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15 Dec 1970

Volume 53, Issue 12, pp. 4409-4726

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Light Scattering from Chemically Reacting Fluids: Coupled Chemical Reactions

Michael Weinberg and Raymond Kapral

J. Chem. Phys. 53, 4409 (1970); http://dx.doi.org/10.1063/1.1673965 (5 pages) | Cited 6 times

Online Publication Date: 18 September 2003

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The total light scattering intensity from a fluid where chemical relaxation takes place via a sequence of coupled reactions is calculated and examined. The fast reaction limiting case where the rate coefficients in one of the steps are much greater than those in the other step is studied in considerable detail. It is found that only if the reaction is fast and the effective polarizabilities of the species participating in the fast step are equal will the spectrum be simplified. In this case, the broadening of the Rayleigh peak will be due principally to the slow chemical reaction. When one of the reactions is very fast, the spectrum can be analyzed by assuming chemical equilibrium between the species undergoing rapid reaction.

Photoionization Study of Chlorine Monofluoride and the Dissociation Energy of Fluorine

Vernon H. Dibeler, James A. Walker, and K. E. McCulloh

J. Chem. Phys. 53, 4414 (1970); http://dx.doi.org/10.1063/1.1673966 (4 pages) | Cited 11 times

Online Publication Date: 18 September 2003

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Mass spectra and photoionization yield curves are obtained for the molecular and atomic ions of chlorine monofluoride. The atomic ions are formed both by ion‐pair and by dissociative ionization processes, although the F+ ion formed by the latter process is too weak for quantitative measurements. The ClF+ curve exhibits a weak onset at 12.55 eV, ascribed to a hot band. An intense onset at 12.65 eV is ascribed to the (0, 0) transition. The observed thresholds for the Cl+ ion support the spectroscopic determination of D(ClF)  =  2.558eV and, combined with a recent determination of the heat of formation of ClF, support the previously reported photoionization value of D0°(F2)  =  1.34eV.

Molecular Momentum Distributions and Compton Profiles. I. General Theory and Boron Hydrides

Irving R. Epstein and William N. Lipscomb

J. Chem. Phys. 53, 4418 (1970); http://dx.doi.org/10.1063/1.1673967 (7 pages) | Cited 40 times

Online Publication Date: 18 September 2003

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A method is described for the calculation of momentum distributions and Compton profiles of polyatomic molecules. Distributions, profiles and momentum expectation values are calculated for the boron hydrides B2H6, B4H10, B5H9, B5H11, and B6H10. Contour maps of total and difference densities in momentum space are presented for diborane. The results are analyzed in terms of localized orbitals. The analysis shows that traditional concepts of two‐ and three‐center electron pair bonds may find great utility in interpreting momentum space distributions.

Molecular Momentum Distributions and Compton Profiles. II. Localized Orbital Transferability and Hydrocarbons

Irving R. Epstein

J. Chem. Phys. 53, 4425 (1970); http://dx.doi.org/10.1063/1.1673968 (12 pages) | Cited 61 times

Online Publication Date: 18 September 2003

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Momentum distributions, expectation values, and Compton profiles are calculated for methane, ethane, ethylene, acetylene, methyl acetylene, trans‐butadiene, cyclopropane, and benzene by transforming SCF wavefunctions from position space to momentum space. Agreement with available experimental profiles is found to be somewhat better than for earlier calculations. Distributions and profiles for localized molecular orbitals (LMO's) in hydrocarbons are computed and are found to show a high degree of transferability. With the addition of LMO distributions and profiles representing various functional groups, formulas are given for predicting the distributions and profiles of several homologous series of organic molecules. The problem of quantitatively comparing similar profiles is discussed briefly.

