bluuebunny/crossref_metadata_2025 huggingface dataset:
Remarks on the Description of Excited Electronic States by Configuration Interaction Theory and a Study of the (π → π*1) State of H2CO
Authors: Whitten J. L.
Published: February 2004

Several effects which have been found to be important in the CI description of excited electronic states are discussed and quantitative applications are presented for the ground and (π → π*1) excited states of formaldehyde. Specific remarks deal with the importance of σ → σ* excitations in causing a contraction of the spatial extent of (π → π*1) states, the overestimation of the σ → σ* effect on transition energies at the single excitation CI level and the inclusion of higher order effects in the generation of configurations. One physically important aspect of σ → σ* excitations is treated in terms of a polarization of localized components of a CI wavefunction. Calculations are presented on the ground and (π → π*1) states of H2CO for three internuclear distances. The results show a Franck-Condon intravalence transition at 9.9 eV and a significant lowering of the transition energy on CO stretch.
Enumeration of Permutational Isomerization Reactions
Authors: Klemperer W. G.
Published: February 2004

Rearrangement reactions of certain stereochemically nonrigid molecules may be described by permutation operations. The usefulness of these permutation operations in solving quantum mechanical and stereo-chemical problems has already been demonstrated. In this paper it is shown how the point group of a molecule renders certain permutations equivalent. This equivalence is used to generate classes of equivalent permutations, i.e., classes of equivalent isomerization reactions. Two types of equivalent reactions are defined: indistinguishable permutational isomerization reactions and nondifferentiable permutational isomerization reactions. The classes of equivalent permutations generated are shown to be conjugacy classes and double cosets, respectively, of the symmetric group without respect to a subgroup. Formulas are provided which enumerate these classes. Nonrigid trigonal bipyramidal and octahedral molecules are treated as examples.
Electronic States of H2O+ Produced by Electron Bombardment of H2O
Authors: Lindemann Ellen , Rozett R. W. , Koski W. S.
Published: February 2004

The abundance of the electronic states of H2O+ produced by electron bombardment of H2O vapor in the energy range 12–70 eV have been determined by studying the attenuation of the H2O+ ion beam in nitrous oxide. The ground state (2B1), the first excited state (2A1), and probably the second excited state (2B2) were found to be present, and their abundance was found to be a function of the electron bombarding energy and the water vapor pressure in the ion source.
Calculation of the Elastic Constants of Nematic Liquid Crystals
Authors: Nehring Jürgen , Saupe Alfred
Published: February 2004

The ratio of the elastic constants of nematic liquid crystals is calculated using a simple inner field model. The result obtained is k11′: k22 : k33′: k24 : k13(2)=5:11:5:-9:-6. The first three constants, which are the constants for splay, twist, and bend, respectively, are found to be positive, in contrast with the result of an earlier calculation which was based on the same model but neglected second order splay-bend contributions to the deformation energy.
Total Energy in the Multiple Scattering Formalism: Application to the Water Molecule
Authors: Connolly J. W. D. , Sabin John R.
Published: February 2004

A scheme for obtaining the statistical total energy in the multiple scattering formalism is presented. Calculations are then carried out on the water molecule, which has been thoroughly investigated by ab initio LCAO MO SCF and experimental methods, in order to test the reliability of the method. The one-electron energies, ionization potentials, and vibrational potential curves are reported. Some advantages and limitations of the method are discussed in light of these results.
Self-Diffusion in Solid Ammonia
Authors: O'Reilly D. E. , Peterson E. M.
Published: February 2004

Refined measurements of the rotating frame relaxation time (T1p) in solid ammonia from 166°K to the melting point (196°K) are presented and interpreted as due to vacancy diffusion. The data are represented by a self-diffusion coefficient D=(2.2 × 10−1) exp[−(9.4 ± 0.6)/RT] cm2 sec−1. In the calculation of the jump times from the T1ρ data both the intermolecular and intramolecular dipolar interactions are taken into account. It is proposed that similar T1ρ data measured by Van Steenwinkel in benzene, cyclohexane, and hexamethylbenzene are due to vacancy diffusion and not to molecular rotations at a lattice site which are inconsistent with the crystal symmetry of the solid. The observed pre-exponential factor of D is compared with a theory of self-diffusion based on a Maxwell-Boltzmann distribution of molecular velocities in the solid. Entropies of migration and vacancy formation are evaluated for a hypothetical fee form of ammonia. The calculated pre-exponential factor (0.14) is in good agreement with the observed value (0.22). Lennard-Jones parameters for ammonia are derived by comparison of the model system with experimental data.
Application of the Coherent Potential Approximation to the Excited Electronic States of Substitutionally Disordered Molecular Crystals
Authors: Hoshen Joseph , Jortner Joshua
Published: February 2004

In this paper we apply the coherent potential approximation for the calculation of the density of excited electronic states and of the optical properties of a variety of isotopically mixed molecular crystals where the pure crystal exciton band structure and density of state is determined by one, two, and three dimensional interactions. The crystal Hamiltonian is characterized by a random diagonal part and by a translationally invariant off diagonal part. Numerical results are provided for the following systems:

(a) a one dimensional chain in the amalgamation limit, in the persistence case and in the separated bands limit;

(b) the lowest triplet state of naphthalene in the separated bands case;

(c) the lowest singlet state of naphthalene in the amalgamation limit, in the persistence case and in the separated bands limit.

(d) The lowest singlet state of benzene in the persistence case and in the separated bands limit.

