bluuebunny/crossref_metadata_2025 huggingface dataset:
Depolarization ratio studies on liquid water
Authors: Cunningham K. , Lyons P. A.
Published: February 2004

Accurate laser Raman band shapes and depolarization ratios have been obtained for the stretching bands of H2O and D2O between 0 and 100°C. The depolarized band shapes differ from those previously measured using mercury arc instruments in that the low frequency maxima of H2O (3259 cm−1) and D2O (2380 cm−1) are more pronounced, especially in D2O at temperatures close to the melting point. The depolarization ratio spectra display approximately temperature-invariant behavior at 3230 and 3630 cm−1 for H2O and at 2300 and 2670 cm−1 for D2O; depolarization ratios at the extreme high and low frequency band edges are increasing functions of temperature and those in the middle are decreasing functions of temperature. The depolarization ratio spectra have an over-all sigmoidal shape. These results have been interpreted in terms of a simple model which contains elements of the continuum approach of Schiffer and Hornig and the mixture model of Walrafen.
Raman intensities of the uncoupled OD oscillators in liquid water
Authors: Mundy W. C. , Gutierrez L. , Spedding F. H.
Published: February 2004

Raman data were obtained for both polarizations of the OD stretching vibration of HDO in solutions containing different amounts of D2O(1–10 mole%) in H2O in order to assess the extent to which interand intramolecular couplings might perturb the OD stretching vibrations of HDO. The results were extrapolated to infinite dilution and the extrapolations are presented as the relative molar intensities for the uncoupled OD vibrations in liquid water. As the amount of D2O in each solution was increased noticeable, regular shifts in the frequency of the peak intensities and the bandwidths of the OD spectral band were observed. Although these shifts are small, apparently the presence of D2O and the effects due to coupled OD oscillators still make measurable perturbations to the OD vibrations for solutions containing as little as 1 mole% D2O. Consistent depolarization ratios were also obtained which clearly demonstrate that the value of this ratio is not constant across the OD stretching region. In addition functional fits to the spectral band data were made and their results are presented.
Intermolecular potential and width of pressure broadened spectral lines. IV. Influence of the nonrigidity of the molecules; diatomic molecules case
Authors: Giraud M. , Robert D. , Galatry L.
Published: February 2004

The influence of the nonrigidity of two colliding molecules on the infrared linewidths of the absorbing one is studied for the same rotational transition in various vibrational bands. For monatomic perturbers (Ar, Xe, Kr), the isotropic part of the potential energy is the main broadening mechanism in the vibrational bands of HCl and describes the large observed variation from the 0–0 to 0–2 vibrational bands. On the other hand, for couples of diatomics (HCl–HCl and CO–N2), the long range of the electrostatic contribution to the potential prevents the previous effect from occurring, and hence, less important variations appear for the calculated linewidth from one vibrational band to another. This is in agreement with the experimental results. Moreover, in this case further investigation displays another effect for the first few rotational lines due to the influence of the vibration-rotation coupling on the broadening mechanism.
Temperature dependence of deuterium fluoride vibrational relaxation
Authors: Hinchen J. J.
Published: February 2004

Vibrational relaxation times for DF–DF and HF–HF have been measured by laser fluorescence over the temperature range 300–1000 °K. The results coincide with shock tube data above 1000 °K and show temperature dependence for DF relaxation similar to that for HF. Also, DF–HF relaxation times, determined up to 573 °K, were found to reside between the values for DF and HF self-relaxation. Comparisons are made with current theories for vibrational relaxation.
Test of three new corresponding states potentials for Ne, Ar, Kr, and Xe with application to thermal diffusion
Authors: Neufeld P. D. , Aziz R. A.
Published: February 2004

The Barker-Pompe, Barker-Fisher-Watts, and Parson-Siska-Lee potentials for Ar have been studied as universal corresponding states models for Ne, Ar, Kr, and Xe. Optimum values of the scaling parameters ε and Rm have been found by fitting the potentials to second virial and viscosity data. The new models give a better fit to transport properties than the Lennard-Jones (12–6) for all the gases except Ne and are roughly comparable to the 11–6–8. The three new models, as well as the 11–6–8, predict a positive minimum for the thermal diffusion factor αT for all gas mixtures, suggesting that the recently reported positive minimum for Kr–Ar is theoretically reasonable. If this is so, then the negative minima reported for Ar–Ne and other systems contradict the law of corresponding states. Transport properties predicted by the Kr–Ar potential of Parson et al. were found to deviate badly from experiment.
Bending potential of an H2O molecule
Authors: Nee T. W.
Published: February 2004

The effect of small O–H bond vibration on the bending potential of an H2O molecule is derived. It changes the equilibrium bending angle and is experimentally observable.
Dipole moment of water from Stark measurements of H2O, HDO, and D2O
Authors: Clough Shepard A. , Beers Yardley , Klein Gerald P. , Rothman Laurence S.
Published: February 2004

The equilibrium dipole moment of the water molecule has been determined from Stark effect measurements on two H2O, one D2O, and six HDO rotational transitions. The variation of the dipole moment projection operator with rotational state is taken into account and expressions are given for this operator evaluated in the ground vibrational states of the three isotopes. The value obtained for the equilibrium dipole moment is |0μx| = 1.8473 ± 0.0010 D. The effective dipole moments in the principal axis energy representation are |μb (HOH)| = 1.8546 ± 0.0006 D, |μb (DOD)| = 1.8558 ± 0.0021 D and |μb (DOH)| = 1.7318 ± 0.0009 D, |μa (DOH)| = 0.6567 ± 0.0004 D.
Observations on hot bands in the molecular and dissociative photoionization of acetylene and the heat of formation of the ethynyl ion
Authors: Dibeler Vernon H. , Walker James A. , McCulloh K. E.
Published: February 2004

