Showing papers in "Canadian Journal of Physics in 1965"

A composite nuclear-level density formula with shell corrections

Abstract: At low excitation energies a "constant nuclear temperature" representation of nuclear-level densities is used, and at high excitation energies the regular Fermi gas formula is adopted. A method is ...

Some low-energy atomic stopping cross sections

Abstract: The electronic stopping cross sections for protons in aluminum are reported in the energy interval 10 < E < 70 keV. Stopping cross sections below 150 keV in carbon targets for projectiles with , an...

Anomalous rotational line intensities in electronic transitions of polyatomic molecules: axis-switching

Abstract: It is convenient when performing calculations on a vibrating and rotating molecule to define an axis system which is somehow fixed to the molecule. The orientation of the usual molecule-fixed axis system, however, depends not only upon the instantaneous positions of the nuclei, but also upon the equilibrium positions from which the nuclei are regarded as being displaced. Thus, when a molecule of low enough symmetry undergoes an electronic transition accompanied by a change in geometry, it will, in general, be necessary to consider two molecule-fixed axis systems, corresponding to the two different electronic states. This change in axis system from one electronic state to another will be called axis-switching. The two axis systems can be related to each other by the 3 × 3 rotation matrix which brings them into coincidence. The elements of this matrix are functions of the equilibrium geometries of the two electronic states as well as of the instantaneous positions of the atoms in the molecule. Axis-switchin...

The crystal dynamics of uranium dioxide

Abstract: The frequency/wave-vector dispersion relation for normal modes of vibration propagating along the [00ζ], [ζζ0], and [ζζζ] directions in uranium dioxide at 296 °K has been determined by studying the...

The absorption spectrum of no2 in the 3 700-4 600 a region,

Abstract: An investigation of the absorption spectra of both 14NO2 and 15NO2 has revealed a long progression of red-degraded bands in the region 3 700–4 600 A. The rotational analysis shows that these bands ...

Absorption spectrum of the ccn radical.

Abstract: A new transient absorption spectrum, attributed to the CCN free radical, has been discovered in the flash photolysis of diazoacetonitrile, HC(CN)N2; three electronic transitions, between 3 500 A and 4 700 A, have been photographed for both CC14N and CC15N. The ground state of the radical is a 2Πr electronic state, and the three excited states observed are A2Δ, B2Σ−, and C2Σ+. The 2Π and 2Δ states show evidence of Renner–Teller interaction between the vibrational and electronic angular momenta, an effect not observed previously for 2Δ states. Theoretical expressions for the vibrational energy levels of linear triatomic molecules in 2Δ electronic states have been derived, in terms of a parameter η associated with the quartic terms in the potential energy. They are compared with the observed pattern in the ν2 = 1 level of the A2Δ state. The principal molecular constants for CC14N (in cm−1) are as follows:

THE INFLUENCE OF THE ELECTRON–ION INTERACTION ON THE PHONON FREQUENCIES OF SIMPLE METALS: Na, Al, AND Pb

Abstract: The phonon frequencies of simple metals are calculated from an effective interaction between ions arising from the direct Coulomb interaction between ions and the conduction-electron response to the ion motion. The response of the electrons is treated by the many-body perturbation theory. The central quantity in the theory is the scattering amplitude for Bloch electrons from the displaced ions (electron–ion matrix element). The screening effects produced by the electron–electron interaction are taken over from the free-electron theory. The electron–ion matrix element naturally splits into two parts: the potential due to the conduction electrons within the Wigner–Seitz cell and the potential which enters the one-particle Schroedinger equation for the electrons in a periodic lattice. The former is the major term for small momentum transfer, , and characterizes the magnitude of the screening contribution to the frequencies, while the latter dominates for large momentum transfer. This leads to a fundamental d...

The 2 700 a bands of the n3 molecule

Abstract: The 2 700 A absorption bands found by Thrush in the flash photolysis of HN3 have been studied at high resolution. The rotational fine structure of the strongest band has been analyzed, and it has b...

The correlation of the symmetry classifications of states of nonrigid molecules

Abstract: The rovibronic and vibronic energy levels of some nonrigid molecules occur in nearly degenerate sets, whose splitting is due to tunneling between symmetrically equivalent regions of vibrational phase space. When the splitting is negligible, it is convenient to classify the different sets of energy levels according to a symmetry group that is determined by any one of the symmetrically equivalent regions, whereas when the splitting is appreciable, the individual split levels can be classified further according to a larger group that is determined in a similar way by a region containing all these equivalent regions. The former group is a subgroup of the latter.A simple correlation rule is proved, by means of which the symmetry species (in the larger group) of the individual split levels can be obtained from the symmetry species (in the smaller group) of the nearly degenerate set of levels. Some examples of the application of this rule to rovibronic and vibronic species are given.