These calculations demonstrated the general features of the density of states in substitutionally disordered crystals, such as the erosion of the Van Hove singularities in the band(s), and the nature of the intensity distribution such as number of Davydov components, their relative intensities, location, and widths. The predictions of the CPA for the moments of the density of states and for the optical properties concur with the predictions of the general moment expansion method for a configurationally averaged crystal. A general CPA scheme is provided to handle tertiary mixed crystals, which are of some experimental interest. To account for the concentration dependence of the optical properties of isotopically mixed benzene, we provide a semiquantitative extension of the CPA scheme, where the isotope effect on the environmental shift term is incorporated into the virtual crystal Hamiltonian resulting in concentration dependent diagonal terms in the crystal Hamiltonian.
ESR and Optical Spectra of the ScS and YS Molecules
Authors: McIntyre N. S. , Lin K. C. , Weltner W.
Published: February 2004

ESR spectra of the ScS and YS molecules in their ground 2Σ+ states were measured while trapped in solid argon or neon matrices at 4°K. g tensors and hyperfine structure constants for interaction with the metal nuclei were accurately derived, within the ambiguity of multiple matrix sites. Earlier ESR data on ScO were also more accurately analyzed, and a comparison is given of the magnetic parameters for the diatomic oxide and sulfide molecules of Sc, Y, and La. The ir spectra of ScS and YS in argon matrices yielded bands at 554 and 483 cm−1, respectively, and the A 2Π← X 2Σ transition of YS was observed at 7300 Å.
Three-Particle Collision Integrals for a Gas of Hard Spheres
Authors: Sengers J. V. , Ernst M. H. , Gillespie D. T.
Published: February 2004

In order to predict the first density corrections to the transport coefficients of gases, it is necessary to evaluate collision integrals which account for the correlations in the position and velocity variables of three molecules. These correlations are both of a statistical and dynamical nature. For a gas of hard spheres the statistical correlations reduce to excluded volume effects and the dynamical correlations are brought about by sequences of binary collisions among three molecules. It is shown how a systematic analysis of these two types of correlations leads to a decomposition of the three-particle collision integrals in terms of symmetric collision integrals associated with the dynamics of one, two, three, and four successive collisions among three molecules. These collision integrals are derived explicitly for the coefficients of thermal conductivity, viscosity, and self-diffusion.
High Energy-Resolution Studies of Electron Impact Optical Excitation Functions I. The Second Positive System of N2
Authors: Finn T. G. , Aarts J. F. M. , Doering J. P.
Published: February 2004

The relative emission cross section for the N2 second positive system (0, 0) and (1, 0) bands excited by electron impact has been measured for incident electron energies from threshold to 17 eV. By using a high energy-resolution electron spectrometer coupled to an optical detection system, it was possible to perform the measurements with an incident electron beam having an energy half width of 50 meV (FWHM). Observation of various scattering resonances in nitrogen and helium provided an accurate calibration of the incident electron energy. The maximum of the N2 second positive system (0, 0) band emission cross section (λ3371 Å) was found to be at 14.02 ± 0.05 eV. The maximum for the (1, 0) second positive band (λ3159 Å) was found to be at 14.3 ± 0.1 eV. Two small structural features corresponding to the onset of additional channels for population of the N2 C 3IIu state were observed at 11.48 eV and between 11.8 and 12.3 eV. The first feature was pressure independent and appeared only in the (0, 0) band emission cross section. This feature apparently arises as a consequence of decay of the compound state responsible for the 11.48 eV N2 elastic scattering resonance to the N2 C 3Πu(v′=0) state. The second feature was broad and pressure dependent. It appeared more strongly in the (1, 0) band cross section than in that for the (0, 0) band. Collisional quenching of the N2 E 3Σg+ state via a collision-induced crossing into the vibrational states of the N2 C 3IIu state appears to be the best explanation of this effect.
Semiclassical Theory of Electronic Transitions in Low Energy Atomic and Molecular Collisions Involving Several Nuclear Degrees of Freedom
Authors: Miller William H. , George Thomas F.
Published: February 2004

A semiclassical theory is developed for describing electronic transitions in low energy atomic and molecular collisions, such as A+BC, that involve quantized nuclear degrees of freedom (i.e., rotation and vibration) as well as translation. The principal physical idea is that in this low energy regime the dynamics is essentially classical motion of the nuclei on electronically adiabatic potential energy surfaces, with transitions between surfaces being events which are localized in space and time. The quantum principle of superposition is incorporated in the formulation in that classical dynamics is used to construct the classical limit of amplitudes (i.e., S matrix elements) for transitions from a specific initial electronic-rotational-vibrational state of A+BC to a specific final electronic-rotational-vibrational state of A+BC or AB+C, etc. Approximate and ``exact'' versions of the theory are developed, and in the ``exact'' version it is seen clearly that electronic transitions are inherently a ``classically forbidden'' process in that the classical action along the trajectories appropriate for such transitions has an imaginary contribution.
Vibrational Spectra and Structure of Azomethane and Azomethane-d6
Authors: Durig J. R. , Pate C. B. , Harris W. C.
Published: February 2004

