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15 Jun 1985

Volume 82, Issue 12, pp. 5307-5762

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Low‐temperature X‐band EPR study of Mn2+‐, Cu2+‐, and Co2+‐doped NH4I single crystals

Prem Chand, G. C. Upreti@f@f, Sushil K. Misra, and M. Bartkowski

J. Chem. Phys. 82, 5307 (1985); http://dx.doi.org/10.1063/1.448613 (3 pages) | Cited 5 times

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X‐band EPR of Mn2+,Cu2+, and Co2+ ions doped in ammonium iodide single crystals have been studied at low temperatures. The Mn2+ and Cu2+ spectra show the presence of only one type of complex for each with features similar to those observed at room temperature with no unusual changes. The results on Co2+ ion, reported here for the first time, reveal the presence of three equivalent Co2+ complexes having tetragonal symmetry with their tetragonal axes orthogonal to each other. The charge‐compensation mechanism and possible vacancy complexes are discussed, and the spin‐Hamiltonian parameters reported.
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76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)

Zeeman quantum beat spectroscopy applied to the math 1A2–math 1A1 transition of SO2

Hajime Watanabe, Soji Tsuchiya, and Seiichiro Koda

J. Chem. Phys. 82, 5310 (1985); http://dx.doi.org/10.1063/1.448614 (8 pages) | Cited 19 times

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Zeeman quantum beats were observed in the fluorescence from a number of rovibronic levels of SO2 in the math 1A2 state. Rotationally cooled SO2 was prepared by supersonic expansion of its seeded mixture in Ar and was excited to the first electronically allowed 1A2 state by a frequency‐doubled dye laser in the wavelength range 260–320 nm. In the time‐resolved fluorescence measurements, a number of rovibronic lines were found to exhibit beating fluorescence decays in the presence of a weak magnetic field. The beating phenomena were analyzed on the basis of Zeeman quantum beat theory; of particular concern are the oscillation amplitude of the beating and the g value. It was found that almost all rotational levels of upper vibronic states of various bands (D, F, L, and N in Clements’ notation) possess sizable magnetic moments. On the other hand, only a limited number of rovibronic lines of several less perturbed bands (E and G) showed beating fluorescence decays. The derived g values and fluorescence lifetimes distribute rather irregularly over a wide range, but an almost linear relationship between the g value and the lifetime was found for the rR0(0) lines of various vibronic transitions. The intramolecular coupling mechanism needed to explain the anomalous behaviors of these excited rovibronic states are discussed. It is suggested that the dominant mechanism is spin‐orbit coupling.
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33.50.Dq Fluorescence and phosphorescence spectra
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Internal mode vibrational interaction in plastic crystals: Application to the Raman spectra of strongly IR active modes

W. Breyman, R. M. Pick, and M. Yvinec

J. Chem. Phys. 82, 5318 (1985); http://dx.doi.org/10.1063/1.448615 (11 pages) | Cited 3 times

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The systematic development of the harmonic, intermolecular, internal mode interaction energy in terms of symmetry adapted Wigner functions of the molecular orientations is given for a plastic crystal. This development is used for the study of the Raman profile of a mode with a strong induced dipole‐induced dipole interaction between the vibrating molecules. An approximate form of the profile is proposed, and compared with measurements made on NF3 by Gilbert and Nectoux.
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78.30.Hv Other nonmetallic inorganics
62.20.F- Deformation and plasticity

Multiphoton ionization photoelectron spectroscopy of phenol: Vibrational frequencies and harmonic force field for the 2B1 cation

Scott L. Anderson, Lionel Goodman, Karsten Krogh‐Jespersen, Ali G. Ozkabak, Richard N. Zare, and Cheng‐fa Zheng

J. Chem. Phys. 82, 5329 (1985); http://dx.doi.org/10.1063/1.448968 (11 pages) | Cited 41 times

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A molecular beam of phenol, cooled by a supersonic expansion, is crossed at right angles by the output of a pulsed frequency‐doubled dye laser, causing 1+1 resonance enhanced multiphoton ionization. The kinetic energy of the resulting photoelectrons is determined as a function of laser wavelength with time‐of‐flight analysis, permitting the assignment of 11 vibrational frequencies for the 2B1 phenol‐h6 cation and ten vibrational frequencies for phenol‐d5. Of these, all but the lowest frequency one in each case are in‐plane vibrations of which phenol has a total of 19. An approximate harmonic force field for the in‐plane modes of the phenol cation is derived along with its associated frequencies and mode forms. This in turn facilitates the vibrational analysis. Analogous force field calculations have been carried out on the ground (1A1) and first excited (1B2) states of the neutral parent, permitting conclusions to be reached concerning bonding changes upon removal of an electron from the phenol electron system.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.60.+q Photoelectron spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

