Volume 45, Issue 1, 01 July 1966
Index of content:
45(1966); http://dx.doi.org/10.1063/1.1727289View Description Hide Description
The fraction of radiant energy incident on an absorber which may appear as work is limited by the radiation entropy and entropy gained in irreversible transfer from the radiation field to an absorber. Irreversibility may result from directionality of the radiation field, and some irreversibility is necessary to cause a net flow of energy from a radiation absorber into work or free‐energy storage. Impedance in the conversion apparatus may further limit the efficiency. Maximization of power storage under these constraints is discussed, and the general arguments are then applied to photoelectrical and photochemical systems; in these systems nonresonant decay of the excited state represents a major source of inefficiency, which may be minimized by appropriate choices for the Boltzmann temperature and optical density of the absorber. The relationships are developed for narrow‐band absorption, and application to broad‐band systems is discussed only briefly.
45(1966); http://dx.doi.org/10.1063/1.1727359View Description Hide Description
The deuterium nuclear quadrupole coupling constants of CH3–C≡C–D, Cl–C≡C–D, and F–C≡C–D have been determined in order to investigate the effect of substitution on the electron distribution in the C—D bond. The results along the C—D bond yield χD=208±10 kc/sec for CH3–C≡C–D, χD=212±10 kc/sec for F–C≡C–D, and χD=225±18 kc/sec for Cl–C≡C–D. The results show equal deuteron field gradients within experimental error and therefore show that the C—D bond is relatively insensitive to the substitution at the other end of the acetylenic bond.
Electric Dipole Polarizability of Atoms by the Hartree—Fock Method. III. The Isoelectronic 10‐Electron Series45(1966); http://dx.doi.org/10.1063/1.1727290View Description Hide Description
Results are presented for the electric dipole polarizabilities of the neon isoelectronic series in the presence of a finite electric field. The calculations were done analytically, but sufficient numbers of carefully chosen and optimized basis functions were used in order to assure a good fit to the exact solution for the Hartree—Fock equations. Shell polarizabilities are given, and these exhibit some interesting relationships. Approximate hyperpolarizabilities are given.
45(1966); http://dx.doi.org/10.1063/1.1727296View Description Hide Description
The bipolar angle average of a two‐center, two‐particle function f(ra1, rb2, r 12; R) isA bipolar angle average weight function L 0 is derived from geometrical considerations such thatThe L 0 is independent of f and has a different, although simple, functional form in each of 42 regions of ra1—rb2—r 12 space. However, the 〈f〉 have different functional forms in only four regions of ra1—rb2 space. The expressions which we derive for the bipolar angle average are surprisingly simple and general, requiring only the evaluation of integrals of the form ∫fr 12 dr 12 and ∫fr 12 2 dr 12. The bipolar angle averages are very useful in the evaluation of two‐center, two‐particle integrals. Many of our relations are greatly simplified by the use of homogeneous coordinates. Bipolar angle averages are also developed for functions f(ra1, rb1, rb2, r 12; R) which involve the additional variable rb1.
Arrhenius Activation Energy of Electrical Conductance of Aqueous Lithium and Cesium Chloride Solutions in the −2°‐+12°C Range45(1966); http://dx.doi.org/10.1063/1.1727310View Description Hide Description
The electrical conductivities of aqueous 0.001, 0.01, 0.1, 1.0, and 3.0M LiCl and of 0.001, 0.01, 0.1, and 1.0M CsCl solutions have been measured at 1 atm over the temperature range −2°‐+12°C. Although LiCl is a water structure maker and CsCl a structure breaker the Arrhenius activation energies of electrical conduction both show maxima near the temperature of maximum density.
Thermal‐Energy Ion—Neutral Reaction Rates. V. Measured Rate Constants for C+ and CO+ Reactions with O2 and CO245(1966); http://dx.doi.org/10.1063/1.1727315View Description Hide Description
The rate constants for the charge‐transfer reactions of CO+ with O2 and CO2, and the ion—atom interchange reactions of C+ with O2 and CO2 have been measured at 300°K in a pulsed‐discharge flowing‐afterglow system. These reactions are all efficient, having rate constants ∼10−9 cm3/sec except for CO+charge transfer to O2 which has a rate constant 2×10−10 cm3/sec.
