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15 Dec 1987

Volume 87, Issue 12, pp. 6789-7349

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Theoretical K‐shell ionization spectra of N2 and CO by a fourth‐order Green’s function method

G. Angonoa, O. Walter, and J. Schirmer

J. Chem. Phys. 87, 6789 (1987); http://dx.doi.org/10.1063/1.453424 (13 pages) | Cited 60 times

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A recently developed complete fourth‐order Green’s function method referred to as ADC(4) was used to calculate ionization energies and relative intensities of 1s hole states in N2 and CO. Very accurate 1s electron binding energies and a good qualitative description of the shakeup spectra at low and medium energies have been obtained. For the N1s and C1s results comparison is made with previous large‐scale configuration interaction treatments. New results are presented for the O1s shakeup spectrum of CO. Here striking differences with respect to the C1s spectrum are found which are explained in terms of charge–transfer effects induced by electronic excitation. We also present results for shakeup states of symmetries other than 2Σ+ which are not observed in the usual photoemission experiment.
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33.60.+q Photoelectron spectra
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Picosecond spectroscopic measurement of a solvent dependent change of rotational diffusion rotor shape

G. J. Blanchard

J. Chem. Phys. 87, 6802 (1987); http://dx.doi.org/10.1063/1.453373 (7 pages) | Cited 27 times

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The rotational diffusion behavior of cresyl violet is observed to be solvent dependent, producing an induced orientational anisotropy function with single exponential decays in both ethylene glycol at 26 °C and 1‐dodecanol at 37 °C, but a two‐component decay in 1‐dodecanol at 26 °C. It is clear from this data that cresyl violet is experiencing significant changes in its local solvation environment. Without knowledge of the orientation of the transition moment within the molecule, however, the interpretation of these results is ambiguous. A simple calculation is presented which allows for the estimation of the intramolecular orientation of the transition moment, thereby removing ambiguity from the interpretation. The observed behavior is shown to be consistent with cresyl violet reorienting as an oblate rotor in ethylene glycol and 1‐dodecanol at 37 °C, and as a prolate rotor in 1‐dodecanol at 26 °C.
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78.47.-p Spectroscopy of solid state dynamics
31.70.Dk Environmental and solvent effects
33.50.Dq Fluorescence and phosphorescence spectra

The rotational hindrance potential of NH3 groups in Ni(NH3)6I2

Herma Blank and Gordon J. Kearley

J. Chem. Phys. 87, 6809 (1987); http://dx.doi.org/10.1063/1.453374 (7 pages) | Cited 5 times

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The INS librational spectra of Ni(NH3)6I2 and Ni(ND3)6I2 are shown to be consistent with the motions of a single‐type ammine rotor in a hindrance potential of the form cos(3ϕ). A barrier height of 18.6 meV is derived. The three peaks which arise in the spectrum of the tunnel‐split ground state are attributed to ammine:ammine interactions and do not simply reflect the local symmetry at the nickel atom. A qualitative study of the differing behavior of these three tunneling peaks on changes in temperature, partial deuteration, and pressure shows that the NH3:NH3 coupling is sensitive to the rotational states of neighboring groups and changes to the order parameter as the II–I phase transition is approached. Direct interaction of the NH3 groups with the anion seems to be very slight.
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78.30.Hv Other nonmetallic inorganics
64.70.K- Solid-solid transitions
61.50.-f Structure of bulk crystals

Depolarization ratios of the resonance Raman bands of soluble trans‐polyacetylene

S. Fuso, C. Cuniberti, P. Piaggio, G. Dellepiane, S. Luzzati, R. Tubino, and M. Z. Zgierski

J. Chem. Phys. 87, 6816 (1987); http://dx.doi.org/10.1063/1.453375 (3 pages) | Cited 7 times

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Depolarization ratios for the totally symmetric Raman lines in soluble polyacetylene have been measured for various exciting wavelengths in the resonance region. The origin of the unusually high values of the depolarization ratios and their variations with the exciting wavelength are discussed in terms of two overlapping electronic transitions in the visible region.
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36.20.Kd Electronic structure and spectra
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.20.Kf Visible spectra

