Chemiluminescence Channels Research Articles

Updating the Chemiluminescence Oxygen-Aftereffect Method for Determining the Rate Constant of the Peroxy-Radical Self-Reaction: Oxidation of Cyclohexene.

Updating the facile chemiluminescence oxygen-aftereffect method, most suitable for determining the rate constant (kt ) of the peroxy-radical self-reaction (main chemiluminescence channel), pertained to considering the sensitivity of such a method toward a disturbing influence of the peroxy radicals of the initiator of the chain oxidation process. Such a disturbance may derive from the side chemiluminescent reaction, which involves peroxy radicals of both hydrocarbon and initiator. To examine the applicability and limitations of the chemiluminescence method under present scrutiny, cyclohexene was used as the model oxidizable hydrocarbon substrate. Computer simulations of the reaction and chemiluminescence kinetics have demonstrated the validity of the considered methodology at the value of the rate constant of the propagation of the overall chain process by peroxy radicals of the initiator higher than 1 m-1 s-1 . Despite that the chemiluminescence time profile and the stationary level of the total chemiluminescence intensity depend on the kinetics of the side chemiluminescence channel and on the ratio of the excited-state generation yields in the mentioned reaction channel and in the main chemiluminescence process, the value of kt assessed by the oxygen-aftereffect method has been found independent of variation of these characteristics.

A two-dimensional sensor based on dielectric barrier discharge molecular optical emission and chemiluminescence for discrimination analysis of volatile halohydrocarbons

In this work, a two-dimensional sensor based on dielectric barrier discharge (DBD) molecular optical emission and liquid phase chemiluminescence (CL) was constructed for the discrimination analysis of hazard volatile halohydrocarbons (VHCs) including dichloromethane, chloroform, tetrachloromethane, 1,1,2,2,-tetrachloroethane, 1,4-dichloropropane, 1,2-dichloroethane, bromoform and iodomethane without any separation. Atmospheric pressure DBD induced not only multi-channel molecular optical emission spectroscopy (MES), but also chemiluminescence through the reaction of the DBD-split VHCs with luminol in aqueous solution. The DBD-MES and CL pattern of each analyte were unique, and the linear discriminant analysis (LDA) demonstrated the robustness of this optical sensor. Principal component analysis (PCA) revealed that MES and CL channels contributed at varied concentrations to the good discrimination capability due to the two distinct sensing mechanisms. The miniaturized optical sensor possessed the advantages of simple construction, low power consumption, and high sensitivity to VHCs, especially chlorinated hydrocarbons. It demonstrated for highly discriminative and precise identification of VHCs in air samples.

State-to-state chemiluminescence in reactions of Mn atoms with S2Cl2

A combined experimental and time-dependent density functional theory (TDDFT) investigation of the title reaction is presented. Both 'hot' and 'cold' laser-ablated Mn atom beams have been employed to determine the translational excitation functions for production of MnCl*(c(5)Σ(+), d(5)Π, e(5)Δ, e(5)Σ(+), A(7)Π). Analysis in terms of the multiple line-of-centres approach shows that the 'hot' results are dominated by reactions of the second metastable state of Mn, z(8)P(J), all with very low thresholds; while the first metastable state, a(6)D(J), and the ground state, a(6)S, are the precursors in the 'cold' results, all with significant excess barriers. The post-threshold behaviour of most z(8)P(J) and a(6)D(J) reaction channels implies that the transition states shift forward with increasing collision energy. The TDDFT calculations suggest that, while Mn*(z(8)P(J), a(6)D(J)) insertion into the S-Cl bond is facile, the observed chemiluminescence channels mostly derive from abstraction in a preferred linear Mn-Cl-S configuration, and that the low z(8)P(J) thresholds originate from attractive but excited reagent potentials which either reach a seam of interactions in the product valley or (in the c(5)Σ(+) case) lead to an octet potential very close in energy to the product sextet. The excess barriers in the Mn*(a(6)D(J)) and Mn(a(6)S) reactions appear for the most part to derive from exit channel mixing with lower-lying product potentials. The observed transition state shifts are consistent with the system being forced to ride up the repulsive wall of the entrance valley as collision energy increases, the location of that wall being different for the z(8)P(J) and a(6)D(J) cases.

