bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of electronic energy quenching: The reaction of H2(B)+He
Authors: Pibel Charles D. , Carleton Karen L. , Moore C. Bradley
Published: July 2002

The room temperature rate constants for quenching of the fluorescence of H2, HD, and D2 B1Σ+u by 4He have been measured as a function of the initially excited rotational and vibrational levels of the hydrogen molecule. The effective quenching cross sections increase with increasing vibrational energy from about 1 Å2 up to a maximum of about 6 Å2. The effective cross sections for D2 (B, v′ = 0) were independent of the rotational level excited for 0 < J′ ≤ 7, and the cross sections for (v′ = 0, J′ = 0) were about 80% of the values for (v′ = 0, J′ ≳ 0) for all three isotopes studied. Quenching occurs via formation of an electronically excited (H2He)* collision complex followed by crossing to the repulsive H2(X)–He potential energy surface. The vibrational state dependence of the quenching cross sections fits a vibrationally adiabatic model for complex formation. From the vibrational state dependence of the quenching cross section, the barrier height for the quenching reaction is found to be 250±40 cm−1, and the difference in the H–H stretching frequencies between H2(B) and the H2–He complex at the barrier to reaction is 140±80 cm−1. Both values are substantially smaller than results from ab initio calculations. The rotational state dependence of the quenching cross sections suggests that quenching occurs with H2 rotating in a plane perpendicular to the relative velocity vector, in qualitative agreement with the rotational anisotropy of the H2(B)–He ab initio electronic potential energy surface.
Collision energy dependence of Penning ionization electron spectra in crossed supersonic beams: He*(2 1S)+N2
Authors: Dunlavy D. C. , Martin D. W. , Siska P. E.
Published: July 2002

Penning ionization electron spectra are reported at five collision energies E in the range 1.6–4.9 kcal/mol. A preliminary analysis of the E dependence of the intensities, shapes, and positions of the vibronic lines reveals details of the ionization dynamics, features of the highly anisotropic potential surface, and connections with N2 orbital structure.
Photoelectron spectroscopy and electronic structure of clusters of the group V elements. II. Tetramers: Strong Jahn–Teller coupling in the tetrahedral 2E ground states of P+4, As+4, and Sb+4
Authors: Wang Lai-Sheng , Niu B. , Lee Y. T. , Shirley D. A. , Ghelichkhani E. , Grant E. R.
Published: July 2002

High resolution HeI (584 Å) photoelectron spectra have been obtained for the tetrameric clusters of the group V elements: P4, As4, and Sb4. The spectra establish that the ground 2E states of tetrahedral P+4, As+4, and Sb+4 are unstable with respect to distortion in the ν2(e) vibrational coordinate. The E⊗e Jahn–Teller problem has been treated in detail, yielding simulated spectra to compare with experimental ones. Vibronic calculations, extended to second order (quadratic coupling) for P+4, account for vibrational structure which is partially resolved in its photoelectron spectrum. A Jahn–Teller stabilization energy of 0.65 eV is derived for P+4, which can be characterized in its ground vibronic state as being highly distorted, and highly fluxional. Linear-only Jahn–Teller coupling calculations performed for As+4 and Sb+4, show good qualitative agreement with experimental spectra, yielding stabilization energies of 0.84 and 1.4 eV, respectively.
Fluorescence excitation spectrum of silver–argon van der Waals complex
Authors: Jouvet C. , Lardeux-Dedonder C. , Martrenchard S. , Solgadi D.
Published: July 2002

Fluorescence excitation spectra of silver–argon van der Waals complexes are presented. An alternative experimental technique to laser evaporation has been used to produce the cold complexes. The van der Waals states observed correlate with the (4d10 5s1) 2S Ag ground state and (4d10 5p1)2P0 Ag first excited state. The excited state of the Ag–Ar complex is found to be 1235 cm−1 deep, which is unusually large for such metal–rare gas complexes. A perturbation due to a state correlating with the (4d9 5s2)2D metastable Ag state is also observed and analyzed.
Autoionization structure and rotational contours in the multiphoton ionization spectrum of carbon dioxide
Authors: Johnson Philip , Wu Ming
Published: July 2002

The structure of the multiphoton ionization spectra of carbon dioxide in the vicinity of 4f and 5f resonances is analyzed in detail. The rotational contour of the f  complex is calculated using the frame transform method of Chang and Fano. It is found that only one electronic splitting constant k4f=7 cm−1 is needed to attain a reasonable approximation to the experimental spectrum. This would indicate that the Rydberg electron is relatively atomic-like and excluded from the core. It is also found that the dominant contribution to the three-photon excitation strength comes from the ΔΩ=3 path. The additional sharp structure to the blue of the 4f and 5f resonances is due to four-photon resonances with autoionization states belonging to Rydberg series converging on the Ã and B̃ states of the ion. The unusual strength of these lines arises from a coincidence between the photon energy and the energy of B̃←X̃ core transitions and the predissociation of the nearby bound resonances, which limits their strength.
Microwave measurements and theoretical calculations on the structures of NNO–HCl complexes
Authors: Pauley D. J. , Roehrig M. A. , Adamowicz L. , Shea J. C. , Haubrich S. T. , Kukolich S. G.
Published: July 2002

