Index of content:
Volume 44, Issue 11, 01 June 1966
44(1966); http://dx.doi.org/10.1063/1.1726582View Description Hide Description
The infrared absorption spectra of Ce3+ in LaF3 and of CeF3 have been observed in the region of 3 to 6 μ. The four absorption lines for Ce3+ in LaF3 at 2160, 2240, 2635, and 2845 cm−1 that persist at liquid‐helium temperature are identified as transitions originating on the ground Stark component of the 2 F 5/2 and terminating on the four Kramers‐degenerate Stark levels of the 2 F 7/2. Observation of the temperature dependence of the spectrum has revealed two additional transitions beginning on a 2 F 5/2 Stark level 150 cm−1 above the ground state and ending on the two lowest levels of the 2 F 7/2. The results are essentially the same for CeF3 and are in substantial agreement with the results of temperature‐dependent studies of the magnetic susceptibility and Faraday rotation of CeF3 and tysonite.
Intensity Variation with Scattering Angle of Electronic Transitions in H2O Excited by Electron Impact44(1966); http://dx.doi.org/10.1063/1.1726583View Description Hide Description
Electron‐impact spectra of water vapor have been investigated at 400‐ and 500‐V electron kinetic energy. The relative intensities of the five peaks associated with the A and BRydberg transitions have been studied as a function of the scattering angle. The results suggest a new method of identification of vibrational levels where a high‐resolution study of rotational structure is not feasible.
44(1966); http://dx.doi.org/10.1063/1.1726584View Description Hide Description
The electron‐impact spectrum of carbon monoxide has been investigated at electron energies of 400 and 200 V. The intensity distribution among vibrational levels of the A 1Π←X 1Σ+ transition has been studied as a function of the scattering angle and electron kinetic energy. The experimental data have been compared with theoretical predictions based on the Born approximation. The results indicate that in the range of the present measurements (θ<6°) the relative intensities are independent of the scattering angle. This observation agrees with the approximate theory of Craggs and Massey. The relative intensities agree fairly well with the Franck—Condon factors calculated by Nicholls except at high vibrational quantum numbers.
44(1966); http://dx.doi.org/10.1063/1.1726585View Description Hide Description
Quantum‐mechanical calculations for a Lennard‐Jones (12, 6) potential are presented showing the dependence of the reduced phase shift η* on the quantum parameter Λ* for a fixed reduced effective potential and various reduced energies E *. The observed oscillatory behavior of η* (Λ*) is due primarily to the inclusion of the physically unimportant contribution of Mπ to the phase shift, where M is the number of quasibound (virtual) states of energy less than E *. A modified reduced phase shift η*, defined by excluding this contribution, displays only the sharp inflections associated with barrier penetration under resonance conditions. Except for the resonance contribution, the phase shifts may be accurately reproduced by a second‐order JWKB procedure. This method also accurately predicts the resonance energies (i.e., the energies of the quasibound states). In the region of a resonance, the scattering cross section varies rapidly with energy in a typical resonance manner. If they do not seriously overlap, the resonance ``lines'' should be observable as perturbations on an otherwise smooth background in low‐energy beam‐scattering experiments. The first‐order JWKB treatment of the barrier penetration problem by Ford, Hill, Wakano, and Wheeler suffices for the purpose of estimating the level widths and lifetimes of the virtual states as well as the main features of the resonant phase shifts, but does not accurately reproduce the quantal calculations.
Spectroscopic Basis of Carbonyl Photochemistry. I. The Role of Excited‐State Geometry in the Photodecomposition of Formaldehyde44(1966); http://dx.doi.org/10.1063/1.1726586View Description Hide Description
The photochemistry of formaldehyde is correlated with its spectroscopy within a molecular orbital framework. According to the picture, photodecomposition arises from one electron population of a pair of C<H2 antibonding orbitals, one of which is H–H bonding and yields H2+CO and the other H–H antibonding yielding H+HCO or 2H+CO. These orbitals are populated in singlet states by radiationless transitions from the nonplanar 1(n, π*) state.
44(1966); http://dx.doi.org/10.1063/1.1726587View Description Hide Description
A flowing, steady‐state afterglow system has been utilized to measure room‐temperature ion—neutral reaction rates. A description of the apparatus and technique is given. Measuredrate constants for He+reactions with O2, N2, CO, NO, and CO2 are reported, as well as upper limits for the reactions of He+ with H2, Ne, and Ar, and an estimate for the reaction of He2 + with Ne and N2.
The reactions of He+ with O2, N2, CO, NO, and CO2 are all rapid, the rate constants all being ≈10−9 cm3 sec−1, implying essentially a reaction per collision.
44(1966); http://dx.doi.org/10.1063/1.1726588View Description Hide Description
A pulsed, flowing afterglow has been utilized to measurerate constants at room temperature for the following reactions involving NO:In addition the following related reactions have been measured:Some additional information concerning the end products of N++O2 is offered.