Collision Energy Dependence Measurement of the Total De-excitation and the CF3* Chemiluminescence Cross Sections in the Ar(3P) Reaction with CF3H

Abstract The collision energy dependences of the total de-excitation and the CF3* chemiluminescence cross sections were measured in the reaction of Ar(3P) with CF3H using conventional and cross-correlation TOF methods. In the latter method, which is favorable for detecting weak signals, we employed a pseudorandom pulse discharge to generate a metastable argon beam. The collision energy dependence for the CF3* chemiluminescence channel gives a positive slope as a function of the collision energy with a threshold of 0.10 eV. The collision energy dependence of the total de-excitation in the entrance channel, on the other hand, shows a steep decrease as a function of collision energy without any threshold. These results provide insight into the detailed dynamics at crossing points of the potential energy surfaces.

Transition state observation of excited harpoon reactions, within Ca-HX van der Waals complexes

The observation of reactions through the excitation of van der Waals precursors allows for the spectroscopic investigation of the reaction surface of the excited state adducts. This method has been applied to the reaction of calcium 1D and 1P with the various hydrogen halide molecules, the reaction being endothermic with ground state calcium by less than 1 eV. The complexes were produced by supersonic expansion following laser ablation of the calcium atom. The chemiluminescent channel producing the CaX (A 2Π, B 2Σ) molecules is found to be an important channel and was investigated through action spectra. These spectra reveal the local electronic excitation of the calcium atom within the complex with the local orbital symmetry A′ or A″ of the Cs molecular complex. The band structure has been analyzed in terms of the intermolecular modes, the bending mode being prominent in the A″ state correlating with Ca 1P1. This state can be characterized by a single generic two dimensional reaction surface (bending+H-X reaction coordinate) common to the HX molecules. This surface is characterized by an identical entrance valley in the bending and reaction coordinates opened to the products through a transition state characterized by a channel of variable size depending upon the halogens. The experimental results have been successfully simulated on this model surface by performing one- and two-dimensional wave packet propagation calculations. The position of the bands in the spectrum are related to the bending modes and their bandwidth to the opening in the channel. These excited state reactions appear through their various characteristic as a generic model for excited state harpoon type reactions and display resonances despite the high cross sections for the reactions observed in collisions.

Reaction cross-section and product polarization in the reaction

Abstract The Ca ( 1 D 2 ) + HBr → CaBr(A,B) + H reaction has been studied by measuring its chemiluminescence at an average collision energy of ET = 0.16 eV under beam-gas conditions. Absolute values of the reaction cross-section for both chemiluminescence channels (e.g., A and B electronic states) were found to be σ A = 2.2 ± 0.9 A 2 and σ B = 0.52 ± 0.24 A 2 . In addition, the product polarization of the chemiluminescence emission was also measured, indicating a strong product rotational angular momentum alignment. The results are discussed in the light of a recent stereodynamical model for these, heavy + heavy-light, kinematically constrained reactions.

Emission spectra and effect of molecular orientation on branching of chemiluminescent channels in the trifluoroacetonitrile + argon(3P) reaction

The effect of molecular orientation on the branching of the chemiluminescent channels of the formation of the CN * (B), the CN * (A), and the CF 3 * radicals has been studied in the reaction of Ar * with the oriented CF 3 CN molecule. The branching ratio of the formation of the CF 3 * radical has been found to be very small compared to that of the CN * (B) and of the CN * (A) radicals. The CN-end attack has been observed to be more favorable than the CF 3 -end attack in the formation of CN * (B) and of CN * (A), and the steric asymmetries in the reaction are almost equal to each other

