Product Vibrational Distributions Research Articles

Effect of reagent rotational energy on product-state distribution in the reaction Ca + HF → CaF + H

The effect of reagent rotation on the product vibrational state distribution is reported for the reaction Ca( 1S) + HF(X 1∑ +, υ = 1. J

Product vibrational state distributions in thermal energy associative detachment reactions: F−+H,D → HF(v), DF(v)+e−

Nascent product vibrational state distributions are obtained by the method of spectrally resolved infrared chemiluminescence for the associative detachment reactions: F−+H → HF(v≤5)+e−, ΔH=−238.3 kJ mol−1 and F−+D → DF(v≤7)+e−, ΔH=−245.3 kJ mol−1. These reactions are carried out under thermal energy conditions in a flowing afterglow. The nascent distribution for HF(v) is Nv=1=0.0+0.06−0.0, Nv=2=0.09±0.01, Nv=3=0.21±0.01, Nv=4=0.41±0.02, Nv=5=0.30±0.02 with an average fraction of energy deposited into vibration, 〈fv〉=0.72±0.03 and for DF(v): Nv=1=0.08+0.01−0.07, Nv=2=0.09±0.01, Nv=3=0.15±0.02, Nv=4=0.11±0.02, Nv=5=0.15±0.01, Nv=6=0.24±0.03, Nv=7=0.18±0.02 with 〈fv〉 ≤0.61±0.04. Simple kinematic effects based on angular momentum constraints are not able to explain the broader distribution observed for DF as compared to HF. Several possibilities for this difference are discussed. In an argon buffer, which is much less effective than helium for rotational relaxation, the DF emission exhibits highly nonthermal rotational excitation.

The Reaction X + Cl 2→XCl + Cl (X = Mu, H, D). II. Comparison of experimental data with theoretical results derived from a new potential energy surface

We consider experimental implications for the Mu + Cl 2, H + Cl 2, and D + Cl 2 reactions of the extended London—Eyring—Polanyi—Sato (LEPS) potential energy surface derived from experimental data in paper I. In the present calculations, it is necessary to make additional implicit and explicit assumptions concerning the three-dimensional (3D) nature of the potential surface, since the inversion procedure of paper I yields information only on the collinear (1D) part of the surface. We have performed accurate 1D quantum calculations of reaction probabilities, which are then transformed into 3D by an information theoretic 1D → 3D transformation incorporating a constraint to allow for angular momentum transfer effects in light+heavy—heavy atom reactions. This procedure implicitly accounts for the 3D nature of the potential surface. The calculated vibrational and vibrotational product distributions are in good agreement with those determined in thermal chemiluminescence experiments. The Sato parameters for the 1D surface also define a full 3D surface. This is used as an approximation to the true surface, and its properties are explored in 3D quasiclassical trajectory calculations. Comparison is made for the H and D reactions with available chemiluminescence, molecular beam and kinetic experimental data for differential and total reaction cross sections, energy disposal, rate coefficients and Arrhenius parameters. Some kinetic isotope effects in the Mu, H, and D reactions are discussed using vibrationally adiabatic theory. Comparison is also made with results from other calculations in the literature for the H + Cl 2 and D + Cl 2 reactions.

Infrared multiphoton isomerization and fragmentation reactions of organic molecules

Abstract

Nascent product vibrational state distributions of ion–molecule reactions: The proton transfer reactions F−+HX→HF(v)+X−, X = Cl, Br, and I

