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15 Jun 1967

Volume 46, Issue 12, pp. 4553-4998

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Long‐Range First‐Order Interaction Energy between Two Excited Hydrogen Atoms in Either 2s or 2p States

Hojing Kim and Joseph O. Hirschfelder

J. Chem. Phys. 46, 4553 (1967); http://dx.doi.org/10.1063/1.1840600 (2 pages) | Cited 4 times

Online Publication Date: 3 May 2004

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The long‐range interactions between two hydrogen atoms in either 2s or 2p states yields the first‐order perturbation energy matrix which is still nondiagonal even after the symmetry adaptation of the zero‐order degenerate functions. In the diagonalization process of the nondiagonal blocks, it is found that the familiar series expansion of the interaction potential energy in inverse powers of the internuclear separation is not practicable even up to 60 Bohr units.

Selective Enhancement in Hydrogenlike Molecules with the Rare Gases. II. HD and D2 with Ar and Kr

S. Takezawa, F. R. Innes, and Y. Tanaka

J. Chem. Phys. 46, 4555 (1967); http://dx.doi.org/10.1063/1.1840601 (7 pages) | Cited 10 times

Online Publication Date: 3 May 2004

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Recent work on selective enhancement of the H2 spectrum in Ar and Kr discharges has been extended to HD and D2. Similar phenomena are expected and can be observed in the spectra of these molecules when excited in Ar but not in Kr. The explanation given of the processes involved in the case of H2, namely, resonance fluorescence and collisions of the second kind involving allowed transitions, was supported also by the observed evidence in the present work. Vibration levels in the ground state of HD and D2 were greatly extended and the highest levels which occur in these states can now be estimated at (v= ) 17 and 21, respectively.

Vacuum‐Ultraviolet Photolysis of Acetylene in Inert Matrices. Spectroscopic Study of the Species C2

Dolphus E. Milligan, Marilyn E. Jacox, and Luce Abouaf‐Marguin

J. Chem. Phys. 46, 4562 (1967); http://dx.doi.org/10.1063/1.1840602 (9 pages) | Cited 75 times

Online Publication Date: 3 May 2004

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The vacuum‐ultraviolet photolysis of acetylene isolated in Ar, Ne, and N2 matrices at 4° and at 14°K is shown to lead to the appearance of a number of visible‐ultraviolet absorption bands which may be assigned to the species C2, as well as to an 1848 cm−1 infrared absorption assigned, with the aid of isotopic substitution studies, to the free radical HC2. The (0, 0) band of the Mulliken system of C2 is observed with great intensity at 2382 Å (Ar matrix) or at 2323 Å (Ne matrix) and the (2, 0), (3, 0), and (4, 0) bands of the Phillips system of C2 are observed in an Ar matrix at 8700, 7675, and 6880 Å, respectively, indicating that the x 1Σg+ state of C2 is the ground state of this species not only in the gas phase but also in the matrix. Features assigned by previous workers to the Swan transition of triplet C2 appear at 5206 and 4725 Å. A third member of the progression, not previously observed, appears at 4334 Å. Experiments utilizing C2D2 and C2H2 (58% 13C) support the assignment of these features to C2. The 5206‐Å band system decreases in intensity and finally disappears when the sample is subjected to radiation of wavelength near 2500 Å. Problems associated with the assignment of these features are discussed, and a possible mechanism for their photolytic destruction is suggested.

On Static and Dynamic Compressibilities of Debye Solids at High Pressures

Y. K. Huang

J. Chem. Phys. 46, 4570 (1967); http://dx.doi.org/10.1063/1.1840603 (6 pages) | Cited 5 times

Online Publication Date: 3 May 2004

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Investigations show that static compressibility of a Debye solid can be deduced from shock‐compression data and vice versa. In this paper three different approaches are considered for the evaluation of static and dynamic compressibilities. Except for the linear law of shock propagation and the Born—Mayer type of energy function, which are semianalytical, all other equations are derived on a full analytic basis. It is of interest to show that the entropy and temperature are implicit functions of shock compression. These implicit functions are then determined in closed form, and they turn out to provide a means for the calculation of thermal properties of the Debye solid at high pressures in terms of purely mechanical parameters. Some calculated results are given according to the pseudo‐Hugoniot approach only, and the validity range covers pressures from 104−107 atm and temperatures from 102−103K.