Photoion yield curves in the vicinity of threshold are obtained for the molecular and the ethynyl ions of acetylene and acetylene-d2 at ion source temperatures of 360, 298, and 130 °K. Weak ionization below the adiabatic threshold for C2H2+ and C2D2+ is ascribed to the ionization of molecules excited by one quantum of the bending vibrations, ν4 and ν5. Consideration of selection rules suggests a change in symmetry from the linear ground state molecule to a bent gound state ion. The 0 °K curves for C2H+ and C2D+ are estimated from the observed 130 °K data. Satisfactory agreement is obtained when the 298 °K data are compared with a curve calculated from the 0 °K curve by convolution with vibrational and rotational distributions. The 0 °K thresholds corrected for kinetic energy are used to calculate Δ H f0°(C2H+)=17.47 ± 0.01 eV (402.8 ± 0.2 kcal mol−1) and ΔH f °0(C2D+) = 17.43 ± 0.02 eV (402.0 ± 0.5 kcal mol−1). The ionization energy of the ethynyl radical is estimated to be 11.96 ± 0.05 eV.
Determination of the structure of ArHCl
Authors: Novick Stewart E. , Davies Paul , Harris Stephen J. , Klemperer William
Published: February 2004

The radio frequency and microwave spectra of K = 0 states of ArHCl and ArDCl have been measured by molecular beam electric resonance spectroscopy. The rotational and hyperfine structure constants for the lowest vibrational state of the four isotopic species are ArH35 ClArD35 ClB̄ = (B+C)/2 = 1.678511 (5)GHzB̄ − 2DJ = 1.657596 (10)GHzDJ=20.33 (20)kHz(eqQ)aC1 = −36.250 (20)MHz(eqQ)a=−23.027(10)MHz(eqQ)aD = +102.3 (50)kHzμa=0.81144(10)Dμa=1.00355(70)DArH37 ClArD37 ClB̄ − 2DJ = 1.631566 (5)GHzB̄ − 2DJ = 1.611876 (10)GHzOnly the lowest vibrational state has been observed. The molecule is extremely nonrigid. The average Ar–Cl distance is 4.006 Å in ArHCl and 4.025 Å in ArDCl. The Ar–Cl–H angle is acute and the amplitude of the zero point angle bending is extremely large. The average Ar–Cl–H angle is near 45°, while the average Ar–Cl–D angle is near 34°. The vibrational frequency of Ar–HCl bond stretching is computed to be 32.2 cm−1 from the observed centrifugal distortion constant.
Infrared spectrum, structure, and properties of the O2–Ar van der Waals molecule
Authors: Henderson Giles , Ewing George E.
Published: February 2004

The infrared spectrum of a gaseous mixture of oxygen and argon at 93 °K reveals descrete features which are attributed to absorption by the O2–Ar van der Waals molecule. The spectrum occurs near the infrared inactive vibration of O2. One band, ν1, corresponds to the stretching frequency of O2 within O2–Ar. An analysis of the P and R envelope of this band provides an approximate intermolecular distance for O2–Ar of Re = 3.5 Å. Other absorption features extend as much as 50 cm−1 to the high and low frequency of the ν1 fundamental. These features are assigned as libration or hindered rotation of O2 within the van der Waals molecule in combination with the ν1 fundamental. A model is developed to account for these rotatory energy levels in which the anisotropic intermolecular interaction in O2–Ar is approximated by a simple sinosoidal potential. The internal rotatory energy levels are then obtained from a quantum mechanical calculation. Using this model the infrared data are shown to be consistent with an angular interaction which favors a ``T'' orientation with a barrier to internal rotation of 30 cm−1 (85 cal/mole). Thus a picture of O2–Ar emerges in which molecules with rotatory energy less than the barrier height undergo librational motion and will appear semirigid or ``locked'' into a ``T'' configuration. van der Waals molecules with rotatory energies greater than the barrier height will undergo hindered internal rotation. This study, in addition to other recent work, indicates the power of spectroscopy to provide a mapping of intermolecular interactions of small molecules.
Low-frequency molecular vibrations in solid n -paraffins by neutron inelastic scattering: n -Pentane, n -hexane, n -heptane, and n -octane
Authors: Logan Kenneth W. , Danner Horace R. , Gault John D. , Kim Hyunyong
Published: February 2004

The torsional and skeletal bending fundamentals in solid n -pentane, n -hexane, n -heptane, and n -octane are measured by the method of cold neutron inelastic scattering. For this series of n -paraffins, the maximum frequencies of the skeletal torsion and skeletal bending modes approach 190 and 500 cm−1, respectively, in agreement with previous measurements on polyethylene. The average frequency of the two end-methyl torsions is found to be 240 cm−1. A normal coordinate analysis, performed using only intramolecular valence force fields for each molecule, is used as a guide in spectral assignments. These results are compared to theoretical dispersion curves of polyethylene, with and without intermolecular forces. Chain-end effects appear to be of little significance for these low-frequency modes, even in chain lengths as short as seven or eight carbons.
Pulse radiolysis of liquids at high pressures. IV. Hydrogen-atom reactions in aqueous 0.1M HClO4 solutions
Authors: Farhataziz  , Mihalcea Ion , Sharp Louis J. , Hentz Robert R.
Published: February 2004