An infrared spectroscopic study of the rotation of methane in solid nitrogen

Bengt Nelander

J. Chem. Phys. 82, 5340 (1985); http://dx.doi.org/10.1063/1.448616 (6 pages) | Cited 13 times

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Infrared spectra of CH4, CH3D, and CD4 in solid nitrogen have been recorded with 0.05 cm−1 resolution at temperatures between 5.5 and 20 K. The data show that methane rotates in nitrogen. The proton spin states of CH4 interconvert very slowly at 5.5 K but rapidly at 20 K.
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33.20.Ea Infrared spectra
61.50.-f Structure of bulk crystals

General theory of dynamic light scattering from cylindrically symmetric particles with translational‐rotational coupling

Sergio R. Aragón S. and Robert Pecora

J. Chem. Phys. 82, 5346 (1985); http://dx.doi.org/10.1063/1.448617 (8 pages) | Cited 11 times

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The general solution to the scattered electric field time autocorrelation function for a dilute system of cylindrically symmetric, optically anisotropic particles undergoing coupled translational‐rotational diffusion is presented. The solution is exact within the Rayleigh–Gans–Debye approximation. The scattered time autocorrelation function is an infinite series of decaying exponentials with time constants τ−1Ms =q2D+[s(s+1)+wMs(γ)−γ/3]Θ⊥, (M=0,1,2; s=0,1,2, ⋅ ⋅ ), containing both translational and rotational diffusion coefficients and spheroidal harmonic eigenvalues. The latter depend on the coupling parameter γ=q2 (ΔD)/(Θ⊥), where ΔD is the anisotropy in the translational diffusion coefficient. The dynamical terms are weighted by structure factors that depend on scattering geometry, the particle geometry, and the coupling parameter. These structure factors are given for arbitrary geometries and polarization of the radiation. In general, the weights for two to six exponentials will be significant depending on the scattering geometry and particle size. The domain of applicability of the theory is also discussed.
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61.25.H- Macromolecular and polymers solutions; polymer melts
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Accurate ground state potential of Cs2 up to the dissociation limit

W. Weickenmeier, U. Diemer, M. Wahl, M. Raab, W. Demtröder, and W. Müller

J. Chem. Phys. 82, 5354 (1985); http://dx.doi.org/10.1063/1.448618 (10 pages) | Cited 102 times

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Using the method of Doppler‐free double resonance polarization spectroscopy transitions from selectively pumped levels (v′, J′) of the D1Σ+u state down to levels (v″, J″) of the X 1Σ+g state with v″= 0–140 have been measured with high accuracy. A long range analysis, based on 21 outer turning points of the IPA potential with v″=110‐130 and on calculated exchange energies and second order van der Waals coefficients Cn with n=6, 8, 10, and 12 leads to a dissociation energy De =3649.5±0.8 cm−1 (0.452 49 eV). The influence of the third order C11 contribution and the hyperfine structure on the correct value of De are briefly discussed.
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33.15.Fm Bond strengths, dissociation energies
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
82.20.Kh Potential energy surfaces for chemical reactions

High‐pressure Brillouin scattering studies in the cubic phase of CsCN

K. Strössner and H. D. Hochheimer

J. Chem. Phys. 82, 5364 (1985); http://dx.doi.org/10.1063/1.448619 (4 pages)

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The pressure and temperature dependence of the elastic constants of CsCN have been studied in the orientationally disordered cubic phase by Brillouin spectroscopy. A softening of the symmetry adapted elastic constants (c11−c12)/2 and c44 is observed in the temperature range 193 to 300 K as the order–disorder phase transition is approached from above. This behavior is seen in the whole pressure range up to 0.6 GPa. The pressure dependence the volume corrected elastic constants has been determined and a comparison with the corresponding values of the other alkali cyanides has been made.
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62.20.D- Elasticity
78.35.+c Brillouin and Rayleigh scattering; other light scattering
64.60.Cn Order-disorder transformations
64.70.K- Solid-solid transitions

