Ion Imaging Study of NO3Radical Photodissociation Dynamics: Characterization of Multiple Reaction Pathways

The photodissociation of NO(3) has been studied using velocity map ion imaging. Measurements of the NO(2) + O channel reveal statistical branching ratios of the O((3)P(J)) fine-structure states, isotropic angular distributions, and low product translational energy consistent with barrierless dissociation along the ground state potential surface. There is clear evidence for two distinct pathways to the formation of NO + O(2) products. The dominant pathway (>70% yield) is characterized by vibrationally excited O(2)((3)Σ(g)(-), v = 5-10) and rotationally cold NO((2)Π), while the second pathway is characterized by O(2)((3)Σ(g)(-), v = 0-4) and rotationally hotter NO((2)Π) fragments. We speculate the first pathway has many similarities to the "roaming" dynamics recently implicated in several systems. The rotational angular momentum of the molecular fragments is positively correlated for this channel, suggesting geometric constraints in the dissociation. The second pathway results in almost exclusive formation of NO((2)Π, v = 0). Although product state correlations support dissociation via an as yet unidentified three-center transition state, theoretical confirmation is needed.

Threshold Photoelectron-photoion Coincidence Imaging of Dissociation Dynamic of NO+ atc3Π(v′=0) State

The photodissociation of NO+ at c3Π(v′ = 0) state is studied by threshold photoelectron-photoion coincidence imaging method. By some assumptions, the relations between velocity in center of mass (CM) coordinates and most probable center of mass (MPCM) coordinates, time of flight and displacement in the velocity map image of fragment ions are derived using vector addition of velocity and displacement on the condition of perpendicular molecular beam. Using these relations the velocity in CM coordinates, the velocity and angular distribution of N+ fragment ions in MPCM coordinates are obtained and discussed, respectively.

A new imaging method for understanding chemical dynamics: Efficient slice imaging using an in-vacuum pixel detector

The implementation of the Timepix complementary metal oxide semiconductor pixel detector in velocity map slice imaging is presented. This new detector approach eliminates the need for gating the imaging detector. In time-of-flight mode, the detector returns the impact position and the time-of-flight of charged particles with 12.5 ns resolution and a dynamic range of about 100 μs. The implementation of the Timepix detector in combination with a microchannel plate additionally allows for high spatial resolution information via center-of-mass centroiding. Here, the detector was applied to study the photodissociation of NO(2) at 452 nm. The energy resolution observed in the experiment was ΔE/E=0.05 and is limited by the experimental setup rather than by the detector assembly. All together, this new compact detector assembly is well-suited for slice imaging and is a promising tool for imaging studies in atomic and molecular physics research.

A combined crossed-beam and ab initio study of the atom–radical reaction dynamics of O(3P) + C2H5→ C2H4 + OH: analysis of nascent internal state distributions of the OH product

The oxidation reaction dynamics of ethyl radicals (C(2)H(5)) in the gas phase are investigated by applying a combination of high-resolution laser induced fluorescence spectroscopy in a crossed-beam configuration and ab initio theoretical calculations. The supersonic atomic oxygen (O((3)P)) and ethyl (C(2)H(5)) reactants are produced by photodissociation of NO(2) and supersonic flash pyrolysis of a synthesized precursor (azoethane), respectively. An exothermic channel leading to the C(2)H(5) + OH (X(2)Pi: upsilon'' = 0, 1) products is identified. The nascent rovibrational state distributions of the OH product show substantial bimodal internal excitations consisting of low- and high-N'' components with neither spin-orbit nor Lambda-doublet propensities in the ground and first excited vibrational states. The averaged vibrational population (P(upsilon'')), partitioning with respect to the low-N'' components of the upsilon'' = 0 level, shows a comparable population ratio of P(0)ratioP(1) = 1 ratio 1.06. On the basis of comparison between the population analyses using ab initio and prior statistical calculations, the title atom-radical reactive scattering processes are governed by dynamic characteristics. The reaction mechanism can be rationalized by two competing mechanisms: abstraction versus addition. The major low N''-components can be described in terms of the direct abstraction process responsible for the comparable vibrational populations, while the minor but hot rotational distribution of the high N''-components implies that some fraction of radical reactants is sampled to proceed through the short-lived addition-complex forming process.

The infrared spectroscopy and photochemistry of NO3 trapped in solid neon

NO(3) can be stabilized in solid neon either by codeposition at 4.3 K of a Ne:O(2) mixture with a Ne:NO mixture that has been passed through a microwave discharge or, in higher yield, by codeposition of a Ne:NO mixture with a Ne:O(2) mixture, followed by annealing of the deposit at approximately 7 K and exposure of the solid to near ultraviolet radiation. All of the previously reported bands of NO(3) between 700 and 3000 cm(-1) were observed, most with neon-matrix shifts of less than 2.5 cm(-1). The infrared spectra of eight isotopic species of NO(3) were obtained. The observed isotopic shifts demonstrate the occurrence of extensive mixing of ground-state levels of e(') symmetry and their strong vibronic interaction with the B (2)E(') state. Photodissociation of NO(3) by irradiation of the deposit at wavelengths longer than 520 nm leads to new absorptions near the fundamentals of NO and O(2) and other new absorptions at relatively low frequencies. These absorptions were depleted and NO(3) regenerated by subsequent near ultraviolet irradiation of the deposit, suggesting the stabilization of a weakly bound NO(O(2)) complex in solid neon.

