- XCN (X=Cl, Br and I): a novel source of isocyanogen
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Ambient light photolysis of gaseous BrCN, ClCN, and ICN results in the production of isocyanogen (NCNC) as the sole CN containing product. The flash vacuum pyrolysis of BrCN (1100°C and E-5 mbar) generates NCNC, NCCN, HOCN, HNCO and the CN radical.
- Blanch, Rodney J.,McCluskey, Adam
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- Kinetics of the NCN + NO reaction over a broad temperature and pressure range
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Rate coefficients for the reaction 3NCN + NO → products (R3) were measured in the temperature range 251-487 K at pressures from 10 mbar up to 50 bar with helium as the bath gas. The experiments were carried out in slow-flow reactors by using pu
- Welz, Oliver,Olzmann, Matthias
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p. 7293 - 7301
(2012/09/22)
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- Halogenated xenon cyanides ClXeCN, ClXeNC, and BrXeCN
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We report on the preparation and characterization of three new noble-gas molecules ClXeCN, ClXeNC, and BrXeCN. These molecules are synthesized by 193 nm photolysis and thermal annealing of ClCN and BrCN in a xenon matrix. The absorption spectra are measured in the mid- and far-infrared regions, and the assignment is supported by isotope substitution and quantum chemical calculations at the B3LYP and MP2 levels of theory. The present results demonstrate a way to prepare other noble-gas molecules of this type.
- Arppe, Teemu,Khriachtchev, Leonid,Lignell, Antti,Domanskaya, Alexandra V.,Raesaenen, Markku
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p. 4398 - 4402
(2012/05/31)
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- Kinetics of the CCO + NO and CCO + NO2 reactions
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The kinetics of the reaction of CCO radicals with NO and NO2 were studied using time-resolved infrared diode laser absorption spectroscopy. The rate constants were determined to be kCCO+NO = (5.36 ± 0.5) × 10-11 and k
- Thweatt, W. David,Erickson, Mark A.,Hershberger, John F.
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- Treatment of the K-quantum number in unimolecular reaction theory: Insights from product correlations
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The connection between the K-quantum number and product correlations in the barrierless unimolecular dissociation of symmetric-top molecules is explored to establish a qualitative diagnostic for the treatment of the K-rotor dynamics in unimolecular reaction theory. We find that fragment scalar and vector correlations can provide guidance in this matter, and the photodissociation dynamics of thermal NCNO to form CN and NO at several dissociation wavelengths are presented to demonstrate the utility of this approach. The goodness of the K-quantum number can be related to the amount of energy in the conserved vibrational modes at the inner transition state. On the basis of measured correlated vibrational distributions, the K-quantum number is found to be approximately conserved at the inner transition state for the photodissociation of NCNO at 514, 520, and 526 nm. The methodology, involving a comparison of product distributions from the photodissociation of jet and thermal ensembles at identical wavelengths, is general and may be applied to previously studied systems that dissociate along barrierless potential energy surfaces, CF3NO and CH2CO. In addition, vector correlations serve as a means to probe the K-mixing at the outer transition state, and measured v-j correlations in the photodissociation of thermal NCNO are presented.
- McGivern, W. Sean,North, Simon W.
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p. 14472 - 14477
(2007/10/03)
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- Probing the nature of the K-rotor in unimolecular reactions: Scalar and vector correlations in the photodissociation of NCNO
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The photodissociation of NCNO at 520 and 532 nm was examined using transient frequency modulation Doppler spectroscopy in order to study vector and scalar correlations in the dissociation. A small correlation between v and J was observed corresponding to Β00(22) bipolar moments ranging from 0.00±0.02 to -0.03±0.02 at 532 nm and 0.00±0.02 to -0.01±0.02 at 520 nm. These were well described by a helicity unrestricted PST formulation at both wavelengths.
- McGivern, W. Sean,North, Simon W.