Reaction between Ba and N2O in large Arn clusters

The collision between a Ba atom and an Arn cluster carrying N2O molecules has been investigated under crossed molecular beam conditions. The argon cluster acts as a solvent for the Ba+N2O reaction, which is monitored through its chemiluminescent channel forming electronically excited BaO. The effects of cluster size and the number of N2O molecules per cluster have been investigated systematically as have the effects of extra molecules present upon the cluster (CH4). It has been shown that (i) the BaO reaction product either stays solvated in the cluster or is lost from the cluster; (ii) the reaction probability between Ba and N2O is approximately unity for the clusters considered here; (iii) the chemiluminescence quantum yield decreases as the number of N2O molecules per cluster is increased. The effect of a thermal bath (the argon cluster) on the dynamics of the well studied gas phase reaction Ba+N2O is discussed.

The possible resurrection of the Chapman mechanism for atmospheric sodium chemiluminescence and ruminations on NaO reaction dynamics

AbstractA critical reappraisal and kinetic modeling is presented of a sodium/N2O system. The analysis provides a compelling argument that previously reported kinetic decay rates may refer not to the reaction of O with NaO but rather to that of O with Na2O. The system shows pronounced propensity for a significant portion of the NaO to be quantitatively converted to Na2O on a time scale commensurate with that of the Na/N2O titration reaction. The O atom in the system does appear to originate from the photolysis of a residual level of NaO. The observed Na(2P) chemiluminescence, used to track the O atom decay rates, can be consistent with the O + NaO reaction as previously surmised. It is unlikely that the alternate O + Na2 and O + Na2O chemiluminescent channels can generate the observed intensity levels. This reanalysis, which provides for the observed first order dependences on N2O(Na2O) and O atom concentrations has significant implications for the Chapman atmospheric mechanism of the sodium airglow. Its conclusions resurrect the viability of the original scheme which requires efficient branching of the O + NaO reaction to Na(2P). Recent suggestions invoking the participation of NaO(A2Σ+) require the latter to have a metastable nature with respect to its radiative and collisional quenching (N2, O2) channels, for which there is no current evidence.An additional evaluation of the rate constant measurements for the fast reactions of NaO with NO or CO indicates that these most probably are kinetically complex and involve longlived transition states. Their rate constants are predicted to have small negative activation energies and pressure dependences. In the case of NaO with CO this may explain its low Na(2P) chemiluminescent efficiency. For the NaO + O reaction, a rate constant of about 4 ×10−11 cm3 molecule−1s−1 is predicted at room temperature. This is similar to that used in earlier atmospheric models. Its magnitude circumvents the consequences of the reaction's large entropy decrease which otherwise implies too large a cross‐section for the reverse reaction. A smaller value also is more likely to be consistent with a normal short‐lived collisional transition state, which will allow for a more significant Na(2P) quantum efficiency. © 1993 John Wiley & Sons, Inc.

Chemiluminescent channels in reactions of Ba(1P1) with water, alcohols, and ethers

The present paper investigates chemiluminescence in reactions of excited barium atoms (6s6p 1P1) with water and a series of alcohols and ethers. The electronically excited product molecule from the reaction with H2O (and D2O) is BaOH (and BaOD) in the A 2Π, A′ 2Δ, and B 2Σ levels. The product molecule is always Ba–ORx in reactions with alcohols ROH, whatever the size of the alcohol (methanol to butanol), and whatever its class (primary to tertiary). By comparison, no chemiluminescence was observed when the reactant was dimethyl and diallyl ether although allowed energetically. The nature of the product molecules in reaction with alcohols, and the absence of reaction with ethers that were found here are remarkably close to what was found by Davis et al. (submitted to J. Chem. Phys.) for the formation of ground state products in reactions of Ba(6s5d 1D2) with water, methanol, and dimethyl ether. The present work thus allows us to extend the model of Davis et al. for the reactivity of Ba(6s5d 1D2) as a powerful and general description of the reactivity of electronically excited barium atoms—the close approach of excited barium to water or alkyl alcohol molecules induces migration of the H atom that is bonded to oxygen. The reaction and the nature of the reaction product is determined by the departure of this H atom. The present paper also provides as side results determination of the Ba–OCH3 binding energy 3.8±0.1 eV, and spectroscopic information on several barium monoalkoxides.