The infrared spectra of gaseous and polycrystalline CH3NNCH3 and CD3NNCD3 have been recorded from 33 to 4000 cm−1. The corresponding Raman spectra of the liquid and solid samples have been measured from 100 to 4000 cm−1. The vibrational data provide definitive verification of a trans structure with C2h symmetry. A vibrational assignment is proposed for the 24 fundamental modes based upon the observed band contours, isotopic shift ratios, and group frequency correlations. The au and bg torsional modes were assigned to bands at 222 and 223 cm−1, respectively, and the internal rotational barrier of the methyl group was calculated to be ∼ 2.7 kcal/mole. A number of the internal fundamentals were observed to be split into doublets in the spectra of the solids which suggests that there are at least four molecules per unit cell in azomethane. The inversion center is apparently retained in the crystal since the rule of mutual exclusion was found to be operative.
Hanle Effect Measurement of the Lifetime of the A 1π State of CS
Authors: Silvers Stuart J. , Chiu Chi-Lian
Published: February 2004

Four different atomic emission lines which coincide with absorption lines of the A 1Π−X 1Σ+ system of CS are used to excite and make Hanle effect measurements on the A 1π levels: v′=2, J′=6; v′=0, J′=8; and v′=0, J′=12. Each level's signal width in the limit of zero pressure determines its radiative lifetime if the g factor is known. For v′=2 a pure 1π g factor is used; the g factors of the v′=0 levels, perturbed by interactions with a′ 3Σ+(v=10) and k 3Π(v=4), are calculated. The v′=2 lifetime is 203± 12 nsec. The v′=0 lifetime, corrected for lengthening by triplet mixing, is 176± 14 nsec. Pressure broadening of the v′=2 signal is observed, and narrowing of the v′0 ones with pressure is attributed to radiation trapping.
Analytic Continuation of Classical Mechanics for Classically Forbidden Collision Processes
Authors: Miller William H. , George Thomas F.
Published: February 2004

Classically forbidden processes are those that cannot take place via ordinary classical dynamics. Within the framework of classical S-matrix theory, however, classical mechanics can be analytically continued and classical-limit approximations obtained for these classically forbidden, or weak transition amplitudes (i.e., S-matrix elements). The most powerful and general way of analytically continuing classical mechanics for a complex dynamical system is to integrate the equations of motion themselves through the classically inaccessible regions of phase space. Success in calculating these analytically continued trajectories is reported in this work; with certain special features of these complex-valued trajectories recognized and taken account of, it is seen that they are essentially as easy to deal with numerically as ordinary (i.e., real) classical trajectories. Application to the linear A+BC collision (vibrational excitation) gives excellent results; transition probabilities as small as 10−11 (the smallest ones available for comparison) have been obtained, agreement with the exact quantum mechanical values being within a few percent.
Molecular Orbital Theory of Magnetic Shielding and Magnetic Susceptibility
Authors: Ditchfield R.
Published: February 2004

Hartree-Fock perturbation theory of magnetic susceptibility and magnetic shielding is developed using a basis set of gauge invariant atomic orbitals. The theory is used to calculate magnetic shielding and spin-rotation constants associated with the nuclei in LiH and HF giving results in good agreement with experimental values.
Span of a Polymer Chain
Authors: Rubin Robert J.
Published: February 2004

The x span of a polymer chain is defined as the difference between the largest x coordinate and the smallest x coordinate of any segments in the chain. The polymer chain is represented by a nearest-neighbor lattice-model random walk in which the mean square displacement of each component of a single step is 13. The distribution function of the x span of an N step random walk is obtained; and the following asymptotic formulas are obtained for its first and second moments, respectively, 2(2N/3π)1/2 and 4 ln2 N/3. The corresponding moments of the magnitude of the x component of the end-to-end distance are (2N/3π)1/2 and N/3. Excluded volume effects are not considered. It is noted that the problem of calculating the first moment of the x span is identical with the one-dimensional case of the Dvoretzky-Erdös problem, namely, the calculation of the average number of different lattice sites visited in an N-step random walk on a d-dimensional lattice.
Fine Structure, Dipole Moment, and Perturbation Analysis of a 3Π CO
Authors: Wicke Brian G. , Field Robert W. , Klemperer William
Published: February 2004

Theedio-frequency spectrum of the a 3Π state of carbon monoxide from 5 to 1000 MHz has been measured in a molecular beam electric resonance spectrometer. Lambda doubling transitions in Ω=2, J=2–8, v=0–5 and several in Ω=1 have been measured to an accuracy of 1 kHz as a function of electric field. A simultaneous least squares fit to optical and radio-frequency data on a 3Π determines a set of fine structure constants which reproduce the optical and radio-frequency measurements within their respective experimental errors. The vibrational dependence of the constants which determine the lambda doubling in the a 3Π state is accounted for. v=4 and 5 of a 3Π are perturbed by v=0 and 1 of a′ 3Σ+, respectively. Analysis of the radio-frequency lambda doublings and perturbed optical spectra determines two vibration-independent matrix elements of the Hamiltonian off diagonal in electronic state which describe the a 3Π-a′ 3Σ+ interaction, 〈 a 3Π, v|AL+/2|a′ 3Σ+, v′〉/〈 v|v′〉=0.74± 0.15 cm−1 and 〈 a 3Π, v|BL+|a′ 3Σ+, v′〉/〈 v|B|v′〉=0.154± 0.005 unitless. Extensive Stark effect measurements determine the dependence of the dipole moment of a 3Π on v, J, and Ω. Analysis of the v=4 and 5 Stark effect data determines the transition moment between a 3Π and a′ 3Σ+, 〈 a 3Π | |μ| |a′ 3Σ+〉=0.504± 0.01 D, and the dipole moment of the a′ 3Σ+ state, μ=−1.06± 0.2 D (C−O+).
Luminescence of the Tetrachloroferrate(III) Ion
Authors: Flint C. D. , Greenough P.
Published: February 2004

