Note of correction: Broadening of NO γ-band lines

Errors in Ref. 1 are corrected. Using the new data, the collisional broadening coefficient of NO γ-band lines by N₂ is 2390 (±220) atm^-1-K (old value = 1270±200) and the optical collision diameter is 13.3±0.6 Å (instead of 3.5±0.3 Å). Values for argon (2150±200 atm^-1-K) and CO₂ (2040±200 atm^-1-K) yield the optical collision diameters of 13.2 and 13.1 Å, respectively.     

The magnetic moments and halflives of the 5/2− states in199Hg and197Hg and the discrepancies in the experimental hyperfine fields at Hg in Fe

The Larmor-precession frequencies for¹⁹⁷Hg in Fe have been determined to beω _L = 1291 ±25 MHz at 293 K andω _L = 1334±25 MHz at 105 K. For¹⁹⁹Hg in Feω _L =1372±50 MHz has been measured at 293 K. The half-lives of the 5/2^? states in¹⁹⁷Hg and¹⁹⁹Hg have been remeasured asT _1/2(¹⁹⁷Hg)=8.1±0.16 nsec andT _1/2(¹⁹⁹Hg)=2.45±0.05 ns, respectively. The magnetic moment of the 5/2^? 158keV state in¹⁹⁹Hg was redetermined by the integral perturbed angular correlation method in an external magnetic field of 47kG asμ(5/2 ^? ) = 0.905±0.091 nm. With this new value consistency for the magnetic hyperfine fields at Hg in Fe measured with the TDPAC-method and with the NMR/ON-method is obtained. This fact is used to determine theg-factors of the 5/2^? states in¹⁹⁷Hg and¹⁹⁹Hg more precisely fromω _L -values given above:g(¹⁹⁷Hg)=0.342(6);g(¹⁹⁹Hg)=0.352(13). The magnetic moments of the first excited 2⁺ states in^198–204Hg isotopes which rely on calibrations with the¹⁹⁹Hg-g-factor, are revised.     

The Absorption Spectrum of UF6, from 2000 to 4200 Å

The absorption spectrum of UF₆ between 3400 and 4200 Å, is well-documented,^(1–3) but the region below 3400 Å has not been studied in any detail. We present here a spectrum of UF₆ between 2000 and 4200 Å that shows significant structure below 3400 Å. The absorption in this region must be observed at very low pressures and relatively short path lengths.     

Electron paramagnetic resonance in deuterated nickel fluosilicate

Electron paramagnetic resonance measurements in single crystals of NiSiF₆. 6D₂O were made at K, Ku and Ka bands at 4.2 K and between 77 K and 300 K. The measured g values were in the range 2.23–2.26, while the zero-field splitting parameter D varied from ?(0.185 ± 0.005) cm^?1 at 4.2 K to ?(0.53 ± 0.01) cm^?1 at 298 K. The parameters of the trimolecular hexagonal unit cell were determined to be approximately a = 9.28 Å, c = 9.58 Å from powder X-ray diffraction measurements at room temperature.     

Linewidth and intensity measurements of SO2 lines at 94 GHz with self-broadening and broadening by H2O and N2

In the frequency range between 91.5 and 95.5 GHz, three rotational lines of the ³²S¹⁶O₂ and two rotational lines of the ³⁴S¹⁶O₂ molecules in the fundamental vibrational state, and also two lines of the ³²S¹⁶O₂ molecule in the v₂ vibrational state, have been investigated. Center frequencies and absolute absorptions have been measured and compared with theoretical values. Furthermore, the self-broadening and broadening by H₂O and N₂ of the transition 23(6,18)–24(5,19) with the line center at 94.064 GHz have been investigated. The following linewidth parameters were found: SO₂-SO₂, 18.2±0.3 MHz/torr; SO₂-N₂, 3.8±0.1 MHz/torr; SO₂-H₂O, 15.2±0.2 MHz/torr. The bridge spectrometer and the measuring method used are also described.     