Shock‐Tube Study of Chain Branching during the Induction Period of the Hydrogen—Oxygen Reaction

David Gutman and Garry L. Schott

J. Chem. Phys. 46, 4576 (1967); http://dx.doi.org/10.1063/1.1840604 (9 pages) | Cited 20 times

Online Publication Date: 3 May 2004

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The growth of ``blue continuum'' emission has been measured during the induction period of the reaction of H2 (0.5%, 1.5%, and 5%)☒CO (3.3% and 33%)☒O2 (0.5%)☒Ar mixtures between 1100° and 1700°K. For sensitivity, the reacting gas behind reflected shock waves was viewed axially through a large end plate window and lens. The observed intensity I, representing the integral of I′ (x)dx between reflected shock front and end plate, exhibited 2 to 3 decades of exponential growth, I = I0 exp(αt). α is related to the branching chain kinetics of H2☒O2 combustion through the proportionality of I′ (x) to the product [CO][O]. α was found to be satisfactorily proportional to density and independent of [CO], and its dependence upon [O2] and [H2] was analyzed to yield rate coefficients for
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and
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between 1290° and 1667°K. These are represented by
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(±10%) over our range, and
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from combination of our mean result with literature data at 400°K.

Near‐Molecular Hartree—Fock Wavefunction for CH3−

R. E. Kari and I. G. Csizmadia

J. Chem. Phys. 46, 4585 (1967); http://dx.doi.org/10.1063/1.1840605 (6 pages) | Cited 6 times

Online Publication Date: 3 May 2004

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Ab initio LCAO—MO—SCF calculations have been performed on CH3− with a C☒H bond length of 1.95 Bohr atomic units, using Gaussian‐type functions (GTF) as the basis set. By successive increases in the size (N) of the basis set of GTF (N = 12, 20, 28, 36, 40) it was possible to approach the estimated molecular Hartree—Fock limit within 0.06 Hartree atomic units. The best calculated total energy was −39.4798 hartrees. The Hartree—Fock limit has been estimated to be −39.535 hartrees for the equilibrium C☒H distance, and as high as −39.501 hartrees for the above C☒H separation. The variation of the geometry of CH3− indicated that the molecule is pyramidal in its ground state, with the HCH angle approximately equal to 115°. The inversion‐barrier height is estimated to be 1.22 kcal/mole. The charge distribution, as deduced from Mulliken's population analysis, was such that there was approximately 1.099 negative charge on the carbon atom and 0.033 positive charge on each of the three hydrogen atoms. Due to its symmetry, the planar molecule possessed zero dipole moment but it assumed finite values in pyramidal conformations. The total electron density as well as the near‐Hartree—Fock molecular‐orbital densities are presented in the form of contour maps. Within the framework of a single Slater determinantal wavefunction, estimation for the energy values of some of the low‐lying electronic excited states of CH3− have been made.

Some Thermodynamics of Photochemical Systems

Robert T. Ross

J. Chem. Phys. 46, 4590 (1967); http://dx.doi.org/10.1063/1.1840606 (4 pages) | Cited 44 times

Online Publication Date: 3 May 2004

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A limit on the thermodynamic potential difference between the ground and excited states of any photochemical system is established by evaluating the potential difference at which the rate of photon absorption and emission are equal; the relationship between absorption and emission is given by a Planck‐law relation, provided that there is thermal equilibrium between the sublevels of each electronic band. The actual potential developed may be evaluated if the quantum yield of luminescence is known. The maximum amount of power storage obtainable is evaluated by lowering the potential difference until the product of the potential difference and the fraction of the quanta retained is maximized. The history and applications of the Planck‐law relation between absorption and emission spectra are discussed briefly, and applications of the potential difference calculation are mentioned.

