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15 Dec 1968

Volume 49, Issue 12, pp. 5209-5558

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Absorption Spectrum of Silver Atoms in Solid Argon, Krypton, and Xenon

L. Brewer, B. A. King, J. L. Wang, B. Meyer, and G. F. Moore

J. Chem. Phys. 49, 5209 (1968); http://dx.doi.org/10.1063/1.1670036 (5 pages) | Cited 23 times

Online Publication Date: 18 September 2003

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The uv absorption spectrum of trapped silver atoms has been studied in Ar, Kr, and Xe matrices at 20°K and above. With respect to the gas phase, transitions corresponding to 2P ← 2S were observed to be shifted to the blue by an amount characteristic of the particular matrix. In each matrix, four absorption bands were observed with half‐widths ranging from 170–300 cm−1. With increasing temperature the absorption maxima exhibit further shifts together with increasing half‐widths. For Xe and Kr these changes were found to be reversible between 20°K and ⅓ of the melting point of the matrix.

Accurate “Effective” Intermolecular Pair Potentials in Gaseous Argon

David A. Copeland and Neil R. Kestner

J. Chem. Phys. 49, 5214 (1968); http://dx.doi.org/10.1063/1.1670037 (9 pages) | Cited 38 times

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The “effective” intermolecular potential in gaseous argon has been determined, accurate through first order in density, for various assumed argon–argon potentials and the triple‐dipole interaction. This potential should lead to the correct radial‐distribution function. The calculations do not agree with the 1965 analysis of experimental data by Mikolaj and Pings [Phys. Rev. Letters 15, 849 (1965) ]. Our results suggest a density dependence of the minimum of the effective potential of only about 17 math (in degrees Kelvin), where math is the density in grams per cubic centimeter. This constant has a sizeable temperature dependence but only a small variation proportional to density. The contribution of other nonadditive effects is briefly examined as is the small contribution of nonadditive effects to the x‐ray structure factor of the liquid.

Aromatic Carbonyl Spectra. I. The Polarized Absorption Spectrum of Single‐Crystal 4,4′‐Dichlorobenzophenone

Martin Vala and Jiro Tanaka

J. Chem. Phys. 49, 5222 (1968); http://dx.doi.org/10.1063/1.1670038 (13 pages) | Cited 11 times

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The polarized spin‐allowed electronic absorption spectrum of single‐crystal 4,4′‐dichlorobenzophenone has been measured at room temperature and liquid‐helium temperature. Three absorption bands have been observed and characterized: the nπ* band in the 25 000–32 000‐cm−1 region and the 1B2u analog and intramolecular charge‐transfer bands in the 32 000–41 000‐cm−1 range. In the nπ* band, we have been able (1) to determine the polarization of the nπ* transition moment as exclusively parallel to the carbonyl axis; (2) to observe the 0–0 transition at 25 552 cm−1 indicating the electronic‐allowed character of the transition; (3) to definitely exclude the possibility of a magnetic dipole transition or vibronic coupling via non‐totally symmetric b‐type vibrations as sources of intensity; (4) to observe and assign the torsional oscillations of the substituent phenyl rings; and, further (5) to observe and analyze the torsional doubling of the totally symmetric (in C2) vibration, ν3′, due to the nonbonded interaction between the phenyl rings. We have found no evidence to indicate that the excited state is nonplanar (i.e., pyramidal carbonyl group). The most probable source of intensity gain of the normally symmetry‐forbidden nπ* transition is shown to be the breakdown of local carbonyl symmetry (i.e., a delocalization of the oxygen nonbonding orbital) such that there is significant mixing between the nonbonding orbital and the phenyl‐ring π orbitals.

