Volume 46, Issue 5, 01 March 1967
Index of content:
46(1967); http://dx.doi.org/10.1063/1.1840897View Description Hide Description
The electron spin resonance(ESR)spectrum of the dioxygen monofluoride radical (O2F) has been observed in an argon matrix at 4.2°K. The radical was produced by the reaction of O2 with fluorine atoms obtained from the photolytic decomposition of F2. Computeranalysis of the spectrum gave the following values for the components of the g factor and fluorine hyperfine‐splitting tensors:g 1=2.0080, g 2=2.0008, and g 3=2.0022; A 1/h=±288.4, A 2/h=∓141.1, and A 3/h=∓39.2 Mc/sec. Theoretical considerations suggest that A 1 is negative, and that Axis 1 lies along the O–F bond, Axis 2 is perpendicular to the molecular plane, and Axis 3 lies along the O–O bond. The ESRspectrum of O2F was found to contain normally ``forbidden'' lines in which the electron spin transition is accompanied by a nuclear spin flip. These lines may be responsible for some of the complicated changes in the appearance of this spectrum which accompany changes in temperature and matrix. By using the experimental value of g 3 to evaluate a critical parameter in a semiempirical molecular‐orbital treatment of O2F, values were obtained for the charge distribution and bond order in this radical. The results agree with conclusions drawn from infrared spectroscopy, and suggest that this radical is stabilized by resonance which permits the fluorine to form a weak O–F bond without any loss of the O–O bond strength.
46(1967); http://dx.doi.org/10.1063/1.1840898View Description Hide Description
Straightforward evaluation of electronic interaction integrals for many‐electron atoms using Laguerre polynomial radial wavefunctions leads to sums of differences of large numbers. An alternate formulation is presented which does not have this disadvantage.
46(1967); http://dx.doi.org/10.1063/1.1840899View Description Hide Description
The widely different relaxation times and frequency shifts, observed for the quadrupole resonance lines of piperazine, are treated theoretically as the effects of small‐amplitude torsional motions undergone by the molecule. The torsional frequencies and the ratio of relaxation times are calculated.
46(1967); http://dx.doi.org/10.1063/1.1840900View Description Hide Description
Effect of Deuteration of Durene on the Lifetime of the Phosphorescent Triplet State of Naphthalene in a Durene Host Crystal46(1967); http://dx.doi.org/10.1063/1.1840901View Description Hide Description
The observation of a pronounced increase in the lifetime of the lowest triplet state of naphthalene in a single crystal of durene produced by deuteration of the durene is reported. For naphthalene‐d 8 at ∼298°K the increase in mean life is from 0.8 to 10.8 sec. It is shown that the decay in question is an exponential triplet—singlet intramolecular transition.
46(1967); http://dx.doi.org/10.1063/1.1840902View Description Hide Description
The symmetric‐top spectra of 10 isotopic species of GeH3CN have been observed and measured. From the rotational constants obtained the following structural parameters have been derived: r(C–N)=1.155±0.001 Å and r(Ge–C)=1.919±0.001 Å, assuming r(Ge–H)=1.529 Å and a tetrahedral distribution about the Ge atom. From an analysis of the splittings observed in the 1→2 transitions of GeH3CN a quadrupole coupling constant for the nitrogen nucleus of −5.0±0.1 Mc/sec has been obtained. Analysis of the Stark effect gives a dipole moment of 3.99±0.05 D.
46(1967); http://dx.doi.org/10.1063/1.1840904View Description Hide Description
A configuration‐mixing method is described for single‐bonded diatomic molecules, in which both the orbitals from which the configurations are constructed, as well as the mixing coefficients, are optimized by way of solving SCF‐type equations. The method properly describes molecular formation, which is not in general possible when using the Hartree—Fock molecular‐orbital method. Numerical results are presented for the Li2 molecule. The calculated potential curve is closely parallel to an empirical curve obtained by using spectroscopic constants. The difference between the two curves may be interpreted as the correlation energy of the core electrons, and is essentially constant over the complete range of internuclear distances of chemical interest.
46(1967); http://dx.doi.org/10.1063/1.1840905View Description Hide Description
A formula has been derived for the second‐order contribution of the dipolar broadening to the second moment of the resonance lines in pure quadrupole resonance experiments.