Numerical Solutions for the Energy Distributions of Reactive Atoms in Gases. V

T. T. Phillips and M. D. Kostin

J. Chem. Phys. 53, 4436 (1970); http://dx.doi.org/10.1063/1.1673969 (5 pages) | Cited 5 times

Online Publication Date: 18 September 2003

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From the equation of continuity, an integrodifferential form of the time‐dependent Boltzmann equation is derived which can be used to obtain numerical solutions for the energy distributions of reactive atoms for the case of realistic scattering collisions. Application of the integrodifferential equation is made to the problem of computing the energy distributions as a function of time of tritium atoms reacting with molecular hydrogen and molecular iodine and moderated by helium. A numerical procedure for efficiently obtaining the energy distribution at large times is reported. For those systems where the deviation from equilibrium is small a differential equation is derived which gives accurate results even though large changes in kinetic energy during scattering collisions can occur.

Longitudinal Modes in Hydrogen and Deuterium Halide Crystals

H. B. Friedrich and R. E. Carlson

J. Chem. Phys. 53, 4441 (1970); http://dx.doi.org/10.1063/1.1673970 (3 pages) | Cited 14 times

Online Publication Date: 18 September 2003

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The observation of four bands in the Raman spectra of the internal modes of crystalline HCl, DCl, HBr, and DBr has previously been explained either by assuming a four‐molecule primitive cell, which is different than the structure suggested by diffraction studies, or by assuming that two of the bands were due to longitudinal modes. We have used the experimental infrared intensities with a dipolar coupling model appropriate to the cell symmetry to compute the LO frequencies. The calculated frequencies are in excellent agreement with those observed in the hydrogen and deuterium halide crystals.

Infrared Dispersion in Liquid Benzene and Benzene‐d6

A. J. Zelano and W. T. King

J. Chem. Phys. 53, 4444 (1970); http://dx.doi.org/10.1063/1.1673971 (7 pages) | Cited 7 times

Online Publication Date: 18 September 2003

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The intensities of the major infrared absorption bands in liquid C6H6 and C6D6 were measured by an interferometric method. The intensities of the very intense a2u modes were found to be 14 450 ± 110 and 8600 ± 110 cm−1 cm2/mM for C6H6 and C6D6, respectively. Small, but significant deviations from the predictions of the “oriented gas model,” used to interpret these measurements, were observed.

Radiationless Transitions in the Eu3+ Center in LaAlO3

G. Blasse, A. Bril, and J. A. de Poorter

J. Chem. Phys. 53, 4450 (1970); http://dx.doi.org/10.1063/1.1673972 (4 pages) | Cited 14 times

Online Publication Date: 18 September 2003

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Three different types of radiationless transitions play a role in the radiationless decay of the luminescent Eu3+ center in LaAlO3: (a) a temperature‐independent process from the charge‐transfer state, (b) a temperature‐dependent process (ΔE  =  0.15eV) from this state, (c) a temperature‐dependent process (ΔE  =  1.1eV) from the 5D0 level. All three processes are of importance because the charge‐transfer state of Eu3+ is situated at low energies in LaAlO3. If, however, this state is situated at higher energies, as it is in other host lattices, only process (b) will be observed in the conventional range of temperatures.

Small‐Angle Scattering of X Rays from Carbon Dioxide in the Vicinity of Its Critical Point

B. Chu and J. S. Lin

J. Chem. Phys. 53, 4454 (1970); http://dx.doi.org/10.1063/1.1673973 (13 pages) | Cited 10 times

Online Publication Date: 18 September 2003

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Intensity measurements of x rays scattered at small angles by carbon dioxide are reported for various equilibrium states in the critical neighborhood of the temperature–density diagram. From our studies we have observed that (1) the K2 dependence in a plot of reciprocal relative scattered intensity (Is−1) versus scattering angle is obeyed over the following ranges: 2.66 × 10−4Å−2 < K2  =  (16π2 / λ2)sin2(θ / 2) < 8.06 × 10−3Å−2,0.343°  ≤  T − Tc  ≤  5.640°K,87.5  ≤  ρ  ≤  356.5 amagat, and along the liquid side of the coexistence curve and (2) the temperature dependence of the isothermal compressibility (βT) and the long‐range correlation length (ξs) have the forms: βT  =  fϵ−γ and ξs  =  ξ0ϵ−ν, where ϵ  =  (T − Tc) / Tc; f,γ and ν are constants with respect to temperature. We have obtained γ  =  1.32−0.10+0.09 and ν  =  0.67 ± 0.05 at the critical isochore, and νliquid  ≈  0.58 along the liquid side of the coexistence curve. Using an empirical equation of the form Is−1∝[τ − τsp(ρ)]γ with τsp  =  Tsp / Tc and Tsp being the pseudospinodal temperature, we have obtained γ  =  1.20 ± 0.09 at ρ  =  268.3 amagat and γ  =  1.13±0.09 at ρ  =  192.4 amagat. Moderate success is obtained in testing a more general scaling equation for Is.