The photodissociation of NO 2 in the second absorption band: Ab initio and quantum dynamics calculations

The photodissociation of NO 2 in the second absorption band (217 nm) is investigated by electronic structure as well as quantum mechanical and classical dynamics calculations. Potential energies are calculated for the five lowest 2A′ states using the internally contracted multi-reference configuration interaction method and the standard correlation consistent polarized quadruple zeta basis set. The two N–O bond lengths and the O–N–O bond angle are varied over wide ranges. Our calculations unambiguously verify that the second absorption band is due to excitation of state 3 2A′ (2 2B 2 in C 2 v ), which is the only state with non-vanishing transition dipole moment in this energy range. State 3 2A′ correlates diabatically with O( 1D) + NO( 2Π), but it connects adiabatically with the ground-state product channel O( 3P) + NO( 2Π). In the present study, we construct a three-dimensional potential energy surface (PES) for only one adiabatic state, 3 2A′, and primarily focus on the absorption cross-section due to excitation of this state. The general form of the absorption spectrum and the progression of diffuse vibrational structures are well reproduced by the quantum mechanical calculations. The vibrational and rotational state distributions of NO in the O( 3P) + NO( 2Π) channel are also determined. The predicted internal energy distributions are relatively narrow over the entire range of the absorption spectrum – in quantitative agreement with the experimental result for dissociation at 226 nm, but in severe qualitative disagreement with measurements near 202 nm.

Release of Oxygen Atoms and Nitric Oxide Molecules from the Ultraviolet Photodissociation of Nitrate Adsorbed on Water Ice Films at 100 K

Production of O((3)P(J), J = 2, 1, 0) atoms from the 295-320 nm photodissociation of NO(3)- adsorbed on water polycrystalline ice films at 100 K was directly confirmed using the resonance-enhanced multiphoton ionization technique. Detection of the O atom signals required an induction period after deposition of HNO3 onto the ice film held at 130 K due to the slow ionization rate of HNO(3) to H+ and NO(3)- with a rate constant of k = (5.3 +/- 0.2) x 10(-3)s(-1). Translational energy distributions of the O atoms were represented by a combination of two Maxwell-Boltzmann energy distributions with translational temperatures of 2000 and 100 K. Direct detection of NO from the secondary photodissociation process was also successful. On the atmospheric implications, the influence of the direct release of the oxygen atoms into the air from NO(3)- adsorbed on the natural snowpack was included in an atmospheric model calculation on the mixing ratios of ozone and nitric oxide at the South Pole, and the results compared favorably with the field data.

Demonstration of the combination of slice imaging and Rydberg tagging for studies of photodissociation dynamics.

The slice-imaging variant of photofragment ion imaging is combined with Rydberg tagging. The photodissociation of NO(2) at 355 nm is used as the test system and the NO fragments are Rydberg tagged by two-photon two-color excitation via the intermediate A (2)Sigma(+) state. Images obtained by this method are compared with ion images obtained in the same apparatus using the approach of Kitsopoulos and co-workers [Rev. Sci. Instrum. 72, 3848 (2001)]. Comparable resolution and angular distributions are obtained in the two cases. It is proposed that the method demonstrated here could provide a complementary approach to existing ion-imaging methods, especially where resonantly enhanced multiphoton ionization detection of fragments is problematic.

Two-photon photodissociation of NO through Rydberg levels in the 265–278 nm region: Spectra and photofragment angular distributions

The spectroscopy and dynamics of the NO photodissociation through Rydberg levels near 74 000 cm−1 have been investigated following two-photon excitation. The 6dπ−(v=1) and 5sσ(v=3) levels overlap near 74 070 cm−1. Assignment of the rotational transitions for these levels has been aided by the use of the photoproduct angular distributions measured using product imaging techniques. Product imaging was also used to investigate the 8dπ−(v=1) and 5sσ(v=2) regions assigned by previous investigators. In all cases, the major products were N(2D)+O(3P). The angular distributions vary strongly with rotational transition and with the assumed intermediate in the two-photon excitation scheme and can, for the most part, be predicted by calculation. They demonstrate that, for the Rydberg levels examined, the major contribution to the two-photon line strength is a Π intermediate, likely the C 2Π state, with less than a 30% amplitude contribution from either a Σ or Δ intermediate.