Electron Spin Relaxation in Gases. I. Bis(perfluoromethyl) Nitroxide

Tjeerd J. Schaafsma and Daniel Kivelson

J. Chem. Phys. 49, 5235 (1968); http://dx.doi.org/10.1063/1.1670039 (6 pages) | Cited 11 times

Online Publication Date: 18 September 2003

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The ESR spectra of the relatively large bis (perfluoromethyl) nitroxide (BFMN) radical has been studied in the gas phase. At low pressures, i.e., below 0.1 atm, the spectrum consists of a 480‐G‐wide Gaussian line which presumably arises from the unresolved nuclear hyperfine and spin–rotational lines. (The rootmean‐square spin–rotational coupling constant is about 3.7 G.) As the pressure is increased by adding more radical or a diluant diamagnetic gas, the line narrows and becomes more Lorentzian. At total pressures, of radical plus diluant, above 10 atm the lines are Lorentzian and their widths vary as the inverse total pressure. This behavior can be explained semiquantitatively by assuming that the angular momentum, and hence the spin–rotational interaction, is relaxed by intermolecular collisions which can be understood in terms of a simple kinetic model. The cross sections for the relaxation of the angular momentum of the BFMN radical have been measured and the ratios, eJ, of these cross sections to the kinetic or van der Waals cross sections were determined. Approximate values of eJ are 0.28, 0.45, 0.70, and 0.84 for BFMN with N2, CF4, CF3H, and BFMN, respectively. As expected, eJ increases as the size and polarity of the colliding molecule increases. At high total pressures and low radical partial pressures the spin–rotational interactions are quenched and the nuclear hyperfine splitting is observed. At high total pressure and relatively high radical partial pressures (above 0.25 atm) the hyperfine splitting is coalesced into a single‐exchange narrowed line. The cross section for spin exchange between BFMN radicals is about 0.04 of the kinetic cross section; the amount of exchange is, of course, proportional to the BFMN partial pressure.

Ultrasonics and Water Structure in Urea Solutions

Donald V. Beauregard and Robert E. Barrett

J. Chem. Phys. 49, 5241 (1968); http://dx.doi.org/10.1063/1.1670040 (4 pages) | Cited 9 times

Online Publication Date: 18 September 2003

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Ultrasonic absorption and velocity in aqueous urea solutions have been measured for concentrations up to 15m and at temperatures down to − 10°C. The velocity itself was measured at pressures up to 2000 lbs/in.2. The structural part of the absorption decreases with increasing concentration of urea, until a limiting value is reached. The slope of the velocity‐vs‐pressure curve as a function of temperature shows that urea solutions look like water at high temperatures. These data suggest that the net effect of dissolving urea is to cause the clusters in water to be broken up.

Thermochemistry of UOS; Evaporation of US☒UO2 Mixtures; On the Attainment of Equilibrium in Knudsen Cells

E. David Cater, E. G. Rauh, and R. J. Thorn

J. Chem. Phys. 49, 5244 (1968); http://dx.doi.org/10.1063/1.1670041 (10 pages) | Cited 2 times

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Evaporation of mixtures of US and UO2 and of UOS has been studied by molecular effusion, and the gaseous species have been investigated mass spectrometrically. A eutectic occurs in the system US☒UO2 at 2240°K and at approximately 45% dioxide. In the vapor the gaseous species in order of decreasing partial pressures are: UO, UO2, UOS, US, S, U, and O. Because of the formation of the gaseous monoxide, the total pressure is about twice the sum of the vapor pressures for US and UO2 along. Calculated as though the vapor had the molecular weight of the monoxide, the total “effective” vapor pressure is given by
math
below the eutectic temperature and
math
above this temperature. The energy of atomization of gaseous UOS is 300 ± 7 kcal/mole at 0°K. In general, the mass‐spectrometric measurements were much less precise and reproducible than those in previous studies of simpler systems with the same equipment. This was believed to be due to nonequilibrium conditions in the condensed phases in the Knudsen cell. It was concluded that one must study the condensed phases as well as the vapor phase before assuming that mass spectrometrically studied isomolecular reactions will yield equilibrium thermodynamic data.