Pulsed-beam Fourier transform microwave spectroscopy was used to measure a and b dipole transitions for the N2O–H35Cl, N2O–H37Cl, N2O–D35Cl, and 15NNO–H35Cl van der Waals complexes. The observed transition frequencies were fit to determine the spectroscopic constants A–DK, B, C, DJ, DJK, eQqaa(Cl), and eQqbb(Cl). The structure of the complex appears to be a planar asymmetric top with a centers-of-mass separation Rc.m. ≊ 3.51 Å. The angle θ between Rc.m. and the HCl axis is approximately 110°. The angle φ between the N2O axis and Rc.m. is approximately 77°. The structure was fit using a weighted least squares fit to B and C isotopic rotational constants with Rc.m., θ, and φ as the adjustable parameters, and this procedure yielded three local minima with standard deviations less than 5 MHz. Principal axis coordinates for the Cl, H, and terminal N atoms in the complex were determined with single isotopic Kraitchman analysis to aid in the selection of the ‘‘best’’ structure. In a second structural analysis Rc.m. θ, and φ values were determined from the spectroscopic constants B, C, and eQqaa(Cl). The ‘‘best fit’’ structure parameters for N2O–HCl are Rc.m. =3.512(2) Å, θ =110(9)°, and φ = 77(2)°. Ab initio calculations of N2O–HCl structures using gaussian86 with MP2 yielded three energetically stable equilibrium conformations. One of the bound structures is very similar to the present experimental vibrationally averaged structure.
Time-dependent Hartree–Fock second-order molecular properties with a moderately sized basis set. I. The frequency dependence of the dipole polarizability
Authors: Spackman Mark A.
Published: July 2002

Time-dependent coupled Hartree–Fock calculations of the frequency-dependent mean polarizability α(ω) and its anisotropy Δα(ω) are presented for a wide range of molecules containing first and second row atoms. The Cauchy moments S(−2) and S(−4), which describe the dispersion in α(ω), are systematically underestimated by 20% and 40%, respectively, with the 6-31G(+sd+sp) basis set. The dispersion in Δα(ω) is also underestimated, typically by 50%. Many exceptions to this behavior are observed, most of which appear to be an underestimate of the experimental dispersion in Δα(ω) by a greater amount. This seems to be the result of systematic experimental overestimates of dispersion in Δα(ω) for molecules with very small Rayleigh depolarization ratios (ρ0<10−2), suggesting that the vibrational Raman contribution in these experiments is not only important, but significantly frequency dependent.
Converged three-dimensional quantum mechanical reaction probabilities for the F+H2 reaction on a potential energy surface with realistic entrance and exit channels and comparisons to results for three other surfaces
Authors: Lynch Gillian C. , Halvick Philippe , Zhao Meishan , Truhlar Donald G. , Yu Chin-hui , Kouri Donald J. , Schwenke David W.
Published: July 2002

Accurate three-dimensional quantum mechanical reaction probabilities are presented for the reaction F+H2→HF+H on the new global potential energy surface 5SEC for total angular momentum J=0 over a range of translational energies from 0.15 to 4.6 kcal/mol. We find that the v′=3 HF vibrational product state has a threshold as low as for v′=2. We also find considerable structure in the reaction probability and cumulative reaction probability curves which may be indicative of resonance structures. We compare these results to those for another potential energy surface 5SEC-W, which differs from surface 5SEC in the magnitude of the van der Waals well in the entrance channel, and to those for two previous potential energy surfaces.
Detection of C2(B′ 1Σ+g) in the multiphoton dissociation of acetylene at 193 nm
Authors: Bao Yihan , Urdahl R. S. , Jackson William M.
Published: July 2002

The first observation of C2(B′ 1Σ+g) in the 193 nm photodissociation of jet-cooled acetylene is reported. Nascent C2(B′ 1Σ+g, v″=0,1,2) is detected using laser-induced fluorescence via the D 1Σ+u state.
Negative ion formation and dissociation in scattering of fast O2 and NO from Ag(111) and Pt(111)
Authors: Reijnen P. H. F. , van Slooten U. , Kleyn A. W.
Published: July 2002

Results of scattering of 80–300 eV O2 and NO from Ag(111) and Pt(111) single crystal surfaces are presented. Molecular negative ion formation occurs on both surfaces. For O2 scattering around 80 eV for θi=70° from Ag(111), the O−2 distribution is detected in the specular direction, whereas an off-specular shift towards the surface is observed for scattering from Pt(111). For the Pt(111) surface, a degree of dissociation is observed that is much larger than for the Ag(111) surface. Both observations are consistent with the low dissociative sticking probability for thermal O2 on Ag(111) reported and the high dissociative sticking probability for thermal O2 on Pt(111). For NO−, the degree of dissociation is approximately equal to the degree of dissociation for O2 at the same Pt(111) surface.
A pyrolysis jet spectroscopic study of the rotationally resolved electronic spectrum of dichlorocarbene
Authors: Clouthier Dennis J. , Karolczak Jerzy
Published: July 2002

The rotationally resolved, gas phase vibronic spectrum of dichlorocarbene has been recorded using the technique of pyrolysis jet spectroscopy. The rovibronic analysis has established the band origin of the Ã 1B1–X̃ 1A1 electronic transition to be at 17 255.67 cm−1. The observed vibrational frequencies in the ground and excited states are very close to published values from matrix isolation data. The excited state structure has a 131.4° ClCCl angle and a 1.652 Å CCl bond length.
On the ion association at low salt concentrations in polymer electrolytes; a Raman study of NaCF3SO3 and LiClO4 dissolved in poly(propylene oxide)
Authors: Schantz S.
Published: July 2002