The effect of vibrational excitation (3≤v″≤19) on the reaction Na2 (v″)+Cl→NaCl+Na*

The variation of the total integral cross section for the chemiluminescent channel with the vibrational excitation 3≤v″≤19 is investigated using laser-induced fluorescence or coherent population transfer, a new method employing delayed interaction with two cw lasers to populate vibrationally excited levels. The cross section increases with v″ by about 0.76% per vibrational level. The results are in agreement with the results of phase-space calculations, as well as with those from simple curve crossing models.

ChemInform Abstract: The Effect of Incident Spin‐Orbit State on the Chemiluminescent Reactions of Ba(3DJ) with Several Oxidants

Abstract(Cl2, Br2, CCl4, N2O, and NO2) is determined by utilizing optical pumping state selection.

Spin–orbit effects in chemical reactions. Investigation of ground-state products from reactions of Ba(3D)

The dependence of the cross-sections for production of ground-state barium halide products on incident spin–orbit state has been determined by means of optical-pumping state selection for the reaction of metastable Ba(6s5d3D) with HCl, CH3Cl, HBr and CH3Br. In addition, cross-sections for the metastable 1D level were related to those of the 3DJ multiplet by optical pumping on an intercombination line. For alkyl halide (RX) reactants, the spin–orbit dependence of the reactivity for the ground-state channel was substantial with an ordering J= 1 > J= 2 > J= 3. This is an opposite ordering to that previously observed for the chemiluminescence channels in analogous reactions. The hydrogen halide reactions exhibited a varying spin–orbit dependence with vibrational level. For the most highly populated vibrational levels v, the spin–orbit dependence was comparable in sign and magnitude to that for RX reactants, while a significantly diminished variation of reactivity with incident J was observed for lower v. The variation of spin–orbit effect with product vibrational level is believed to be due to the dependence of the reaction dynamics on incident impact parameter.

The effect of incident spin-orbit state on the chemiluminescent reactions of Ba(3D J) with several oxidants

The dependence of the chemiluminescence channels on incident spin-orbit state has been determined by utilizing optical pumping state selection for the reactions of metastable Ba(6s5d 3DJ) with Cl2, Br2, CCl4, N2O, and NO2. The cross sections for the neighboring metastable 1D level were related to those for the 3DJ multiplet by optical pumping on an intercombination line. For the halogen-containing reagents, the spin-orbit dependence of the reactivity was substantial for BaX B–X emission and was in the order J=3>J=2>J=1. The differences in reactivity were somewhat less for the C–X chemiluminescence channel in the Cl2 and Br2 reactions. Essentially no spin-orbit dependence was observed in the N2O and NO2 reactions.

Dependence of the chemiluminescence cross section on spin-orbit state for the reaction of Ca(3P0J) with alkyl bromides

The dependence of the chemiluminescence cross section on initial spin-orbit level has been measured for the reaction of metastable Ca(4s4p 3P0J) with Cl2, CH3Br, CH2Br2, CH2=CHCH2Br, and C6H5CH2Br, using an optical pumping state selection technique. Optical pumping depletion was also used to determine what fraction of the chemiluminescence was due to the second metastable Ca(4s3d 1D) level present in the incident atomic beam. Chemiluminescence cross sections for both the 3P0 and 1D reactions were separately determined; total attenuation and intramultiplet mixing cross sections were also estimated. The Ca(3P0) spin-orbit dependence for the chemiluminescence channel in all the reactions studied was substantial and of similar magnitude, with an order of reactivity J=2>J=1>J=0. This spin-orbit selectivity is related to differences in the evolution of the asymptotic spin-orbit states onto the various electrostatic surfaces at smaller separations. It is remarkable that this selectivity persists with polyatomic reagents.