FTIR spectra of the HF−2 and H2F−3 anions isolated in solid argon and neon

Rodney D. Hunt and Lester Andrews

J. Chem. Phys. 87, 6819 (1987); http://dx.doi.org/10.1063/1.453376 (5 pages) | Cited 15 times

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Argon diluted samples of HF were bombarded by low energy electrons (150–400 eV) from a thermionic electron source during condensation at 12 K. Several polyfluoride anions, which have extremely strong hydrogen bonds, were characterized using matrix infrared spectroscopy. Three principal ions were trapped in the argon matrix: HF−2 (1377 cm−1), H2F−3 (1815 cm−1), and ArnH+ (904 cm−1). Electron impact experiments performed with HF/DF mixtures gave counterpart absorptions: DF−2 (965 cm−1), HDF−3 (1707 cm−1), D2F−3 (1391 cm−1), and Arn D+ (644 cm−1). The 1377 cm−1 matrix band is assigned to ν3 of linear, centrosymmetric HF−2, based on agreement with solid state and matrix ion pair spectra, and ab initio calculations, and a proper H/D ratio (1.427) for a linear centrosymmetric species. However, this assignment challenges the recent 1848 cm−1 gas phase assignment to ν3 of HF−2 using laser spectroscopy; the 1848 cm−1 absorption exhibits an H/D ratio (1.323) that is too low for the ν3 vibration of centrosymmetric HF−2, and it should be reassigned to the ν1+ν3 combination band. The 1815 cm−1 matrix band is assigned to the out‐of‐phase H–F stretching fundamental of C2vH2F−3, which is in agreement with solid K+H2F−3 spectra.
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33.20.Ea Infrared spectra
33.20.Tp Vibrational analysis

Identification of resonant excitation and shakeoff contributions to the C KVV Auger line shapes of several gas phase hydrocarbons

F. L. Hutson and D. E. Ramaker

J. Chem. Phys. 87, 6824 (1987); http://dx.doi.org/10.1063/1.453377 (14 pages) | Cited 13 times

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We have consistently interpreted the C KVV Auger line shapes of five hydrocarbons (methane, ethane, cyclohexane, benzene, and ethylene) and compared the results with those previously reported for three different solids (polyethylene, diamond, and graphite). We show that an interpretation procedure normally used for solids, namely, a self‐fold of the one‐electron DOS and incorporation of hole–hole correlation effects utilizing the Cini expression, is also adequate for molecules, and thus direct comparison of the gas phase and solid phase results is possible. In contrast to the solids, the normal kvv line shape accounts for only about half of the total experimental intensity for the gas phase molecules. The remaining part of the experimental line shape can be attributed to three different satellite contributions; namely resonant excitation (ke–vve), initial‐state–shake (kv–vvv), and final‐state–shake (k–vvv) satellites. The normal kvv Auger line shapes are seen to reflect delocalized holes, however correlation effects are evident. In contrast, the three‐hole final state of the kv–vvv process reflects holes localized primarily on a single methyl group. The results indicate that long range polarization effects are not important in the extended solids; short range π electron screening is important in the alkenes and in graphite.
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33.60.+q Photoelectron spectra
33.80.Eh Autoionization, photoionization, and photodetachment

Diode laser spectroscopy of the ν3 and ν2 bands of FHF− in 1300 cm−1 region

Kentarou Kawaguchi and Eizi Hirota

J. Chem. Phys. 87, 6838 (1987); http://dx.doi.org/10.1063/1.453378 (4 pages) | Cited 58 times

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The ν3, ν2, and ν1+ν3−ν1 bands of a linear molecular anion FHF− have been detected by diode laser spectroscopy in 1300 cm−1 region. The previously reported 1848 cm−1 band [K. Kawaguchi and E. Hirota, J. Chem. Phys. 84, 2953 (1986)] was reassigned to the ν1+ν3 combination band. Analysis of the observed spectra gave the fundamental frequencies ν1=583.0539(13), ν2=1286.0284(22), and ν3=1331.1502(7) cm−1 with three standard deviations in parentheses. From the rotational constants obtained, the equilibrium F–F internuclear distance was calculated to be 2.277 71(7) Å.
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33.20.Ea Infrared spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Dj Interatomic distances and angles