Density functional study on geometry and electronic structure of nitrile hydratase active site model

AbstractNitrile Hydratase (R. Sp. 771, NHase, EC. 4.2.1.84, CAS registration no. 82391‐37‐5), the enzyme that plays an important role in the industrial production of acrylamide, is studied theoretically in this article. For the first time the electronic structure of the active site of nitrosylated form with a proper oxidation state of the cysteine ligands is calculated using the density functional theory (DFT) method with the Becke, Lee, Yang, and Paar (B3LYP)6‐31G* functional. The optimized geometries of six and five coordinated complexes are different, showing that the photodissociation of NO triggers a substantial relaxation of the NHase active site. The major structural change is a shift of the position of iron with respect to the four equatorial ligands, which resembles a heme doming observed in myoglobins. Calculated charge distribution supports the role of Fe as a possible Lewis acid in catalytic cycle. We found that the cysteine‐sulfinic residue (Cys112) is very strongly polarized in NHase. Sulfur atom Sγ Cys112 is predicted to be the most positively charged center. This result gives independent support to a very recent finding of the critical role of an oxidation in the position Cys112 for preserving catalytic activity of the enzyme (Endo, I.; Nojiri, M.; Tsujimura, M.; Nakasako, M.; Nagashima, S.; Yohda, M.; Odaka, M. J Inorgan Biochem 2001, 83, 247). © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Impact of the new rate coefficients for the O atom vibrational deactivation and photodissociation of NO on the temperature and density structure of the terrestrial atmosphere

Recent laboratory work has arrived at a value of the rate coefficient for the room temperature O atom vibrational relaxation of NO(v=1) which is nearly one third the previously accepted value [Fernando and Smith, 1979]. Laboratory measurements have also established a new value for the rate coefficient for the photodissociation of NO which is ∼1.6 times the previously accepted value. Since the NO(v=1→v=0) emission, around 5.3 μm, is a very important cooling process in the lower terrestrial thermosphere, the new values of the two rate coefficients lead to a decrease in the amount of NO as well as the rate at which it cools. Using the global mean model [Roble, 1995] of the mesosphere, thermosphere, and ionosphere, we find that the new rate coefficients introduce large changes in the thermal and density structure of the atmosphere. The resulting model atmosphere appears unrealistic. We find that these large changes are moderated and the resulting neutral temperatures agree better with the Mass Spectrometer Incoherent Scatter (MSIS) model when the value of the CO2+O rate coefficient for excitation of the bending vibration is increased two fold to the value arrived at by modeling the 15 μm emission from CO2 from the lower terrestrial thermosphere. Finally, we describe the results of a number of runs with the thermosphere/ionosphere/mesosphere electrodynamics general circulation model (TIME‐GCM) to examine the global temperature, composition, and circulation changes that result from using the new rates for both NO and CO2.

Water penetration and binding to ferric myoglobin.

Flash photolysis investigations of horse heart metmyoglobin bound with NO (Mb(3+)NO) reveal the kinetics of water entry and binding to the heme iron. Photodissociation of NO leaves the sample in the dehydrated Mb(3+) (5-coordinate) state. After NO photolysis and escape, a water molecule enters the heme pocket and binds to the heme iron, forming the 6-coordinate aquometMb state (Mb(3+)H2O). At longer times, NO displaces the H2O ligand to reestablish equilibrium. At 293 K, we determine a value k(w) approximately 5.7 x 10(6) s(-1) for the rate of H2O binding and estimate the H2O dissociation constant as 60 mM. The Arrhenius barrier height H(w) = 42 +/- 3 kJ/mol determined for H2O binding is identical to the barrier for CO escape after photolysis of Mb(2+)CO, within experimental uncertainty, consistent with a common mechanism for entry and exit of small molecules from the heme pocket. We propose that both processes are gated by displacement of His-64 from the heme pocket. We also observe that the bimolecular NO rebinding rate is enhanced by 3 orders of magnitude both for the H64L mutant, which does not bind water, and for the H64G mutant, where the bound water is no longer stabilized by hydrogen bonding with His-64. These results emphasize the importance of the hydrogen bond in stabilizing H2O binding and thus preventing NO scavenging by ferric heme proteins at physiological NO concentrations.

The photolysis of NO 2 at 193 nm

Infrared kinetic spectroscopy has been used to investigate the photo-dissociation of NO 2 at 193 nm. The O( 1D)/(O( 1D)+O( 3P)) branching ratio was measured as 0.55±0.03 by adding a large excess of H 2 to the system, and comparing the amount of NO 2 removed during the photolysis to the amount of OH formed by the subsequent fast reaction between O( 1D) and H 2. The rate constant for the reaction between O( 1D) and NO 2 was measured as (1.5±0.3)×10 −10 cm −3 s −1 , and the 193 nm absorption cross-section for NO 2 was estimated as (2.9±1.2)×10 −19 cm 2 .