Nonadiabatic Effects in the Internal Rotation of ⋅CH2COO− in Irradiated Zinc Acetate Dihydrate

Robert G. Hayes, Daniel J. Steible, William M. Tolles, and John W. Hunt

J. Chem. Phys. 53, 4466 (1970); http://dx.doi.org/10.1063/1.1673974 (4 pages) | Cited 15 times

Online Publication Date: 18 September 2003

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The EPR spectrum of the ⋅CH2COO− radical in a single crystal host displays nonadiabatic motional effects. A phenomenological theory is suggested, based on the density matrix of the spin system, and a technique is described for rapid calculation of simulated spectra.

Molecular Zeeman Effect of Cyclobutene, Methylene Cyclopropane, and Methylene Cyclobutane

R. C. Benson and W. H. Flygare

J. Chem. Phys. 53, 4470 (1970); http://dx.doi.org/10.1063/1.1673975 (9 pages) | Cited 10 times

Online Publication Date: 18 September 2003

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The rotational Zeeman effect has been observed in cyclobutene, methylene cyclopropane, and methylene cyclobutane. The molecular g values, magnetic susceptibility anisotropies, and molecular quadrupole moments were obtained and they are listed below (the a and b axes are in the molecular plane; the a axis is perpendicular to the carbon–carbon double bond in cyclobutene, and it is along the carbon–carbon double bond in methylene cyclopropane and methylene cyclobutane). The units of χ are 10−6 erg/G2⋅mol and the units of Qxx are 10−26 esu⋅cm2:
math
The above results, in particular the magnetic susceptibility anisotropies, are compared with similar ring molecules. Local and nonlocal (ring current) contributions to the magnetic susceptibility anisotropies are discussed and an additivity scheme is proposed for local group anisotropies in hydrocarbons.

Molecular Zeeman Effect and the Determination of the Molecular Magnetic Moments (g Values), Magnetic Susceptibilities, and Molecular Quadrupole Moments in Methyl Formate and Glycolaldehyde

J. H. S. Wang and W. H. Flygare

J. Chem. Phys. 53, 4479 (1970); http://dx.doi.org/10.1063/1.1673976 (7 pages) | Cited 2 times

Online Publication Date: 18 September 2003

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The high‐field first‐ and second‐order Zeeman effect has been observed in methyl formate and glycolaldehyde. The molecular parameters in the inertial axis system for both molecules are listed below. Only the relative signs of the molecular g values are obtained experimentally. However, the absolute signs are conclusively assigned in both molecules by an analysis of the second moment of the charge distribution or molecular quadrupole moments. For methyl formate, the measured g values and magnetic susceptibility anisotropies are gaa  =  − 0.1267 ± 0.0013,gbb  =  − 0.0391 ± 0.0010,gcc  =  − 0.0168 ± 0.0017,2χaa − χbb − χcc  =  (11.0 ± 1.0) × 10−6erg/G2⋅mol, and 2χbb − χcc − χaa  =  (3.1 ± 1.0) × 10−6erg/G2⋅mol. The molecular quadrupole moments are Qaa  =  (2.3 ± 0.8),Qbb  =  (4.2 ± 1.0), and Qcc  =  − (6.5 ± 1.3) all in units of 10−26 esu⋅cm2. For glycolaldehyde, the measured g values and magnetic susceptibility anisotropies are gaa  =  − 0.1239 ± 0.0013,gbb  =  − 0.0726 ± 0.0010,gcc  =  − 0.0178 ± 0.0010,2χaa − χbb − χcc  =  (7.1 ± 2.5) × 10−6erg/G2⋅mol, and 2χbb − χcc − χaa  =  (18.8 ± 2.0) × 10−6erg/G2⋅mol. The molecular quadrupole moments are Qaa  =  − (5.6 ± 2.0),Qbb  =  (3.8 ± 1.8) and Qcc  =  (1.8 ± 3.3) in units of 10−26 esu⋅cm2. Using the molecular structures allows a determination of the diagonal elements in the paramagnetic susceptibility tensor and the anisotropies in the second moment of the charge distribution. Using the bulk susceptibilities, gives the diagonal elements in the total magnetic susceptibility tensor and the individual elements of the second moment of the charge distribution. The results in these two molecules are compared to similar systems.