44(1966); http://dx.doi.org/10.1063/1.1726589View Description Hide Description
The solvation shell of nickelous ion in aqueous solution at room temperature was observed using 17O nuclear magnetic resonance. The hyperfine interaction A between the unpaired electrons of the nickelous ion and the 17O nucleus was found to be 3.0×107 cps. The relaxation time of the electron, assuming T 1e =T 2e , was found to be 4.3×10−12 sec. Calculations show that the relaxation of the 17O nucleus occurs through the scalar coupling with the unpaired electrons, whereas the relaxation of the protons occurs through the dipolar coupling. Consequently, in the latter case the calculated electron relaxation time is very sensitive to the Ni–H distance, whereas in the former it is independent of the Ni–O distance, but governed by the independently determined hyperfine coupling constant. It is also pointed out that in the expression for the dipoledipole interaction between the nuclei and the unpaired electrons it is necessary to distinguish between the longitudinal and transverse relaxation times of the electrons.
The rate constant at 298°K for the exchange of water between the hydration shell and the bulk was found to be (3.0±0.3)×104 sec−1, and the enthalpy of activation 10.8±0.5 kcal/mole.
44(1966); http://dx.doi.org/10.1063/1.1726590View Description Hide Description
Gas‐phase and N2 matrix vibrational spectra of HN3, DN3, H15NNN, 15NNNH, D15NNN, and 15NNND are reported. The pure rotation spectrum of HN3 is given as well. Strong vibration—rotation interaction is evident in the v 5, v 6spectra, in the changes of the Arotational constant by 4%−8% in the hydrogen stretching and bending fundamentals, and in the pure rotation spectrum of HN3. Normal coordinates and eight force constants are determined using 22 vibrational frequencies from six molecules. A large (HNN bend)—(HN–N stretch) interaction force constant is found. Its magnitude and sign are readily understood in terms of the electronic structure of hydrazoic acid.
44(1966); http://dx.doi.org/10.1063/1.1726591View Description Hide Description
The dielectric constants and losses at wavelengths of 0.428, 0.860, 1.249, 1.850, and 3.220 cm and the static dielectric constant at 149.9 m have been measured for methoxypentafluorobenzene, pentafluorobenzene, trifluoromethoxybenzene, and anisole in cyclohexane solutions at 25°C. Measurements were also carried out on trifluoromethoxybenzene in decalin solution at 25°C. Dielectric relaxation times have been evaluated and the results for methoxypentafluorobenzene, trifluoromethoxybenzene, and anisole have been interpreted in terms of two relaxation times, one corresponding to molecular rotation and the other to intramolecular group rotation. Consideration has been given to the shortening of the methoxy group relaxation time in the pure liquid state compared with that in dilute solution. Mesomeric moments have been estimated from the dielectric data.
44(1966); http://dx.doi.org/10.1063/1.1726592View Description Hide Description
Analytical wavefunctions for the first three 2 D states of lithium isoelectronic atomic sequence have been obtained using a split‐shell core function plus a generalized orbital form for the outer electron. Values of ionization potentials for the outer electron in the three 2 D states have been calculated by the ``frozen‐core'' approximation, and these compare very well with experimental results. The use of an extended wavefunction for the lowest 2 D state obtained by superposing (2p)2 1 S function on the split‐shell function for the core leads to energy values within 0.01 a.u. of experimental values.
44(1966); http://dx.doi.org/10.1063/1.1726593View Description Hide Description
A mass‐spectrometric and thermogravimetric study of the equilibrium interaction between Al2O3 and Nb between 1800° and 2200°K has been conducted. The reaction proceeds principally as ; two secondary reactions of about equal importance under neutral conditions are and . The latter reaction can dominate under oxidizing conditions. The weight loss caused by the gaseous reaction products is about one hundred times the weight loss caused by the evaporation of alumina under neutral conditions. Calculations show that yttria and some other oxides can be used with Nb at high temperatures with no significant reaction.
44(1966); http://dx.doi.org/10.1063/1.1726594View Description Hide Description
Measurements were made of the primary and afterglow emission decay times of some of the emitting species in an expanded nitrogen flow when excited by a 10‐kV electron beam. Both the first negative system of N2 + and the second positive system of N2 were observed in the afterglow to persist for about 2×10−6 sec. The origin of the afterglow is explained by the possible transfer of energy from ground‐state N2 + ions and secondary electrons to ground state N2 molecules. This is substantiated by observations of the departure from a Boltzmann distribution of the rotational energies in the N2 molecules.