Absorption spectra were determined for various times after a 10-nsec radiation pulse to 0.1M HClO4 solutions containing AgClO4 with and without tert-butyl alcohol (TBA). The spectra and their time dependence, which show the same features at 1 atm and 6.6 kbar, are interpreted in terms of the following reactions: H + Ag+ → H+ + Ag [2], OH + Ag+ → OH− + Ag2+ [5], Ag + Ag+ → Ag2+ [6]. Scavenging of OH by TBA prevents formation of Ag2+ which has an absorption peak near 270 nm. For solutions containing TBA, a 60-nsec spectrum with a peak at 370 nm is assigned to Ag and a 7-μsec spectrum with a peak at 310 nm and shoulder at 260 nm is assigned to Ag2+. Growth and decay of Ag absorption at 410 nm were studied with solutions containing TBA at 29 °C and six pressures in the range 1 atm–6.7 kbar; the reactions of H with glycerol and ethylene glycol were studied by their competition with Reaction [2] in solutions also containing glycerol or ethylene glycol. The results give atmospheric-pressure specific rates of 2.8 × 1010, 3.8 × 107, and 1.9 × 107M−1·sec−1 and pressure-independent activation volumes of 1.7, − 5.0, and − 4.2 ml mol−1 for the reactions of H with Ag+, glycerol, and ethylene glycol, respectively. Results of this study and a previous γ-radiolysis study are combined to give best values of (1) ΔV‡ = 2 ml mol−1 for the diffusion-controlled reactions of H with Ag+ and O2 and (2) ΔV‡ = − 5 ml mol−1 for each of 15 presently studied reactions of H not controlled by diffusion. From such results it is concluded that (1) diffusion of H is governed in some manner by the viscosity of water and (2) V̄ (H) = 5 ml mol−1 and is incompressible.
Reaction of BF3 with NH3: Microwave spectrum of BF2NH2
Authors: Lovas Frank J. , Johnson Donald R.
Published: February 2004

Microwave spectra assignable to gas phase aminodifluoroborane (BF2NH2) have been detected in the reaction of BF3 with NH3. A centrifugal distortion analysis has been carried out on the species 11BF2 14NH2 and 10BF2 14NH2. Distortion corrected rotational constants have also been obtained for 11BF2 15NH2, 10BF2 15NH2, 11BF2 14ND2, and 10BF2 14ND2. The molecule has been found to be planar with the following geometry: rB–F = 1.325(12) A, rB–N = 1.402(24) Å, rN–H = 1.0029(18) Å, ∠FBF=117.9(17)° and ∠HNH=116.94(30)°. The observed dipole moment of BF2NH2 is μ=2.595(30) D.
Reorientation cross sections for molecular hydrogen
Authors: McCourt F. R. , Moraal H.
Published: February 2004

Previous expressions for reorientation cross sections based on the assumption of a pure-P2 potential are extended to include the second dominant intermolecular term, that of the quadrupole-quadrupole interaction. One particular result is that the semiempirical method of analysis previously developed is essentially unaffected by the inclusion of the quadrupole-quadrupole interaction. Explicit expressions are given which show how the cross section depends upon the two above-mentioned interactions.
Electron ranges in liquid alkenes, dienes, and alkynes: Range distribution function in hydrocarbons
Authors: Dodelet J.-P. , Shinsaka K. , Kortsch U. , Freeman G. R.
Published: February 2004

Free ion yields have been measured as functions of temperature T and electric field strength E in hydrocarbon liquids. A range distribution of the secondary electrons in hydrocarbons, suitable for use in the one-ion-pair-per-spur model, is F(y)=(4y2/π1/2bGP3)exp(−y2/bGP2), y<2.4 bGP;F(y)=(4y2/π1/2bGP3)exp(−y2/bGP2)+0.5(bGP2/y3), y>2.4 bGP;where F(y)dy is the fraction of thermalized electron-ion pairs that have initial separation distances between y and y+dy, and bGP is the dispersion parameter. This equation is suitable for all of the liquids that have been studied thus far, at all values of T and E that have been used. The value of bGPd for a given liquid is independent of T, where d is the liquid density. The density-normalized ranges in a family of hydrocarbons with the same number of carbon atoms and analogous carbon skeletons decrease in the order alkane>alkene-1>alkyne-1. Two terminal double bonds are more effective than one terminal triple bond in reducing the electron range. Conjugation of the double bonds appears to have no special influence on electron de-energization. The range in a trans-alkene-2 is essentially the same as that in the corresponding alkene-1, but otherwise, internal double bonds are less effective than terminal double bonds in de-energizing the electrons. Ranges in cis-alkenes are greater than those in the corresponding trans-alkenes. Increasing the amount of chain branching in a family of alkanes or alkenes increases the electron range. An internal triple bond increases the range over that in an alkane.
Raman scattering by the hydroxyl ion in sodium chloride
Authors: Peascoe Judith G. , Klein Miles V.
Published: February 2004