Pressure‐Induced Microwave Absorption of Nonpolar Gases

J. Gersten and H. M. Foley

J. Chem. Phys. 49, 5254 (1968); http://dx.doi.org/10.1063/1.1670042 (11 pages) | Cited 7 times

Online Publication Date: 18 September 2003

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A theory is developed which describes the microwave absorption of nonpolar gases. The contributions arising from collisionally induced absorption and from dimers are evaluated separately. It is found that at low enough temperatures the absorptive properties of such gases are dominated by the dimeric states. This accounts for the observed anomalous temperature dependence of the absorption coefficient. A comparison of the theoretical predictions with experimental data on carbon dioxide and nitrogen yields good agreement.

General Theory of the Long‐Range Pair‐Correlation Function

J. Brunet and K. E. Gubbins

J. Chem. Phys. 49, 5265 (1968); http://dx.doi.org/10.1063/1.1670043 (5 pages) | Cited 3 times

Online Publication Date: 18 September 2003

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A general theory is presented for the long‐range behavior of the pair‐correlation function in a multi‐component mixture, based on the thermodynamics of inhomogeneous systems. A set of nonlinear, coupled differential equations are obtained for the correlation function, and these reduced to linear equations under well‐defined approximations. When applied to a one‐component system, it is found that previously proposed equations of Ornstein and Zernike, and Hart are included as special cases of the linear theory. The assumptions implicit in these equations are clarified. The theory has also been used to obtain an asymptotic solution for the pair‐correlation functions of a binary mixture. The conditions under which these equations reduce to expressions similar to those for pure fluids are investigated.

Molecular Reorientation in Collisions between an Atom and a Diatomic Molecule

James L. Kinsey, John W. Riehl, and John S. Waugh

J. Chem. Phys. 49, 5269 (1968); http://dx.doi.org/10.1063/1.1670044 (7 pages) | Cited 37 times

Online Publication Date: 18 September 2003

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Collisions between atoms and diatomic molecules that result in reorientation of the molecular rotation relative to a laboratory‐fixed frame are treated theoretically. An expression for the cross section in terms of elements of the scattering matrix is derived, and approximate numerical methods for calculation in a specific example, the low‐energy scattering of H2 by He, are discussed.

Spin–Lattice Relaxation and the Anisotropic Part of the He☒H2 Intermolecular Potential

John W. Riehl, James L. Kinsey, John S. Waugh, and John H. Rugheimer

J. Chem. Phys. 49, 5276 (1968); http://dx.doi.org/10.1063/1.1670045 (6 pages) | Cited 40 times

Online Publication Date: 18 September 2003

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The spin–lattice time T1 of gaseous mixtures of H2 and He has been measured as a function of composition and of temperature in the range 77°–300°K at pressures such that T1 is proportional to the density. The relationship between the experimental T1 and cross sections for molecular reorientation of H2 is given. From comparison of computed cross sections to the data, experimental values are obtained for parameters in an approximate form for the He☒H2 anisotropic intermolecular potential.

Elastic Constants of Ammonium Bromide. II. High‐Pressure Ultrasonic Investigation of the Phase Transitions

Carl W. Garland and Robert A. Young

J. Chem. Phys. 49, 5282 (1968); http://dx.doi.org/10.1063/1.1670046 (12 pages) | Cited 31 times

Online Publication Date: 18 September 2003

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The abiabatic elastic constants of single‐crystal ammonium bromide have been measured at 20 MHz as functions of temperature and pressure in the region from 180°–240°K and from 0–6 kbar. A new high‐pressure ordered phase, denoted as OII, has been discovered in this temperature range. The acoustic properties of the new OII phase were investigated with emphasis on the regions of the first‐order phase transition from the OII phase to the ordered tetragonal phase and the lambda transition from the OII phase to the disordered cubic phase. The region of the lambda transition from the ordered tetragonal phase to the disordered cubic phase was also studied. A detailed comparison is made with the behavior of ammonium chloride near its order–disorder phase transition.