44(1966); http://dx.doi.org/10.1063/1.1726595View Description Hide Description
Photometric measurements of ozone decomposition following flash photolysis of O3—inert‐gas mixtures are interpreted in terms of the time‐dependent quantum yield. Decomposition occurs in time segments which contribute increments to the quantum yield that depend on temperature, pressure, and sample composition. A major portion of the reactionis complete during the photolysis flash and has no temperature dependence in the range 205°—298°K. Processes which further enhance the quantum yield are much slower and depend on temperature, inert‐gas pressure, and composition in a way that has some correlation with the effectiveness of the gas in deactivating vibrationally excited O2†. In N2 a factor of 2 less O3 is decomposed by the end of a flash than in He or Ar, indicating deactivation of the O(1 D) by N2. The quantum yield is smaller in N2 than in He or Ar but qualitatively similar in its pressure dependence. Some limitations in accounting for the results by an energy chain mechanism are discussed.
44(1966); http://dx.doi.org/10.1063/1.1726596View Description Hide Description
In the fourth positive system, A 1Π←X 1Σ+, of CO, electric quadrupole transitions (ΔJ=2) have been observed for the first time in bands of an electric dipole allowed transition. This system also represents the first example of an electric quadrupole transition to be observed in a heteronuclear diatomic molecule. The quadrupole transition probability has been determined to be ≈1.1×103 sec−1. This value compares well with the value of ≈2.0×103 sec−1 determined for the quadrupole transition probability of the electric dipole forbidden a 1 Π g ←X 1Σ g + transition in the isoelectronic N2 molecule.
44(1966); http://dx.doi.org/10.1063/1.1726597View Description Hide Description
The retarded interaction between neutral systems with no permanent moments, i.e., relativistic dispersion forces, is analyzed by quantum electrodynamics and the two‐photon exchange potential is computed for three cases: (i) When both systems are in their ground states, where the potential is the Casimir—Polder potential which falls off for separations R greater than λ/, the characteristic reduced wavelength in dipole transitions, as R −7; (ii) when one system is in an optically allowed excited state where the potential at short distances is the well‐known resonance potential proportional to R −3; and (iii) when both molecules are in excited states. The interaction energies are computed at all separations larger than a few molecular radii, so all overlap and Pauli effects are not considered. The asymptotic forms are given both for R>λ/ and R<λ/ (but still larger than molecular size). The latter give the familiar London and resonance potentials. The former are new results and show a very much slower falloff like a modulated inverse distance or distance squared. This effect is due to the true radiation field of a dipole containing in the radiation zone fields which fall off as R −1. The London potentials, calculated normally by Coulomb interaction only, arise in the fully retarded theory from the near‐zone fields which fall off as R −3.
44(1966); http://dx.doi.org/10.1063/1.1726598View Description Hide Description
The electron paramagnetic resonance results of three chromium nitrosyl complexes are reported (pentacyano, penta‐aquo, and penta‐amino). Hyperfine structure with the nucleus of the metal as well as with the nuclei of some of the ligands is observed. We attempt to explain the interaction with the ligand nuclei by mixing the ground state with excited states(charge transfer) by means of the exchange with the unpaired electron. Different possibilities for the configuration of the ground state are discussed.
44(1966); http://dx.doi.org/10.1063/1.1726599View Description Hide Description
The absorption spectra of Mn2+, Fe2+, and Co2+ in dihydrated halide crystals have been studied as a function of temperature and with polarized incident radiation. The Mn2+ spectrum is quite adequately explained by considering the combined effects of a tetragonally distorted cubic potential and vibrational and/or spin—orbit perturbation on the electronic levels. The data for the Fe2+ and Co2+ crystals support the existence of potential fields of symmetry lower than tetragonal.
44(1966); http://dx.doi.org/10.1063/1.1726600View Description Hide Description
A determination of the homogeneous nucleation rate of water vapor in helium is made. A procedure is established for determining an ``effective'' adiabatic index which may be used to find the final temperature obtained in an isentropic expansion of a real gas. A numerical integration technique is employed in analyzing experimental data. Results for supersaturations near 5 agree closely with the Becker and Doring theory.
44(1966); http://dx.doi.org/10.1063/1.1726601View Description Hide Description
The pure nuclear quadrupole resonance frequency of 14N in hexamethylenetetramine has been studied as a function of pressure and temperature. At constant (atmospheric) pressure the temperature dependence was studied from 4.2° to 340°K. The isothermal pressure dependence was measured at three temperatures, 77°, 196°, and 299°K. These data were analyzed by two methods. In one case, following the method of Brown, the torsional frequency of vibration of the molecules is assumed to decrease as the temperature increases, and this temperature dependence is determined by fitting the quadrupole frequency temperature dependence at atmospheric pressure with Bayer theory. In the second method the volume dependence of the NQR frequency is determined following the method of Kushida, Benedek, and Bloembergen; the parameters involved in this case are found to be intrinsically temperature dependent.