Nascent vibrational state distributions are obtained for the HF products of the proton transfer reactions F−+HX→HF(v)+X−, X = Cl, Br, and I. The reactions are carried out in a flowing afterglow apparatus in which the reagents are fully thermalized (300 K). The product states are measured by low resolution infrared chemiluminescence spectra obtained with a Ge:Cu infrared detector and a circular variable filter. The nascent HF(v) distributions are as follows: for F−+HCl, N1:N2:N3 = 0.46:0.33:0.21; for F−+HBr, N1:N2:N3:N4 = 0.28:0.27:0.24:0.21; for F−+HI, N1:N2:N3:N4:N5 = 0.20:0.23:0.22:0.20:0.15. All three reactions channel the available exothermicity quite efficiently into product vibration. Product rotational state information cannot be obtained due to collisions with the He carrier gas. In spite of the deep attractive wells of the F−+HX potential energy surfaces, in all three cases the degree of vibrational excitation in the ion–molecule reaction is remarkably similar to, although distinctly smaller than, that of the corresponding neutral F+HX reactions. The results strongly suggest that these ion–molecule reactive collisions are direct encounters and that the kinematic effect of the mass combination (transfer of a light particle between two heavy particles) dominates over the influence of the shape of the potential energy surface in determining the product vibrational state distributions.

Nascent product vibrational state distributions of ion–molecule reactions: The H+F−→HF(v)+e− associative detachment reaction

The nascent product vibrational state distribution is obtained for the thermal energy associative detachment reaction H+F−→HF(v?5)+e−, ΔH = −57.0 kcal/mol. The relative vibrational populations are as follows: Nv = 10 = 0.00±0.06; Nv = 20 = 0.23±0.04; Nv = 30 = 0.27±0.03; Nv = 40 = 0.29±0.03; and Nv = 50 = 0.21±0.03. Arguments are presented that suggest that Nv = 00 = 0. The average fraction of the total energy deposited in product vibration is <fv≳ = 0.64±0.03. The release of the very light electron as one of the reaction products places severe angular momentum constraints on the reaction system. A simple kinematic model predicts a highly non-Boltzmann HF rotational state distribution which increases with increasing J up to some cutoff level. The high degree of vibrational excitation in the HF product has been accounted for by theoretical calculations of Gauyacq using the zero-range potential approximation.

A classical mechanical study of the LiFH system

A three dimensional and collinear quasiclassical study of the Li + HF → LiF + H reaction is performed on the Zeiri—Shapiro semi-empirical potential energy surface. The results are compared to a recent experimental study. In agreement with experiment ≈43% of available energy is channeled to the internal (vibrational and rotational) mode of the LiF product, most of which, we show, ends up as rotation (≈33%) and only the remaining 10% as vibration. The differential cross section is shown to peak in the forward—backward directions as also observed experimentally. The calculated cross section is more backward peaked than the experimental one. The accuracy of the quasiclassical method for this system is assessed by comparison of collinear results with available quantal calculations. It is shown that the average product vibrational distributions are adequately given by the quasiclassical method. The results are analyzed using periodic-orbit-dividing surfaces which predict correctly the onset of the various dynamic barriers.

A classical reactive study within the infinite order sudden approximation: integral cross sections for the reactions F + H 2vi = 0) → HF( vf = 0,1,2,3) + H

Integral reactive classical cross sections and product vibrational distributions are presented for the F+H 2 system. The calculations were made within the infinite order sudden approximation (IOSA) and the results compared with recent quantum-mechanical IOSA and exact classical results.

On differences between quasi-classical and quantu,-mechanical vibrational product distributions in the collinear H+Cl2 (v=2) and D+Cl2 (v=2) reactions

Vibrational product distributions for the collinear reactions H+Cl2 (v=2) and D+Cl2 (v=2) have been determined at low translational energies (≤0.1 eV) both by quantum-mechanical and by quasiclassical trajectory methods. An optimized extended LEPS potential surface has been used. There is a distinct quantum effect giving rise to trimodal distributions in the D reaction, whereas the corresponding quasiclassical distribution is bimodal. At the energy investigated for the H reaction, bimodal distributions result with either method, although there are quantitative differences. At the same time, above the classical threshold the average amount of vibrational excitation is predicted correctly by the quasi-classical calculations. Collinear quasi-classical trajectories are thus not fully adequate for determining detailed vibrational product distributions in the title reactions.