Viscosity‐Dependent Ion Recombination Luminescence in Organic Liquids and Solids from Electron and Gamma Irradiation

James A. Leone and William H. Hamill

J. Chem. Phys. 49, 5294 (1968); http://dx.doi.org/10.1063/1.1670047 (11 pages) | Cited 16 times

Online Publication Date: 18 September 2003

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Recombination luminescence of triphenylamine (TPA), both fluorescence and phosphorescence, has been used to investigate ionic processes in (a) γ‐irradiated 3‐methylpentane (3MP) at 77°K, (b) thermoluminescence (TL) in γ‐irradiated 3MP, and (c) in 1‐MeV electron‐pulse‐irradiated paraffin oil and squalane from 215°–298°K. The shape of the time‐dependent decay of luminescent intensity, I(t), in (a) was independent of a 500‐fold change in irradiation dose, providing evidence for substantially complete correlation of geminate charge pairs. Photoionization of TPA under otherwise similar conditions led to the same I(t), which provides evidence that the distribution, P(R), of charge separation produced by γ irradiation is determined by very low‐energy electrons. TL curves in part (b) showed two well‐defined maxima of intensity I′ attributed to recombination of TPA+− e− at 83°K and I″ attributed to TPA+− TPA−  at ∼95°K. The ratio I″ / I′ increased with the concentration of TPA, I′ decreased with ir bleaching of solvent‐trapped e− or addition of CO2 while both I′ and I″ decreased with addition of methyltetrahydrofuran, a hole trap. In part (c) intensity I was measured from 10−6–10−3 sec as appropriate at various temperatures and solvent viscosities which ranged from 1– ∼ 103 P. Excepting Cerenkov radiation, the luminescence spectrum coincides with TPA fluorescence, the phosphorescence intensity being negligible since its half‐life is ∼ 2 sec. Linear plots of lnIvst can be resolved into two exponential decays, with t1/2 of the slow component proportional to (viscosity)1/2, and attributed to recombination of TPA+ with TPA−. The faster component of I is attributed to recombination of TPA+ with e−, but t1/2 was too short for reliable measurement over most of the range. The dependence t1/2 ∝ η1/2 demonstrates the inapplicability of Stokes' law (which requires t1/2 ∝ R3) to recombination of isolated ion pairs, the high field reducing the randomness of relative ion displacements R. If the probability per ion jump mean free path λ against the central field at R is P  =  exp(− e2λ / ϵR2kT), the net displacement for dN jumps is dR  =  [1 − exp(− e2λ / ϵR2kT)]λdN. This leads to t1/2 ∝ Rm with 1  ≤  m  ≤  3. This relation combined with dn± / dt  =  (dn± / dR)(dR / dt) gives the ion pair distribution dn± / dR. From this expression and an assumed dependence Rn ∝ N for free charge one obtains the free‐charge distribution function.

Charge Separation and Similarities of Ionic Processes in the Radiolysis of Alkanes and of Water

James A. Leone and William H. Hamill

J. Chem. Phys. 49, 5304 (1968); http://dx.doi.org/10.1063/1.1670048 (7 pages) | Cited 7 times

Online Publication Date: 18 September 2003

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The charge‐pair separation distribution function,
math
is consistent with results from the rate of correlated ion‐pair recombination, as well as the temperature and field dependence of the electrical conductivity of n‐hexane under x irradiation for data reported by Allen et al. The T dependence derives from (1) and Rescape  =  e2 / ϵkT. The combined T and E dependence fits the description
math
where g is a geometric factor and gλ′5 × 10−7 cm (which implies λ′∼102 Å for energy gained from the field), while (1) and (2) together account for the E dependence. The integral distribution function is
math
for separation ≥ R, with P  =  1 at Rm ≅ 100Å. It is shown that many electron reactions in organic liquids and glasses fit a common concentration dependence, which is predictable from (3). It is also shown that in the region of ∼ 10−4 − 10−1 M solute in water, the yield of chemical reduction obeys the same concentration dependence as liquid alkanes. This effect is attributed to a population of electrons which are not trapped and do not become hydrated. Consequently their electrical behavior depends upon the high‐frequency dielectric constant, accounting for similar behavior in cyclohexane and in water.