Autodetachment spectroscopy and dynamics of CH2CN− and CD2CN−

K. R. Lykke, D. M. Neumark, T. Andersen, V. J. Trapa, and W. C. Lineberger

J. Chem. Phys. 87, 6842 (1987); http://dx.doi.org/10.1063/1.453379 (12 pages) | Cited 49 times

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The technique of autodetachment spectroscopy is utilized in a study of two electronic states of CH2CN− and CD2CN−. The ground electronic state is a normal valence state while the outermost electron in the excited state is bound by the dipole moment of the neutral radical. Autodetachment occurs from excited rotational levels of this dipole bound state, giving some 5000 sharp features near the photodetachment threshold. All of these features were assigned and spectroscopic constants for both states are reported. The binding energy of the electron in this latter state is determined to be ≲66 cm−1 and analysis of the autodetachment spectrum shows the electron affinities of CH2CN and CD2CN to be ∼12 500 and ∼12 430 cm−1, respectively. The dynamics of the autodetachment process is studied and various mechanisms for detachment are described.
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33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.80.Eh Autoionization, photoionization, and photodetachment

The carbon chemical shift tensor in polyoxymethylene

W. E. J. R. Maas, A. P. M. Kentgens, and W. S. Veeman

J. Chem. Phys. 87, 6854 (1987); http://dx.doi.org/10.1063/1.453380 (5 pages) | Cited 5 times

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The complete chemical shift tensor of the carbons in crystalline polyoxymethylene is determined via the two‐dimensional dipolar correlated 13C chemical shift NMR technique. The orientation of the tensor is determined by the local tetrahedral symmetry of the C2H2O2 unit and not by the overall symmetry of the helical chains. In an accompanying paper this shift tensor is used to study ultraslow motions in polyoxymethylene.
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76.60.Cq Chemical and Knight shifts
61.50.-f Structure of bulk crystals

Ultraslow molecular motions in crystalline polyoxymethylene. A complete elucidation using two‐dimensional solid state NMR

A. P. M. Kentgens, E. de Boer, and W. S. Veeman

J. Chem. Phys. 87, 6859 (1987); http://dx.doi.org/10.1063/1.453730 (8 pages) | Cited 38 times

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The slow magic angle spinning 2D exchange NMR experiment applied to semicrystalline polyoxymethylene shows the existence of ultraslow molecular rotations in crystalline regions of the material. By simulating the two‐dimensional spinning sideband spectra, which are characteristic for the molecular motion involved, it is found that a rotation of the polyoxymethylene helical chains over 200° is responsible for the observed spectra. The activation energy is 20 kcal/mol in good agreement with values obtained for the α relaxation in dynamic mechanical and dielectric studies.
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76.60.Cq Chemical and Knight shifts
61.50.-f Structure of bulk crystals

Theory of line shapes for zero field NMR in the presence of molecular motion

P. Meier, G. Kothe, P. Jonsen, M. Trecoske, and A. Pines

J. Chem. Phys. 87, 6867 (1987); http://dx.doi.org/10.1063/1.453381 (10 pages) | Cited 7 times

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Dynamic molecular processes modulate dipolar and quadrupolar interactions in nuclear spin systems. Zero field NMR measures evolution arising purely from these interactions, and thus can be used to characterize molecular dynamics in disordered samples. A theory is presented which numerically simulates the effect of molecular reorientation in zero field NMR for a spin‐1 nucleus or pairs of dipolar coupled spin‐1/2 nuclei. Representative zero field NMR simulations are compared to their high field NMR analogs to demonstrate features which make zero field NMR a potentially useful tool for the study of molecular dynamics.
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76.60.Es Relaxation effects
61.50.-f Structure of bulk crystals