Raman spectra of poly(propylene oxide) (PPO) complexed with LiClO4 and NaCF3SO3, respectively, reveal the presence of both ion pairs and solvated ions. The amount of dissociated and paired ions has been calculated using a two-component band analysis of the ν1(A1) anion vibration. The degree of dissociation is approximately constant in the low concentration range of monomer (i.e., oxygen) repeating unit to salt ratio O:M=1000–30. For larger concentrations, it gradually decreases with increasing salt content. Association constants for the two systems are estimated from the concentration quotients at low salt contents using the Debye–Hückel theory. Extrapolation to zero concentration indicates a dissociation minimum at concentrations lower than O:M=1000. Large and positive values of ΔS0 (100±40 and 120±40 Jmol−1 K−1 for PPO–NaCF3SO3 and PPO–LiClO4, respectively) are obtained for the ‘‘free’’ ion–ion pair equilibria, which may reflect the increasing configurational freedom of polymer chains upon forming ion pairs. Comparisons with conductivity data suggest that single ions rather than charged multiplets are responsible for the conduction. The increase of ion association at high concentrations is too small to explain the conductivity drop at O:M<20. The σ drop is mainly due to reduced mobility as reflected in increasing values of viscosity.
Branching ratios and bond dissociation energies from the excimer laser photolysis of group 6 metal carbonyls
Authors: Rayner D. M. , Ishikawa Y. , Brown C. E. , Hackett P. A.
Published: July 2002

Photolysis of the group 6 (Cr, Mo, W) metal carbonyls in the gas phase, at excimer laser wavelengths, may lead to more than one primary product. Branching ratios between these products have been measured as a function of photolysis wavelength, buffer gas pressure, and temperature using time-resolved infrared spectroscopy. The results are modeled using a sequential dissociation mechanism in which branching ratios are determined by competition between unimolecular dissociation and collisional relaxation. The sensitivity of the results to thermochemical input parameters and assumptions concerning energy disposal mechanisms is discussed. Under qualified assumptions the branching ratio measurements provide estimates for CO bond dissociation energies for coordinatively unsaturated metal carbonyls. For Mo and W the individual bond dissociation energies are close to the average values but for Cr the first three ligands coordinated are significantly less strongly bound than the last three. This finding is discussed in terms of recent ab initio calculations on bonding in metal carbonyls.
An examination of the corrected centrifugal sudden approximation for the calculation of line broadening and shifting coefficients for HF in He
Authors: Thachuk Mark , McCourt Frederick R. W.
Published: July 2002

By utilizing the lineshape theory of Shafer and Gordon [J. Chem. Phys. 58, 5422 (1973)], pure rotational pressure broadening and shifting coefficients for the infrared spectral lines of HF in He have been calculated using the close-coupled (CC) method, the centrifugal sudden (CS) approximation, and the corrected centrifugal sudden (CCS) approximation of McLenithan and Secrest [J. Chem. Phys. 80, 2480 (1987)]. Comparison of the results obtained from these three methods were made at the total angular momentum dependent, kinetic energy dependent, and temperature dependent levels. In the latter comparisons, a semiclassical method was also included. The CS results agree very well with the CC calculations for the pressure broadening coefficients, but deviate slightly for the pressure shifting coefficients. The CCS results were essentially identical to those obtained from the CS approximation calculations. The semiclassical method was accurate to within about 15% of the CC values for the pressure broadening coefficients. The pressure shifting coefficients have been found to be very sensitive to the number of closed channels included in the calculations. As well, while collisionally inelastic contributions to the effective cross sections were not found to be negligible, their effect on the final calculated pressure broadening and shifting coefficients was found to be insignificant for this particular system at room temperature.
Longwave properties of the orientation averaged Mueller scattering matrix for particles of arbitrary shape. II. Molecular parameters and Perrin symmetry
Authors: Shi Yaoming , McClain W. M. , Tian Duan
Published: July 2002

In Part I of this paper, we started from a dipole array model of elastic light scattering, and found the longwave asymptotic formulas for all 16 elements of the orientation averaged Mueller scattering matrix. However, the Perrin symmetry of the scattering matrix was not obvious from the formulas obtained in Part I. In this paper, Part II, we carry the analysis further, finding the molecular parameter identities which result in the Perrin symmetries. The formulas we present provide a very practical method for model calculations in the longwave limit. After evaluation of ten sums over pairs of the dipolar subunits of the model, the orientation averaged Mueller scattering matrix, as a function of scattering angle, is given by simple trigonometric polynomials. For models containing several hundred subunits the computation is easily carried through by a desktop computer. We verify the asymptotic formulas by numerical comparison with our analytic orientation averaging program PMAT2. We use a helical model with spherical subunits, in which the first Born approximation gives excellent results for the dipole elements (symmetry DSE). In this same model the first, second, and third Born approximations are utterly worthless for calculating the helicity-retardation elements M13 and M23 and their transposes, but fourth Born gives nearly the exact result. These observables therefore use four bounces to feel out the helicity of the array, and may be more sensitive to structural variations than the traditional circular difference observable M14, which responds after only two bounces.
NH (X 3∑−, v=1–3) formation and vibrational relaxation in electron-irradiated Ar/N2/H2 mixtures
Authors: Dodd James A. , Lipson Steven J. , Flanagan Dorothy J. , Blumberg William A. M. , Person James C. , Green Byron David
Published: July 2002