Excitation of a series of compounds containing the FeCl4− ion with ultraviolet or blue radiation at 85°K gave in each case a broad featureless luminescence band in the near infrared. Analysis of the decay curves obtained by using monochromatic excitation pulses and different observation wavelengths indicates that two emissive processes contribute to the emission. Excitation into a d→ d absorption band produces 4T1(G)→6A1 luminescence, whereas excitation into the low energy tail of the charge transfer absorption gives a second luminescence process, there being little or no tendency for the ion to cross from this luminescent state to the 4T1(G) although the latter is probably the lowest excited state. The FeBr4− ion under similar conditions gives a broad, near infrared luminescence band which also appears to consist of two transitions.
Examination of the Stochastic Process Underlying a Simple Isomerization Reaction
Authors: Keizer Joel
Published: February 2004

A characterization of the concentration fluctuations in the isomerization reaction A+X rightleftarrowsB+X is given based on the Liouville equation for the conditional probability. By separating the relaxation process into four qualitatively distinct time regimes, the approach in time to the birth and death equations of the usual stochastic theory can be followed. It is shown that these equations are approximately solved by a normal distribution which is generated by a modified Langevin-type equation. In this time domain the stochastic process is stationary and Markov and as the fourth time domain is approached the process also becomes Gaussian as predicted by the fluctuating force theory of this reaction. Since the time scale in this last regime is the order of the time constant for the reaction, it is concluded that the fluctuating force theory is valid only near equilibrium.
Van der Waals Forces in Electrolytes
Authors: Davies B. , Ninham B. W.
Published: February 2004

The continuum theory of van der Waals forces due to Lifshitz is extended to include the interaction between media which exhibit spatial as well as frequency dispersion. The case of electrolytes is considered in detail and the generalization of the theory to admit nonuniform equilibrium due to double layers is developed.
Raman Spectrum of Antimony Pentafluoride in the Gaseous Phase as a Function of Temperature. Evidence for a Trigonal Bipyramidal Shape for the Monomeric Species
Authors: Alexander Lesley E. , Beattie I. R.
Published: February 2004

The gas phase Raman spectrum of antimony pentafluoride as a function of temperature shows clearly the dissociation of a polymeric species. The infrared spectrum of the gas (under conditions where the Raman spectrum shows no evidence for the presence of monomer) is closely similar to that of the liquid. This spectrum is also similar to that found in previous matrix isolation studies when monomer was thought to be present. It is likely that the earlier assignment of a C4v shape to monomeric antimony pentafluoride is erroneous.
Absorption Spectrum of Matrix-Isolated Ca Atoms
Authors: Francis J. E. , Webber S. E.
Published: February 2004

The absorption spectra of Ca atoms isolated in Ar, Kr, and Xe matrices at 16–20°K were obtained from 3000 to 7000 Å. In Kr and Xe matrices an asymmetric triplet was observed which was assigned to the 1P1←1S0 transition. In concentrated Kr: Ca samples new low-energy peaks appear which are assigned to well-defined metal aggregates, probably Ca2. The results for Ar: Ca could not be correlated with the other matrices, and it is suggested that atomic isolation was not attained in this matrix.
ESR and Optical Spectroscopy of MnO4 2− in BaSO4
Authors: Kosky C. A. , McGarvey B. R. , Holt S. L.
Published: February 2004

The single crystal electron spin resonance spectra and polarized optical absorption spectra of MnO4 2− in BaSO4 have been recorded at liquid helium temperatures. The ESR data yielded anisotropic g and hyperfine tensors. The single unpaired electron of the d1 configuration was found to be in an essentially dz 2 orbital. The optical spectra taken in the near infrared, visible and ultraviolet regions were interpreted with C2ν symmetry. The crystal field transition e-t2 has been assigned to a weak band at 10 000 cm−1 and charge transfer and vibronic structure have also been interpreted.
Collision Transfer of Vibrational Energy from Highly Excited Polyatomics. Transition Probabilities and Cross Sections for Inefficient Bath Gases
Authors: Georgakakos J. H. , Rabinovitch B. S.
Published: February 2004

Collisional de-excitation of vibrationally excited (∼45 kcal mole−1) 2,4-dimethylpentyl-2* and 2,4-dimethylpentyl-2-d1* alkyl radicals by bath molecules H2 and D2, respectively, was studied in both the ``high'' and ``low'' pressure regions. The behavior with the stronger collider CF4 was also investigated at ``high'' pressures. Both symmetry and unimportance of the endothermic (5ts) isomerization of this radical promoted greater accuracy of experimentation. Comparison of experimental rate behavior with model stochastic computations yields values of 〈 Δ E〉, the average amount of energy transferred per collision, of 1.5, 2.2, and 4.6 kcal mole−1 for H2, D2, and CF4, respectively. Independently of any uncertainty in collision cross sections, the data establish that the preferred forms of the distribution of the transition probabilities pij are exponential (or related type) for weak colliders, and stepladder (or Gaussian-like) for CF4. The data support earlier conclusions that gas kinetic (viscosity)-derived collision cross sections are appropriate for this type of energy transfer process; that inefficient bath gases are not such because of a preponderance of elastic collisions.
Second Moment of Dipolar Interaction for Arbitrary Directions of Magnetic Field and Arbitrary Spin Values in NQR
Authors: Grigolini P.
Published: February 2004