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p. 7027 - 7034
(2007/10/03)
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- Channeling of products in the hot atom reaction H + (CN)2 → HCN/HNC + CN and in the reaction of CN with CH3SH
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Infrared transient absorption spectroscopy was used to determine the total product branching fractions for the gas-phase hot atom reaction H + (CN)2 → HCN/HNC + CN (a) and the reaction CN + CH3SH → HCN/HNC + CH3S/CH2SH (b) at 293 K. The reactive H atoms had an initial mean translational energy of 92 kJ mol-1, with a 38 kJ mol-1 fwhm Gaussian energy distribution. The branching fractions determined for the product channels forming HCN and HNC, respectively, are 0.88 and 0.12 (±0.05) for reaction (a) and 0.81 and 0.19 (±0.08) for reaction (b). The bimolecular rate constant for reaction (b) was measured to be (2.7 ± 0.3) × 10-10 cm3 molec-1 s-1 at 293 K. The observed product branching fractions for reaction (a) are consistent with the assumption that the average reactive cross sections for the two product channels are approximately equal above their respective energy thresholds. The results for reaction (a) are compared with the related H + XCN (X = Br, Cl) reactions. The large rate coefficient for reaction (b) suggests an interaction via a long-range intermolecular potential, which is facilitated by the small ionization energy of CH3SH and large electron affinity of CN. The results for reaction (b) are compared with the related reactions of Cl and OH with CH3SH.
- Decker, Brian K.,Macdonald, R. Glen
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p. 6817 - 6825
(2007/10/03)
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- Energy disposal in CN(X 2Σ+) produced in the 157 nm photodissociation of acrylonitrile
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The rovibrational population distribution for the CN(X) fragment produced in the 157.6 nm photodissociation of acrylonitrile was measured. It was observed that the average energies in vibration and rotation of CN were approximately equal and represented about 5% of the available energy with vinyl radical as the co-fragment. It was suggested that dynamical factors played a significant role in energy disposal as the vibrational and rotational distributions were not in good agreement with an energy-conserving prior distribution.
- Guo,Carrington,Filseth
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p. 8411 - 8417
(2007/10/03)
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- Kinetics of the C2(a3IIu) radical reacting with selected molecules and atoms
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Rate coefficients for reactions of the C2 radical in its a3IIu electronic state with H, N and O atoms and with C3O2, C4F6, H2, NO, N2O, C2H2, C2H4, C3 H4 and C6H6 were determined. This work represents the first study of reactions of C2(a3IIu) radicals with the atoms investigated at room temperature and 4 Torr total pressure. The bimolecular rate constants obtained for the atom reactions were kc2+o = (9.8 ± 1.0) × 10-11- , kc2+N = (2.8 ±1.0) × 10-11 and kc2+N-14, in units of cm3 s-1. In addition, the reaction C2 + O was found to be independent of total pressure in the range 2-60 Torr. For the reaction C2(a3IIu) + ethene (C2H4) a temperature and pressure independent rate constant of (9.5 × 1.2) × 10-11 cm3 s-1 was obtained in the temperature range 298-1000 K at 100 Torr total pressure and in the pressure range 5-100 Torr at 298 K. The following rate constants were determined at room temperature and a total pressure of 4 Torr for the reactions of C2(a3IIu) radicals with benzene (C6H6), acetylene (C2H2) and allene (C3H4): kc2+C6H6 = (4.9 ± 0.1) ×10-10, kc2+C2H2 = (1.0 ± 0.1) ± 10-10 and kc2+C3H4 = (1.9 ± 0.3) ×10-10, in units of cm3 s-1. The reaction C2 + NO was investigated at room temperature and 100 Torr total pressure, a rate constant kc2+NO = (6.8 ± 0.3) × 10-11 cm3 s-1 was obtained. The reaction C2 + N2O was studied at 4 Torr total pressure in the temperature range 300-700 K for which a temperature independent rate constant kc2+N2O = (3.1 ± 0.4)X 10-14 cm3 s-1 was determined. by Oldenbourg Wissenschaftsverlag, Muenchen.