Infrared spectrum of the ν2 vibration‐inversion band of H3O+

Di‐Jia Liu, Nathan N. Haese, and Takeshi Oka

J. Chem. Phys. 82, 5368 (1985); http://dx.doi.org/10.1063/1.448620 (5 pages) | Cited 33 times

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High resolution infrared spectra of the 1−←0+ and 1+←0− ν2 vibration‐inversion bands of H3O+ have been observed in the ac glow discharge by using tunable diode lasers and the velocity modulation technique. The two band origins were found to be at 954.4003(25) and 525.8237(13) cm−1 for the 1−←0+ and 1+←0− bands, respectively. The band origins, rotational constants, and observed relative band strengths are compared with predictions based on ab initio theory. The discharge chemistry of H3O+ is discussed with reference to the observed line strength‐gas composition relation and known ion–molecule reactions.
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33.20.Ea Infrared spectra

Optical spectra, energy levels, and crystal‐field analysis of tripositive rare‐earth ions in Y2O3. IV. C3i sites

John B. Gruber, Richard P. Leavitt, Clyde A. Morrison, and N. C. Chang

J. Chem. Phys. 82, 5373 (1985); http://dx.doi.org/10.1063/1.448621 (6 pages) | Cited 44 times

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We report an analysis of new and previously existing optical absorption and fluorescence data, far‐infrared data, and electronic Raman scattering data for Eu3+, Dy3+, and Er3+ in the C3i sites of Y2O3 and R2O3, where R=a rare earth. Our previous analysis of C2‐site spectra yields an effective point‐charge model for the host lattice that allows initial estimates to be calculated for the C3i‐site crystal‐field parameters Bkm. Best‐fit values of B20, B40, and B43 are obtained for Eu, and best‐fit values of all Bkm allowed by symmetry are obtained for Dy and Er. The best‐fit Bkm are in relatively poor agreement with the model; in particular, B20 has the opposite sign from and B44 is much smaller than the model predictions. From the best‐fit Bkm we obtain phenomenological crystal‐field components Akm, from which we predict Bkm and C3i ‐site energy levels for the ground states of Tb3+, Ho3+, Tm3+, and Yb3+. While the effective point‐charge model is apparently too crude to make accurate, quantitative, a priori predictions, the model and the data allow one to predict confidently the behavior of ions doped into C3i sites for which no data exist.
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78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
71.70.Ch Crystal and ligand fields
78.55.Hx Other solid inorganic materials

The singlet states of styrene. Theoretical vibrational analysis of the ultraviolet spectrum

R. J. Hemley, D. G. Leopold, V. Vaida, and M. Karplus

J. Chem. Phys. 82, 5379 (1985); http://dx.doi.org/10.1063/1.448622 (19 pages) | Cited 20 times

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Vibrational analyses of the ground and lowest excited singlet states of styrene are performed using an extended PPP‐CI model. Franck–Condon factors calculated from the model are used to analyze the intensity distribution of the ultraviolet absorption bands of the jet‐cooled molecule from 34 000–46 000 cm−1. For the weak first absorption system (S1←S0) the small amount of vibrational excitation found experimentally is well described by the theoretical model. The relatively intense second absorption band shows more extended vibrational development. The model predicts that two electronic transitions S2←S0 and S3←S0 contribute to the absorption spectrum in this region and that a large number of vibrational excitations involving carbon–carbon stretching motions are active. For the S1←S0 and S2←S0 transitions a refinement of the theoretical model is performed to calculate the excited state equilibrium geometries from the measured spectra. Because of the large number of vibrations and the evidence for mixing among them in the excited states (Duschinsky effect), the full multimode treatment of the ground and excited state dynamics is required for an analysis of the spectrum.
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33.20.Lg Ultraviolet spectra
33.20.Tp Vibrational analysis
31.15.V- Electron correlation calculations for atoms, ions and molecules

Stochastic theory of resonance Raman line shapes of polyatomic molecules in condensed phases