45(1966); http://dx.doi.org/10.1063/1.1727319View Description Hide Description
Four electron paramagnetic resonance transitions of the SO free radical generated in a gas‐phase discharge of SO2 have been observed and assigned. The lines result from electric‐dipole transitions between the Zeeman levels of the K = 1, J = 1 → K = 2, J = 1 states of the 3Σ− electronic ground state of 32S16O and 34S16O. The rotational constantB 0 and the splitting constants λ and μ have been obtained from the microwave investigation of Powell and Lide. The g values of the electron spin, the orbital, and the rotational magnetic moments of 32S16O as determined from least‐squares fitting of the EPR data are gs = 2.00197, gl = 0.00371, and gr = 0.00019. The frequencies of the corresponding transitions for the less abundant species, 34S16O, have been calculated from the isotope corrected 32S16O parameters. The relative intensities and linewidths of the SO spectrum are discussed. The linewidth is attributed to the collision broadening of SO by SO2.
Simultaneous Donor Quenching and Acceptor Sensitization in Phosphorescence Studies of Triplet Energy Transfer: The Biacetyl—Benzil System45(1966); http://dx.doi.org/10.1063/1.1727333View Description Hide Description
The simultaneous measurement of donor quenching and acceptor sensitization of a triplet‐energy‐transfer system as studied by phosphorescence techniques is presented. The quenching constant (KQ = 900±90 liter mole−1) is found to be different than the sensitization constant (KS = 390±40 liter mole−1). A general mechanism is proposed which accounts for these results, and also for cases where KS = KQ. Arguments are presented for the reevaluation of the triplet energies of benzil and anisil, and the newly appraised values are ET (benzil) = 19 000 cm−1 and ET (anisil) = 19 300 cm−1.
Mass Spectrometry of Free Radicals and Vibronically Excited Molecules Produced by Pulsed Electrical Discharges45(1966); http://dx.doi.org/10.1063/1.1727346View Description Hide Description
Free radicals and metastable molecules produced by short‐duration pulsed electrical discharges have been studied with a mass spectrometer employing a collision‐free molecular‐beam sampling system. Nitrogen atoms generated by extremely short pulses (0.035‐μsec half‐width) have been used to study the dynamics of the gas‐sampling system. NH free radicals produced by electrical discharges in ammonia were detected in the X 3Σ−ground state and in the a 1Δ electronically excited state. It is estimated that approximately 22% of the NH radicals were in the a 1Δ state. Direct measurement of the ionization potential of NH in the ground state gives I (NH) = 13.1 eV. Vibronically excited nitrogen molecules from a discharge in a N2–He mixture have been observed with excitation energies up to about 9 eV, indicating that either or both of the metastable electronic states, a 1Π g and a′ 1Σ u −, are substantially populated by the discharge. Evidence for excitation of N2 X 1Σ g + ground‐state molecules to high vibrational quantum numbers has been obtained from the appearance‐potential curve of the N2 + ion.
45(1966); http://dx.doi.org/10.1063/1.1727353View Description Hide Description
Mass‐spectrometric studies of the methylene free radical, produced by short‐duration pulsed electrical discharges in methane, give for the ionization potential the value I (CH2) = 10.33±0.1 eV, in good agreement with the spectroscopically determined value I (CH2) = 10.396 eV, thereby removing the large discrepancy that had previously existed between electron‐impact and the optical spectroscopic measurements of the ionization potential. The absence of resolved structure in the CH2ionization curve indicates that the energy separation between the ground states of the two known modifications of CH2, the linear form in the 3Σ g − state and the bent form in the 1 A 1 state, is small but the information is insufficient to establish which is the true ground state of the molecule. In the course of the work, the ionization potential of the methyl radical was remeasured with the result I (CH3) = 9.86 eV, in excellent agreement with the spectroscopically known value I (CH3) = 9.843 eV.