Vacuum‐Ultraviolet Absorption Spectrum of Carbon Suboxide

John L. Roebber, J. C. Larrabee, and R. E. Huffman

J. Chem. Phys. 46, 4594 (1967); http://dx.doi.org/10.1063/1.1840607 (7 pages) | Cited 19 times

Online Publication Date: 3 May 2004

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Absorption coefficients of carbon suboxide have been measured from 2000 to 1050 Å photoelectrically and the absorption spectrum has been photographed from 1000 to 600 Å. The background light sources were the H2, He, and Ar continua. The region from 1650–1050 Å is dominated by a ns←π Rydberg series converging to the first ionization potential at 10.60 eV. Diffuse structure on the short‐wavelength side of three of the Rydberg bands is probably caused by vibrational progressions in the C☒C and C☒O symmetric stretching frequencies but may be due to two other fragmentary Rydberg series. Several very strong diffuse bands are present below 1000 Å which have not yet been assigned. A system of 14 bands around 1780 Å may be a vibrational progression in a 400 cm−1 bending mode or a vibrational sequence. Neither the experimental evidence nor theoretical considerations allow a definite assignment to be made. However, the gradual emergence of the vibrational structure from the underlying continuum strongly supports the progression explanation.

Thermal Diffusion Factors from the Measurements on a Trennschaukel: Ar☒He and Kr☒Ne

B. P. Mathur, R. K. Joshi, and S. C. Saxena

J. Chem. Phys. 46, 4601 (1967); http://dx.doi.org/10.1063/1.1840608 (3 pages) | Cited 5 times

Online Publication Date: 3 May 2004

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Measurements of the thermal diffusion factors αT are made on an eight‐tube glass trennschaukel with its two ends at about 0° and 100°C. The two systems investigated are Ar☒He and Kr☒Ne at a composition for which some special interest exists. The αT results are compared with the other available literature values, and the previously observed anomalies are explained on the basis of these new measurements. For the Ar☒He mixture containing 81.6% Ar we get an αT value of 0.30 at 318.6°K. Similarly for a Kr☒Ne mixture (27.5% Ne) the value is found to be 0.303 at 318.5°K.

Long‐Wavelength, Infrared‐Active Fundamental for Uranium, Neptunium, and Plutonium Hexafluorides

Boris Frlec and Howard H. Claassen

J. Chem. Phys. 46, 4603 (1967); http://dx.doi.org/10.1063/1.1840609 (2 pages) | Cited 8 times

Online Publication Date: 3 May 2004

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The long‐wavelength, infrared‐active fundamentals, ν4, have been observed for uranium, neptunium, and plutonium hexafluorides at 186.2, 198.6, and 206.0 cm−1, respectively. The corresponding values predicted earlier from combination bands were 184, 198, and 203 cm−1. From the P—R branch separations Coriolis zeta constants have been calculated for these bands.

Microwave Spectrum and Rotational Isomerism of Ethyl Formate

José M. Riveros and E. Bright Wilson

J. Chem. Phys. 46, 4605 (1967); http://dx.doi.org/10.1063/1.1840610 (8 pages) | Cited 40 times

Online Publication Date: 3 May 2004

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The microwave spectrum of ethyl formate reveals the presence of at least two rotational isomers. Both isomers have the ethyl group cis to the carbonyl oxygen atom but they differ in the orientation of the methyl group about the ☒CH2☒O bond. The trans isomer has the conformation with the heavy‐atom skeleton coplanar, while in the gauche isomer the methyl group is 95° out of the plane. The relative intensity measurements show the trans isomer to be lower in energy with the difference between the lowest states of the two isomers (gauche—trans) equal to 186±60 cal/mole. Five vibrationally excited states for the trans and one excited state of the gauche are assigned to the torsion about the ☒CH2☒O bond. The relative intensities of these excited states and their rotational constants are used to derive, in the one‐vibration approximation, the potential function for the internal rotation of the ethyl group. This potential function yields an estimated 1100±250 cal/mole for the trans—gauche potential barrier. The dipole moment of both isomers is calculated from Stark‐effect measurements, yielding μ = 1.98±0.02 D for the trans and μ = 1.81±0.02 D for the gauche form.

Photochromism. I. The Spectroscopy and Energy Levels of Salicylideneaniline

Michael Ottolenghi and Donald S. McClure

J. Chem. Phys. 46, 4613 (1967); http://dx.doi.org/10.1063/1.1840611 (8 pages) | Cited 22 times

Online Publication Date: 3 May 2004

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As a prerequisite to understanding the photochemistry of salicylideneaniline, its energy levels and their characteristics are deduced from absorption and emission spectra, and by comparison with related molecules. Theoretical calculations are used to help to establish relations between stilbene, benzylideneaniline, azobenzene, and salicylideneaniline (SA). It is concluded that all the ππ* bands observed in SA below 6 eV have analogs in the allowed or forbidden transitions of stilbene. From a study of solvent effects, it is concluded that the internal hydrogen bond of SA causes large changes of band intensity, but relatively small energy changes. The luminescence of SA appears to come from the second triplet rather than the first. This could be understood if the two lowest triplets have quite different geometries. The problem of the triplets is discussed further in the second part of this series.