Measurements of the dynamics of NH(X3∑−, v =1–3), created in electron-irradiated N2/H2 and Ar/N2/H2 mixtures, have been performed. Time-resolved Fourier spectroscopy was used to observe NH(v→v–1) vibrational fundamental band emission. Time-dependent populations were then determined by spectral fitting. Subsequent kinetic fitting of these populations using a single-quantum relaxation model and a power-law dependence of kv on v yielded the following NH(v =1–3) relaxation rate constants (units of 10−14 cm3 s−1): kv=1(N2)=1.2±0.5, kv=2(N2)=3.8±1.5, kv=3(N2)=7.5±2.5; kv=1(Ar)=0.2±0.1, kv=2(Ar)=0.5±0.2, kv=3(Ar)=0.8±0.3; kv=1(H2)≤50, kv=2(H2)≤100, kv=3(H2)≤150. In addition, the N2/H2 data provided a measurement of the nascent excited vibrational state distribution resulting from the reaction N(2D)+H2→NH(X,v)+H. The ratio NH(1):NH(2):NH(3) was found to be 1.0:0.97:0.81 (±0.28 in each value). Comparison of the observed nascent distribution with that of a statistical model suggests that the ratio NH(0):NH(1)=0.47. Using this derived distribution, we find the average product level 〈v〉 =1.6, and the fraction of the available product energy in vibration 〈fv〉 =0.44. The present evidence confirms that a single reaction mechanism dominates NH formation, and suggests that the reaction proceeds by direct H atom abstraction rather than the formation of a long-lived H–N–H intermediate.
Quantum interference effects on the collisional excitation of the Fermi doublet states of CO2 by hot electrons and hot H(D) atoms
Authors: Zhu Lei , Hewitt Scott A. , Flynn George W.
Published: July 2002

The vibrational excitation probability of the Fermi doublet states of CO2 has been determined following collisions with hot electrons and hot H(D) atoms. Similar, though not identical excitation probabilities are found for the two strongly mixed Fermi states in hot H(D) atom scattering; however, there is a dramatic preference for the upper energy member of this Fermi mixed pair in electron scattering experiments.
Low lying singlet states of α, ω-dithienylpolyenes: α, ω-dithienylbutadiene, α, ω-dithienylhexatriene, and α, ω-dithienyloctatetraene
Authors: Birnbaum Duane , Kohler Bryan E. , Spangler Charles W.
Published: July 2002

Fluorescence and fluorescence excitation spectra for low temperature n-alkane solutions of α,ω-dithenylpolyenes with two, three, and four polyene double bonds have been measured. The fundamental frequencies in the vibronic development of the fully resolved spectra are either nearly identical to modes seen for unsubstituted polyenes or nearly identical to modes seen for polythiophene oligomers. The degree to which thiophene ring modes contribute to the spectra decreases with increasing polyene chain length. In the tetraene, the 2 1Ag state is 2760 cm−1 lower in energy than the 1 1Bu state, in the triene it is 1570 cm−1 lower, and in the diene these two states are nearly degenerate. The 2 1Ag and 1 1Bu excitation energies are well fit by a simple theoretical model which also gives a description of the π-electron distributions in the 1 1Ag, 2 1Ag, and 1 1Bu states.
High pressure study on molecular conformational equilibria of n-pentane
Authors: Katō Minoru , Taniguchi Yoshihiro
Published: July 2002

The n-pentane molecule has the basic conformations, TT, TG, and GG. It is important for understanding the conformational behavior of chain molecules. We have studied the effect of pressure on the conformations of n-pentane in the condensed phase by using high pressure infrared spectroscopy with a diamond anvil cell up to 28.9 kbar. Compression of liquid n-pentane increases the concentration of the more globular conformers, while the TT conformer only exists as a high pressure solid. The volume changes for TT to TG, TG to GG, and TT to GG forms are −1.0±0.2, −1.1±0.3, and −2.1±0.3 cm3/mol, at 20 °C, respectively. The conformational volume changes in liquid n-alkanes are discussed in terms of the solvent-excluded volume.
Photodissociation of acetone at 193 nm: Rotational- and vibrational-state distributions of methyl fragments by diode laser absorption/gain spectroscopy
Authors: Hall G. E. , Vanden Bout D. , Sears Trevor J.
Published: July 2002

Diode laser transient absorption/gain spectroscopy is used to monitor time-dependent populations of CD3 fragments formed in the photodissociation of acetone-d6 at 193 nm. Selected rotational lines have been measured in the ν2 ‘‘umbrella’’ fundamental and first two hot bands, and in the ν3 asymmetric stretching fundamental band. Substantial growth is observed in the vibrationless state on the time scale of vibrational relaxation. We estimate that only about 15% of the nascent CD3 population is formed in the vibrational states we detect: ν2=1 and 2, ν3=1, and the vibrationless state. Most of the nascent methyl population is evidently spread among many undetected vibrational states. These results complement previous measurements of acetone photofragments by infrared emission, multiphoton ionization, and laser-induced fluorescence. Our inferred global vibrational distribution is consistent with a two-step fragmentation.
Photodissociation processes in carbon monoxide at 193 nm
Authors: Forch Brad E. , Merrow Clifton N.
Published: July 2002

The photodissociation of carbon monoxide at 193 nm has been investigated using resonance enhanced multiphoton ionization detection of atomic oxygen and carbon fragments. The results of these experiments indicate a quadratic photodissociation process in CO at 12.8 eV. In addition, the nascent fine structure branching ratios of atomic oxygen 2p4 (3P2,1,0) produced in the 193 nm photodissociation of CO are reported using both multiphoton laser induced fluorescence and ionization detection. Analysis of the experimental data and computer generated simulations indicate that the distributions are not statistical.
Naphthalylnaphthalene, a molecule with remarkable photophysical properties: Violation of the energy-gap law in radiationless transitions
Authors: Cai Jianjian , Lim E. C.
Published: July 2002

We report here highly novel emission characteristics of naphthalylnaphthalene which are manifestations of the violation of the energy-gap law in radiationless transitions.
Product internal-state distribution for the reaction H+HI→H2+I
Authors: Kliner Dahv A. V. , Rinnen Klaus-Dieter , Buntine Mark A. , Adelman David E. , Zare Richard N.
Published: July 2002