In this paper a theory for the calculation of the second moment for NQR lines with arbitrary direction of the magnetic field is presented. Furthermore the treatment of higher order nth moments is also given. The theory can be applied to determine the shift of the line center produced by dipolar interaction.
Jahn-Teller Distortion of s-Triazine in Its Lowest Excited Singlet State
Authors: Fischer Gad , Small Gerald J.
Published: February 2004

An assignment of the lowest excited singlet state of s-triazine as 1E″, nπ*, is made based on the vapor and polarized crystal absorption spectra of both the perproto and perdeutero isotopes. A theory of vibronic intensities is presented for the case in which one and the same vibrational motion can both derive intensity for a forbidden doubly degenerate state and remove the orbital degeneracy. Spectral results are presented which indicate that s-triazine undergoes a Jahn-Teller distortion in the 1E″ state.
U Band in Cesium Halides
Authors: Singh R. S. , Mitra S. S. , Tanton G. A. , Shatas R. A.
Published: February 2004

The U band shape in CsCl, arising from the first singlet to singlet electronic transition of substitutional H− and D− impurities replacing the anions, has been measured in the temperature range of 8–300°K. At 8.4°K, the absorption peak and half width for the H− center were found to be 5.425± 0.005 and 0.24± 0.005 eV, respectively; while those for the D− center were 5.440± 0.005 and 0.21± 0.005 eV, respectively. Along with the previously obtained data for CsBr and CsI, the U band peak position was found to follow Mollwo-Ivey relation having the exponent of the near-neighbor distance of −1.54. The U band shape in CsCl has been analyzed by the method of moments. The temperature dependence of the half-width can be explained by means of an effective phonon frequency. The single effective phonon frequencies of the U band in CsCl-type crystals were compared with the weighted mean phonon frequencies of the host crystals obtained from a recent lattice-dynamical calculation. Little correlation was noted.
Hyperfine Spectra of 7Li35Cl and 7Li37Cl
Authors: Gallagher Thomas F. , Hilborn Robert C. , Ramsey Norman F.
Published: February 2004

Using a newly constructed electric resonance molecular beam apparatus the hyperfine spectra of 7Li35Cl and 7Li37Cl have been measured. At present the most distinctive feature of the apparatus is its 212-m-long C region, allowing linewidths of 300 Hz in this experiment. Some of the details of the design and operation of the apparatus are presented. The spectra were measured in zero magnetic and low electric fields with the results listed below.

Lithium chloride hyperfine constants in kilohertz 7Li35Clν =0ν=1ν=2ν=3eqQCl−3059.51(15)−3442.1(9)−3808(7)−4175(7)eqQLi249.93(50)244.6(20)237(10)225(10)cCl1.946(20)1.98(7)cLi0.956(3)0.92(9)c30.511(20)0.55(6)c40.025(20)0.03(6)7Li37CleqQCl−2410.9(6)−2711(7)eqQLi250.0(10)250(10)cCl1.66(5)cLi1.03(6)c30.42(4)c40.02(3)
Vibronic Interactions in Doubly Degenerate Electronic States
Authors: Sloane C. S. , Silbey R.
Published: February 2004

The effect of more than one pair of degenerate vibrational modes on the energy levels and spectrum of a doubly degenerate electronic state is discussed. The dynamic Jahn-Teller effect for this case is treated by exact numerical methods and by approximation schemes. The effect of quadratic terms in the vibrational coordinates is also treated by these methods. The use of adiabatic surfaces in treating these problems is critically examined.
ESR Spectroscopy and Chemical Bonding in CdCN and HgCN Molecules
Authors: Knight Lon B. , Lin K. C.
Published: February 2004

The radical molecules CdCN and HgCN were trapped in rare gas matrices at 4°K and investigated via ESR spectroscopy. The g tensors and hyperfine structure constants (hfs) for interaction with 111Cd, 113Cd, 199Hg, and 201Hg were determined. These measurements indicate that CdCN and HgCN have 2Σ ground electronic states and predict the presence of 2IIr excited states near 2700 Å. The ionicity of these molecules are discussed based on an (ns)2S M+ limiting model and compared with previous results obtained for the more covalent CdH and HgH molecules.
On a Study of Spin-Lattice Relaxation Times of 19F, 31P, 1H, and 2H in Solutions of PF6− and PO3F2− in D2O and H2O
Authors: Froix Michael F. , Price Elton
Published: February 2004

The spin-lattice relaxation times of fluorine, phosphorus, protons, and deuterons in solutions of sodium hexafluorophosphate and sodium monofluorophosphate in water and deuterium oxide have been measured at 25 MHz by pulsed techniques over the temperature range 250–363°K. The fluorine and phosphorus spin-lattice relaxation times in both salt solutions have been found to be the sum of interactions due to spin-rotation and dipole-dipole contributions. The spin-rotation constants for fluorine and phosphorus in PF6− are 3.56 and 3.86 kHz, respectively. The spin-rotation constants for fluorine and phosphorus in PO3F2− are 23.6 and 21.4 kHz. Spin-rotation constants were also calculated from chemical shielding data. The results for the nearly spherical PF6− anion are in accord with rotation diffusion theory. The 31P relaxation data seem to indicate that the PF6− anion follows the J-diffusion model of McClung whereas the 19F relaxation data indicate that the M-diffusion model is followed. The reorientation correlation times of water and deuterium oxide molecules have also been determined for solutions containing PF6− and PO3F2− ions. These ions seem to affect the correlation times of the H2O and D2O molecules differently.
Laser Excitation and Equilibration of Excited Vibrational States in CH3F
Authors: Weitz Eric , Flynn George , Ronn A. M.
Published: February 2004