Shaul Mukamel

J. Chem. Phys. 82, 5398 (1985); http://dx.doi.org/10.1063/1.448623 (11 pages) | Cited 65 times

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A stochastic model is proposed for the calculation of resonance Raman line shapes of polyatomic molecules in condensed phases. The model assumes that the random force exerted on the molecule by the solvent causes a stochastic modulation of the electronic energy gap. Explicit expressions are derived for the absorption, the excitation spectra, and the dispersed Raman line shapes. The model interpolates all the way from homogeneous broadening (fast modulation) to inhomogeneous broadening (slow modulation). The effects of line broadening cannot be incorporated into the Kramers–Heisenberg formula, commonly used to interpret these spectra, since dephasing‐induced terms appear which dominate the line shapes for large dephasing rates. A simple explanation is provided for the nature of the homogenous linewidth and for the broadening of the dispersed Raman line shapes, without having to assume an unrealistically short lifetime.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.70.Jg Line and band widths, shapes, and shifts
78.30.-j Infrared and Raman spectra

Variation of inverse Raman spectrum near resonance

S. Saikan, N. Hashimoto, T. Kushida, and K. Namba

J. Chem. Phys. 82, 5409 (1985); http://dx.doi.org/10.1063/1.448624 (6 pages) | Cited 35 times

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The inverse Raman band shape in the vicinity of single photon resonance is interpreted in terms of both a double quantum transition and a dynamical Stark effect. It is pointed out that what is measured in the inverse Raman spectroscopy is not identical with what is measured in the corresponding Raman gain spectroscopy. The absorption change due to the dynamical Stark effect is shown to explain well the band shape as well as the position of the inverse Raman spectrum.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.70.Jg Line and band widths, shapes, and shifts

Exact analysis of polycrystalline electron spin echo envelope modulation including mutual nuclear arrangements and quadrupole interactions and its application to methyl radicals in irradiated crystals of lithium acetate dihydrate

Machio Iwasaki and Kazumi Toriyama

J. Chem. Phys. 82, 5415 (1985); http://dx.doi.org/10.1063/1.448574 (9 pages) | Cited 11 times

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The method of exact analysis including mutual nuclear arrangements and quadrupole interactions is developed for electron spin echo envelope modulation (ESEM) from polycrystalline samples using the formulation in an arbitrary laboratory coordinate system, which makes it possible to perform an exact angular integration. In order to assess polycrystalline ESEM by comparing with electron nuclear double resonance (ENDOR) data, the method is applied to analyze deuterium hyperfine modulation on the two‐pulse electron spin echo (ESE) envelope decay observed for methyl radicals radiolytically produced in CD3COOLi ⋅ 2H2O and CH3COOLi ⋅ 2D2O. The results are totally consistent with our previous study by single crystal 1H ENDOR. Through this application, importance of the nuclear quadrupole term is also shown based on the exact method. The rigid deuterons in the water of crystallization show a marked quadrupole effect as compared with those in the freely rotating CD3 group. The contributions from the distant nuclei to the modulation pattern are also studied by the exact method using the crystallographic data. We have further clarified that the origin of the disagreement of a previous Li ESEM with our ENDOR is mainly in the use of a unit spin density on the spin probe despite its reduction by delocalization to the environment.
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82.50.-m Photochemistry
76.30.Rn Free radicals

Absolute total cross section for the scattering of low energy electrons by methanea)

Robert K. Jones

J. Chem. Phys. 82, 5424 (1985); http://dx.doi.org/10.1063/1.448575 (4 pages) | Cited 38 times

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The absolute total electron scattering cross section for methane (inelastic+elastic, integrated over all angles) was measured with a time‐of‐flight electron transmission spectrometer for incident energies from 1.3 to 50 eV. The major discrepancies that exist between recent absolute measurements of the total cross section are discussed with careful consideration of probable error limits. Comparisons are also made with recent calculations of the elastic cross section.
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34.80.Gs Molecular excitation and ionization
34.80.Bm Elastic scattering

Local modes and complex formation in H+OH collisions: Collinear reactions

Robert E. Howard and Donald L. Thompson

J. Chem. Phys. 82, 5428 (1985); http://dx.doi.org/10.1063/1.448576 (9 pages) | Cited 6 times

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We compute quasiclassical trajectories on the Schinke–Lester potential energy surface to study complex formation in collinear H+OH collisions at relative translational energies between 0.5 and 1.0 eV. At all energies except those just above the entrance channel barrier, the great majority of collisions are direct. Vibrational phase relationships and energy resonances determine the probability of forming a complex and its lifetime. At 0.5 eV we found two trajectories that followed regular, periodic paths for 10–12 vibrations. At higher energies long‐lived complexes are characterized by chaotic motion, a pattern of beats between local modes, and a tendency to share energy.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Fd Collision theories; trajectory models