- Becker,Donner,Freitas Dinis,Geiger,Schmidt,Wiesen
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p. 503 - 517
(2007/10/03)
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- Experimental and theoretical determination of the magnetic dipole transition moment for the Br(4p5)(2P1/2←2P3/2) fine-structure transition and the quantum yield of Br(2P1/2) from the 193 nm photolysis of BrCN
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The integrated-absorption coefficients of several hyperfine lines of the magnetic dipole allowed transition of the bromine atom, Br, center at 3685.2 cm-1 were measured, and a value for the square of the magnetic dipole transition moment of the Br atom was determined. A theoretical calculation for the magnetic dipole transition moment was also carried out using a relativistic ab initio atomic structure formulation. The theoretical value was in excellent agreement with the value predicted assuming pure LS coupling, and in reasonable agreement with experiment. The Br atom was generated in equal concentration with the cyano radical (CN) by the 193 nm photolysis of cyanogen bromine, BrCN. The CN radicals were titrated by the rapid reaction with C3H8 to generate HCN and a small amount of HNC. Both time-resolved and frequency-scanned infrared absorption spectroscopy were used to monitor the Br, HCN, and HNC species. The photolysis of BrCN at 193 nm produced both the ground state Br(2P3/2) and the spin-orbit excited Br(2P1/2) atoms, and the yield for the production of Br(2P1/2) atoms was measured to be 0.31±0.01. The rate constants for the quenching of Br(2P1/2) by BrCN and C3H8 at 293 K were also determined.
- He,Seth, Michael,Tokue,Macdonald, R. Glen
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p. 7821 - 7831
(2007/10/03)
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- The photodissociation of carbonyl cyanide CO(CN)2 at 193 nm studied by photofragment translational energy spectroscopy
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The photodissociation of carbonyl cyanide CO(CN)2 at 193 nm was investigated by photofragment translational energy spectroscopy. For all the fragments created (CO, CN, OCCN, NCCN), the kinetic energy distributions were measured and two decay channels identified. The radical decay, CO(CN)2 + hν→OCCN+CN, dominates with a yield of 94%±2% and shows the available energy mainly (82%) channeled into the internal degrees of freedom of the fragments. A fraction of 18%±6% of the nascent OCCN radicals has sufficient energy to spontaneously decay to CO+CN involving a barrier ≤160 kJ/mol. With a yield of 6%±2% the molecular decay produces the fragments CO+NCCN. These fragments acquire a high available energy owing to the formation of the new C-C bond in NCCN. An average fraction of 70% is partitioned into internal fragment energy. Even the fastest fragments are still internally hot, indicating that with the high barrier expected, a substantial exit channel interaction is operative. The isotropic recoil distribution found for the products CN, OCCN, and NCCN further suggests that both the radical and the molecular decay are, on the time scale of a parent rotation, slow and probably indirect.
- Scheld, Heiner A.,Furlan, Alan,Huber, J. Robert
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p. 923 - 930
(2007/10/03)
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- Determination of reaction geometries
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Using polarized light the reaction geometry of selected species can be controlled even in bulk experiments. One reactant A is generated in a photodissociation process and its spatial distribution is completely described by the anisotropy parameter β. The other molecular reactant B is excited in a specific rovibrational state. Its spatial distribution is given by the J- and branch-dependent alignment parameter A0(2). Equations have been developed that allow a relatively easy conversion of experimental results to the angle of attack, γ. The unnormalized probability of an attack of A on B under an angle γ is given by the simple expression P(γ)∝[1 + 1/5βA0(2)P2(cos γ)P2(cos δ)] where δ is the angle between the E + (Combining right arrow above sign) vectors of the dissociating and the exciting laser beam. As an example, we have studied the reaction of A+HCN→HA+CN with A=H,Cl. The experimental results prove a preferred linear reaction geometry, i.e, an end-on attack of atom A on the terminating hydrogen atom of the HCN reactant. However, the cone of acceptance is higher for the Cl+HCN reaction than for the H+HCN one.
- Gericke, Karl-Heinz,Kreher, Christoph,Reinsch, Ernst Albrecht
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p. 10567 - 10572
(2007/10/03)
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- Pressure and Temperature Dependence of the Rate of Reaction between CN Radicals and NO over the Range 99 <= T/K <= 450
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Pulsed laser photolysis, laser-induced fluorescence experiments have been performed on the kinetics of reaction between CN radicals and NO.The measurements cover a range of temperature (99 ; at other temperatures, a smaller range>.Two methods were employed to extract rate constants in the limit of low and high pressure and their temperature dependences from the experimental results.Comparison of the values of the low-pressure rate constants derived from experiment with calculated values suggests that levels derived, in zero order, from the excited S1 and T1 electronic states mix with those in the ground S0 state thereby contributing to the density of NCNO states in the region of the CN + NO dissociation limit and hence to the rate of association in the limit of low pressure.
- Sims, Ian R.,Smith, Ian W. M.