We have measured the nascent H2(v, j) product-state distribution from the H+HI→H2+I abstraction reaction. Laser photolysis of HI at 266 nm generated translationally hot H atoms with center-of-mass collision energies of 1.61 and 0.68 eV in the ratio 64:36. Quantum-state-specific detection of the molecular reaction product was accomplished via (2+1) resonance-enhanced multiphoton ionization and time-of-flight mass spectrometry. The H2 is formed with a high degree of internal excitation, including a vibrational population inversion between v=0 and v=1. Our product-state distribution agrees closely with that of Aker, Germann, and Valentini where comparison is possible. Rotational population distributions derived from the quasiclassical trajectory calculations of González and Sayós are generally too cold, whereas those of Aker and Valentini nearly reproduce the experimental distributions. Both calculations fail to predict, however, the observed vibrational inversion.
Electronic energy transfer from B ′ 2Δ to B 2Σ+ in SiCl
Authors: Jeffries Jay B.
Published: July 2002

Efficient electronic energy transfer to the B 2Σ+ state is observed by collision induced B–X emission when SiCl molecules in the B′ 2Δ state collide with rare gas atoms. The rate constants for the collisional removal from B′ 2Δ v′=0 and 1 are measured by time resolved laser-induced fluorescence and found to be large for He, Ne, and Ar ranging from 1–8×10−11 cm3/s. The fraction of the total quenching if the B′ 2Δ which results in electronic-to-electronic energy transfer from B′ 2Δ to B 2Σ+ is measured to be between 0.3 and 0.6. The nascent vibrational distribution of the product B 2Σ+ shows a surprising variation with collider.
Influence of substituents on the reorientational motion of 9-anthracene derivatives studied by depolarized light scattering and fluorescence anisotropy decay
Authors: Dorfmüller Th. , Daum B. , Hanschmidt A.
Published: July 2002

The influence of substituents on the reorientational motion of 9-anthroates is studied by depolarized light scattering (DLS) and fluorescence anisotropy decay (FAD). We investigate the dependence of the reorientational relaxation times on the length of flexible chains of 9-alkylanthroates and on the size of rigid substituents such as t-butyl, cyclohexyl, and adamantyl. Temperature-dependent measurements are performed in CCl4 and paraffin, respectively, with the two methods, which monitor the reorientation of different axes. Our results are discussed taking into consideration models for alkyl chain dynamics.
A time-development operator formulation of the kinetic theory of dilute polymeric solutions
Authors: Curtiss C. F.
Published: July 2002

For dilute solutions of polymeric molecules, the distribution function in the configuration space of a single molecule is determined by the so-called ‘‘diffusion equation.’’ In the present discussion, we transform the problem of solving this diffusion equation to that of solving a different linear differential equation involving a Hermitian operator ℋ associated with the unperturbed system and an operator 𝒲=κ:ℳ̂, which describes the effects of the velocity gradient κ°. It is shown that the eigenvalues of ℋ are the reciprocals of the time constants associated with the decay of perturbations of the system from equilibrium. It is then shown that the stress tensor may be written simply in terms of matrix elements of an operator ℳ and a time-development operator 𝒰 with respect to the eigenfunctions of ℋ as the bases. This development then leads to an expression for the relaxation modulus of linear viscoelasticity, which is of the form of the ‘‘generalized Maxwell model.’’ A formal expression for the relaxation modulus involves an exponential operator which may easily be expanded leading to a series in powers of the time variable. This then leads to quite general expressions for the high frequency limiting values of the real and imaginary parts of the complex viscosity. These expressions are evaluated for the special case of the finitely extensible nonlinear elastic (FENE) dumbbell and the results shown to be consistent with earlier asymptotic results.
Differences in thermal conformation fluctuation between two models for semiflexible chains
Authors: Soda Kunitsugu
Published: July 2002

Differences in thermal conformation fluctuation, particularly in longitudinal deformation, have been examined for two semiflexible chain models of the longitudinally stiff (LS) and the longitudinally flexible (LF) chains. The LF chain exhibits fairly large, longitudinal conformation fluctuations: The mean fluctuation of the tangent-vector length amounts to 44% of its average. General formulas for the correlation functions of various quantities related to chain bending and stretching are given for the LF chain. It is shown that, though the motion of an LF chain can be decomposed into mutually independent normal modes, the longitudinal stretching and transverse bending motions are made in some correlated manner. Depending on its contour shape and external forces, a complex distribution of internal stresses is produced in each cross section of an LS chain. It varies along the chain, which ensures the nearly inextensible nature of the LS chain. It is concluded that, if the motion of an LS chain is described by a series of normal modes, their amplitudes will change with time in a strongly correlated manner quite distinct from the case of LF chains.
High resolution infrared spectroscopy of deuterium in p-H2 matrix
Authors: Chan Man-Chor , Xu Li-Wei , Gabrys Charles M. , Oka Takeshi
Published: July 2002

The high resolution spectrum of the fundamental band of deuterium impurity embedded in solid parahydrogen has been studied using a difference frequency laser spectrometer. This observation represents the first case of high resolution matrix spectroscopy in solid hydrogen. Both the Q1←0(0) and Q1←0(1) transitions were resolved into sharp features with a typical linewidth of ≲ 10 MHz, while both the S1←0(0) and S1←0(1) transitions appeared to be much broader with widths of ∼0.07 cm−1. A discussion of the linewidths based on homogeneous broadening is presented.
The Li2 C 1Πu state studied by a single-frequency ultraviolet laser
Authors: Ishikawa Kiyoshi , Kubo Shunji , Katô Hajime
Published: July 2002