CH3F, when its ν3 mode is pumped by the P(20) line of the 9.6-μ band of a CO2 Q-switch laser, exhibits fluorescence from the ν1 and ν4 modes at 3000 cm−1. This fluorescence has a risetime ≤ 5  μsec at 1 torr and a decay rate of 0.59± 0.02 msec−1·torr−1. The diffusion coefficient measured from the low pressure fluorescence decay curves is 0.076± 0.011 cm2·torr msec−1. A very efficient near resonant energy transfer process is probably responsible for propagation of energy up the vibrational manifold. Similar processes may be important for laser induced chemical reactions. A square dependence of the intensity of fluorescence on incident cw laser power has been observed. This appears to arise mainly from population changes caused by a general temperature increase in the gas which occurs after absorption of laser energy and equilibration of all degrees of freedom of the molecule.
Electron Impact Cross Sections for Argon
Authors: Peterson L. R. , Allen J. E.
Published: February 2004

A reasonably complete set of phenomenological discrete and ionization cross sections for argon is given using combinations of data and theoretically meaningful extrapolations of the generalized oscillator strengths. After including estimates of inner-shell cross sections, the degradation of electrons in Ar is considered. Calculations of the final populations for each excited state are given as a function of incident energy and when applied to ionization, results in electron volts per ion pair values near 29 eV. Inner shells in our work appear to contribute by adding on the order of 5% to the loss function at energies above a kilovolt.
Ozone Ultraviolet Photolysis. IV. O2† + O(3P) Vibrational Energy Transfer
Authors: Webster Henry , Bair Edward J.
Published: February 2004

The rate of relaxation of vibrationally excited O2† in high vibrational levels of the X  3Σg− ground state was measured following flash photolysis of O3−Ar mixtures. The relaxation rate is proportional to the O(3P) concentration when the [O(3P)]/[O3] ratio is not small. The data are analyzed assuming that the constants conform to the systematic relationship, kij = k10[1+β(i−1)] exp[−γ(i−j−1)], where i is the initial state and j is the final state with i>j. β determines the dependence on energy level and γ the dependence on multiple quantum transitions. Using k10 = 6 × 108 liter/mole·sec from Kiefer and Lutz, the values β=0.04 and γ=0 best represent the data. That is, the large increase in relaxation rate with energy level is best explained by multiple quantum transitions. With this interpretation the shock-tube studies of Kiefer and Lutz, the trajectory calculations by Brieg, and the results of this study are self-consistent.
Vibrational Energy Transfer Processes in Collisions between Diatomic Molecules
Authors: Kelley J. Daniel
Published: February 2004

Vibrationally inelastic collisions between two diatomic molecules are discussed. The system is represented by two harmonic oscillators, not necessarily identical, coupled by a time-dependent interaction potential. The time-dependent Schrödinger equation for this system is solved by obtaining the time-evolution operator, and expressions for vibrational-vibrational-translational energy transfer probabilities between any initial and final state are obtained. Numerical examples are presented which indicate among other things that multiquantum transitions can be important in vibrational-vibrational energy transfer between vibrationally excited molecules.
Magnetothermodynamics of Antiferromagnetic, Ferroelectric β-Gd2(MoO4)3. III. Heat Capacity, Entropy, Magnetic Moment of the Electrically Polarized Form from 0.4 to 4.2°K with Fields to 90 kG along the b Crystal Axis
Authors: Brodale G. E. , Fisher R. A. , Hornung E. W. , Giauque W. F.
Published: February 2004

The magnetic moment of a 2.49 cm diam spherical single crystal of electrically polarized β-Gd2(MoO4)3 has been measured with fields of 500, 1000, 1500, 2500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G, along the b crystal axis, and over the range 0.3–4.2°K. The approach to saturation was measured at about 0.45°K over the range 35 to 90 kG. The temperature independent susceptibility along the b axis (diamagnetic) was determined as −3.6× 10−4 cm3/mole Gd3+ and the limiting saturation value was found to be 38 805  G· cm3/mole Gd3+, corresponding to gb=1.985=ga=gc. The heat capacity has been measured in fields of 0, 1000, 2500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G over a range from 0.4 to 4.2°K. The heat of vaporization of momentum, h/2π, from the essentially saturated state, was found to be 23.10 and 16.48 cal/mole of h/2π at 90 and 65 kG, respectively. This may be compared with the work of this process, gbβH, which is 23.85 and 17.22 cal/mole of h/2π at these two respective fields. Temperature-field observations on thirty-one isentropes were used to correlate the entropies along the ten isoerstedic heat capacity series. The zero of entropy of the electronic and lattice systems was located at magnetic saturation by means of the heat capacity series at 90 and 65 kG. Smoothed correlated values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment and its isoerstedic temperature coefficient, the differential magnetic susceptibility, and the isothermal work of magnetization, have been tabulated over the range 0–90 kG and 0.4–4.2°K.
Electron Impact Relative Ionization Cross Sections and Fragmentation of U, UO, UO2, and UO3
Authors: Blackburn P. E. , Danielson P. M.
Published: February 2004