The following assumptions have been made: The nuclei undergoing the resonant transitions have spin ½; all resonant spins experience the same electric‐field gradient which has a small amount of axial asymmetry; the dipolar interaction strength is small compared with the separation of the two resonance lines.
46(1967); http://dx.doi.org/10.1063/1.1840906View Description Hide Description
The evaporation—condensation coefficient for very small droplets is derived in the form α(a) =δ·φ(a), where δ is the free‐angle ratio and φ(a) is the size coefficient which is expressed in terms of the droplet radius a, the absolute temperature, and other characteristic variables of the liquid phase and the gas—liquid interface. With the inclusion of α(a) into the rate equations of Fuchs and of Monchick and Reiss, the rate of evaporation per unit area increases with decreasing droplet radius, reaches a maximum at droplet radii ranging between 1 and 0.01 μ, then decreases to zero as the radius approaches zero. Numerical results were obtained for H2O, He, and Hg at their respective freezing and boiling points.
46(1967); http://dx.doi.org/10.1063/1.1840907View Description Hide Description
Dissociativecharge exchange of rare‐gas ions with C2F6 and C3F8 has been studied. The data was obtained with a single‐stage Nuclide mass spectrometer by operating the ion source in the Čermák—Herman mode. A charge‐transfer mass spectrum was obtained for C2F6 and C3F8 with each rare‐gas ion except Xe. The relative ionic abundances were interpreted as portraying the dissociation of C2F6 + and C3F8 + as a function of their excitation energy. The normalized abundance of CF8 + as a funetion of excitation energy shows two maxima which indicates that two processes contribute to CF3 + formation from C2F6 and C3F8.
46(1967); http://dx.doi.org/10.1063/1.1840908View Description Hide Description
The infrared spectrum of europium acetylacetonate has been observed from 4000 to 200 cm−1 and a normal‐coordinate calculation for the in‐plane vibrations of the 1:1 single ring complex has been carried out. The Eu–O stretching frequencies are found to be in the region from 400 to 200 cm−1 and the Eu–O stretching force constant is estimated to be about 1.43×105 dyn/cm. The interpretation of the spectrum is discussed generally.
46(1967); http://dx.doi.org/10.1063/1.1840909View Description Hide Description
Starting from coupled Hartree—Fock perturbation theory, approximate expressions are derived for the magnetic shielding of a nucleus in a magnetic field. Some of these expressions are compared with existent approximate formulas which have been derived by other methods. The concept of localized contributions is explored and illustrated in the case of the diatomic molecules LiH and BH, for which exact coupled Hartree—Fock calculations have been performed.
46(1967); http://dx.doi.org/10.1063/1.1840910View Description Hide Description
Emission and excitation spectra of single and double thallous ion fluorescence are measured in KI:Tl 0.06 mole %) at 5°K. Spectra are also measured of the emission during x irradiation, of the emission stimulated after irradiation, and of the phosphorescence after irradiation. There are differences between the stimulated emission, which is entirely the result of recombination of electrons and holes, and the x‐ray‐induced emission. Two possible interpretations of the differences are discussed and the suggestion favored that hot electrons produced in the radiation shower excite optically available states of the thallium ion.
46(1967); http://dx.doi.org/10.1063/1.1840911View Description Hide Description
The conductivity of hexane under 1500‐kV x rays was studied at fields up to 40 kV/cm. Conditions were attained under which the theoretical proportionality to dose rate and to plate separation was strictly obeyed. Data are also reported for diethyl ether and 1,4‐dioxane, and for hexane irradiated by 2.4‐keV electrons from 37Ar. Onsager's formula for probability of escape of a single ion pair describes the behavior of the conductivity of low‐dielectric‐constant liquids under high‐energy x rays, but fails when applied to the results from 2.4‐keV electrons, where an appreciable probability exists of escape of more than one ion pair from a group.