Effect of the Internal Coulomb Field upon the Viscosity of a Fused Salt

Graham Morrison and John E. Lxtra1nd

J. Chem. Phys. 49, 5310 (1968); http://dx.doi.org/10.1063/1.1670049 (7 pages) | Cited 3 times

Online Publication Date: 18 September 2003

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An experimental determination is made of the effect of the internal Coulomb field in a fused salt upon the viscosity of the fluid. Two fluids of isoelectronic molecules are compared: the salt tetrabutylammonium tetrabutylboride and the nonelectrolyte 5,5‐dibutylnonane. The molecules of these fluids are identical except for the charge on the nucleus of the central atom and their coefficients of viscosity are compared at the same temperature and particle number density between 120° and 180°C. The salt viscosity varies from 10 times that of the nonelectrolyte to less than 5 times as the temperature and volume increase. The Brownian model of Kirkwood and Rice yields a ratio of 2 for a similar model system and suggests that the deviation of this ratio from unity is not necessarily caused by the dissipation arising directly from the Coulomb field. Rather it is caused by the repulsive forces which are more effective in the salt because of the shorter intermolecular distances demanded by the Coulomb field of the salt at any given density.

Infrared Spectra of Acetonitrile and Acetonitrile‐d3

E. L. Pace and Lewis J. Noe

J. Chem. Phys. 49, 5317 (1968); http://dx.doi.org/10.1063/1.1670050 (9 pages) | Cited 44 times

Online Publication Date: 18 September 2003

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The infrared spectra of acetonitrile and acetonitrile‐d3 have been studied at − 50°C for the high‐temperature (β) crystalline phase and at − 65°, − 115° and − 192°C for the low‐temperature (α) crystalline phase. A powder x‐ray pattern obtained at liquid‐nitrogen temperature indicates that the unit cell is primitive orthorhombic and that it contains eight molecules. It is shown that the consideration of all available structural data together with the site group and factor group splittings for the α crystal tends to favor D2h1(Pmmm) and D2h9(Pbam) as possible space groups.

Positron Annihilation in the Neon Isoelectronic Series, Diamond and Solid Iodine

A. S. Klotz and D. W. Hafemeister

J. Chem. Phys. 49, 5326 (1968); http://dx.doi.org/10.1063/1.1670051 (5 pages) | Cited 4 times

Online Publication Date: 18 September 2003

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The angular correlation of the annihilation quanta has been measured in the neon isoelectronic series (neon–neon configuration). Although the curves had different shapes, they were analyzed in terms of a single parameter Γ, the full width at half‐maximum with the result: NaF[100], 9.7 ± 0.2 mrad; MgO[100], 12.1 ± 0.2 mrad; AlN(polycrystalline), 11.1 ± 0.2 mrad; and SiC (polycrystalline), 12.0 ± 0.2 mrad. The increase between NaF and MgO is attributed to the increase in the ionic charge, and the decrease for AlN and SiC is attributed to the onset of covalency. A single [100] crystal of diamond was investigated and compared with data on Si[100] and Ge[100]. There appears to be a linear relationship between Γ and r0−1, the inverse of the lattice parameter. The SiC also agreed with this trend. Finally, Γ was obtained for KI(7.1 ± 0.2 mrad) and solid iodine (9.2 ± 0.2 mrad). The relative broadening in Γ for these two compounds is consistent with Mössbauer isomer‐shift data and with the known atomic configurations Wigner–Seitz cellular‐model calculations which were performed for the positron wavefunction for the NaF, MgO, KI, and I2 lattices roughly describe several aspects of the data.

Matrix‐Isolation Study of the Vacuum‐Ultraviolet Photolysis of Trifluorosilane. The Infrared Spectrum of the Free Radical SiF3

Dolphus E. Milligan, Marilyn E. Jacox, and William A. Guillory

J. Chem. Phys. 49, 5330 (1968); http://dx.doi.org/10.1063/1.1670052 (6 pages) | Cited 19 times

Online Publication Date: 18 September 2003

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In studies of the vacuum‐ultraviolet photolysis of SiHF3 suspended in argon, nitrogen, and carbon monoxide matrices at 14°K, evidence has been obtained indicating that H‐atom detachment occurs and that the SiF3 free radical is stabilized. All of the vibrational fundamentals of SiF3 have been observed in these experiments. The appearance of two stretching fundamentals requires that the molecule be non‐planar. A more detailed consideration of the pattern of vibrational absorptions indicates that the angle between each Si☒F bond and the threefold symmetry axis of the molecule is approximately 71°, close to the value characteristic of sp3 hybridization of the valence electrons about the central atom. Force constants have been estimated using a four‐constant valence‐force potential, and the thermodynamic properties of SiF3 have been calculated.