Electron impact relative ionization cross sections and fragmentation patterns of U, UO, UO2, and UO3 have been measured using 4–60-V electrons. Because the molecules are extensively fragmented, both total relative ionization cross sections and cross sections for production of parent ions are given. Values are tabulated as a function of ionizing voltage. The total cross sections at 40 V fail to conform to the additivity rule with the cross section of UO3 about half of that for U. Five volts above threshold, the total cross section ratio of UO3 to U is 0.08. Because of UO3 fragmentation, a smaller ratio in terms of parent ions of 0.025 is found. All three oxide molecules are severely fragmented by electron impact. At 40 V 85% of the ions produced from UO3 are fragments. For the U-O system, use of theoretical atomic ionization cross sections and the additivity rule leads to sizeable errors at high voltages and far greater errors at low voltage.
Collisional Quenching and Photochemistry of trans-Glyoxal (3Au) Molecules
Authors: Yardley James T.
Published: February 2004

The time dependence of phosphorescence from gaseous trans-glyoxal 3Au at relatively low pressures excited by a tunable dye laser has been studied in the presence of pure argon and in gas mixtures containing O2, NO, and di-tert-butyl nitroxide. Apparent quenching cross sections for trans-glyoxal 3Au have been measured for these collision partners at 300°K. Some measurements have been carried out with trans-glyoxal-d2. The magnitudes of the cross sections are discussed in terms of possible photochemical or photophysical quenching. A new model, which is consistent with the known photochemistry and with the quenching rates measured here, is proposed for the photodecomposition of trans-glyoxal 3Au to form CO.
Electron Spin Resonance Spectra of ClCO and ClOO
Authors: Adrian Frank J. , Cochran Edward L. , Bowers Vernon A.
Published: February 2004

We have observed the electron spin resonance (ESR) spectra of ClCO and ClOO trapped in polycrystalline CO and Ar, respectively, at 4°K. The radicals were prepared by reaction of a Cl atom, produced by photolytic decomposition of Cl2, with CO and O2. The ESR spectra of these radicals are complicated by, among other things, the Cl nuclear quadrupole interaction. For ClCO the g factor tensor is gz = 1.9980, gx = 2.0061, gy = 2.0003; the hyperfine splitting (hfs) tensor is Az = 227, Ax = 58, Ay = 50 MHz; and the nuclear quadrupole coupling constants are e2Qq = 76 MHz and η = 0.25. For ClOO these spin Hamiltonian parameters are: gz = 2.0100, gx = 1.9987, gy = 1.9915  ; | Az | = 50, | Ax | = 9, | Ay | = 16 MHz; and e2Qq = 105 MHz. The z principal axis is along the Cl bond, and the x principal axis is perpendicular to the molecular plane. The signs of the hfs tensor components of ClCO were assigned in accordance with previous results for FCO. This assignment led to a value of 0.42 for the unpaired electron density in the Cl 3p orbital of ClCO.
Theory of Optical Rotation by Helical Polymers
Authors: Philpott Michael R.
Published: February 2004

The theory of the optical rotation of infinite single-stranded helical polymers is developed using the multipole Hamiltonian and the exciton approximation. The optical rotation formulas are obtained without using any sum rules. Contributions to the optical rotation from electric dipoles, magnetic dipoles, and electric quadrupoles of the monomers are considered explicitly.
Electric Dipole Moment of Diatomic Molecules by Configuration Interaction. III. Open-Shell Molecules CO a3II and CS A 1II
Authors: Green Sheldon
Published: February 2004

The CI technique developed for closed-shell molecules is extended to open-shell cases, retaining a 200 configuration limit, but including higher-than-double excitations and employing the iteration to natural orbitals as suggested by Bender and Davidson. For CO the effect of different initial molecular orbitals and different Slater-type basis sets is examined. For CO a3II, the Hartree—Fock, CI, and experimental dipole moments (in debye) are 2.30, 1.55, and 1.38, respectively. The remaining error in the CI value is attributed more to inadequacies in the Slater-type basis used than to the CI technique. For CS A1II the CI dipole moment of 0.63-D C−S+ is in excellent agreement with the experimental value of 0.63 ± 0.04 D; the Hartree—Fock value is 0.09 D in the wrong direction.
Classical Limit of Fredholm Theory for Elastic and Inelastic Scattering; Inability of Phase Space Integrals to Describe Inelastic Transitions
Authors: Miller William H.
Published: February 2004

Using a classical phase space integral to approximate certain quantum mechanical operations, the classical limit of the Fredholm determinant for a general multichannel scattering system is derived. This statistical form of the classical limit of scattering is found to give exactly the same ``classical S matrix'' for the case of potential scattering as does a dynamical treatment of the classical limit. For inelastic scattering, however, the classical S matrix which results from this Fredholm determinant is only an approximation to that obtained by exact classical dynamics. Reasons for this failure of the statistical version of the classical limit for inelastic scattering are discussed.
EPR Studies of Copper-Doped L-Alanine Crystals: Ultraviolet-Induced Conversion in Cu2+ Complexes
Authors: Fujimoto M. , Tomkiewicz Y.
Published: February 2004

Copper-doped L-alanine crystals exhibit an absorption band in the ultraviolet region. EPR observations indicate that as a result of this uv absorption, multiple conversion takes place in the Cu2+ complexes. In addition to the complexes originally formed by the impurity ions, two others were identified during uv irradiation at 77°K. These were distinguished by their tensor parameters and thermal stabilities, as well as an absence of ligand nitrogen hyperfine structures. The EPR spectra also indicated the formation of free radicals which, however, were not positively identified. On increasing the temperature, these underwent an irreversible transformation accompanied by the formation of yet another copper complex showing a quintet ligand hyperfine structure of 1:2:3:2:1 intensity ratio.
Theoretical Studies of the Binding Energy and Geometry of the H5+ Molecular Ion
Authors: Huang Jan-Tsyu J. , Schwartz Maurice E. , Pfeiffer Gary V.
Published: February 2004