Chemiluminescence study of the Ca( 1D) + BrCN reaction: Estimate of the CaCN dissociation energy

Chemiluminescence resulting from the reaction of Ca( 1D) + BrCN under single-collision conditions has been observed. The spectra show the major chemiluminescence channel to be the formation of the excited calcium monocyanide. From the short-wavelength cutoff of the chemiluminescence spectrum, a lower bound of 3.91 ± 0.05 eV is placed on D 0 0(CaCN). An absolute chemiluminescence cross section of 19.0 ± 1.0 Å 2 has been found for the above reaction.

Spin-orbit effects in chemical reactions: The reaction of spin-orbit state-selected Ca(3P J) with Cl2, Br2, and CH3Cl

An optical pumping state selection technique is employed to investigate the effect of atomic spin-orbit state on chemical reactivity for the Ca(3P0) level, for which the spin-orbit splitting is small. The spin-orbit dependence of the chemiluminescence and chemi-ionization cross sections has been determined for the reactions of Ca(3P0) with Cl2, Br2, and CH3Cl. For the CaCl A–X and B–X chemiluminescence channels of the Cl2 and Br2 reactions, the spin-orbit dependence is substantial, and the order of reactivity is J=2>J=1>J=0. The differences in reactivity of the spin-orbit states for these channels in the CH3Cl reaction are much smaller, as is true also for the chemi-ionization channels of all three reactions. No significant differences in reactivity were found for the C–X chemiluminescence channel in the Cl2 and Br2 reactions. The nonreactive intramultiplet mixing cross sections were estimated by modeling the dependence of the Ca(3P0→1S) emission intensity vs scattering pressure. These experimental results are interpreted in terms of the expected dynamics of these reactions. The spin-orbit selectivity is related to how the asymptotic spin-orbit states evolve into the different electrostatic covalent surfaces at smaller separations.

Energy partitioning and reaction dynamics in the chemiluminescent channel of the reaction: HS + O 3 → HSO* + O 2

The title reaction forms electronically excited HSO(Ã 2A′) directly, with considerable vibrational and rotational excitation as well. The internal excitation of the HSO fragment is the maximum possible consistent with the concurrent formation of an O 2( 1Δ g) molecule as the other reaction product. The observed vibrational excitation peaks in the υ′= 2 level of the υ 3 mode. No evidence about possible excitation of the other vibrational modes of HSO could be obtained.

Reaction of Ba with ICl and IBr

The chemiluminescence from the reactions of Ba with ICl and IBr have been studied. Emission could be observed only from BaCl and BaBr. A broad emission in the near-IR could not be unambiguously assigned. The formation of IX-Ar (X = Cl, Br) van der Waals complexes quenched the chemiluminescence channel.

Electronic energy partitioning in reactions occurring on more than one potential energy surface: Metastable Mg(3P) atoms with halogen molecules

For the reactions metastable Mg(3P) atoms and dihalogen molecules F2, Cl2, and Br2 we have measured by a beam-gas experiment the absolute cross sections for all three electronic reaction channels: formation of MgX(X 2Σ+) ground state, MgX(A 2Π) chemiluminescent products and MgX+(1Σ+) chemi-ions. The chemiluminescence and chemi-ion yields both turn out to be of the order of 1% in all three systems. By qualitative MO theory, it is shown that the dynamical bottleneck in the adiabatic chemiluminescence channel is an early barrier and in the diabatic chemi-ionization process a spin flip occurring during the approach phase, following a long-range electron transfer. An information theoretic analysis reveals considerable dynamic bias associated with most of the CL and CI products [except for MgCl (A 2Π)], and the surprisal plots are nonlinear for all three reactions.