The coupling between intramolecular and intermolecular motion in large van der Waals complexes

Martin L. Sage and Joshua Jortner

J. Chem. Phys. 82, 5437 (1985); http://dx.doi.org/10.1063/1.448577 (5 pages) | Cited 11 times

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In this paper we present a theoretical study of the coupling between intermolecular and intramolecular vibrational motion in large van der Waals complexes, which rest on the expansion of the total vibrational wave function in terms of the ‘‘free’’ molecule wave function, resulting in a set of coupled differential equations for the expansion coefficients. The application of Van Vleck perturbation theory results in explicit first‐order and second‐order kinetic energy and potential energy corrections. These corrections lead to a shift of the intramolecular vibrational frequencies and to intermolecular vibrational energies which depend on the vibrational quantum numbers for the intramolecular modes. Consideration of the intermode coupling in a model system consisting of one harmonic, intramolecular mode, and one intermolecular mode, predicts a linear dependence of the intermolecular vibrational energy on the vibrational quantum number for the intramolecular motion. This prediction is in accord with the recent experimental results for the S0→S1 transition of the trans‐stilbene ⋅ Ar complex.
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33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Vibrational energy transfer between CO and CH4, CD4, and CF4 in liquid Ar

Hamzeh Abdel‐Halim and George E. Ewing

J. Chem. Phys. 82, 5442 (1985); http://dx.doi.org/10.1063/1.448578 (10 pages) | Cited 15 times

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Vibrational relaxation of CO (υ=1) by CH4, CD4, and CF4 in liquid Ar at 87 K has been studied. The IR fluorescence decay from CO (υ=1) excited by a blackbody source was used to monitor the rate of vibrational energy transfer. Order of magnitude calculations for the variety of V–V and V‐T processes possible in these systems were used to select reasonable relaxation channels. These feasibility calculations together with decay measurements on several concentrations of CO and its collision partners enabled liquid state relaxation rate constants to be assigned. For the CO–CD4 and CO–CF4 systems, near‐resonance energy transfer and conditions of concentration enabled us to measure the V‐T rate constants for the first time for the relaxation of CD4 and CF4 by liquid Ar. These V–V and V‐T rate constants were compared with the gas phase values obtained at the same temperature. We find that the liquid phase and gas phase rate constants are essentially the same. These results are found to be in reasonable accord with the predictions of simple models of vibrational relaxation in the liquid state.
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34.50.Ez Rotational and vibrational energy transfer

Multiphoton metastable ion spectra and ion dissociation kinetics: Analysis of the decay channels of the aniline cation with a reflectron time‐of‐flight instrument

H. Kühlewind, H. J. Neusser, and E. W. Schlag

J. Chem. Phys. 82, 5452 (1985); http://dx.doi.org/10.1063/1.448579 (5 pages) | Cited 16 times

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Multiphoton mass spectrometry when carried out in conjunction with a reflecting field time‐of‐flight mass spectrometer is shown to yield rich new metastable ion spectra of polyatomic molecules, here aniline. The reflecting field acting also as an energy analyzer is shown to be particularly suitable for sensitive metastable ion detection without interference from stable fragment ions. With this technique several new metastable ion decay channels of the aniline cation have been observed. On the basis of the measured metastable ion spectrum a reasonable fragmentation pathway for the aniline cation C6H7N+ after multiphoton excitation is presented. The prominent intensity of the metastable ion peak C5H+6 points to a narrow energy distribution within the aniline cation typical for a ladder switching multiphoton excitation mechanism.
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33.80.Wz Other multiphoton processes
33.15.Ta Mass spectra

Concentration‐dependent fluorescence quenching and electron scavenging in liquids