A newly constructed single-frequency, autoscan laser spectrometer operating in the ultraviolet in combination with a collimated molecular beam has been used to obtain a high resolution fluorescence excitation spectrum in the region 30 850–31 400 cm−1. Eight hundred and seventy five rotational lines of the 7Li2 C 1Πu(v′=2–8)–X 1Σ+g and 6Li7Li C 1Π(v′=2–4)–X 1Σ+ transitions are assigned. The molecular constants of the C 1Πu state are determined and the potential curve is constructed using the Rydberg–Klein–Rees (RKR) method. By comparing the calculated Franck–Condon factors with the line intensities of the dispersed fluorescence spectrum, we determine the dependence of the electric dipole transition moment on the internuclear distance.
Self-consistent theory of polymer dynamics in melts
Authors: Szleifer Igal , Wilson Jeffrey D. , Loring Roger F.
Published: July 2002

We present a model describing the dynamics of a flexible linear polymer in a monodisperse melt. The polymer is represented by a freely jointed chain that moves by two coupled dynamical processes. The first is a kink–jump motion that may be blocked by obstacles, and the second is a slithering motion that mimics reptation. The obstacles relax with a distribution of time scales. This distribution is determined self-consistently by the requirement that it be identical to a distribution of time scales associated with the relaxation of the slowest internal modes of the chain. The calculation of observables is shown to be equivalent to the solution of a random walk problem with dynamical disorder. We determine this solution by applying the dynamical effective medium approximation. Within the resulting theory, the mean squared displacement of a polymer bead on any time scale may be determined by solving a fifth order algebraic equation and inverting a Laplace transform. We present calculations of the self-diffusion coefficient in a melt and of the tracer diffusion coefficient of a chain of a given molecular weight at infinite dilution in a melt of another molecular weight. For the self-diffusion coefficient, the theory predicts results consistent with the Rouse model for short chains and behavior consistent with the reptation picture for long chains. The crossover between these limiting behaviors is described. Comparison is made to measurements of tracer and self-diffusion in polystyrene melts.
Rotational temperature dependence of the branching ratio for the reaction of O+ with HD
Authors: Viggiano A. A. , Van Doren Jane M. , Morris Robert A. , Williamson John S. , Mundis Paul L. , Paulson John F. , Dateo Christopher E.
Published: July 2002

Rate constants and branching fractions for the reaction of O+ with HD have been measured as a function of average center-of-mass kinetic energy (〈KEcm〉) at three temperatures: 93, 300, and 509 K. Both OH+ and OD+ were produced. The rate constants were found to equal 1.2×10−9 cm3 s−1, independent of temperature or 〈KEcm〉. The branching into OH+ was observed to increase with 〈KEcm〉. Differences in the branching fractions were seen at a particular 〈KEcm〉 at different temperatures. These differences are attributed to a rotational temperature dependence such that increasing rotational temperature decreases the fraction of OH+ produced. The data are in agreement with a theoretical calculation and previous measurements.
Resonant multiphoton ionization dynamics of N2 via the a 1Πg(v=10–14) states: Preparation of state-selected N+2 X 2Σ+g(v+=0–4) ions
Authors: Ondrey G. S. , Rose C. , Proch D. , Kompa K. L.
Published: July 2002

The photoelectron spectra are reported from resonantly enhanced multiphoton ionization of N2 via the a 1Πg(v=10–14) states. Ionization from these levels is found to follow a (2+1) pathway resulting in N+2 X 2Σ+g(v+=0–4) ions. The observed branching ratios in the photoelectron spectra reveal a strong propensity for forming ground state ions in a single vibrational state. The results are explained qualitatively by favorable Franck–Condon overlap in the ionizing X 2Σ+g–a 1Πg transition.
Many-body calculation of the valence photoemission spectrum of Fe(CO)5
Authors: Ohno M. , von Niessen W.
Published: July 2002

The valence photoemission spectrum of Fe(CO)5 is calculated by the ADC(3) Green’s function method. The overall agreement with the experiment is good. It is shown that the quasiparticle picture (QPP) for the outer and inner valence levels (except the 8a″2 level) derived primarily from CO ligand orbitals breaks down completely due to the one-hole/two-hole–one-particle (1h/2h1p) charge transfer (CT) coupling in the bonded system. Compared to Ni(CO)4 the many-electron effect is much stronger in Fe(CO)5. In Cr(CO)6 and Fe(CO)5 the 3d shell is incompletely filled, but in contrast to Cr(CO)6 in Fe(CO)5 there is no significant contribution from the local metal excitations. It is shown that for the 8a■2 level the 1h state is still more stable than the 2h1p states. Consequently the main line (with an intensity of 0.76) is interpreted as the 1h state where the screening charge resides on the bonding orbital which is more polarized toward the ligand than in the ground state. The satellites are dominated by 2h1p configurations where the bonding to antibonding shake-up excitations occur. For the other CO derived levels the strong mixing of 1h and 2h1p configurations leads to the breakdown of the QPP of the ionization and thus a distinction between main line and satellite line becomes meaningless. For most of the levels, the strong dynamical metal–ligand CT hole–particle excitations, where the creation of two holes in the same metal orbital is involved, lead to the breakdown of the QPP of the ionization. A similar strong many-electron effect is also found in Cr(CO)6. For most of the outer and inner valence levels of these molecules, the QPP of the ionization breaks down.
Time-resolved observation of excitation hopping between two anthryl moieties attached to both ends of polystyrene chains
Authors: Ikeda Tomiki , Lee Bong , Ushiki Hideharu , Horie Kazuyuki
Published: July 2002