Kinetics of Electron and Ion Reactions during the γ Radiolysis of Liquid Neopentane; Dependence of Charge Scavenging Kinetics on Hydrocarbon Molecular Structure

K. Horacek and G. R. Freeman

J. Chem. Phys. 53, 4486 (1970); http://dx.doi.org/10.1063/1.1673977 (4 pages) | Cited 3 times

Online Publication Date: 18 September 2003

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The large free ion yield in neopentane has been confirmed by chemical measurement: for nitrous oxide solutions at 23°C g(N2)fi  =  0.95 and g(N2)max  ≈  4.7. The average number of nitrogen molecules formed per electron scavenged appears to be 1.1 ± 0.1 at all nitrous oxide concentrations. Thus gfi  =  0.9 in neopentane, which is sevenfold larger than that in n‐hexane. The median range of the secondary electrons in liquid neopentane is about fourfold greater than that in n‐hexane. The greater range in neopentane correlates with the more sphere‐like shape of the molecules. In spite of the larger median electron range in neopentane, the ease with which electrons and ions can be scavenged in spurs in that liquid is similar to that in hydrocarbons with distinctly nonspherical molecules. Furthermore, the ratio of efficiences of electron to positive ion scavenging (β− / β+) is 17 in neopentane, similar to the value 13 in the “nonspherical” methylcyclopentane. During the radiolysis of pure neopentane two types of ions are formed: G(PH+)  =  1.7 and G(N+)  =  3.0. PH+ yields hydrogen when neutralized by an electron, but not when neutralized by a massive negative ion. PH+ can also donate a proton to ammonia. N+ does not yield hydrogen upon neutralization, nor does it donate a proton to ammonia. In pure neopentane G(H2)  =  2.5 ± 0.1 and G(CH4)  =  3.9 ± 0.2 at a dose of 1.5 × 1018 eV/g. Scavenging the free ions by either N2O or ND3 reduces g(H2) by about 0.35, but has no effect on the methane yield.

Theoretical Analysis of the Electronic Structure and Molecular Properties of the Alkali Halides. VI. Rubidium Fluoride and Sodium Bromide

Robert L. Matcha

J. Chem. Phys. 53, 4490 (1970); http://dx.doi.org/10.1063/1.1673978 (7 pages) | Cited 13 times

Online Publication Date: 18 September 2003

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The results of Hartree–Fock calculations in the SCF LCAO MO approximation on sodium bromide and rubidium fluoride are presented giving emphasis to a discussion of modecular properties including quadrupole coupling constants, dissociation energies, molecular force constants, and electronic dipole moments.

Study of Equilibria in Nitrogen Dioxide

Harvey Blend

J. Chem. Phys. 53, 4497 (1970); http://dx.doi.org/10.1063/1.1673979 (3 pages) | Cited 15 times

Online Publication Date: 18 September 2003

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The equilibria of a gaseous mixture of nitrogen dioxide and nitrogen tetroxide is studied by measuring the velocity of a sound wave propagated through the gas. The degree of dissociation α and the equilibrium constant Kp are determined as functions of temperature from 0 to 50°C, and pressure from 0 to 1 atm. At 30°C, Kp is found to be 0.214 atm. The heat of reaction ΔH is determined to be 14.59 kcal mol−1 for the second‐law value, and 13.65 kcal mol−1 for the third‐law value.