45(1966); http://dx.doi.org/10.1063/1.1727354View Description Hide Description
The measurement of the Stark effect of the near‐ultraviolet absorptionspectrum of formaldehyde vapor is described. The magnitude of the electric dipole moment of the 1 A 2 (nπ*) state is 1.56±0.07 D and its direction is the same as that of the ground‐state dipole moment. The decrease of dipole moment on excitation (0.78 D) is much smaller than predicted from a naive molecular orbital model, but is in good agreement with the value (0.66 D) corresponding to the previously calculated orbitals of Foster and Boys.
45(1966); http://dx.doi.org/10.1063/1.1727355View Description Hide Description
Stark‐effect measurements of the 0–0 band of the 3820‐Å transition (1 A″←1 A′) have been made. Analysis of the pP subbands with K″ = 9, 10, and 11 yields a value μ a ′ = 0.7±0.2 D. The other component of the dipole moment, μ b ′, of the upper state is not determined. The relatively complex spectrum produced in the Stark effect is readily simulated by computed spectra. The techniques used appear to be applicable to complex spectra.
Far‐Infrared Spectra of Four‐Membered‐Ring Compounds. I. Spectra and Structure of Cyclobutanone, Cyclobutanone‐d 4, Trimethylene Sulfide, and Perfluorocyclobutanone45(1966); http://dx.doi.org/10.1063/1.1727356View Description Hide Description
Two series of very sharp Q branches have been observed in the far‐infrared spectra of cyclobutanone and cyclobutanone‐d 4 vapor. For cyclobutanone, these Q branches have wavenumbers of 35.3, 57.03, 64.99, 72.17, 77.77, 81.85, and 85.33 cm−1, and for cyclobutanone‐d 4 the wavenumbers are (∼30), 47.1, 54.2, 60.6, 65.6, 69.8, 73.2, and 78.9 cm−1. Relative frequency values were calculated with the energy levels of a pure quartic oscillator which fitted rather accurately all the transitions except the first observed one. This suggests that the four‐membered ring of cyclobutanone is planar. The far‐infrared spectrum of trimethylene sulfide revealed at least six Q branches of varying intensity and spacing. Their wavenumbers were 62.27, 84.50, 92.14, 100.18, 105.75, and 139.1 cm−1. It is impossible to fit the series to the energy levels of either a pure quartic oscillator or one perturbed by a quadratic term. Comparison of the statistical entropy with the measured calorimetric entropy indicated a double‐minimum potential with a barrier above the first energy level. In the far‐infrared spectrum of perfluorocyclobutanone no band was observed which could be confidently assigned to the ring‐puckering vibration of this molecule.
45(1966); http://dx.doi.org/10.1063/1.1727357View Description Hide Description
The infrared‐absorption spectra of liquid phenyltrichlorosilane, phenyltrichlorogermane, and phenyltrichlorostannane have been recorded from 4000 to 33 cm−1. The Raman spectra of the liquids have also been recorded and depolarization values have been measured. The phenyl vibrations have been assigned assuming C 2v symmetry, although the molecular symmetry is probably Cs . All the spectra are interpreted in detail, and the 39 fundamental vibrations have been assigned based on previous assignments for substituted benzenes as well as the expected band positions and depolarization values. Comparison of the spectra reported herein to that of the carbon analog suggests the reassignment of a few of the fundamental vibrations in phenyltrichloromethane. The assignment of the lowest observed Raman line in each spectrum to the torsional vibration is discussed, but because of the large values calculated for the sixfold barrier hindering internal rotation it is discarded.