Excitation hopping between two 9-anthryl moieties attached to both ends of polystyrene chains with various molecular weights has been explored by picosecond time-resolved fluorescence anisotropy measurements. The measurements were performed at 77 K in the rigid matrix of 2-methyltetrahydrofuran (MTHF) or methylcyclohexane (MCH) in order to exclude the effect of rotational diffusion of the chromophores to the fluorescence anisotropy. The hopping behavior was found to be very sensitive to such factors as molecular weight (Mn), solvent, and concentration of the samples. In MTHF (good solvent), the excitation hopping was only observed for a sample with Mn∼104; on the other hand, it occurred unequivocally for samples with Mn∼105 in MCH (poor solvent), as evidenced by a clear decay of the fluorescence anisotropy, r(t). Furthermore, the excitation hopping was an intramolecular event only at very low concentration (∼10−7 M based on polymer chain), and at 10−6 M, an intermolecular excitation hopping was observed. Such sharp dependence of the excitation hopping on the concentration was interpreted in terms of chain collapse at low temperature. Simulation of r(t) was performed on the basis of Förster mechanism and Gaussian chain statistics.
Adsorbate–adsorbate interactions for PF3 chemisorbed on Pt(111)
Authors: Agrawal Vijay K. , Trenary Michael
Published: July 2002

To gain a better understanding of adsorbate–adsorbate interactions for chemisorbed polyatomic molecules we have measured the coverage and temperature dependence of the PF3 symmetric bend and P—F symmetric stretch fundamentals of PF3 chemisorbed on Pt(111). The two bands exhibit distinctly different responses to lateral interactions. The P—F stretch shifts from 901 to 951 cm−1 with increasing coverage and at intermediate coverages splits into two components separated by 5–13 cm−1 with a relative intensity which is strongly temperature dependent. By contrast, the symmetric bend shifts from 541 to 562 cm−1 and remains as a single band under all conditions. The symmetric bend displays only a slight asymmetry under conditions where the P—F stretch is split into two components. The different behavior of the two bands along with other considerations indicate that both coupling and chemical shifts determine the P—F stretch frequency for PF3 chemisorbed on Pt(111).
Microscopic expressions for the rigidity constants of a simple liquid–vapor interface
Authors: Blokhuis Edgar M. , Bedeaux Dick
Published: July 2002

We present microscopic equations for the rigidity constants of a simple liquid–vapor interface. These expressions are analogous to the Kirkwood–Buff formula for the surface tension. The rigidity constants are calculated using an approximate expression for the density auto correlation function in the interface near the critical point. This results in k=0.631 kBTc and k=0.239 kBTc.
Electronic spectroscopy of silver dimer rare gas complexes
Authors: Willey K. F. , Cheng P. Y. , Yeh C. S. , Robbins D. L. , Duncan M. A.
Published: July 2002

Vibrationally resolved electronic spectra are reported for the metal dimer-rare gas complexes Ag2–Ar and Ag2–Kr. These spectra are obtained using resonant two-photon photoionization in the energy region near the Ag2 B←X electronic transition (280–285 nm). Both complexes exhibit extensive activity in three vibrational modes, making it possible to determine vibrational constants, anharmonicities, and cross-mode couplings. An unusual cancellation of factors results in the Kr complex (ω′e =72.6 cm−1) having nearly the same metal-rare gas stretching frequency as the Ar complex (ωe=73.9 cm−1). Progressions extending over a significant range of the excited state potential surfaces make it possible to derive the excited state dissociation energies (D′0=755 and 1205 cm−1 for Ar and Kr, respectively). Combination with the red-shifted electronic state origins yields the corresponding ground state dissociation energies (D■0=275 and 394 cm−1 for Ar and Kr, respectively). Potential energy surfaces are investigated for excited and ground states of both complexes.
J dependence of χa(14N) and χa(83Kr) for the Kr–HCN dimer
Authors: Germann T. C. , Emilsson T. , Gutowsky H. S.
Published: July 2002

High-resolution microwave rotational spectra for 84Kr–HCN, 86Kr–HCN, and 83Kr–HC15N have been observed with the pulsed-nozzle, Fourier transform Balle/Flygare Mark II spectrometer. A new method of injecting the gas sample into the Fabry–Perot cavity along the axis of the microwave pulse was used for some transitions to narrow the linewidths. The present work extends that of the original study [J. Chem. Phys. 78, 3483 (1983)] over a wider frequency range (2–18 GHz) and with higher resolution. The 14N nuclear quadrupole coupling constant has been found to increase linearly with J(J+1) for 84Kr–HCN and 86Kr–HCN, with the slope Dχ one-third its value for the analogous Ar–HCN dimer. For 84Kr–HCN, the average HCN bending amplitude θ decreases from 26.85° for J=0 to 26.28° for J=7, while the average Kr to HCN center-of-mass (c.m.) distance R increases from 4.5202 to 4.5246 Å. Similar results are found for 86Kr–HCN. In addition, the 83Kr quadrupole coupling constant for 83Kr–HC15N is dependent on J, increasing from 7.5382 MHz for J=1 to 7.5713 MHz for J=4. This is interpreted with the long-range polarization model used previously to explain rare gas nuclear quadrupole coupling constants in Rg–HX dimers. In particular, the J dependence observed for χa(83Kr) is consistent with the J dependencies of θ and R inferred from χa(14N) in the 14N species. Radial and angular motions of HCN are strongly coupled.
Radiative and nonradiative processes affecting higher-excited-state luminescence of Ni2+ in several chloride lattices
Authors: May P. Stanley , Güdel Hans U.
Published: July 2002