Photochromism. II. Photochemistry of Salicylideneaniline

Michael Ottolenghi and Donald S. McClure

J. Chem. Phys. 46, 4620 (1967); http://dx.doi.org/10.1063/1.1840612 (10 pages) | Cited 15 times

Online Publication Date: 3 May 2004

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The processes following electronic excitation of salicylideneaniline include the photochemical formation of a colored orthoquinonelike molecule, phosphorescence, and several modes of radiationless decay back to the ground state. These pathways are examined in detail to learn the steric requirements, relative yields, temperature effects and the electronic states involved for each. It is shown that the photochemistry occurs from the lowest singlet (nπ*) level, and that phosphorescence (τ=80 μsec in EPA at 77°K) is in competition with it. An independent parallel radiationless process appears to lead from the lowest ππ* singlet to the lowest ππ* triplet. Evidence for the latter state is a metastable absorption at 5000 Å, τ=330 μsec in EPA at 77°K. The steric inhibition of the photochemistry was investigated by using a mixed crystal system, salicylideneaniline in dibenzyl.

Theoretical Model for Metal Electrode in Electrolytic Solution. I. Electrical‐Double‐Layer Structure in Equilibrium

T. Hashino

J. Chem. Phys. 46, 4630 (1967); http://dx.doi.org/10.1063/1.1840613 (9 pages) | Cited 1 time

Online Publication Date: 3 May 2004

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A model for the potential barrier which arises at the interface as a result of a contact equilibrium between a metal electrode and an electrolytic solution is discussed in an analogy to the electrical junction model of the metal rectifier. Every type of so‐called electrode reaction can be represented by a general expression. Involving heterogeneous chemical process in the metal‐rectifier model and approaching in terms of the behavior of real charged species from the standpoint of statistical thermodynamics and solid‐state physics, the picture of the so‐called electrical double layer becomes quite a modified structure compared with that in existing electrochemistry. According to this model it is possible to define unambiguously the so‐called preelectrode state and the differential dielectric constant region. This model may be quite useful in problems of electrostatic and kinetic phenomena and also useful in the rate theory of electron‐transfer reaction.

Theoretical Model for Metal Electrode in Electrolytic Solution. II. Absolute Rate Theory of Heterogeneous Electron‐Transfer Reaction

T. Hashino

J. Chem. Phys. 46, 4639 (1967); http://dx.doi.org/10.1063/1.1840614 (7 pages)

Online Publication Date: 3 May 2004

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A theory of the electron‐transfer reaction at the boundary between an electrode and an electrolytic solution is discussed as a heterogeneous process, in analogy with the metal‐rectifier theory, according to the contact model proposed in the previous paper. Using the theory of the absolute reaction rate, the rate constant is related to the partition function of the substances participating in this reaction. The relation between the faradaic current and the applied polarization, i.e., the so‐called overpotential, can be theoretically derived in a similar form with the familiar expression. Various kinetic parameters, e.g., α value, rate constant etc., may be exactly rearranged as a problem of statistical mechanics and electromagnetism.

Molecular Orbitals and Inner‐Electron‐Shell Chemical Shifts for Sulfur and Chlorine Oxy‐anions

Rolf Manne

J. Chem. Phys. 46, 4645 (1967); http://dx.doi.org/10.1063/1.1840615 (7 pages) | Cited 49 times

Online Publication Date: 3 May 2004

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Approximate MO LCAO SCF calculations have been performed on the ions SO42−, S2O32−, SO32−, ClO4−, ClO3−, and ClO2−. The results are applied to a discussion of chemical effects in x‐ray spectra and inner‐shell photoelectron spectra. Good agreement is obtained with charge distributions estimated from shifts of the Kα12 emission line of sulfur and chlorine. The valence‐electron molecular‐orbital structure differs considerably from that obtained from Wolfsberg—Helmholz calculations and agrees with ESR measurements on SO4− and S2O3−.