We have measured Raman scattering from OH− ions in several NaCl:OH− crystals at low frequency shifts and in the O–H stretching region. The best results were obtained with an impurity concentration of 170 ppm. At low temperatures and frequencies we have observed an A1g-Eg ``tunneling'' transition at 3.2 cm−1, plus other Eg and T2g lines, but no A1g lines. In the stretching region there is a set of resolved lines that show a complicated temperature dependence merging into broad T2g and E bands at temperatures higher than 28 K. To develop a consistent explanation for these Raman data and for previous infrared data, we adopted a model due to Keller and Kneubühl. We assigned many of the transitions to the motion of the displaced center of mass of the OH− ion, with the O–H bond direction following adiabatically. The problem then reduces to that considered by Devonshire. The fitted values for the Devonshire potential parameter K were 16 and 7.5 cm−1 for ground and excited stretching states, and the moments of inertia were 13 and 16 amu · Å2, respectively. The experimental Raman cross sections were compared with those calculated using wavefunctions valid in 2 limits; tight-well tunneling and free rotor. The experimental situation represents an intermediate case. The comparisons yielded values for the anisotropic part of the polarizability tensor, its derivative with respect to the stretching coordinate, and the derivative of the trace of the polarizability tensor. The broad, depolarized higher temperature bands could be understood semiquantitatively by assuming that the nearly free rotational states are strongly affected by ``collisions'' with phonons, collisions that are not frequent enough to cause true rotational diffusion. The A1g stretching line showed collisional narrowing. We applied a theory that assumed the unnarrowed line shape would be caused by a difference between the rotation constants for ground and excited stretching states. The theory yielded estimates of the rotational correlation time that imply a mean angle of turn between collisions of about 1 rad.
Temperature dependence of the intramolecular kinetic isotope effect in the reaction system Cl + HD
Authors: Yaakov Y. Bar , Persky A. , Klein F. S.
Published: February 2004

The relative rates of the two competing isotopic reactions, (1) Cl + HD → HCl + D and (2) Cl + DH → DCl + H were measured as a function of reaction temperature in the range of 297–443 °K. The ratio of rates can be expressed as an Arrhenius type equation; k1/k2 = (0.81 ± 0.04) × exp[(460 ± 50)/RT]. The very fast reaction of the hydrogen atoms formed with residual molecular chlorine, which under conventional experimental conditions would mask any isotope effect, was eliminated by adding NO2 as an efficient hydrogen atom scavenger to the stream of reactants in a fast flow reactor.
Dielectric properties of hydrogen halides. IV. Ferroelectric behavior in HBr
Authors: Cichanowski S. W. , Cole R. H.
Published: February 2004

Ferroelectric properties of HBr in its low temperature solid phase have been studied by superposition of small signal ac and biasing dc fields in a special cell. The low frequency dispersion can be drastically changed by bias fields and thermal history and is attributed to dipole reorientations at domain boundaries, while the much smaller and faster (by a factor 104) high frequency dispersion is unchanged in amplitude and is attributed to dipole reorientations within domain regions. No evidence was found for low frequency dispersion or hysteresis in the low temperature phase of solid HI, and it is concluded that HI is not ferroelectric.
Direct analytical calculation of first-order density matrix elements through third order
Authors: Simons Jack
Published: February 2004

A theory which permits the analytical calculation of atomic and molecular first-order density matrices in a computationally tractable manner is developed. Contour integral techniques are used to derive an equation relating the first-order density matrix γ to certain eigenvectors which arise in our earlier theory of molecular ionization potentials and electron affinities. By analytically evaluating the resulting contour integral, we obtain a closed expression giving γ in terms of Hartree-Fock orbital energies and two-electron integrals.
Phase transition in crystalline pyrazine. Infrared and Raman spectra
Authors: Sbrana G. , Schettino V. , Righini R.
Published: February 2004

The phase transition of crystalline pyrazine-d0 and -d4 has been investigated by means of the infrared and Raman spectra at various temperatures. The spectra of the low temperature phase (form II) are consistent with x-ray structure. Inferences on the unknown structure of the high temperature phase (form I) are given, and arguments in favor of an orthorhombic or monoclinic structure are discussed. The complex pattern of several bands is described and attributed to interaction with combination levels.
Magnetic properties of high purity yttrium, lanthanum, and lutetium and the effects of impurities on these properties
Authors: Spedding F. H. , Croat J. J.
Published: February 2004

Magnetic susceptibility measurements have been carried out on single and polycrystalline specimens of lutetium between 1.5 and 300 °K by the Faraday method. Its susceptibility was found to be paramagnetic and almost independent of temperature. A broad maximum centered at approximately 120 °K was found. Due to the discrepancies in past results of yttrium and lanthanum, their susceptibilities were also measured. Yttrium and lutetium were found to have χa greater than χc. Provided the specimens were of high purity, the relationship χpoly = (2/3)χa + (1/3)χ was well obeyed. Oxygen and hydrogen were found in general to lower the susceptibilities of these metals. The presence of an fcc phase in lanthanum was found to increase its susceptibility relative to a dhcp phase. An estimate of the susceptibility of pure fcc lanthanum is given.
Combining rules for intermolecular potential parameters. II. Rules for the Lennard-Jones (12–6) potential and the Morse potential
Authors: Kong Chang Lyoul
Published: February 2004

A new set of combining rules for intermolecular pair potentials of simple molecules has been formulated based on an atomic distortion model for the repulsive interactions and a geometric mean relationship for the attractive interactions. The rules are shown to be satisfactory in correlating the pair interactions of noble gas atoms when the effective pair interactions are represented by simple analytical potential functions such as the Lennard-Jones (12–6) potential and the Morse potential.
On the calculation of natural orbitals by perturbation theory
Authors: Hay P. Jeffrey
Published: February 2004