Dynamics and mechanisms of CO production from the reactions of CH2 radicals with O(3P) and O2

A cw CO laser has been used to probe the complete CO vibrational energy distributions in the reactions of CH2 radicals with O(3P) and O2 (3∑−g. The CO formed from the reaction with the atom was concluded to be produced via two equally important channels, O+CH2→CO+H2→CO+2H,, with an average vibrational energy of 19 kcal/mole, and an approximate vibrational temperature of ≈104K (for v≤12), which is sufficient to account for previously observed CO stimulated emission from O(3P)+CH2. The population inversion derives mainly from the molecular hydrogen elimination channel. In the reaction of CH2 with molecular oxygen, the CO formed is believed to be produced from both a molecular elimination path giving H2O+CO and from two possible atomic or radical production processes, yielding H+CO+OH. We find from analysis of the CO product vibrational energy distribution that 30% of the CO formed is produced via the former path, and 70% is formed from the latter path. This information is important to the detailed kinetic modeling of acetylene and other hydrocarbon combustion systems.

Chemiluminescence mapping. I. Experimental method and initial measurments on the D+F 2 and F+D 2 reactions

Measurements by a new experimental chemiluminescence method of the nascent DF product vibrational distribution confirm earlier findings for the F + D 2 → DF(ν⩽4) + D reaction. The distribution for D + F 2 → DF(ν⩽15) + F shows a larger fraction (≈ 78%) of the reaction exothermicity channeled into product vibration than is observed by conventional chemiluminescence measurements on the parallel H + F 2 system (58%). The new method, termed chemiluminescence mapping for its simultaneous recording of spectrally and temporally resolved chemiluminescence, differs from the earlier arrested relaxation and measured relaxation techniques by the introduction of a short duty cycle pulsed molecular reagent source, a modified deuterium dissociation source, and signal averaged (time resolved), detection of the DF infrared emission. The chemiluminescence mapping technique results for D + F 2 and F + D 2, are presented; apparent deviation from the energy distribution in the H + F 2 system is discussed.

Integral cross sections for the reaction F + H 2, ( vi = 0) → HF( vf = 0,1,2,3) + H: a quantum-mechanical calculation within the infinite order sudden approximation

Integral reactive quantum-mechanical cross sections and product vibrational distributions are presented for the F + H 2 system. The calculations were made within the infinite order sudden approximation (IOSA) formalism and the results are compared with experimental data and results obtained with other treatments.

A quasi-classical trajectory study of product vibrational distributions in the OH + H 2 → H 2O + H reaction

Product H 2O vibrational distributions are calculated for the OH + H 2 reaction using a fitted ab initio potential surface and a classical perturbation theory method to determine vibrational good action variables. Substantial excitation in all vibrational modes is found.

Vibrational product state distributions of ion–molecule reactions by infrared chemiluminescence: Cl−+HBr,HI→HCl(v)+Br−,I−

Initial vibrational product distributions have been obtained for the thermal proton abstraction reactions, Cl−+HBr→HCl(v=0,1)+Br− and Cl−+HI→HCl(v=0,1,2)+I−. The experimental method utilizes detection of infrared chemiluminescence from the products of the ion–molecule reactions in a flowing afterglow. A detailed description of the apparatus design and characteristics is given. The initial relative HCl product vibrational distribution for the reaction Cl−+HI was determined to be Nv=1=1.0, Nv=2=0.85±0.05. The ratio of the total emission from Cl−+HBr to that from Cl−+HI was measured to be 39±2%. The results suggest substantial disposal of energy into product vibrations in these ion–molecule reactions.

The photodissociation of van der Waals molecules: Complexes of iodine, neon, and helium