Statistical Mechanics of Rodlike Particles. III. A Fluid of Rigid Spherocylinders with Restricted Orientational Freedom

Martha A. Cotter and Daniel E. Martire

J. Chem. Phys. 53, 4500 (1970); http://dx.doi.org/10.1063/1.1673980 (12 pages) | Cited 45 times

Online Publication Date: 18 September 2003

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A scaled particle treatment is applied to a fluid of rigid spherocylinders of radius a and cylindrical length l, with cylindrical axes permitted to point in only three mutually perpendicular directions. Singling out one of these, by means of some arbitrary device such as an infinitesimal applied field, and denoting by s the fraction of rods in each of the directions perpendicular to this “preferred” direction in any given configuration of the system, an expression is derived for the configurational Helmholtz free energy Ac as a function of s, and an equation determining math, that value of s which minimizes Ac, is obtained. At densities below some critical value ρc, the only solution to the latter equation is math  =  ⅓, but for ρ > ρc, an anisotropic solution is also possible. A first‐order anisotropic–isotropic transition is observed and the transition densities, free volume fractions, and entropy change are determined at two values of a and for ratios l / a from 2 through 18. Thus, that transition which Zwanzig observed in a fluid of very long rods (l / a → ∞) is also observed in fluids of relatively short rigid rods. The transition free volume fractions, the entropy of transition, the degree of order S in the anisotropic phase at the transition, and the relative density change Δρ / ρaniso are all seen to increase with increasing l / a, and values obtained for the latter two quantities are compared with experimentally determined values. The isothermal compressibility and the expansivity of the system are also calculated at free volume fractions (densities) near the anisotropic→isotropic transition, but no pretransition effects are observed.

Heavy Atom Effect on the Phosphorescence of Aromatic Hydrocarbons. II. Quenching of Perdeuterated Naphthalene by Alkali Halide

R. H. Hofeldt, R. Sahai, and S. H. Lin

J. Chem. Phys. 53, 4512 (1970); http://dx.doi.org/10.1063/1.1673981 (7 pages) | Cited 17 times

Online Publication Date: 18 September 2003

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The effects of varying concentrations of alkali halide, external heavy atom perturber, on the phosphorescent characteristics of naphthalene‐d8 were investigated in rigid solutions of ethyl alcohol at 77°K. It was found that the total phosphorescence could be considered as being composed of two phosphorescent species existing in equilibrium with each other: an excited, free naphthalene and an excited, 1:1 complex of perturber and naphthalene. The phosphorescent decay rates of the latter were in the range of 0.3–0.4 sec−1 when complexed with alkali iodides. The phosphorescent characteristics did not depend significantly upon the metal ion associated with the halide, and CsF up to 0.9M did not quench the phosphorescence measurably. The phosphorescent intensities and mean durations were calculated based on the proposed charge‐transfer mechanism. The experimental data were correlated very well using this mechanism. The direct spin–orbit interaction mechanism proposed by Lin and Tweed was found to be unimportant in these systems. The phosphorescent state was discussed theoretically from the charge‐transfer viewpoint. The triplet state in the donor was considered to be perturbed by spin–orbit and charge‐transfer interactions which gave rise to two terms: one involving only charge‐transfer interaction and a second, a cross term involving both spin–orbit and charge‐transfer interactions. Thus, it is predicted (and observed) that the mixing of the donor triplet arises only when a charge‐transfer complex is formed and this mixing will give rise to the heavy atom effect if a heavy atomic species is present in the acceptor. The nonradiative processes were also discussed in the light of this mechanism.