Spectroscopic studies of phthalocyanines and their clusters with small molecules

J. A. Menapace and E. R. Bernstein

J. Chem. Phys. 87, 6877 (1987); http://dx.doi.org/10.1063/1.453382 (13 pages) | Cited 8 times

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van der Waals clusters of free base phthalocyanine (H2Pc) and magnesium phthalocyanine (MgPc) with small hydrocarbons [CnH2n+2(n=1,2,3)], hydrogen bonding solvents (H2O, MeOH, EtOH), and CO2 are studied in the gas phase using supersonic molecular jet spectroscopy. Fluorescence excitation spectra of the cluster systems are characterized in the 000 regions of the cluster S1←S0 transitions. Forbidden low frequency cluster chromophore out‐of‐plane vibronic transitions are induced by clustering in the majority of the cluster systems studied. This low frequency motion is characterized using an out‐of‐plane normal coordinate analysis on the H2Pc moiety. Calculations of the binding energy and ground state geometry for the clusters are carried out employing Lennard‐Jones (6‐12‐1) and hydrogen bonding (10‐12‐1) potentials. Comparison between the calculations and experiments allow for the identification of specific configurations responsible for the cluster vibronic transitions observed. The cluster vibronic spectra and theoretical calculations suggest that stable H2Pc and MgPc solvation sites are located over the phthalocyano core and not over peripheral ring centers. The H2Pc/hydrocarbon cluster experimental and calculational results parallel those obtained for benzene and N‐heterocycle/hydrocarbon clusters studied previously. The H2Pc and MgPc/alcohol cluster spectra and calculated geometries suggest that the solvent OH group is intimately involved in the intermolecular interactions and contributes significantly to the observed spectroscopic shifts.
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36.40.-c Atomic and molecular clusters
33.50.Dq Fluorescence and phosphorescence spectra
33.20.Kf Visible spectra
33.15.Fm Bond strengths, dissociation energies

Temperature dependence of the Raman spectrum of ammonia solid I

C. L. Nye and F. D. Medina

J. Chem. Phys. 87, 6890 (1987); http://dx.doi.org/10.1063/1.453383 (5 pages) | Cited 5 times

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The Raman spectrum of ammonia solid I in the lattice and intramolecular regions has been studied at temperatures between 93.6 and 213.5 K. The three most intense lines in the lattice region, one librational and two translational modes, have frequencies and linewidths whose temperature dependence can be explained by anharmonic interactions. In the intramolecular region, all bending modes studied have unusually large decreases in frequency with temperature. However, there is no indication in support of the recently reported critical‐like behavior of the compressibility near the melting line.
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78.30.Hv Other nonmetallic inorganics

NMR line shape analysis for two‐site exchange in rotating solids

Asher Schmidt and Shimon Vega

J. Chem. Phys. 87, 6895 (1987); http://dx.doi.org/10.1063/1.453384 (13 pages) | Cited 49 times

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The theory for the analysis of magic angle spinning (MASS) NMR spectral line shapes of spin systems in the solid state undergoing two‐site chemical exchange is presented. The theoretical approach which is based on the Floquet formalism is valid for the whole range of exchange rates—from slow to fast, as well as for any sample spinning rate. The effect of the exchange on the widths and positions of the center and sidebands is discussed. For fast and slow exchange rates expressions for these parameters are derived using perturbation theory. Spectral line fitting between calculated and experimental spectra can provide information on the rate constants and the activation energies for the exchange processes together with relative structural parameters of the sites involved, thus extending the line shape analysis methods to include MASS.
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76.60.Es Relaxation effects

Spectroscopic identification of rovibronic levels lying above the potential barrier of the EF 1Σ+g double‐minimum state of the H2 molecule

P. Senn and K. Dressler

J. Chem. Phys. 87, 6908 (1987); http://dx.doi.org/10.1063/1.453385 (7 pages) | Cited 16 times

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Spectroscopic data on the higher vibrational levels of the EF 1Σ+g state of the H2 molecule are scarce. Here we report new identifications of energy levels with J=0–5 which fall into the range between vEF=9 and 20, i.e., the energy region above the potential barrier of the double‐minimum EF potential curve. Some previously published line assignments and term values are hereby corrected. The results are mostly based on new assignments of EF 1Σ+g–B 1Σ+u bands in Dieke’s hydrogen molecule wavelength tables published in 1972. The newly identified states are of interest in multiphoton spectroscopy and in comparisons of experimental properties with results of ab initio calculations.
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34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
82.20.Kh Potential energy surfaces for chemical reactions
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.20.Ea Infrared spectra