Proton Magnetic Resonance Study of Hydrated Potassium Trioxalatoaluminate: Free Rotation of Proton Pairs

G. Rangarajan and J. Ramakrishna

J. Chem. Phys. 49, 5336 (1968); http://dx.doi.org/10.1063/1.1670053 (6 pages) | Cited 1 time

Online Publication Date: 18 September 2003

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A proton magnetic resonance study of hydrated potassium trioxalatoaluminate revealed that the lines are extremely narrow and intense at room temperature and much broader at 90°K, indicating the presence of free rotation of the proton pairs. Detailed investigations were carried out on both single‐crystal and powder samples, and it was found that the p–p vectors rotate about the c‐axis generating a cone having a semi‐vertical angle of about 33°. The temperature variation of the second moment showed a transition around 155°K. This is in agreement with Saha's susceptibility measurements on the isomorphous chromium salt. Similar rotational narrowing was observed in the chromium and ferric salts, also. The Pake method was used to determine the length and orientation of the p–p vectors in the rigid lattice (at 90°K). The hydrogen‐bond schemes suggested by the x‐ray workers did not satisfy the criterion of parallelism between the p–p line and the line joining the acceptor oxygen atoms. Alternate schemes could not be found. An order‐of‐magnitude calculation gave a very low value for the barrier hindering the rotation (≈ 2kcal/mole). These results suggest that hydrogen bonds are either absent or, if present, extremely weak and are consistent with the presence of free rotation. A preliminary infrared study gave an insignificant shift of the O☒H stretching frequency thus supporting our conclusions.

Temperature Dependence of Kinetic Isotope Effects in Gas‐Phase Reactions. I. Theory of the High‐Temperature Limit

E. Tschuikow‐Roux and Digby D. Macdonald

J. Chem. Phys. 49, 5342 (1968); http://dx.doi.org/10.1063/1.1670054 (4 pages) | Cited 4 times

Online Publication Date: 18 September 2003

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The theory of the high‐temperature limit of the temperature dependence of the kinetic isotope effect in gas‐phase reactions is discussed in detail and the resulting high‐temperature limit is interpreted in terms of contributions from the initial states and activated complexes.

Temperature Dependence of Kinetic Isotope Effects in Gas‐Phase Reactions. II. The Hydrogen‐Atom–Formaldehyde Reaction

Digby D. Macdonald and E. Tschuikow‐Roux

J. Chem. Phys. 49, 5345 (1968); http://dx.doi.org/10.1063/1.1670055 (5 pages) | Cited 1 time

Online Publication Date: 18 September 2003

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Kinetic isotope effects of atom‐transfer reactions and their temperature dependences at high temperatures have been calculated for various hydrogen‐atom–formaldehyde reactions. In the case of the “abstracting atom” kinetic isotope effect, a negative temperature coefficient is predicted in the high‐temperature limit. The theoretical calculations are compared with experimental results in the literature and satisfactory agreement is obtained.

Molecular Acoustic and Spectroscopic Studies on the Internal Rotation in 1‐Fluoro‐1,1,2,2‐tetrachloroethane

R. A. Pethrick and E. Wyn‐Jones

J. Chem. Phys. 49, 5349 (1968); http://dx.doi.org/10.1063/1.1670056 (5 pages) | Cited 4 times

Online Publication Date: 18 September 2003

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An ultrasonic relaxation observed in liquid 1‐fluoro‐1,1,2,2‐tetrachloroethane has been attributed to a perturbation of the equilibrium between the trans and gauche isomers. From the temperature dependence of the relaxation parameters, the rates of isomerization have been derived. The temperature dependence of the rate constants were found to obey the Arrhenius and Eyring rate equations giving the following parameters:
math
The vibrational frequency of the torsional oscillations of the trans isomer is 86 cm−1, which is equivalent to a torsional barrier (ΔHgt+) of 8.89 kcal/mole. The acoustic and spectroscopic barrier are compared to the potential barrier found from a recent NMR study, (ΔHgt+  =  7.25kcal/mole).