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- Gas-Phase Atom-Radical Kinetics of Atomic Hydrogen, Nitrogen, and Oxygen Reactions with CHF Radicals.
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The absolute rate constants for the reactions of atomic hydrogen, nitrogen and oxygen with CHF radicals have been measured in a gas-flow system with photoionization mass spectrometry detection.CHF(1A') radicals were produced by dissociation of CH2F2, CH2FCl, or CHFBr2 in a radiofrequency discharge.CHFBr2 proved unsatisfactory as a precursor for CHF in kinetics studies.Atomic reactants were produced by dissociation of the corresponding elemental gas in a microwave discharge.The pressure was 1.7 Torr.The rate constants for CHF decay under pseudo-first-order conditions at 293 K in units of cm3 molecule-1 s-1 are (4.9 +/- 0.9) * 10-10 for CHF + H, (2.4 +/- 0.4) * 10-11 for CHF + N, and (1.4 +/- 0.2) * 10-10 for CHF + O.These reactions appear to proceed by an association-elimination mechanism.
- Tsai, Cheng-ping,McFadden, David L.
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p. 3298 - 3300
(2007/10/02)
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- Matrix Infrared Studies of the HCN + O3 and HCN + O Systems
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Codeposition of argon-diluted samples of O3 and HCN produced a unique 1:1 O3-HCN complex where the C2v symmetry of O3 is retained and HCN appears to form weak hydrogen bonding interactions with both terminal atoms of O3.Complexes with isotopic
- Mielke, Zofia,Andrews, Lester
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p. 3519 - 3525
(2007/10/02)
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- Experimental study of HCN+ and HNC+ ion chemistry
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We report the results of a room temperature selected ion flow tube study of reactions of HCN+ and HNC+. Electron impact on HCN was found to produce a mixture of HCN+ and HNC+ isomers. HCN+ was found to be isomerized efficiently to HNC+ by reaction with CO or with CO2, and isomerization is expected to occur for any other species M having a proton affinity PA(CN at C) a forth and back proton transfer mechanism. A monitor gas technique was used to distinguish between the isomers. With CF4, HCN+ was reactive (k = 1.2 × 10-9 cm3 s-1) and HNC+ unreactive. With SF6 both isomers react at the collision rate but HCN+ yields only SF5+ as the product ion whereas HNC+ yields only HNCF+. Thermodynamic data established in this work include Δr(HNC+) ≤ 1373 kJ mol-1, and hence PA(CN at N) ≥ 595 kJ mol-1.
- Petrie, Simon,Freeman, Colin G.,Meot-Ner, Michael,McEwan, Murray J.,Ferguson, Eldon E.
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p. 7121 - 7126
(2007/10/02)
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- Correlated product state distributions in the unimolecular reaction of NCNO
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Following excitation to S1, expansion-cooled NCNO undergoes nonradiative couplings to S0 and predissociates to CN and NO.Doppler profiles of selected CN B 2Σ+ X 2Σ+ rotational lines were recorded using LIF at several excess energies between 0 and 3000 cm-1.This yields NO V,R distributions associated with specific CN(X 2Σ+) rotational states.The profiles can be fit using the statistical PST/SSE model, and the correlated distributions show no evidence of dynamical bias or exit channel barriers.Doppler profiles generated with polarized lasers show little or no spatial anisotropy parameters β ca. 0. even at excess energies where predicted unimolecular lifetimes are 1 ps.Possible causes for the lack of spatial anisotropy are discussed.Analyses of NO fragment LIF spectra obtained at excess energies of 2348 and 2875 cm-1 show a slight preference for the Π(A') Λ-doublet component for J 30.5, suggesting planar dissociation.An in-plane orientation of the singly occupied p? lobe in NO is to be expected for dissociation on the ground (A') electronic potential energy surface.
- Qian, C. X. W.,Ogai, A.,Reisler, H.,Wittig, C.