Rotational energy transfer within the B 3Πg v=3 manifold of molecular nitrogen

Ashraf Ali and Paul J. Dagdigian

J. Chem. Phys. 87, 6915 (1987); http://dx.doi.org/10.1063/1.453386 (12 pages) | Cited 28 times

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An optical–optical double resonance experiment has been carried out to study rotationally inelastic collisions of N2 B 3Πg v=3 by argon with initial and final state resolution. Nitrogen molecules in the metastable A state are generated by collisional excitation transfer from metastable argon atoms in a flow system. Specific B state rotational levels are prepared by pulsed pump laser excitation of isolated rotational lines in the B 3Πg–A 3Σ+u (3,0) band near 688 nm. After a short delay, a probe laser interrogates the rotational populations in the B state by fluorescence excitation in the C 3Πu–B 3Πg (0,3) band near 406 nm. Collisional transfer from incident levels in all three spin–orbit manifolds of the B state was investigated. For molecules initially in the F1 (Ω=0) manifold, a preference for conservation of fine‐structure label with even ΔJ changes was observed. This propensity is very pronounced for the J=0 level but is considerably relaxed for the higher levels investigated. By contrast, inelastic collisions involving the F2 (Ω=1) and F3 (Ω=2) manifolds do not exhibit a significant propensity to conserve fine‐structure label. A slight residual preference for even ΔJ changes is observed in collisional transitions within the F2 manifold. These experimental results are compared to the propensity rules expected for homonuclear 3Π rotationally inelastic collisions, both in the case (a) and (b) limits. The reduction of the predicted propensities by the transition to intermediate case coupling and ‘‘orbital‐correlated’’ scattering is discussed. The latter term refers to the difference potential for the N2–Ar interaction when the N2 unfilled π orbital is in or perpendicular to the triatomic plane. An unsuccessful attempt to detect collisional interelectronic transfer from the B state to the W 3Δu state by G–W laser fluorescence excitation is also reported.
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34.50.Ez Rotational and vibrational energy transfer
33.40.+f Multiple resonances (including double and higher-order resonance processes, such as double nuclear magnetic resonance, electron double resonance, and microwave optical double resonance)

Circular dichroism in photoelectron angular distributions from two‐color (1+1) REMPI of NO

J. R. Appling, M. G. White, R. L. Dubs, S. N. Dixit, and V. McKoy

J. Chem. Phys. 87, 6927 (1987); http://dx.doi.org/10.1063/1.453387 (7 pages) | Cited 30 times

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A detailed experimental and theoretical study of dichroic effects in photoelectron angular distributions is reported for (1+1), two‐color REMPI of NO via the A 2Σ+, v=0 state. Optically aligned A state rotational levels are probed through ionization by circularly polarized light. Resultant photoelectron angular distributions exhibit significant left–right asymmetry, the phase and magnitude of which are shown to be related to the curvature of the excited state MJ distribution. Theoretical calculations involving a full ab initio treatment of the ionization dynamics result in circularly dichroic angular distribution (CDAD) parameters in good agreement with those derived experimentally. Additional effects including hyperfine depolarization and coherence are also discussed in relation to the observed CDAD data.
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33.60.+q Photoelectron spectra
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Laboratory measurements of gas‐phase reactions of polyatomic carbon ions C+n(n=1–6) and CnH+(n=2–5) with carbon monoxide

Diethard K. Bohme, Stanisław Włodek, Leslie Williams, Leonard Forte, and Arnold Fox

J. Chem. Phys. 87, 6934 (1987); http://dx.doi.org/10.1063/1.453388 (5 pages) | Cited 8 times

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The selected‐ion flow tube (SIFT) technique has been employed in the study of reactions of carbon monoxide with the polyatomic carbon cations C+n(n=1−6) and CnH+(n=2–5) at 296±2 K in helium buffer gas at ∼0.34 Torr and 1.1×1016 atoms cm−3. The polyatomic carbon cations were generated by electron impact on a suitable parent molecule. Carbon monoxide was observed to add rapidly to C+n(n=2–6) twice in succession to form polyatomic carbon monoxide and dioxide cations, and once to CnH+ to form polyatomic carbon monoxide cations. Further additions did not occur with measurable specific rates. This remarkable behavior is attributed to double bond formation at the terminal carbon atoms of the polyatomic carbon cations. The specific rate for the addition of CO was observed to vary with the size of the polyatomic carbon cation, increasing to a maximum for reactions with five atoms in the reacting ion. This trend is attributed to an increase in the lifetime of the intermediate addition complex.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
98.38.Bn Atomic, molecular, chemical, and grain processes
98.38.Er Interstellar masers
98.58.Bz Atomic, molecular, chemical, and grain processes
98.58.Ec Interstellar masers