Natural orbitals are calculated by the application of perturbation theory without the use of many-body techniques. They are obtained by diagonalization of a one-electron density matrix, the elements of which are approximated by perturbation theory using the Bk method. Calculations on the H2O and O2 molecules demonstrate that these approximate NO's do not differ significantly from the exact NO's and that these NO's may be used to reduce the amount of effort in a configuration interaction calculation. Comparisons are also made with the iterative natural orbital approach.
Stability of HeH3+
Authors: Poshusta R. D. , Agrawal V. P.
Published: February 2004

The stability of HeH3+ is examined using a basis of polarized Gaussian orbitals and four VBCI wavefunctions containing varying amounts of ionic, convalent, and correlation effects. The results indicate that HeH3+ is stable by about 100 cm−1 with respect to He and H3+. A previous SCF calculation yields the same prediction, although a previous CI calculation appeared to show HeH3+ to be unstable. Equilibrium geometry and vibrational frequencies of this ion are estimated. Mass spectrometric experiments below 140 °K are recommended to prove the stability of this ion.
ITFITS model for vibration-translation energy partitioning in atom-polyatomic molecule collisions
Authors: Shobatake K. , Rice Stuart A. , Lee Yuan T.
Published: February 2004

A model for vibration-translation energy partitioning in the collinear collision of an atom and an axially symmetric polyatomic molecule is proposed. The model is based on an extension of the ideas of Mahan and Heidrich, Wilson, and Rapp. Comparison of energy transfers computed from classical trajectory calculations and the model proposed indicate good agreement when the mass of the free atom is small relative to the mass of the bound atom it strikes. The agreement is less satisfactory when that mass ratio becomes large.
Molecular reorientation in plastic crystals: Infrared and Raman band shape analysis of neopentane
Authors: Livingston R. C. , Rothschild Walter G. , Rush J. J.
Published: February 2004

An infrared and Raman band shape analysis of the broadened 924 cm−1 fundamental for neopentane in its liquid and plastic crystal phases is presented. Correlation functions and times for molecular reorientation derived from both the infrared and Raman data show the liquidlike behavior of the plastic phase of neopentane, with the molecules rotating ``freely'' through ∼ 10° (175 °K) to ∼ 30° (300 °K) around an inertial axis with the corresponding reduced intermolecular torques (1/2/kT) decreasing from 8.2 to 3.8. Futhermore, the linewidth and correlation time results show no indication of a change in rotational behavior in passing through the plastic crystal-liquid phase transition. Theoretical fits of our experimental infrared and Raman correlation function with Gordon's M and J diffusion models, as extended by McClung for spherical molecules, show that the experimental results lie between the functions predicted by these two models. The time between rotational ``collisions'' (angular momentum correlation time) varies continuously from 0.4 × 10−12 sec for the room-temperature liquid to 0.2 × 10−12 sec at the lowest temperature in the plastic phase. Activation energies for molecular reorientation of 4.1 and 3.6 kJ/mol are obtained, respectively, from the experimental half-widths and from the angular momentum correlation times, in good agreement with previous NMR and neutron scattering results. The results prove that neopentane melts in two stages: near 140 °K, the rotational degrees of freedom of the (rigid) molecule are liberated, whereas near 253 °K the translational degrees of freedom are liberated without observable change of the characteristics of the rotational motion.
On the molecular structure of methane sulfonyl chloride as studied by electron diffraction
Authors: Hargittai Magdolna , Hargittai István
Published: February 2004

The molecular structure of methane sulfonyl chloride in the vapors was studied by electron diffraction. Three models were found in excellent agreement with experiment differing largely in the values of the O–S–O angle and the mean amplitudes of vibration for some of the nonbonded distances. The favored model has the following geometrical parameters (with their errors parenthesized): C–H 1.101 (0.013) Å, S–O 1.424 (0.003) Å, S–C 1.763 (0.005) Å, Cl–S 2.046 (0.004) Å, ∠ Cl–S–C 101.0° (1.5°), ∠ O–S–O 120.8° (2.4°), ∠ Cl–S–O 107.1° (0.7°), ∠ H–C–H 112.0° (2.0°). The structure of SO2Cl2, CH3SO2Cl, and (CH3)2SO2 are compared.
Association and the assignment of the OH overtones in hydrogen bonded alcohols
Authors: Bourdéron C. , Sandorfy C.
Published: February 2004

The long-standing problem of the assignment of the first overtone of the OH stretching vibration of hydrogen bonded alcohols is examined for the cases of methanol, ethanol, and tertiary butanol. The spectra of the related deuterated alcohols were measured and isotopic isolation experiments were carried out at temperatures ranging from 25° to − 190°C. Dilute solutions were studied as well as the pure liquids. For the latter the second overtones were also measured. The first OH overtones, although overlapped by CH + OH combination bands were definitely identified and the anharmonicity constants were determined. They show a moderate but appreciable increase with respect to free OH stretching vibrations. Bands due to simultaneous excitation or coupling of two contiguous OH groups bound together by hydrogen bonds are also present.
Velocity of hypersonic waves in liquid oxygen
Authors: Clouter M. J. , Kiefte H.
Published: February 2004