A new method for finding heterogeneous energy distributions from physical adsorption isotherms

Abstract: A model is described which assumes that a heterogeneous surface has a distribution of adsorption energies ƒ(E) for physical adsorption. A new solution is presented giving ƒ(E) for a number of step-type local isotherms, which are chosen to represent varying degrees of adsorbate–adsorbate interaction. The solution permits ƒ(E) to be obtained quite simply from isotherm data at one temperature. This solution for ƒ(E) may then be used to calculate isotherms at other temperatures. The latter isotherms represent predictions of the model and may be compared with experimental data.

Photoionization and absorption coefficients of no in the 600 to 950 å region

Abstract: Absolute photoionization and absorption coefficients of nitric oxide gas have been measured in the 600 to 950 A region, using a 1-meter Seya-Namioka scanning vacuum ultraviolet monochromator. The H...

The Reflection and Ducting of Atmospheric Acoustic‐Gravity Waves

Abstract: A simple form is derived for the differential equations governing the propagation of acoustic–gravity waves in an atmosphere whose temperature and horizontal wind velocity vary in an arbitrary mann...

A study of solar evolution

Abstract: Evolutionary sequences of solar models have been calculated using the Henyey method of model construction. These sequences were started at the threshold of stability, at which the released gravitat...

Vortices in sphere wakes

Abstract: The formation and structure of vortices characteristic of sphere wakes corresponding to a range of Reynolds numbers extending from 200 to 500 have been examined. The manner in which vorticity is re...

Collision-induced absorption of compressed gases in the far infrared, part i

Abstract: A study is being made of the far infrared absorption occurring in compressed rare-gas mixtures, and compressed homonuclear diatomic gases. The region investigated lies between 20 and 400 cm−1. The spectra are obtained from the Fourier analysis of interferograms produced by a dynamic Michelson interferometer. It is possible to obtain accurate absolute absorption coefficients for broad bands using this method provided care is exercised in the analysis of the interferograms. The necessary precautions are discussed in detail. The precision of the method obtained in practice is demonstrated using the far infrared bands of hydrogen and nitrogen as examples. Only the experimental techniques are discussed in this paper; the detailed results follow in a separate paper.

LIFETIMES OF THE 16O 6.13-MeV LEVEL AND THE 17O 0.871-MeV LEVEL

Abstract: The mean lifetimes of the 0.871-MeV state of 17O(E2) and the 6.13-MeV state of 16O(E3) have been measured by a new recoil method using a Ge(Li) gamma-ray detector. The data yield mean lifetimes of (2.33 ± 0.27) × 10−10 and (2.5 ± 0.2) × 10−11 sec for the states in 17O and 16O respectively. The recoil method is generally applicable to the measurement of lifetimes greater than about 5 × 10−12 sec and provides a technique for a region of time where neither direct electronic timing nor Doppler-shift attenuation methods are accurate.

Propagation in a waveguide with glide reflection symmetry.

Abstract: An exact formulation of the boundary value problem for an infinite lossless iris-loaded periodic wave guide with glide reflection symmetry has been obtained for TM wave propagation. The characteristic equation for the fundamental propagation constant β0 is solved for real as well as complex roots. The solutions are plotted in the form of k–β diagrams. The effect of variation of certain parameters is studied. On the basis of the periodicity of the solutions for β0 it is demonstrated that the effective period of this structure is half its translation period. A discussion of the k–β plots is presented and some comments on the properties of the complex waves in lossless periodic wave guides are included.

Role of the symmetry energy in atomic mass formulas.

Abstract: Cameron has interpreted the heavy uranium mass yield curve from the Mike thermonuclear explosion as indicating that conventional atomic mass formulas do not give realistic values of neutron binding...

THERMOELECTRIC PROPERTIES OF Bi2Te3–Sb2Te3 ALLOYS

Abstract: Alloys of nominal composition Bi2−xSbxTe3+y were prepared in an evacuated, sealed ampule by a horizontal zone melting method. Single-crystal samples were cut from the ingots, and measurements of Se...

Composition of matter in nuclear statistical equilibrium at high densities

Abstract: Properties of dense matter in nuclear statistical equilibrium analyzed at high densities and temperatures in connection with stellar evolution

Analysis of physical adsorption isotherms on heterogeneous surfaces at very low pressures

Abstract: A method previously described for finding heterogeneous energy distributions ƒ(E) from physical adsorption isotherms is applied to experimental data for argon, nitrogen, and helium obtained in an ultrahigh vacuum apparatus in the pressure range Torr. The adsorbent was Pyrex and matching temperatures were 77.4, 90.2, and 4.2 °K for the three gases respectively. ƒ(E) was found to be asymmetric about a maximum energy whose location depended critically upon the magnitude of assumed adsorbate–adsorbate interaction (Q). However, the isotherms calculated at temperatures other than the matching temperature were insensitive to Q, and hence to the detailed form of the local isotherm. These calculated isotherms showed excellent agreement, not only with the data on Pyrex, but also with the data of several workers using various adsorbents and temperatures. The latter result suggests a similar adsorbing surface for all these adsorbents.