Random spin models and chemical kinetics

Lloyd Demetrius

J. Chem. Phys. 87, 6939 (1987); http://dx.doi.org/10.1063/1.453389 (8 pages) | Cited 4 times

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Lyapunov exponents constitute a class of parameters which describe the asymptotic behavior of a large class of dynamical processes in chemistry and physics. This paper gives a variational characterization of the largest Lyapunov exponent for a class of models of chemical kinetics described by products of random nonnegative matrices. We show that for this class of models the largest Lyapunov exponent satisfies an extremal principle formally identical to the minimization of the quenched free energy in random spin models. This extremal principle, which yields a computable expression for the Lyapunov exponent, implies that fluctuations in the Lyapunov exponent, due to a certain class of perturbations in the matrix elements, are determined by a macroscopic parameter which is the analog of the mean energy in random spin systems. These results characterize a class of random models in chemical kinetics that are thermodynamically stable in the sense that they possess an asymptotic limit in which analogs of the laws of equilibrium thermodynamics hold.
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82.40.Bj Oscillations, chaos, and bifurcations

Diffusional theory of termolecular recombination and association of atomic species in a gas

M. R. Flannery

J. Chem. Phys. 87, 6947 (1987); http://dx.doi.org/10.1063/1.453390 (10 pages) | Cited 3 times

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A diffusional treatment of termolecular association of atomic species A and B in a low density gas is presented and applied to positive ion–negative ion recombination over the full range of masses of reactants for various classes of ion–neutral interactions. In contrast to rates given by the diffusional current, excellent results are obtained for general mass species provided a more basic expression for the association rate is introduced.
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34.10.+x General theories and models of atomic and molecular collisions and interactions (including statistical theories, transition state, stochastic and trajectory models, etc.)
34.50.Lf Chemical reactions
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Intramolecular energy transfer and cis–trans isomerization in HONO

Yuhua Guan, Gillian C. Lynch, and Donald L. Thompson

J. Chem. Phys. 87, 6957 (1987); http://dx.doi.org/10.1063/1.453391 (10 pages) | Cited 43 times

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Classical trajectories have been used to investigate cis–trans isomerization and intramolecular energy transfer in nitrous acid. The influence of various initial normal mode excitations has been investigated. Power spectra have been used to examine the intramolecular dynamics. The rate of cis–trans conversion is strongly dependent on the site of initial excitation. The rates for cis–trans isomerization is significantly higher than those for trans–cis. The results show that the OH stretching mode is only weakly coupled to the other modes. Energy transfer out of excited states of the OH mode is slow and preferential partitioning of energy into that mode leads to a reduced rate of isomerization, while excitation of other modes gives rate enhancement. The HON bend interacts with the torsion more strongly than do the other modes.
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82.30.Qt Isomerization and rearrangement
82.20.Rp State to state energy transfer
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
82.20.Pm Rate constants, reaction cross sections, and activation energies

Analytic representation of secondary‐electron spectra

Mitio Inokuti, Michael A. Dillon, John H. Miller, and Kazem Omidvar

J. Chem. Phys. 87, 6967 (1987); http://dx.doi.org/10.1063/1.453392 (6 pages) | Cited 9 times

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The secondary‐electron spectrum, or the energy distribution of the ejected electrons resulting from charged‐particle impact, is a crucial input to the microscopic modeling of radiation actions. The present article shows a general method for systematizing a bulk of data on the secondary‐electron spectrum into a small number of indices. Our method is based on firm theoretical grounds, i.e., on thorough examination of the mathematical physics that governs the secondary‐electron spectrum. We present several examples of the analysis of recent experimental data for proton impact.
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34.50.Gb Electronic excitation and ionization of molecules
82.50.-m Photochemistry

A time‐dependent wave packet analysis of the dynamics of transition state spectroscopy in one dimension