Velocities of hypersonic (3–5 GHz) waves in liquid oxygen have been determined by thermal Brillouin scattering techniques. The incident radiation (λ = 5145 Å) was obtained from a stabilized single-mode argon-ion laser, and the scattered radiation was analyzed at 90° with a piezoelectrically-scanned Fabry-Perot spectrometer. Measurements cover the temperature range from the triple point (54.35°K) to the normal boiling point (90.18°K), and in this range the velocities were observed to decrease linearly with increasing temperature from 1193 to 909 m/sec. These results are compared with ultrasonic (1.2 MHz) velocities as measured by Van Itterbeek and Van Dael at temperatures above 61°K, and no dispersion effects are evident at least up to 3.6 GHz.
On the orbital theories in the spin-correlation problems. II. Unrestricted and spin-extended Hartree-Fock theories
Authors: Nakatsuji Hiroshi
Published: February 2004

A perturbation-variation treatment is applied to interconnect the unrestricted, projected unrestricted, and spin-extended Hartree-Fock wavefunctions with the first order sum-over-state perturbation wavefunction. The restricted Hartree-Fock wavefunction is chosen as a starting point. From these, the interrelations among these theories are clarified not only for the first order correction to the wavefunctions but also for their spin densities. Moreover, the natures of the unrestricted and spin-extended Hartree-Fock theories in the spin-correlation problems are examined in the light of the physical reality of the correlation phenomena in open-shell electronic systems. These results are ascertained numerically by referring the spin densities calculated by these various methods and obtained from experiments.
Conformational statistics of short chains of poly(L-alanine) and poly(glycine) generated by Monte Carlo method and the partition function of chains with constrained ends
Authors: Premilat Samuel , Hermans Jan
Published: February 2004

We have calculated properties of samples of short poly(L-alanine) and poly(glycine) chains generated by Monte Carlo method. We analyzed various distributions and averages of these samples. The average square of the end-to-end distance  and the average end-to-end vector were very close to the values calculated according to the method of Flory. The distribution of  is very different from a Gaussian function for poly(L-alanine) chains of even 20 units, already close to Gaussian for 10 unit poly(glycine) chains. The average fourth power of the end-to-end distance  was compared with that calculated for a Kratky-Porod type wormlike chain, and the agreement was found to be good for all chain lengths, i.e., including those for which the distribution of r2 is decidedly non-Gaussian. The distribution of end-to-end vectors r was found to be approximately cylindrically symmetrical about the average . This distribution shows a pronounced maximum on the axis parallel to . Poly-L-alanine chains with short end-to-end distances are quite rare. By analyzing the distribution of samples in which each chain contains at least one (two, three, four) residue(s) in the ``α-helical'' conformation, it was determined that all chains with very short end-to-end distance have several residues in this conformation. This is confirmed by the observation that the calculated average energy of the chains is several kcal/mole higher at short end-to-end distance. The results are discussed in terms of the ``stiffness'' of these chains, and in terms of the possibility of loop formation. It is found that probabilities of loop formation of short chains calculated on the basis of a Gaussian distribution may be seriously in error. Finally, a new approach is proposed for using Monte Carlo calculations of this type in order to calculate the partition function for looped chains for any fixed relative position-orientation of the first and last unit of the chain (including, of course, true cyclic structures).
Effects of intermacromolecular interactions diffusion. III. Electrophoresis in three-component solutions
Authors: Phillies George D. J.
Published: February 2004

The intensity-intensity correlation function measured in a light-scattering electrophoresis experiment in a three-component solution is composed of a sum of exponentially damped sines and cosines. Its explicit form is calculated for a concentrated three-component solution (including the effects of cross diffusion). A form for the electrophoretic mobility of charged species in a three-component solution in a weak electric field (including the effects of frictional interactions between the Brownian species) is presented. The mutual diffusion coefficient of a species measured in a light-scattering electrophoretic experiment is not unambiguously related to the mutual diffusion coefficient of that same species as measured with conventional light scattering spectroscopy.
Mechanism of fluorescence quenching by acids in N-isopropyl carbazole
Authors: Pfister G. , Williams D. J.
Published: February 2004

The room temperature solution fluorescence spectrum of N-isopropylcarbazole in the presence of bromoacetic acid, maleic acid, picric acid, and trichloroacetic acid and of the electron acceptor trinitrofluorenone was studied as a function of concentration and excitation wavelength. It was found that the acids quench the fluorescence, and that the quenching efficiency is related to the pKa of the acid. It is proposed that quenching by nonaromatic acids involves the protonation of the excited state of the carbazole, and that quenching by acceptor type aromatic acids occurs by excited state electron exchange. The latter mechanism is several orders of magnitude more efficient than the quenching by the protonation reaction. A kinetic model is proposed which accounts for the observed experimental results.
Surface tension and interfacial density profile of fluids near the critical point
Authors: Pressing Jeff , Mayer Joseph E.
Published: February 2004

Presented is a new procedure for the derivation of the density profile ρ(ξ) along the interface between coexisting liquid and gas phases near the critical point. The fundamental equation used is the invariance throughout the fluid of the component of the stress tensor perpendicular to the interface. A general and physically plausible form is suggested for the pair distribution function ρ(2) across the interface, which allows conversion of the fundamental equation to a differential equation which may be solved for the singlet density ρ(ξ). In the limit (ρL − ρG)/ρc ≫ 1, the result reduces to the classical hyperbolic tangent function, but for any T < Tc is fundamentally different. In addition, the equation obtained for ρ(ξ) allows the derivation of several new formulas for surface tension, which reduce to the square-gradient theory result in the limit T → Tc.
Effects of variations in reaction coordinate eigenvalue on heavy-atom kinetic isotope effects: Eigenvectors consisting of one and two nonzero elements
Authors: Kidd Richard W. , Yankwich Peter E.
Published: February 2004