Matrix‐Isolation Spectra of H2S and D2S: An Example of the Application of the Uncoupled Oscillator Approximation

Jacob Pacansky and V. Calder

J. Chem. Phys. 53, 4519 (1970); http://dx.doi.org/10.1063/1.1673982 (6 pages) | Cited 8 times

Online Publication Date: 18 September 2003

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The first direct observation of the ν3 vibration of H2S and D2S is reported. The location of this fundamental in the matrix spectra is consonant with the band center calculated from the overtone‐combination frequencies in the gas phase. General, quadratic, valence force constants are calculated from the isotopic shifts using simple equations based on the uncoupled oscillator approximation.

Response to Double Irradiation of a Nuclear Spin System: General Treatment and New Multiple Quantum Transitions

P. Bucci, M. Martinelli, and S. Santucci

J. Chem. Phys. 53, 4524 (1970); http://dx.doi.org/10.1063/1.1673983 (8 pages) | Cited 32 times

Online Publication Date: 18 September 2003

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A general theory has been developed to calculate the response, in NMR conditions, of a spin system irradiated by two nearly resonant waves having different frequencies and intense enough to produce an appreciable saturation. The absorption signal has been calculated employing the statistical operator technique, treating the electromagnetic field by the second quantization formalism. Two kinds of transitions are expected: The first one arises from processes in which n photons of one wave are emitted and n photons of the other wave are absorbed, the second one arises from processes involving the emission of n photons of one wave and the absorption of n ± 1 photons of the other. In the first case all the transitions coalesce in a single dispersionlike signal, which occurs when the frequencies of the two waves are nearly the same; in the second case a many‐line spectrum occurs in which emission and absorption lines are present. The experimental results here reported strictly agree with theoretical previsions.

Ozone Ultraviolet Photolysis. II. Quantum Yield at Low Ozone Concentration

Henry Webster and Edward J. Bair

J. Chem. Phys. 53, 4532 (1970); http://dx.doi.org/10.1063/1.1673984 (5 pages) | Cited 8 times

Online Publication Date: 18 September 2003

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The relative ultraviolet quantum yield was measured at low ozone concentration (∼ 0.2 torr) in order to identify contributing processes under conditions where the Norrish chain mechanism is not expected. The quantum yield in pure O3 and in O3☒He mixtures exceeds that in O3☒N2 mixtures by a component ϕx  ≈  2 which is attributed to the products of the O(1D) + O3 reaction. These products decompose ozone with a rate constant k  ≤  107liter/mole⋅sec and are not affected by a large excess of inert gas. This result tends to rule out O2(3Σu+) as the reactive product.

Photoelectron Spectra of Bicyclic and Exocyclic Olefins

Daniel A. Demeo and Andrew J. Yencha

J. Chem. Phys. 53, 4536 (1970); http://dx.doi.org/10.1063/1.1673985 (8 pages) | Cited 12 times

Online Publication Date: 18 September 2003

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The construction and operational characteristics of a newly built photoelectron spectrometer are described. The photoelectron spectra of some bicyclic and exocyclic olefins and related saturated hydrocarbons have been recorded and their ionization potentials reported. The lowest ionization potentials are examined and discussed in terms of substitutional and ring strain effects. Ionization potential changes accompanying substitution in these molecules are explained by using empirically generalized substitution rules for saturated and unsaturated hydrocarbons. There appear to be no significant ring strain effects upon the lowest ionization potentials of four‐, five‐, or six‐membered ring exocyclic olefins or for the bicyclic molecules norbornane, norbornene, and norbornadiene. From a comparison of the ionization potential changes between 1, 3‐ and 1,4‐dienes, it is estimated that the two double bonds in norbornadiene are directionally coupled across the ring by an interaction energy of about 0.3 eV. From analyses of the spectral characteristics of the photoelectron spectra, the lowest ionization potentials of all the alkenes studied and the two lowest ionization potentials of norbornadiene are assigned to π ionization.