Jun Jiang and John S. Hutchinson

J. Chem. Phys. 87, 6973 (1987); http://dx.doi.org/10.1063/1.453393 (10 pages) | Cited 9 times

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The transition state absorption spectrum and the dynamics of the excited state are calculated for a one‐dimensional reactive system with the basic features of the reaction K+NaCl→KCl+Na. We have propagated a Gaussian minimum wave packet on two Eckart potential curves coupled by an intense laser field, where the bound states supported by the upper potential well are exactly solved. By applying time‐dependent perturbation theory, the continuum–bound transitions are calculated, and a bound excited state is obtained when the wave packet reaches the interactive region. The transition probabilities show a strong dependence on laser frequency which is well explained by Franck–Condon calculations. By contrast, a Landau–Zener model is quantitatively incorrect. By studying the excited wave packet dynamics and the transition probability spectra at different times, we conclude that the excitation to the upper potential surface is not localized to crossings of the dressed potential curves.
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82.53.-k Femtochemistry
34.50.Rk Laser-modified scattering and reactions
33.20.Kf Visible spectra

State specific electronic quenching rates for 14N+2 and 15N+2

D. H. Katayama, A. V. Dentamaro, and J. A. Welsh

J. Chem. Phys. 87, 6983 (1987); http://dx.doi.org/10.1063/1.453394 (5 pages) | Cited 17 times

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We have conducted laser double resonance experiments to measure the branching ratio for the rates of electronic transfer from the A 2Πui (v=4) state to the X 2∑+g (v=8 and 7) levels for 14N+2 and 15N+2. Because of the propensity for ΔJ∼0 in these electronic transfer processes, the energy gaps can be determined and although they are similar in magnitude for the two isotopes, the branching ratios are significantly different. For 14N+2 the rate from A(v=4) to X(v=8) is about twice as great as to the X(v=7) level whereas for 15N+2, this ratio is approximately 6. This difference is reflected in the dramatic change in shape from 14N+2 to 15N+2 of the radiative decay curve from the A 2Πui (v=4) level. The 14N+2 curve appears to be single exponential in contrast to the double exponential for 15N+2. We use these branching ratios in an electronic relaxation model that describes the observed decay curves well, to deduce the state specific electronic quenching rates for these two isotopes.
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33.50.Hv Radiationless transitions, quenching
33.40.+f Multiple resonances (including double and higher-order resonance processes, such as double nuclear magnetic resonance, electron double resonance, and microwave optical double resonance)

HTP kinetics studies of the reactions of O(2 3PJ) atoms with H2 and D2 over wide temperature ranges

Paul Marshall and Arthur Fontijn

J. Chem. Phys. 87, 6988 (1987); http://dx.doi.org/10.1063/1.453395 (7 pages) | Cited 13 times

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The O+H2(1) and O+D2(2) reactions have been investigated, using the high‐temperature photochemistry (HTP) technique, over the 350 to 1420 and 390 to 1420 K temperature ranges, respectively. O(2 3PJ) atoms were generated from flash photolysis of CO2 and monitored by time‐resolved atomic resonance fluorescence with pulse counting. Above 430 K the rate coefficients are given by k1(T)=7.3×10−21 (T/K)2.93 exp(−2980 K/T) cm3 molecule−1 s−1 and k2(T)=3.1×10−16 (T/K)1.65 exp (−5260 K/T) cm3 molecule−1 s−1. Combination of our data with those from other experiments which isolated the reactions from secondary processes yields our recommendations k1(T)=1.5×10−12 exp (−3540 K/T)+3.7×10−10 exp (−7450 K/T) cm3 molecule−1 s−1 (300 K≤T≤2500 K) and k2(T)=1.4×10−12 exp(−4260 K/T) +2.9×10−10 exp (−7780 K/T) cm3 molecule−1 s−1 (390 K≤T≤1420 K). Accuracy assessments are discussed in the text. k1(T), k2(T), and the kinetic isotope effect compare well with calculations based on recent ICVT/LAG and CEQB ab initio methods, which suggest that the first terms of the double exponential expressions approximate the tunneling contributions.
Show PACS
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.50.Hp Processes caused by visible and UV light
82.20.Tr Kinetic isotope effects including muonium
82.33.Vx Reactions in flames, combustion, and explosions
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