The pentatomic formic acid molecule is used as a model for the survey of the influence on calculated heavy atom kinetic isotope effects of curvature of the potential energy surface (ν1‡ = 0–800i cm−1) along the reaction coordinate at the transition state. Restrictions employed are: invariant geometry and basis diagonal force field; light species reaction coordinate eigenvector consisting of one or two nonzero elements only. The temperature independent factor TIF = (ν1‡/ν1′ ‡) in the rate constant ratio k/k′ generally falls as ν1‡ is increased, but the effect is small. The effect for two-element reaction coordinates of this restricted type is likely the largest such, therefore the influence of barrier curvature on ν1‡/ν1′ ‡ is negligible for practical reaction modeling purposes. The remaining part of k/k′, the temperature dependent factor TDF, arising in isotopic shifts of genuine vibrations, can be strongly affected by barrier curvature. In a few cases, TDF rises slightly as ν1‡ is increased; usually it falls, sometimes so rapidly that the sign of ln(k/k′) is reversed. Since ν1‡ is not an experimental variable, its significance to reaction modeling lies in the fact that graphs of ln(k/k′) vs (1/T) for various reaction coordinates with various ν1‡ do not often intersect at large angles; adjustment of ν1‡ can therefore assist in reducing the redundancy of results of calculations based on a variety of models being compared with experimental results. The barrier curvature and reaction coordinate complexity problem are discussed in terms of the first-order high temperature approximation, ``cut-off procedures,'' and other approaches to the simplification and rationalization of ab initio calculations of kinetic isotope effects.
Line of symmetry for the classical equation of state
Authors: Mulholland George W.
Published: February 2004

The existence and properties of the Widom-Stillinger line of symmetry are examined for the ``classical'' equation of state, that is, an equation of state in which the chemical potential is expressed as a power series in density and temperature. In doing this, the chemical potential is shown to be an analytic function of temperature in the two phase region. This analyticity has been anticipated for a number of years.
Derivation of an integral equation for pair correlation functions in molecular fluids
Authors: Chandler David
Published: February 2004

A new integral equation for equilibrium pair correlation functions in molecular fluids is derived from a systematic functional Taylor expansion. The derivation employs a new Ornstein-Zernike-like equation and a generalization of the functional Taylor expansion techniques frequently employed to derive integral equations for radial distribution functions in simple atomic liquids.
Thermal conductivity of neon, argon, and xenon at high temperatures
Authors: Springer George Ś. , Wingeier Elwood W.
Published: February 2004

Thermal conductivities λ of neon, argon, and xenon were measured at 760 mm Hg in the ranges 1000–1500 °K (neon, xenon) and 1000–2500 °K (argon). The data were correlated by expressions of the form λ = a Tb, where a and b are constants depending upon the gas. The results were compared with (1) existing data, (2) viscosity measurements η, by means of the coefficient f = λ/(2.5ηCv), and (3) values calculated from an extended law of corresponding states. The correlations obtained from the measurements were found to describe well the thermal conductivities of all three gases not only within the temperature ranges of the experiments but also over the range 900–2500 °K.
Lattice dynamics of the pyrazine crystal studied by coherent inelastic neutron scattering
Authors: Reynolds P. A.
Published: February 2004

The lattice vibrational excitations at a number of points in the Brillouin zone for a deuterated pyrazine crystal at room temperature have been measured by means of coherent inelastic scattering of neutrons. These give values for all 9 adiabatic elastic constants, 25 excitations at symmetry points in the Brillouin zone, and dispersion curves in the (0 η0) direction. These have been interpreted in the quasiharmonic, rigid molecules, approximation using an atom-atom 6-exp potential plus electrostatic intermolecular forces. This gives 3 parameters to be fixed. Fitting to the observed excitations gives physically reasonable values for these parameters. The fit obtained is not perfect (χ = 3.4) but good enough [(ωobs − ωcalc)/ωcalc ∼ 7%] to say that this model describes the intermolecular forces in pyrazine well. The C–H ··· N hydrogen bond at long ranges is well described by a 6-exp potential plus an important electrostatic interaction between the N lone-pair electrons and the C–H bond dipole. The asymmetry in the Nitrogen atom electronic distribution does not appear to have any effect on the dynamics other than its electrostatic contribution. It is suggested, from the pattern of the deviations of the dynamics and crystal structure from the model, that the errors in the model derive from neglect of three body atom-atom electronic correlations.
ESR of the quartet states of randomly oriented molecules: Calculation of the line shape and detection of the zero-field splitting
Authors: Brickmann J. , Kothe G.
Published: February 2004

The ESR spectrum of the quartet states of randomly oriented molecules with axial symmetry is discussed. The absorption curves of the Δm = 1, Δm = 2, and Δm = 3 transitions are calculated in first order perturbation approximation. The line broadening is explicitly taken into account. The experimental spectrum of an alternant hydrocarbon agrees sufficiently well with the theoretical predictions. The shape of the absorption curve permits the ready determination of the zero-field parameters of quartet molecules.
Dynamics of the CS2–O2 flame
Authors: Howgate David W. , Barr T. A.
Published: February 2004