46(1967); http://dx.doi.org/10.1063/1.1840912View Description Hide Description
The rotational spectrum of CF3CHF2 has been studied in the 8.4‐ to 26.5‐Gc/sec region, with c‐type, R‐branch transitions being assigned for both the ground vibrational state and the first excited torsional state. With the assumptions that r C–H=1.10 Å, ∠CCH=110°, r F–F=2.162 Å for the CF3 group, that the CF3 group is symmetrical and its axis and the C–C bond are collinear, and that the CHF2 fluorines are equivalent, an approximate structure of r C–F=1.335 Å, ∠FCF=108.14°, r C–C=1.520 Å, r C–F′=1.345 Å, ∠F′CF′=109.06°, and ÅCCF′=109.58° was found to fit the observed moments of inertia and to be consistent with determinations in other molecules. The primed F's refer to fluorine atoms of the CHF2 group. Relative intensity measurements gave a torsional frequency of 74 cm−1 compared with the infrared observation of 73.4 cm−1. From these data, the barrier to internal rotation is 1223±34 cm−1 or 3.51±0.10 kcal/mole.
46(1967); http://dx.doi.org/10.1063/1.1840913View Description Hide Description
The formula for the intensity of the radiation scattered by a liquid with complex molecules is discussed. It is shown that the choice of the molecular center is not arbitrary but determined by the condition that the distance between two molecular centers should have no influence upon the orientation of the molecules concerned. Also it is pointed out that Fourier inversion of the intensity formula is not always possible.
46(1967); http://dx.doi.org/10.1063/1.1840914View Description Hide Description
This article investigates the behavior of several properties of a model binary van der Waals mixture near the solutioncritical point. The behavior of the heat capacity is determined from an exact analysis of the partition function. For the shear and bulk viscosity, the time dependence of the currents appearing in the time correlation function formulas is determined from linearized hydrodynamicequations. For the heat capacity and the shear viscosity the results of this model are identical to those originally obtained by Fixman by a different procedure. Comparison is also made with the results obtained by Zwanzig and Mountain for these quantities in a one‐component van der Waals system near the liquid—vapor critical point. One finds, in qualitative agreement with available experiments, that the shear viscosity of a binary mixture diverges at the critical point.
46(1967); http://dx.doi.org/10.1063/1.1840915View Description Hide Description
Elementary group‐theoretical considerations predict three infrared‐active vibrational modes in KNiF3 which crystallizes with the cubic perovskitestructure.Reflectivity measurements at 300° and 90°K, in the spectral range extending from 80 to 600 cm−1, allow the observation of the above three modes corresponding to the wavenumbers: 148, 244, 441 cm−1 for T=300°K and 144, 248, 452 cm−1 for T=90°K. In addition, we observe a side band near 500 cm−1 at 300°K and 520 cm−1 at 90°K.
Assuming that the dispersion can be interpreted in terms of independent damped oscillators, the reflection data have been analyzed using both the Kramers—Kronig relationships and the classical dispersion formula. The intensity of the extra band and some feature of the vibrational absorptionspectrum in the visible range suggest that this extra band may arise from a one‐phonon process.
The oscillator parameters associated with each observed mode and those deduced from the two methods of analysis are in good agreement with temperature‐dependence considerations.
46(1967); http://dx.doi.org/10.1063/1.1840916View Description Hide Description
A detailed study is given of the time course of a stochastic model for the reversible second‐order chemical reaction A+B⇄C+D. The solutions are obtained by perturbation theory for a range of values of the rate constants of the reaction and the techniques developed may be applied to a variety of other reactions. The main conclusion of this study is that fluctuations in the number of molecules of every component present in the system at any time are negligible even for small systems.
46(1967); http://dx.doi.org/10.1063/1.1840917View Description Hide Description
Relative ionization cross sections for single ionization by electron impact on free gaseous atoms have been calculated by utilizing a summation of the mean‐square orbital radii of outer electrons. A previous calculation of the cross sections by Otvos and Stevenson was in only fair agreement with experimental data due to the use of incorrect mean‐square radii, and to the method of summation of electron‐shell contributions to the total cross sections. Hartree—Fock calculations of orbital wavefunctions have been carried out for all of the elements. Mean‐square radii of atomic orbitals from the Hartree—Fock calculations were corrected approximately for relativistic effects. The ionization cross sections obtained from the summations were normalized at argon and compared with experimental values. The computed maximum cross sections are a considerable improvement over past theoretical values.