R. I. Cukier

J. Chem. Phys. 82, 5457 (1985); http://dx.doi.org/10.1063/1.448580 (13 pages) | Cited 21 times

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We present a theory for the dependence of the fluorescence quenching lifetime τ on quencher concentration and the dependence of the electron‐scavenger rate constant kf on scavenger concentration. At low quencher (scavenger) concentration these quantities are obtained by solution of the Smoluchowski–Debye diffusion equation. For nondilute quenchers we find positive deviations from the linear Stern–Volmer equation for 1/τ and for nondilute scavengers we find positive deviations from linear behavior in kf. With reactants that interact by a long range potential, such as charged fluorophores and quenchers, and electrons with charged scavengers, a length math∼100–300 Å vs the collisional encounter length a ∼1–10 Å is the significant length. Corrections to dilute behavior are found to depend on the effective volume fraction of quenchers (or scavengers) ϕ=4π3math3c/3 which can be much larger than the material volume fraction ϕ=4π3a3c/3 [c is the quencher (or scavenger) number density]. We consider both the initial value and steady state situations and find that, for our exact results, no transient behavior of the rate coefficient enters the initial value expression.
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78.55.Bq Liquids

Reactions of iron clusters with hydrogen. II. Composition of the fully hydrogenated products

E. K. Parks, K. Liu, S. C. Richtsmeier, L. G. Pobo, and S. J. Riley

J. Chem. Phys. 82, 5470 (1985); http://dx.doi.org/10.1063/1.448581 (5 pages) | Cited 46 times

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Reactions of iron clusters with an excess of hydrogen are found to yield fully hydrogenated products FenHm whose compositions remain fixed over a wide range of hydrogen pressures. For n=6 to 131, the observed m values are always even, have narrow ranges, and for many clusters are unique. Up to n=30, nearly stoichiometric 1:1 ratios of m to n are found. Above 30, cluster hydride compositions are consistent with a monolayer of chemisorbed hydrogen on the cluster surfaces. At sufficiently high hydrogen pressures additional hydrogens bind to the clusters, most likely as a second, physisorbed layer. The experimental results are discussed in terms of cluster structure and the relation to bulk iron behavior.
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36.40.-c Atomic and molecular clusters
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

‘‘Direct’’ calculation of quantum mechanical rate constants via path integral methods: Application to the reaction path Hamiltonian, with numerical test for the H+H2 reaction in 3D

Koichi Yamashita and William H. Miller

J. Chem. Phys. 82, 5475 (1985); http://dx.doi.org/10.1063/1.448582 (10 pages) | Cited 94 times

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The method recently proposed by Miller, Schwartz, and Tromp for determining Boltzmann rate constants ‘‘directly’’—by the path integral evaluation of a reactive flux correlation function—is developed within the framework of the reaction path Hamiltonian model for a general polyatomic reaction. The expression for the correlation function, the time integral of which is the rate constant, is reduced to a single path integral over only one degree of freedom (the reaction coordinate). Effects of tunneling, ‘‘frictional’’ effects on the reaction coordinate due to coupling to other degrees of freedom, and the effects of recrossing the transition state dividing surface are all correctly accounted for in the approach. Numerical tests of the formulas for the 3D version of the H+H2 reaction (on the Porter–Karplus potential surface) gives excellent agreement with the (known) accurate results for this system.
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34.50.-s Scattering of atoms and molecules
82.20.Pm Rate constants, reaction cross sections, and activation energies

Kinetics of the reactions of NCO radicals with H2 and NO using laser photolysis–laser induced fluorescence

R. A. Perry

J. Chem. Phys. 82, 5485 (1985); http://dx.doi.org/10.1063/1.448583 (4 pages) | Cited 49 times

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Absolute rate constants for the reaction of NCO radicals with hydrogen (k6; T=592–913K) and nitric oxide (k7;T=294–538K) were measured using excimer laser photolysis‐laser induced fluorescence at 416.8 nm. The following Arrhenius expressions summarize the data: k6=1.43×10−11e(−9000±1500)/RT k7=1.69×10−11e(390±320)/RT cm3 molecule−1 s−1. The experimental technique and results are discussed, and the importance of these reactions to combustion chemistry is addressed.
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82.20.Pm Rate constants, reaction cross sections, and activation energies
82.33.Vx Reactions in flames, combustion, and explosions

A state‐to‐state study of the symmetric charge transfer reaction Ar+(2P3/2,1/2)+Ar(1S0)