Effects of Fluorescence and Energy Transfer in Polystyrene under Excitation in the Vacuum Ultraviolet

M. Leibowitz and A. Weinreb

J. Chem. Phys. 46, 4652 (1967); http://dx.doi.org/10.1063/1.1840616 (8 pages) | Cited 6 times

Online Publication Date: 3 May 2004

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The emission spectrum of solid polystyrene is investigated as a function of excitation wavelength in the region 2540–1216 Å, for various modes of preparation (solid machined disks, films, evaporation layers) and treatment (heating, polishing, etc.). A strong dependence of the spectral distribution on excitation wavelength is observed. Exciting radiation which is more strongly absorbed produces a fluorescence spectrum extending to longer wavelengths. A strong influence of the mode of preparation and treatment of the sample on the fluorescence spectrum is observed. The results are tentatively interpreted as representing the strong influence of the solid‐state structure of the material on intermolecular interactions between segmers.
The fluorescent quantum yield of solid solutions of diphenyloxazole and of anthracene in polystyrene is investigated as a function of the excitation wavelength in the region 3164–584 Å. A strong variation of the quantum yield with excitation wavelength is observed. The results are interpreted in terms of a competition between solvent—solvent and solvent—solute interactions, the probability of each depending on excitation wavelength. The difference in behavior of solutions of PPO and solutions of anthracene is discussed.

Studies of Thermal Annealing of Neutron‐Irradiated Tris(dipyridyl)Cobalt (III) Perchlorate. Redistribution of Electrons among the Donors

Amar Nath and S. P. Vaish

J. Chem. Phys. 46, 4660 (1967); http://dx.doi.org/10.1063/1.1840617 (6 pages) | Cited 2 times

Online Publication Date: 3 May 2004

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Thermally treated and untreated anhydrous samples of tris (dipyridyl) Co(III) perchlorate were ``hydrated'' at 30° in air at a relative humidity of 93%. Some of them were chilled at −78° while others were kept at 30° for a prolonged period before chilling at −78°. The chilled samples were neutron irradiated at −78°. Thermally treated samples chilled immediately after hydration exhibit a much faster rate of thermal annealing as compared to the latter and to the trihydrate. These observations have been interpreted on the basis of the ``variable‐depth‐electron‐donors—isotopic‐exchange'' model which postulates an annealing rate proportional to the free‐electron density. Evidence is presented for the creation of electron traps and electron—hole ``recombination centers'' during thermal treatment of the anhydrous form and for populating of the electron traps with electrons to form shallow donors during hydration through exo‐electron emission. Hence, in the freshly hydrated samples kept at 30° for prolonged periods before chilling and irradiation, a considerable amount of depopulation of the shallow donors takes place resulting in a slower rate of postrecoil thermal annealing. In contrast, the hydrated complex prepared by hydrating the untreated anhydrous sample exhibits a faster rate of annealing on storage at 30° after hydration and prior to irradiation as compared to the samples chilled immediately after hydration. For the trihydrate it has been shown that the electron traps constituted by the crystal imperfections are largely filled up with electrons during crystallization from aqueous solution. However, the process of filling up continues slowly during storage of Co(dipy)3‐(ClO4)3⋅3H2O at 30°C (or at higher temperatures). Consequently, the stored samples show a faster rate of annealing as compared to the freshly prepared ones.