The 7 K luminescence spectra of Ni2+ lightly doped into MgCl2, CsMgCl3, CdCl2, and CsCdCl3, produced by excitation into the 3A2g→3T1g(3P) absorption band of Ni2+, are reported. Luminescence in these compounds originates from two metastable states of Ni2+ : the first excited state, 3T2g; and a higher excited state, 1T2g. Emission from 1T2g, corresponding to transitions to all lower-lying levels, is observed. Rates corresponding to the various radiative and nonradiative transitions from 3T2g and 1T2g at 5 K are given. At low temperature, relaxation from 3T2g is largely radiative in nature, whereas multiphonon emission makes a significant contribution to 1T2g relaxation down to the lowest temperature studied (5 K). In Ni2+:CsCdCl3, there appears to be a significant nonradiative pathway out of 1T2g directly to the ground state, bypassing all intermediate excited states. The temperature dependence of multiphonon emission from 1T2g is modeled using the single configurational coordinate (SCC) approximation, assuming harmonic potentials with equal force constants. As the Ni2+ concentration is increased in these lattices, 1T2g luminescence is deactivated due to Ni2+–Ni2+ cross relaxation. The mechanism of cross relaxation in Ni2+:CsCdCl3 is investigated by analyzing the decay curves of 1T2g luminescence according to the theories of Dexter and Inokuti and Hiroyama. Cross relaxation in Ni2+:CsCdCl3 is best described by a dipole–dipole mechanism. The cross relaxation process is shown to increase the quantum efficiency of 3T2g luminescence in Ni2+:CsCdCl3 and Ni2+:CsMgCl3 at 5 K.
Resonance Raman spectra of the S3←S transition of SO2: Electronic, vibrational, and rotational dynamics in solution
Authors: Yang Tzyy-Schiuan , Myers Anne B.
Published: July 2002

Resonance Raman spectra, including absolute scattering cross sections, of sulfur dioxide in the vapor phase and in hexane solution have been obtained at several excitation wavelengths between 235 and 208 nm, on resonance with the strong S3←S0, 1B2←1A1 electronic transition. Due to the narrow rovibronic linewidths in the isolated molecule, the vapor phase spectra are best described as single vibronic level resonance fluorescence and exhibit intensity patterns that depend strongly on excitation wavelength, while the solution phase spectra are only weakly dependent on excitation frequency due to the increased linewidths of the vibronic transitions. The spectra in hexane are dominated by long overtone progressions in the symmetric stretch and its combination bands with the bend. The relative and absolute cross sections are reproduced fairly well through time-dependent wave packet propagation calculations employing an anharmonic S3 state potential previously developed to fit vibronic energy levels of the isolated molecule. The average vibronic homogeneous linewidth in solution is found to be about 560 cm−1 FWHM, implying an electronic dephasing time of approximately 20 fs, and the absence of significant broad fluorescence indicates that the dephasing is dominated by electronic population relaxation. In contrast, the ground state isotropic Raman linewidths are less than 5 cm−1, even for overtones involving up to six stretching quanta, indicating ground state vibrational dephasing times greater than 2 ps. Analysis of the anisotropic band shapes suggests that the rotational motion is not greatly hindered by solvation.
Velocity selective rotational rainbows for normal incidence/normal detection gas–surface scattering
Authors: Hanisco Thomas F. , Yan Chun , Kummel Andrew C.
Published: July 2002

Velocity selected rotational state distributions of N2 molecules scattered from Ag(111) have been measured. These measurements have been made at normal incidence and normal detection for incident energies of 0.25 and 0.75 eV. This new technique allows us to rapidly study the cross correlation between the exit rotational state and its velocity distribution. A pronounced difference between the rotational distributions of fast and slow scattered molecules is observed, and this difference is much more pronounced for high incident kinetic energy.
The absorption spectrum of a potassium atom in a Xe cluster
Authors: Haug Kenneth , Metiu Horia
Published: July 2002

We calculate the absorption spectrum for a simple model that mimics a potassium atom in a Xe cluster. The time evolution of the electron wave function is calculated by a fast Fourier transform method while the nuclear motion is treated classically. The initial nuclear configurations are generated by a Monte Carlo method. We examine which features in the spectrum are caused by electron, potassium ion or Xe motion and the frequency resolution at which these features appear.
Rotationally resolved V–V transfer in C2D2/Ar collisions: Characterization of a vibrational bottleneck
Authors: Chadwick B. L. , Orr B. J.
Published: July 2002

Time-resolved infrared–ultraviolet (IR–UV) double resonance spectroscopy is employed for rotationally resolved kinetic studies of collision-induced energy transfer between the 4151 and 42 vibrational levels in the ground electronic state of acetylene-d2, C2D2. Second-order rate constants, for intra- and intermolecular V–V transfer and also for V–T,R transfer, are determined.
Calculation of thermal rate coefficients from the quantum flux autocorrelation function: Converged results and variational quantum transition state theory for O+HD↔OD+H and O+HD↔OH+D
Authors: Day Paul N. , Truhlar Donald G.
Published: July 2002

The thermal rate coefficients for the title reactions with zero total angular momentum are calculated by an ℒ 2 basis-set evaluation of the flux autocorrelation function. We use three dividing surfaces, each one separating one arrangement from the other two. The rate coefficients for O+HD↔OD+H or OH+D are converged to within 1.2% over the temperature range 300–1000 K and to within 2.4% at 200 K. The rate coefficients for the reactions H+OD↔D+OH are converged to within 22% at 1000 K and upper bounds to these rate coefficients are given for the temperature range 200–800 K. Flux autocorrelation functions and rate coefficients are calculated for different positions of the dividing surface to show that the computed rate coefficient is stable with respect to varying this position. Rate coefficients are also calculated by a variational version of quantum mechanical transition state theory and the results are compared to the accurate rate coefficients obtained from flux autocorrelation function theory.