C.‐L. Liao, C.‐X. Liao, and C. Y. Ng

J. Chem. Phys. 82, 5489 (1985); http://dx.doi.org/10.1063/1.448584 (10 pages) | Cited 21 times

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The relative state‐to‐state total charge transfer cross sections, σ3/2→3/2, σ3/2→1/2, σ1/2→1/2, and σ1/2→3/2, for the reactions Ar+(2P3/2)+Ar(1S0)  → Ar(1S0)+Ar+(2P3/2)  → Ar(1S0)+Ar+(2P1/2), Ar+(2P1/2)+Ar(1S0)  → Ar(1S0)+Ar+(2P1/2)  → Ar(1S0)+Ar+(2P3/2), respectively, at the laboratory collision energy range of 1–4000 eV, have been determined using the newly constructed crossed ion–neutral beam
photoionization apparatus. This apparatus is equipped with a high resolution photoionization ion source for reactant state selections and a charge transfer detector for product state identifications. The measured profile of the kinetic energy dependence for the probability for 2P3/2→2P1/2 fine‐structure transitions in Ar+(2P3/2)+Ar(1S0) charge transfer collisions [σ3/2→1/2/(σ3/2→3/2+σ3/2→1/2)] is in general agreement with the theoretical prediction of Johnson. However, the theoretical probabilities are approximately 40% greater than those observed in this experiment. The total charge transfer cross section for Ar+(2P3/2)+Ar(1S0)[σ3/2→3/2+σ3/2→1/2] were found to be slightly higher than that for Ar+(2P1/2)+Ar(1S0)[σ1/2→1/2+σ1/2→3/2]. Furthermore, the experimental values for (σ1/2→1/2+σ1/2→3/2)/(σ3/2→3/2+σ3/2→1/2) indicate that the difference in the total charge transfer cross sections for Ar+(2P1/2)+Ar(1S0) and Ar+(2P3/2)+Ar(1S0) diminishes at both low and high collision energies, in accordance with the theoretical expectations. Taking into account the experimental uncertainties, the experimental results are also consistent with detailed balance which requires the value for σ1/2→3/2 to be twice that for σ3/2→1/2 at collisional energies substantially higher than the spin‐orbit splitting of Ar+.
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34.70.+e Charge transfer
34.50.-s Scattering of atoms and molecules

Variational transition state theory calculations of the reaction rates of F with H2, D2, and HD and the intermolecular and intramolecular kinetic isotope effects

Rozeanne Steckler, Donald G. Truhlar, and Bruce C. Garrett

J. Chem. Phys. 82, 5499 (1985); http://dx.doi.org/10.1063/1.448585 (7 pages) | Cited 88 times

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We use variational transition state theory to calculate rate constants and kinetic isotope effects for the reactions F+H2→HF+H (with rate constant k1), F+D2→DF+D(k2), and two other isotopic analogs as functions of temperature. The calculations are performed using a recently proposed partly empirical, partly ab initio potential energy surface, called surface No. 5, and also using a new surface, called surface No. 5A, introduced here to test the effect of a higher classical saddle point on the reaction rates, kinetic isotope effects, and reaction thresholds. The various theoretical results are compared to the available experiments to test the validity of these potential energy surfaces. For those rate constants and kinetic isotope effects for which there is more than one experimental value at a given temperature, the theoretical results for reactions on surface No. 5 agree with experiment about as well as the individual experiments agree with each other. At T>373 K where there is only one experimental measurement for k1 and k2, the theoretical rate constants for surface No. 5 are up to 44% lower than experiment, and at T<190 K where there is only one experimental measurement of k1/k2, the theoretical rate constant ratio is as much as 43% low. These discrepancies could be due to experimental error or they could indicate that the theoretical activation energy is low, but by no more than 0.5 kcal/mol, which is considerably less than the 2.5 kcal/mol discrepancy from the most recently published large‐scale calculation. If, however, the potential energy surface were adjusted to raise the activation energy by even 0.5 kcal/mol above the value for surface No. 5, the threshold energies would no longer be in such good agreement with experiment, and several other aspects of the results presented here would be in much worse agreement with experiment. Taken as a whole then, we interpret the present calculations as providing further confirmation of the methods used to obtain surface No. 5. With this interpretation, the most important implication about the experiments is that Persky’s low‐temperature measurements of k1/k2, especially those for T≤200 K, are systematically high.
Show PACS
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Tr Kinetic isotope effects including muonium
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
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