A supersonic free jet expansion was used to prepare van der Waals complexes of the type I2NeaHeb. Complexes containing as many as seven rare gas atoms were identified as satellites in the fluorescence excitation spectrum of the I2 B (v′=13 to 26) ←X (v″=0) band system by their relative dependence on the concentrations of neon and helium. For a+b?6, the frequencies of the van der Waals satellites follow a simple band shift rule: ν (I2NeaHeb) =ν (I2)+Aa+Bb, where A and B are weak functions of the I2 vibrational state. This observation, along with the failure of the rule for I2Ne7, provide some information concerning the geometry and binding in these molecules. Progressions (w′=0,1, and 2) in van der Waals modes of I2Ne and I2NeHe were also identified. The problem of intramolecular energy transfer was studied by observation of the dispersed emission spectra of the I2* fragments produced upon laser-induced photodissociation of these complexes. The product vibrational state distributions could be determined by using the known Franck–Condon factors and the observed intensities of the iodine transitions. All complexes required at least one I2 stretching quantum per rare gas atom for complete dissociation. Larger species favored dissociation channels involving more than one vibrational quantum per rare gas atom.

Time-dependent theory of electronic-to-vibrational energy transfer. Application to metastable argon atoms with nitrogen molecules

Abstract The product vibrational distribution is calculated for the process Ar( 3 P) + N 2 (X) → Ar + Bi* 2 (C 3 H u ). The evolution of the molecular vibration is treated using simple time-dependent quantum mechanics. The theory fits the oscillations in the vibrational distribution observed recently by Cutshall and Muschlitz.

A theoretical study of energy transfer in the quenching of O(1 D 2) by CO(1Σ+)

Energy transfer processes occurring during the collisional quenching of O(1 D) by CO(1Σ+) are studied using a classical collision complex model together with potentials previously derived for the C(3 P) + O2(3Σ g -) reaction. Room temperature quenching rate constants, electronic-vibrational transfer efficiencies and product vibrational state distributions are in good agreement with experiment. The calculated and experimental temperature dependences of the electronic-vibrational transfer efficiencies and vibrational populations, however, disagree. The effect of using vibrationally excited CO as a quenching partner is studied and shown to result in a lowering of the quenching rate constant by a factor of 4 at room temperature. Enhancement of initial translational energy by the equivalent of a vibrational quantum of energy leads to an even larger decrease in the rate constant. This difference between vibrational and translational energy enhancement is interpreted in terms of an increased centrifugal barrier ...

The dynamics of hydrogen abstraction from polyatomic molecules by fluorine atoms

The reactions of atoms with HCOND 2, CH 3ND 2 and CH 2OD have been studied by arrested relaxation infrared chemiluminescence. The emission spectra of both the HF and DF products of each reaction measured. The resulting product vibrational energy distributions were different for reaction at the C, N or OD bonds. It is suggested that the origins of these differences lie in the dynamics of the attractive interactions exprinced by the F atom during the reaction.

Uni- and bimodal product energy distributions for the reactions H + Cl 2 (υ = 1) and D + Cl 2 (υ = 1)

Vibrotational reaction probabilities for the reactions H + Cl 2 (υ = 1) and D + Cl 2 (υ = 1) at translational energies close to 0.1 eV are predicted to be bimodal, with the D reaction showing the more pronounced bimodality. The corresponding rotational and vibrational product distributions may be either uni- or bimodal. The results are from accurate quantum calculations for the collinear reactions, together with an information theoretic 1D → 3D transformation. An optimized, extended LEPS surface is used.

Transfer of electronic excitation in collisions of metastable argon atoms with nitrogen molecules

Measurements have been made of the product vibrational and rotational state distributions for the process Ar*(3P2,0)+N2(X) →Ar(1S0)+N2*(C,3Πu) by spectrometric observation of the C→B fluorescence at the intersection of supersonic beams of the reactant species over the relative kinetic energy range 0.06–0.41 eV. The results are compared with the predictions of a ’’golden rule’’ model which gives the transition probabilities in the highly impulsive limit as the product of Franck–Condon and density of states factors. Below 0.17 eV, the model fits the experimentally determined v′=0/v′=1 population ratio reasonably well. At higher energies the experimental ratio rises, however, and reaches a maximum at 0.3 eV. A statistical population of rotational levels for v′=0 corresponding to rotational temperatures of 1300 °K and 1100 °K at 0.161 and 0.089 eV relative energy, respectively, is observed, while the ’’golden rule’’ predicts considerably higher rotational excitation in each case.