45(1966); http://dx.doi.org/10.1063/1.1727358View Description Hide Description
Observations are made of the effects of annealing and Y, O, or Na impurities on the growth and reduction of various types of Sm centers in CaF2. Increase of Sm3+fluorescence with increase of annealing time is believed to be indicative of axial center formation. Radiation‐induced reduction of Sm3+ centers in cubic, tetragonal, or trigonal crystalline fields is studied. The absorption spectra after irradiation are shown to be dependent on the original symmetry of the field surrounding the trivalent ions.
Method for Separating the Inter‐ and Intramolecular Contributions to T 1 in Liquids When the Pressure Varies. Rotational Correlation Time vs Pressure45(1966); http://dx.doi.org/10.1063/1.1727360View Description Hide Description
It is shown that to separate the intramolecular and intermolecular contributions to the spin—lattice relaxation timeT 1 in liquidsmeasured as a function of pressure and/or temperature, it is only necessary to perform this separation at a single pressure and temperature if the self‐diffusion coefficient D and density are also known as a function of pressure and/or temperature. T 1 may be separated by solutionmeasurements in which the liquid under study is dissolved in a solvent identical to it but magnetically inert. The intramolecular part of T 1 and, hence, the intermolecular part also are obtained by extrapolation to infinite dilution. Such solutionmeasurements would be cumbersome to perform as a function of pressure and/or temperature. It is argued that the results of such a separation may be extended to other pressures and temperatures if appropriate self‐diffusion and density data are available. To examine the usefulness of this idea, the pressure dependence of the rotational correlation time τ R for benzene is derived from data already in the literature. Cyclohexane (assumed to be a rigid molecule) is similarly treated except that the separation data were not available and had to be determined. The behavior of τ R and D as a function of pressure is compared to the behavior of the viscosity and also to the predictions based on the theories of Debye and Hill. The discrepancies which are observed are discussed in terms of molecular shape and internal reorientation.
45(1966); http://dx.doi.org/10.1063/1.1727361View Description Hide Description
When a thermal beam of N2 is excited by electrons of controlled energy and collides with NO, light is observed. The excitation function shows that this light is produced by excited N2 in metastable states. The spectrum is obtained with very low resolution, and it is identified as the transition A 2π—X 2Σ of NO, the γ bands, from low vibration levels. Experiments with other gases are briefly described.
45(1966); http://dx.doi.org/10.1063/1.1727362View Description Hide Description
Spin—lattice relaxation times (T 1) of various organo—sulfur radicals, each with a different spectroscopic splitting factor g, were measured mainly at 77°K by the method of microwave saturation in electron spin resonance. All these radicals showed T 1's which are smaller than those of organic (carbon) radicals. A remarkable correlation was found to exist between T 1 and Δg max, the maximum deviation of the g factor of a free radical from the free spin g value. These results have led to a conclusion that the spin—lattice relaxation in organo—sulfur radicals takes place mainly through spin—orbit and orbit—lattice coupling.
45(1966); http://dx.doi.org/10.1063/1.1727363View Description Hide Description
Expressions given in an earlier paper are applied to the X 1Σ g + ground state of hydrogen. The second‐order approximations were found to have little effect upon the turning points of the curve, the major correction being an increase in the well depth of 10 cm−1. The method appears to have certain advantages over the Dunham procedure.
45(1966); http://dx.doi.org/10.1063/1.1727364View Description Hide Description
The flash photolysis of H2O2 by itself, and in the presence of D2, Ar, and H2 18O, was studied by the technique of kinetic absorption spectroscopy. The only observable primary products were OH(2Π½) and OH(2Π). These ground‐state levels were populated in a ratio of ∼1:1, respectively, conforming to what is observed with the halogens.
The contribution of Reaction (a) to the primary process was shown in a direct way to be no more than 20% of that of (b). Reaction (c) followed by (d) was shown to make no significant contribution to the OH concentration during the time of our experiments (<200μ sec): Thus, this technique is a convenient one for directly observing reactions of OH. An upper limit to the rate constant of (e) at room temperature was determined to be 5.8±1.8×10−14 cm3 molecule−1·sec−1.
Conditions for generating vibrationally hot molecules in the primary photolytic step are discussed.