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p. 209 - 218
(2007/10/02)
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- Picosecond photofragment spectroscopy. I. Microcanonical state-to-state rates of the reaction NCNO CN + NO
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This paper, the first in a series of three papers, gives a detailed account of our studies on picosecond photofragment spectroscopy.The unimolecular reaction NCNO CN + NO is examined in detail here.Microcanonical state-to-state rates are measured in molecular beams at different energies in the reagent NCNO using pump-probe techniques: one picosecond pulse initiates the reaction from an initial ( v,J) state and a second pulse, delayed in time, monitors the CN radical product in a specific rovibrational state, or the reagent NCNO (transient absorption).The threshold energy for reaction is determined to be 17 083 cm-1 (bond energy = 48.8 kcal/mol).Measured rates are found to be sharply dependent on the total energy of the reagent, but independent of the rotational quantum state of product CN.Results of transient absorption measurements are used to argue that the ground state potential energy surface dominates the reaction in the range of excess energies studied.The energy dependence of the rates, kMC (E), is compared with that predicted by statistical theories.Both standard RRKM (tight transition state) and phase space theory (loose transition state) fail to reproduce the data over the full range of energies studied, even though nascent product state distributions are known to be in accord with PST at these energies.Furthermore, kMC (E) is not a strictly monotonically increasing function of energy but exhibits some structure which cannot be explained by simple statistical theories.We advance some explanations for this structure and deviations from statistical theories.
- Khundkar, Lutfur R.,Knee, Joseph L.,Zewail, Ahmed H.
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- Picosecond Photofragmentation of Tri- and Tetraatomic Molecules: Measurement of State-to-State Reaction Rates
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In this Letter, we report our first results on the picosecond measurements of state-to-state rates of reactions, involving three- and four-atom molecules.These photofragment reactions are ICN -> I + CN and NCNO -> NO + CN.In these experiments, we use one picosecond pulse to initiate the photolysis and a second pulse to probe the produced fragments in their internal vibrational/rotational states.Results are presented for molecules in bulbs and beams, and comparisons with unimolecular theories are given.
- Knee, J. L.,Khundkar, L. R.,Zewail, A. H.
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p. 4659 - 4663
(2007/10/02)
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- Energy partitioning in the 532 nm photofragmentation of nitrosyl cyanide (NCNO)
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The 532 nm photodissociation of gaseous NCNO has been studied by a tandem pulse technique utilizing repetitive nanosecond laser pulses for dissociation and for delayed, time-correlated laser-induced fluorescence probing.Dissociation occurs within less than 3 ns, and both CN(X) and NO(X) have been identified as primary fragments.The central portions of their rotational distributions correspond to Boltzmann distributions with temperatures of (1010+/-50) K for CN and (930+/-50) K for NO.Parent rotation and angular momentum from bending vibrations of the A state levelspopulated at 532 nm account for the observed fragment rotation.Little angular momentum is partitioned into orbital motion of the fragments indicating that the molecule dissociates froma linear or quasilinear nuclear configuration.The observed distribution of the 9300 cm-1 of available energy into internal and relative translational degrees of freedom of the fragments is consistent with predissociation of bound A state levels into the continuum of ground state NCNO.
- Pfab, J.,Haeger, J.,Krieger, W.
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p. 266 - 274
(2007/10/02)
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- Reaction Dynamics during Warm-Up of Matrix-Isolated Cyanogen Azide After Photolysis
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The photolysis products of NCN3 in solid argon and nitrogen have been observed in the IR as well as UV-visible emission upon warm-up.Our IR data are consistent with earlier work on this system except for the observation of three additional bands with photolysis growth independent of each other: 339, 1232, and 1850 cm-1.The warm-up emission is assigned to the CCN radical, C2 (five Swan bands), N atoms (2D 4S), and a strong emission at 6000 Angstroem, yet unidentified.We report here the experimental evidence for a possible mechanism for the photolysis and subsequent warm-up in argon and nitrogen matrices.
- Krogh, Ole D.,Ward, Curtis H.,Hollenbeck, James M.
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p. 2892 - 2895
(2007/10/02)
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- Absolute rate constants for the reactions of CH with O and N atoms
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CH(X 2Π) was produced by multiple infrared photon dissociation of CH3OH in the presence of excess atomic oxygen or nitrogen.Time-resolved measurements of relative CH concentrations were made at 298 K with a tunable dye laser.Rate constants deduced from the dependence of CH decay rate on atom concentration are (9.5 +/- 1.4) * 10-11 cm3 s-1 for CH + O and (2.1 +/- .5) * 10-11 cm3 s-1 for CH + N.
- Messing, I.,Filseth, S. V.,Sadowski, C. M.,Carrington, Tucker
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p. 3874 - 3881
(2007/10/02)
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