The geometry and binding energy of the H5+ molecular ion have been examined by two different ab initio quantum mechanical variational methods. In the first a CI wavefunction was made from the 10 covalent valence-bond structures which could be constructed from 1s orbitals at the nuclei, each 1s orbital being represented by a five-term Gaussian expansion and having a variable scale factor. For geometries identical or similar to the D2d geometry previously predicted from analogous calculations with cruder basis sets, we found no stability with respect to H3++H2. Other geometries were examined, especially those arising naturally from the approach of H3+ and H2; however, binding was never greater than a tiny 0.6 kcal/mole. We thus concluded that the method had failed adequately to describe H5+, as it had for H3+, and that it is probably unreliable for studying ions with small binding energies. The second method used the SCF MO model with a flexible basis set to account for distortion and polarization. This gave an H5+ geometry corresponding to an H3+...H2 complex of over-all C2v symmetry, in which the H2 sits about 3 a.u. from the H3+ apex and perpendicular to the H3+ plane and to a line extending from the midpoint of the base of the H3+, through the H3+ apex, and through the H2 midpoint. The calculated binding energy relative to H3++H2 is 4.25 kcal/mole. Because formation of such a loose molecular complex from two closed-shell systems should produce very little extra correlation energy in the complex, and because of basis set reasons discussed in the text, these results are believed to be reliable.
Vibrational Spectra of Ammonium and Other Scheelite-Type Perrhenates
Authors: Johnson Richard A. , Rogers Max T. , Leroi George E.
Published: February 2004

The far-infrared and laser-excited Raman spectra of several scheelite-type perrhenates have been recorded at 77°K and room temperature in order to obtain frequencies and symmetry assignments for the lattice modes. Both NH4ReO4 and ND4ReO4 were studied to separate ammonium-ion translations and librations. At 77°K the ammonium-ion librational mode is observed at 264 cm−1 in NH4ReO4 and 194 cm−1 in ND4ReO4. Upon warming to 300°K, the ammonium-ion librational mode disappears and is unobservable in both the far-ir and Raman spectra. The Raman-active ammonium-ion fundamental modes have also been observed in both NH4ReO4 and ND4ReO4. The temperature-dependent changes in the intensities and linewidths of the ammonium-ion fundamentals and lattice modes indicate that the ammonium-ion motion undergoes a change between 77 and 300°K.
Triplet-Triplet Spectroscopy of Polyacenes
Authors: Meyer Y. H. , Astier R. , Leclercq J. M.
Published: February 2004

Complete triplet—triplet absorption spectra (2000–10000 Å) were measured in alcoholic solution at 113°K with naphthalene, anthracene, tetracene, and a few methylated derivatives. Several new bands were observed. Calculations of the higher ππ* triplet states energies with the LCAO—MO—SCF Pariser—Parr—Pople method were improved by the use of large configuration interactions. These include many doubly excited configurations with respect to both the ground singlet state S0 and the lowest triplet state T1, thanks to the systematic use of all monoexcitations with respect to S0 plus all monoexcitations with respect to T1. The comparison of all experimental and theoretical results for the three polyacenes allows one to modify a few previous assignments and to give a general tentative assignment for all observed transitions.
Thermal Diffusion of I2 in the Noble Gases
Authors: Edelstein S. A. , Gedeon A. , Davidovits P.
Published: February 2004

The thermal diffusion factors for I2 in He, Ne, Ar, Kr, and Xe have been measured using a two-bulb apparatus. The iodine noble-gas mixture is contained in a closed system the two ends of which are maintained at different temperatures. The I2 density at the cold end is determined by the equilibrium vapor pressure above a temperature-controlled reservoir of solid iodine. The I2 density at the hotter end is obtained by measuring the reaction rate of cesium and thallium atoms with I2. Since the cross sections for the Cs—I2 and Tl—I2 reactions are known, the I2 density in this region can be obtained. The thermal diffusion factors computed from the transport equations are in good agreement with the Kihara approximation to the Chapman—Enskog theory.
Absolute Generalized Oscillator Strengths for Three Transitions in the Mercury Spectrum
Authors: Skerbele Ausma , Lassettre Edwin N.
Published: February 2004

Generalized oscillator strengths have been measured for the 61S0→63P1, 61S0→ 6p′3 P1, and 61S0→ 7p′1 P1 transitions in mercury at 500−eV electron kinetic energy and scattering angles θ = 2° − 7°. These measurements have been put on an absolute basis using previously determined generalized oscillator strengths [J. Chem. Phys. 52, 2708 (1970)] for the 61S0→61P1 transition. These experimental data have been extrapolated to (Δ P)2=0 to obtain the following limiting oscillator strengths: 61S0→63P1, f0 = 0.0285 ± 0.0035 ; 61S0→ 6p′3 P1, f0 = 0.704 ± 0.070 ; 61S0→ 7p′1 P1, f0 = 0.067 ± 0.009.
Theory of Optical Anisotropy of Chain Molecules
Authors: Flory Paul J.
Published: February 2004

The mean-square optical anisotropy 〈γ2〉=32 trace 〈 ∩α∩α 〉, where ∩α is the anisotropic part of the optical polarizability tensor and 〈    〉 denotes the average over all configurations of the chain molecule, is treated according to the revised matrix multiplication method. Simplifications appropriate for symmetric chains permit condensation of the generator matrix to 14 × 14 order in the case of a threefold rotational potential.