Interpretation of Nuclear Quadrupole Coupling in Nitrogen Containing Molecules with Ab Initio Molecular‐Orbital Wavefunctions

Chester T. O'Konski and Tae‐Kyu Ha

J. Chem. Phys. 49, 5354 (1968); http://dx.doi.org/10.1063/1.1670057 (8 pages) | Cited 45 times

Online Publication Date: 18 September 2003

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Electric field gradients were computed at the nitrogen nuclei in a number of small molecules, using LCAO MO SCF wavefunctions constructed with Gaussian‐lobe basis sets. Comparisons with molecular‐quadrupole‐constant data leads to a number of independent values for the quadrupole moment of 14N, which was poorly known. From this work, and other current studies, the best value of Q(14N) is 1.56 × 10−26 cm2. The contributions to the electric field gradient from various molecular orbitals are analyzed in detail for several cases. Procedures for estimating field gradients with the aid of overlap integrals are critically examined.

Molecular Motion and Raman Band Shapes in Liquid Nitrogen and Oxygen

Michael Scotto

J. Chem. Phys. 49, 5362 (1968); http://dx.doi.org/10.1063/1.1670058 (5 pages) | Cited 28 times

Online Publication Date: 18 September 2003

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Spontaneous Raman band shapes have been measured in liquid nitrogen and oxygen. Depolarization ratios have also been measured and compared with those in the gas. Correlation functions are obtained from Q‐branch spectra, and the time dependence of rotational motion is discussed. Motional narrowing and rotational quenching are considered as possible mechanisms which could give rise to the observed spectra.

Gaussian‐Orbital Approximation for the Hydrogen Atom by Minimization of Variance

Marc Rendell and John Arents

J. Chem. Phys. 49, 5366 (1968); http://dx.doi.org/10.1063/1.1670059 (3 pages) | Cited 2 times

Online Publication Date: 18 September 2003

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The determination of an approximate wavefunction in the form
math
by minimization of the variance,
math
, is tested on the H atom. Obstacles to using other definitions of variance are discussed. Results are less favorable than those obtained by minimization of 〈H〉, but improve rapidly as n increases.

Anharmonicity in Polyatomic Molecules. The CH‐Stretching Overtone Spectrum of Benzene

Bryan R. Henry and Willem Siebrand

J. Chem. Phys. 49, 5369 (1968); http://dx.doi.org/10.1063/1.1670060 (8 pages) | Cited 114 times

Online Publication Date: 18 September 2003

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A long series of CH‐stretching overtones in the infrared and visible spectrum of benzene can be analyzed using a single anharmonicity constant (− 57.5 cm−1). This anharmonicity is associated with an independently vibrating local CH oscillator and the spectrum is interpreted in terms of such a local‐mode representation. A transformation is made to normal modes which leads to five different normal‐mode anharmonicity constants, which are representative of the 13 different CH‐stretching anharmonicity constants that characterize benzene. The CH‐overtone spectrum of benzene is described in terms of its normal‐mode components. A method of assigning relative intensities to these components is developed, and, along with the calculated normal‐mode anharmonicity constants, is used to construct the overtone spectrum as a superposition of Lorentzian bands calculated for each individual component. The maxima of these bands compare favorably with the observed band maxima. By adjusting the local‐mode anharmonicity constant from − 57.5 to − 55.2 cm−1, the agreement can be made perfect so that the latter value appears to be the appropriate local‐mode CH‐stretching anharmonicity constant in benzene. This number is relevant to the theory of radiationless transitions in aromatic hydrocarbons. The effect of introducing anharmonic coupling between local modes is investigated and found to be unimportant.
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