Water Molecule Interactions

D. Hankins, J. W. Moskowitz, and F. H. Stillinger

J. Chem. Phys. 53, 4544 (1970); http://dx.doi.org/10.1063/1.1673986 (11 pages) | Cited 258 times

Online Publication Date: 18 September 2003

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Accurate SCF calculations have been carried out to investigate the potential of interaction for pairs and triplets of water molecules. The most stable pair configuration involves a linear hydrogen bond of length ROO  =  3.00Å and strength 4.72 kcal/mole. Three‐molecule nonadditivities are large in magnitude and vary in sign according to the hydrogen‐bond pattern involved. In both aqueous liquids and solids, the net trimer nonadditivity effect amounts to increased binding energy, decreased neighbor distance, and slightly enhanced tendency toward perfect tetrahedral coordination symmetry. The nonadditivity furthermore is inconsistent with the phenomenology of simple mutual electrostatic polarization between neighboring molecules.

Electronic Structures of Polymers Using the Tight‐Binding Approximation. II. Polyethylene and Polyglycine by the CNDO Method

Hiroko Fujita and Akira Imamura

J. Chem. Phys. 53, 4555 (1970); http://dx.doi.org/10.1063/1.1673987 (12 pages) | Cited 70 times

Online Publication Date: 18 September 2003

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Formulas for the calculation of the electronic structure of polymers were derived by the tight‐binding approximation using the CNDO/2 method. This formalism was applied to the calculation of the electronic structure of polyethylene in the all‐trans conformation and polyglycine in the α‐helix form. For polyethylene, conformation analysis was carried out to obtain a fairly good agreement with the experimental results. The results of our conformation analysis were also in fair agreement with the calculation by the extended Hückel method which had already been published in this series of papers. The electronic structure of polyglycine was found to reflect the effect of the hydrogen bond formation in the α‐helix form.

Vibrational Excitation in a Morse Oscillator

Jeong‐long Lin

J. Chem. Phys. 53, 4567 (1970); http://dx.doi.org/10.1063/1.1673988 (8 pages) | Cited 7 times

Online Publication Date: 18 September 2003

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Vibrational excitation in the system He+H2 is studied theoretically by considering H2 as a rotating Morse oscillator. The anharmonicity of molecular vibration is found to have only a small effect on the 0 → 1 transitions. Vibrational transition probabilities are also found to be insensitive to the rotational energy of the diatom. Following the approach of Mies and Shuler, based on the modified wavenumber approximation, three‐dimensional transition probabilities are calculated from one‐dimensional results and the steric factor is obtained as a function of the collision energy.

Microwave Spectrum of Methylhydrazine; Rotational Isomerism, Internal Motions, Dipole Moments, and Quadrupole Coupling Constants

Robert P. Lattimer and Marlin D. Harmony

J. Chem. Phys. 53, 4575 (1970); http://dx.doi.org/10.1063/1.1673989 (9 pages) | Cited 6 times

Online Publication Date: 18 September 2003

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The microwave spectrum of methylhydrazine has been investigated. Two rotamers have been observed, and their spectra have been assigned and analyzed. The ground‐state rotational constants of the inner skew rotamer are A  =  36704.37MHz,B  =  9689.70MHz, and C  =  8531.95MHz, while the values obtained for the outer skew rotamer are A − C  =  29597.20MHz and κ  =  − 0.925849. Strong evidence for the conformational identifications was provided by the measured dipole moment components, which were μa  =  1.04D,μb  =  1.21D,μc  =  0.46D for the inner rotamer and μa  =  0.26D,μb  =  0.60D, and μc  =  1.70D for the outer rotamer. Relative intensity measurements indicate that the inner rotamer is more stable than the outer rotamer by 293 ± 23 cm−1. Spectral splittings produced by inversion and methyl tunneling have been observed. Analysis of the latter effect leads to a barrier of V3  =  1329cm−1 for the inner rotamer. Hyperfine splittings of the inner rotamer spectrum were described by the single set of 14N quadrupole coupling constants, χaa  =  4.09MHz,χbb  =  0.69MHz, and χcc  =  − 4.78MHz.
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