Molecular Resonant Charge‐Transfer Processes; H2+☒H2 and N2+☒N2

J. J. Leventhal, T. F. Moran, and L. Friedman

J. Chem. Phys. 46, 4666 (1967); http://dx.doi.org/10.1063/1.1840619 (7 pages) | Cited 32 times

Online Publication Date: 3 May 2004

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A study has been made of the competition between exothermic ion—molecule reactions and resonant charge‐transfer processes in collisions of diatomic molecule ions and their parent molecules; H2+☒H2 and N2+☒N2. Experimental values of resonant charge‐transfer cross sections are shown to be smaller than values obtained from calculations using an impact parameter method. Much better agreement between experiment and theory is obtained if competition between ion—molecule reaction and charge transfer is assumed and experimental values of both channels of reaction are summed prior to comparison with theory. The mechanisms of the respective processes are illuminated by an examination of the velocity dependences of charge‐transfer cross section for both diatomic systems. With H2+☒H2 where reaction producing H3+ is a probable process, in low‐velocity collisions, the velocity dependence of charge transfer is essentially that of collisions of ions with unperturbed rectilinear trajectories. In a similar low‐energy region, N2+☒N2 is not energetically capable of participating in ion—molecule reactions and the velocity dependence of charge‐transfer cross section is steeper, characteristic of both orbiting collisions and the larger‐impact‐parameter rectilinear trajectory collisions. Experimental cross sections for charge transfer and ion or atom transfer reflect probability of reaction but their velocity dependences clearly isolate the range of impact parameters operative for the respective processes.

Viscous Flow and Electrical Conductance in Ionic Liquids: Temperature and Composition Dependence in the Light of the Zero Mobility Concept

C. A. Angell

J. Chem. Phys. 46, 4673 (1967); http://dx.doi.org/10.1063/1.1840620 (7 pages) | Cited 28 times

Online Publication Date: 3 May 2004

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Using the concept of vanishing mobility consequent on the Gibbs—Dimarzio interpretation of the liquid—glass transition, it is shown by a quasiempirical treatment of the data that the isothermal composition dependence of transport at low temperatures may be understood, and expressed analytically, on the basis that the zero mobility temperature T0, is the only composition‐dependent parameter in the transport equation. T0 reflects the forces of cohesion in the liquid. Simple equations developed on this basis lead to a description of conductance in uni‐divalent nitrate melts, and an account of viscous flow in 0–15N concentrated aqueous solutions which is consistent with the electrical‐conductance behavior of the same solutions. The usefulness of the Tobolsky and related parameters in describing deviations from additivity in the conductance of mixed molten univalent nitrates is interpreted in the same terms, providing a rational basis for the parallel between kinetic and thermodynamic behavior in these melts. Attention is drawn to the importance of pre‐exponential terms to transport composition dependence at higher temperatures.

Fluorescence and Triplet State of Hexafluorobenzene

David Phillips

J. Chem. Phys. 46, 4679 (1967); http://dx.doi.org/10.1063/1.1840621 (11 pages) | Cited 27 times

Online Publication Date: 3 May 2004

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The photochemistry of hexafluorobenzene in the vapor phase has been studied to compare the heavy‐atom substituted molecule with the unsubstituted molecule of the same symmetry. Results show that at all wavelengths below 2800 Å, absorption produces two excited singlet states, one of which is quickly equilibrated to a fluorescent state, the other more slowly. Some process occurs from the latter state with a rate such that collisional loss of energy is barely competitive. This process may be an isomerization. The use of the biacetyl sensitization and Cundall techniques at various wavelengths indicated that the lifetime of the hexafluorobenzene triplet was short, and of the order of 10−7 sec leading to difficulties in absolute measurement of the triplet‐state yields. The quenching of biacetyl phosphorescence excited by 4358‐Å radiation by hexafluorobenzene is observed, and the effect of exciting wavelength upon the fluorescence yields of hexafluorobenzene is discussed. A simple mechanism has been proposed and rate constants and quenching cross sections calculated.

NMR Studies of Single Crystal ND4Cl

Melvin Linzer and Richard A. Forman

J. Chem. Phys. 46, 4690 (1967); http://dx.doi.org/10.1063/1.1840622 (4 pages) | Cited 9 times

Online Publication Date: 3 May 2004

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The 2D and 14N NMR spectra in single crystals of ND4Cl have been studied from room temperature to −175°C. At high temperatures, motion of the ammonium ion narrows the NMR resonances and averages out both dipole—dipole and quadrupole interactions. As the temperature is lowered, a linewidth transition occurs and quadrupole splittings of the 2D spectrum appear. No splitting is found for the 14N spectrum in both NH4Cl and ND4Cl. From crystal rotation studies, the 2D quadrupole coupling is determined to be 180.1±1.0 kHz and the asymmetry parameter to be 0.00±0.01.