The kinetics of the CS2–O2 flame for laser applications is described by a computer program (utilizing 24 contributing reactions) allowing vibrationally excited CO to be created from CS + O. The validity of individual contributing rate coefficients has been established through a comparison with experimental evidence on the oxidation of CS2. [K. H. Homann, G. Krome, and H. Wagner, Ber. Bunsenges. Phys. Chem. 74, 654, (1970); K. H. Homann, G. Krome, and H. Wagner, Ber. Bunsenges. Phys. Chem. 72, 998, (1968); K. H. Homann, G. Krome, and H. Wagner, Ber. Bunsenges. Phys. Chem. 73, 967 (1969)]. Induction time, reaction time, and vibrational energy produced in CO are presented as functions of the initial amount of atomic oxygen so that a comparison can be made between the effects of predissociation, as by an electric discharge, and the formation of atomic oxygen in the chemical chain. The inclusion of simple mixing and heat loss at the boundary in an aerodynamic/thermodynamic mass flow environment has provided a fit with published thermal data [C. Wittig, J. C. Hassler, and P. D. Coleman, J. Chem. Phys. 55, 5524 (1971)] for an operating CS2 – O2 laser. The computer program was used to verify simpler kinetic models for specific cases, for example, a four reaction model: (1) CS2 + O → CS + SO, (2) CS + O → CO + S, (3) S + O2 → SO + O, (4) SO + O2 → SO2 + O to describe the CS2–O2 flame under conditions where a chain reaction is required. Also, the production of vibrationally excited CO at diluent pressures up to 50 torr was found to be adequately described by only Reactions (1)-(3) for input ratios of CS2/O ≃ 1.
Perturbation theories for the calculation of molecular interaction energies. II. Application to H2+
Authors: Chipman Daniel M. , Hirschfelder J. O.
Published: February 2004

The many perturbation expansions reviewed in Paper I [D. M. Chipman, J. D. Bowman, and J. O. Hirschfelder, J. Chem. Phys. 59, 0000 (1973)] are applied to the interaction of a ground state hydrogen atom with a proton to form the 1s σg and 2p σu electronic states of H2+. The calculations were made with high precision for the range of separations R = 0.2–15ao using a large basis set of Slater-type orbitals. For the polarization and symmetrized polarization methods the energies were obtained analytically, these results providing a check on the completeness of the basis set. Also, long range and short range asymptotic formulas are given for the first order wavefunctions and the perturbation energies. The HS and MSMA methods gave the best second order energies. The EL-HAV second order energy is good at intermediate separations but becomes bad at large separations. The expectation value of the Hamiltonian using the wavefunction truncated after the first order (where the coefficient of the zero order function is energy optimized) gave very good results in the OPT, COR, CH, HAV, EL, HS, DEM-I, AM, and SYM-P methods in the order listed; the MSMA and P results were poor due to the use of unsymmetrized wavefunctions. The OPT treatment, which energy optimizes the coefficients of three separate first order functions, has an error of less than 0.04 kcal/mole for the 2p σu state, over the full range of separations, and for the 1s σg state has an error of only 1.4 kcal/mole at the equilibrium separation R = 2ao, becoming much better than this at larger separations. Reasonably good interaction energies can be calculated from the polarization function φ p(1) without using the auxiliary functions θ and ω. In the limit of large separations, we find that the EL-HAV second order energy approaches 41/54 = 0.759 ··· times the exact Coulombic energy, rather than the previously estimated factor of one-half. Also, at large R, the SYM-P, HS, and DEM-I exchange energy agrees with Herring's exact asymptotic expression to within 0.1%.
Theory of chemically induced dynamic electron polarization. II
Authors: Pedersen J. Boiden , Freed Jack H.
Published: February 2004

The earlier theoretical analysis for chemically induced dynamic electron polarization (CIDEP), based on the stochastic-Liouville equation, is generalized to explicitly include the spin-dependent exchange forces in the diffusive trajectories, thus permitting a consistent analysis of the simultaneous effects of exchange on both the spin-selective chemical reaction and CIDEP effects. The semiclassical treatment of diffusion under a ``classical'' force field due to the valence interactions requires the introduction of spin-dependent diffusive and reactive trajectories, and this is discussed for the Brownian-motion model utilized. Our results show that the polarization generated per fractional probability that singlets react (P ∞/F), is not sensitive to the actual details of the spin-selective reactive process (although the absolute polarization P∞ is sensitive to the reactive process), due presumably to the spatial distinction between interradical separations (r) for which the reaction may occur vs those for which CIDEP polarizations are developed. The former require ℏ|J(r)|/kT > 1 while for the latter ℏ|J(r)|/kT < 1, where J(r) is the exchange interaction. It is found that differences in the (nonreactive) diffusive trajectories for singlets and triplets give polarizations that are generally negligible compared to those which develop as a result of the spin-selective reaction (for our overdamped diffusive model). However, our results for more long-range Coulomb interactions between charged radicals show they can produce significant changes on P ∞/F that are quite sensitive to the magnitude of J. Thus ionic-concentration effects on P∞/F should be an important indicator of the CIDEP mechanism. Results are also given for the spin-depolarization process, whereby the effects of spin exchange on a radical pair, which initially collide with residual nonthermal polarization, are to destroy this polarization. The effective range of the spin exchange is found to be weakly enhanced as the range of J(r) is increased. Also, it is shown that, for several variations of a simple exponential dependence of J(r) on r, P∞ / F is hardly affected, although nonexponential dependences can introduce marked changes.