Ficton theory of dynamical systems with noisy parameters

Abstract: The theory of randomly perturbed waves described previously (Bourret 1962a, b) is presented in a form applicable to purely time-dependent systems, classical or quantum mechanical. It is then applie...

High-resolution vacuum ultraviolet absorption spectrum of the e 1π ← x 1σ+ transition in co

Abstract: The (0–0) and (1–0) bands of the E–X transition have been observed in absorption at high resolution. The analysis of the (0–0) band identifies the E state as 1Π, thus confirming recent theoretical calculations. Λ-type doubling of the order of 0.2–0.3 cm−1 is observed at medium J values. The much weaker (0–0) band of 13C16O was also observed and analyzed. The pertinent spectroscopic constants for the E state of 12C16O are as follows: T00 = 92 930.04 cm−1, B0 = 1.9645 cm−1, and D0 = 6.50 × 10−6 cm−1. For the 13C16O molecule the corresponding constants are: T00 = 92 929.62 cm−1, B0 = 1.8773 cm−1, and D0 = 5.94 × 10−6 cm−1.

The thermal expansion of alkali halides

Abstract: Measurements have been made of the coefficient of linear thermal expansion of NaCl, Nal, KCl, and KBr over the temperature range from 7 °K to 300 °K. The measurements were made by monitoring the changes in length of a Fabry–Perot etalon, whose spacer was of the material being studied, as it slowly warmed from liquid-helium temperatures. The detectable change in length of the 2-in. specimen was about 2 A. The results are analyzed by reducing them to values of the Grueneisen γ. The temperature variation of γ at high temperatures is used to obtain values of γ (2s), which are compared with new calculations on a rigid-ion model to give the best fit to the Born exponent for the non-Coulomb interionic potential. The data for low temperatures are not sufficiently accurate to justify detailed analysis; there is some indication that the apparent low-temperature limit of γ is, in fact, the value at a minimum.

A large-volume, coaxial, lithium-drift, germanium gamma-ray spectrometer

Abstract: A high-resolution, germanium p-i-n diode gamma-ray spectrometer has been made using the coaxial method of lithium drift. The detector described is ~ 16 cm3 in sensitive volume, three to four times that of the largest "planar" drifted diodes of this type described to date. Its performance as a spectrometer is comparable with that of smaller diodes; resolutions (fwhm) of 3.3 and 4.8 keV were obtained at γ-ray energies of 122 and 1 333 keV respectively with a detector bias of 1 000 to 1 500 V. Typical γ-ray spectra obtained with sources of 57Co, 60Co, 137Cs, and Th(B + C + C″) are shown. Also shown are curves of intrinsic full-energy peak efficiency over a range of energies. This efficiency is 2.5% at 1 300-keV γ-ray energy—comparable to that of a NaI scintillation spectrometer 1 in. in diameter by 1 in. long.

Vibrational motions in dimethylacetylene.

Abstract: A method is presented for giving a precise meaning to the concept of a "normal mode" in dimethylacetylene for the limiting case of almost free internal rotation. The normal modes so defined are shown to transform according to irreducible representations of the molecular symmetry group discussed in a previous paper. In addition, the effect on the energy levels of Coriolis interaction between the vibrational motion and both the overall rotation and the torsion is discussed for doubly degenerate and quadruply degenerate vibrational states. Selection rules for transitions between the various Coriolis components are presented, which are analogous to the "(+l), (−l) selection rules" for "ordinary" symmetric-top molecules. The effect of a small barrier to internal rotation is discussed briefly.

Induced infrared absorption of nitrogen and nitrogen – foreign gas mixtures

Abstract: The pressure-induced fundamental vibration–rotation absorption band of nitrogen was studied in the pure gas and in nitrogen–argon, nitrogen–hydrogen, and nitrogen–helium mixtures at room temperatur...

The chemisorption of nitrogen on polycrystallin tungsten wires

Abstract: Desorption spectra have been obtained for successively increasing amounts of nitrogen adsorbed on three polycrystalline tungsten wires at room temperature. Two β phases were desorbed, β1 with first-order kinetics and an activation energy of 73 kcal/mole and β2with second-order kinetics and an activation energy of 75 kcal/mole. Surface impurities such as carbon or thorium reduced the size of the β1 phase. Mass spectrometric evidence showed that the small α phase was adsorbed as molecules, and the β1 and β2 phases were adsorbed as atoms.

Level densities in lighter nuclei

Abstract: There has been discussion in the literature as to whether the cumulative number of levels in light nuclei varies more nearly as exp(const. ) or exp(const. E), where E is the excitation energy. The ...

CONSTITUTION AND MAGNETIC AND ELECTRICAL PROPERTIES OF PALLADIUM TELLURIDES (PdTe–PdTe2)

Abstract: The region from PdTe to PdTe2 has been examined by X-ray methods to establish the phase boundaries. The results confirm the existence of a continuous solid solution at high temperatures and narrow ...