Pairwise Trapping of Dissimilar Radical Species and Radical Conversion in a Single Crystal of Monofluoroacetamide γ Irradiated at 77°K as Studied by Electron Spin Resonance

Machio Iwasaki and Kazumi Toriyama

J. Chem. Phys. 46, 4693 (1967); http://dx.doi.org/10.1063/1.1840623 (5 pages) | Cited 18 times

Online Publication Date: 3 May 2004

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This is the first report of the pairwise trapping of dissimilar radical species in irradiated crystals. Besides the isolated radical of ⋅CH2CONH2, a radical pair between ⋅CH2CONH2 and ⋅CHFCONH2 was found in a single crystal of CH2FCONH2, γ irradiated at 77°K. The paired radicals were formed with one specific orientation and separation which were the same as with the molecules in the undamaged crystal. The observed principal values of the D tensor due to the magnetic dipole interaction of the two unpaired electrons gave a mean distance between the paired radicals of 7.03 Å. The alignment of the paired radicals was also determined by the principal directions of the D tensor. Both the separation and the alignment of the paired radicals thus obtained are in very good agreement with those calculated from the structure of the mother crystal. Furthermore, on warming the crystals the isolated radical ⋅CH2CONH2 was quantitatively converted into the radical ⋅CHFCONH2 which is the same species as found in room‐temperature irradiation. The pairwise trapping of dissimilar radicals and the radical conversion found must give important information in considering the primary process of the radiation‐induced reaction.

Pople‐like SCF—LCAO—MO Treatment of 77′,88′‐Tetracyanoquinodimethan and Its Univalent Anion

David A. Lowitz

J. Chem. Phys. 46, 4698 (1967); http://dx.doi.org/10.1063/1.1840624 (20 pages) | Cited 81 times

Online Publication Date: 3 May 2004

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See Also: Erratum

Show Abstract
Roothaan closed‐ and open‐shell SCF—LCAO—MO calculations were carried out for 77′,88′‐tetracyanoquinodimethan (TCNQ) and its univalent anion (TCNQ−), respectively. The dominant integrals were evaluated semiempirically in the manner of Pariser, Parr, McWeeny, and Peacock, including the approximation of total zero‐differential overlap (TZDO). Singlet and triplet spectra for TCNQ0 and doublet and quartet spectra for TCNQ− were calculated by means of a configuration‐interaction treatment involving singly excited states. Good correspondence was obtained with the experimental spectra. In addition, also in the TZDO approximation, we calculated the same spectra based on a semiempirical evaluation of the dominant integrals in the manner of Mataga, Nishimoto, Popkie, and Moffat. The two sets of theoretical spectra can be taken to correspond equally well with experiment. Charge density and spin density in TCNQ− based on an approximation to a projected UHF wavefunction following Amos and Snyder were obtained. Comparisons made with SCF, Hückel, and McLachlan spin‐density values show the usual correspondence, and there is reasonable agreement with an experimental value of the spin density at the unsubstituted ring carbon. Bond lengths obtained from bond orders agree very well with the x‐ray results of Fritchie and Arthur on Cs TCNQ, where they observed two species of TCNQ and assigned one as TCNQ0 and the other as TCNQ−.

Experimental Investigations of Ion—Molecule Reactions of D2+ with D2 and H2

L. D. Doverspike and R. L. Champion

J. Chem. Phys. 46, 4718 (1967); http://dx.doi.org/10.1063/1.1840625 (8 pages) | Cited 25 times

Online Publication Date: 3 May 2004

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The reactions D2++D2→D3++D and D2++H2→(D2H+, H2D+)+(H, D) have been studied using an angular ion‐scattering apparatus in which the kinetic‐energy distributions of the various product ions have been measured for collision energies in the range 2–15 eV. The angular distributions of the D3+ and D2H+ product ions have also been determined, at primary beam energies in the interval 7–11 eV. The observed product‐ion kinetic‐energy distributions show that several endothermic reaction channels exist for these reactions. The most probable channels for D3+ and D2H+ formation are those in which the product ions are formed by a pickup process, in which very little momentum is transferred to the H or D atom. By comparing the results of these isotopic reactions, it is inferred that D3+ is formed not only by D atom transfer to D2+, but also by D+ ion transfer to the target D2 molecule. Furthermore, at low collision energies, reaction channels corresponding to completely inelastic reactions in which all the center‐of‐mass collision energy appears as excitation energy of the product ions were observed for all three product ions.
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