Beweglichkeit von Einfach- und Cluster-Ionen in Argon bei hohen Drucken

A time-of-flight technique is used for the measurement of positive ion mobilities in argon in the 1–100 atm pressure range at 300 °K. The ions are produced by photoionization of gas atoms in the drift region with ultraviolet light from a spark discharge. A mobility is found which varies continuously with the reduced electric fieldE/p ₀ and which exhibits two saturation values at 1.55±0.01 cm²/volt sec (forE/p ₀? 2 volt/cm torr) and at 0.818±0.003 (forE/p ₀? 0.17). The former value is in excellent agreement with the zero-field mobility obtained by Beaty for Ar⁺. The last value is interpreted in terms of the Langevin theory and connected with the formation of the Ar ₃₃ ⁺ labile cluster. This has the Ar⁺ ion as nucleus and is surrounded by two complete shells of 12 and 20 argon atoms respectively. A mean value of the cluster radius is estimated as 6.24 Å.     

Electronic-excitation transfer collisions in flames—II temperature dependence of the quenching of Na(32P)-doublet by H2 and O2

Effective cross sections for quenching of the Na(3²P)-doublet by H₂ and O₂ molecules have been measured in flames in the temperature range 1500–2500 K. The H₂-cross section decreases from (9.3±1.0) Ų at 1500 K to (6.8±1.0) Ų at 2500 K. The O₂-cross section decreases from (39±2) Ų at 1720 K to (31±2) Ų at 2500 K. A critical comparison of the flame values with previous literature data on the H₂-cross section at lower temperatures shows that it decreases systematically when the temperature rises from about 400 to 2500 K.     

Inelastic collision cross section of excited molecules

The (v′=6,J′=43) level in theB ¹Π _u electronic state of Na₂ has been selectively populated by excitation with the 4 880 Å line of the argon laser. Through collisions with He atoms energy is transferred to neighbouring rotational states in Na₂ and the density of these states is determined by observing fluorescence to electronic ground state. From previous measurement of the lifetime of theB ¹Π _u state and new measurements of the intensities of collision induced spectral lines as a function of He pressure, absolute collision cross sections for all rotational transitions up to ΔJ=±5 have been obtained. The total cross section for all rotational transitions observed is σ _rot ^total =65±15 Ų. Preliminary results about collision induced vibrational transitions are also presented.     

Pressure broadening of the NO2 hyperfine multiplet at 93 GHz

Line shapes of the hyperfine NO₂ 26(1,25)←25(2,24) rotational transition have been measured at pressures below 3 torr with a bridge spectrometer originally designed for direct absolute absorption studies. The multiplet consists of six lines with δF=δJ=δN=1 in the vicinity of 93,445 MHz. The same line-broadening parameter of 3.7 MHz/torr and the same maximum absorption of 1.8×10^-5 cm^-1 have been found for all 6 lines. The maximum absorption of the strongly overlapped multiplet at a pressure of 10 torr was measured to be 1.06×10^-4 cm^-1, in good agreement with the theoretical value. The interference effect of the overlapping lines turns out to be below ?10%, so that a simple superposition of lorentzian shapes is a good approximation for this case. The remaining difference can be compensated for by the introduction of an overlap parameter for each line.     

Microwave spectrum and substitution structure of methylene chloride

The microwave spectrum of methylene chloride has been reinvestigated in order to obtain a complete substitution (r_s) structure of well-defined precision. Measurements on the ¹³CH₂Cl₂ species have yielded the following rigid-rotor rotational constants: A = 30746.20 ± 0.10 MHz, B = 3320.63 ± 0.11 MHz, and C = 3053.44 ± 0.10 MHz. These data, combined with revised values reported earlier for other isotopic species, yields the following r_s structural parameters: CCl = 1.767 ± 0.002 Å, CH = 1.085 ± 0.002 Å, ∠HCH = 112.1 ± 0.2°, and ∠ClCCl = 112.2 ± 0.1°.     

Raman scattering cross section and density measurements of UF6

We have applied laser Raman scattering to the measurement of the density of UF₆ vapor. A linear relation between scattering intensity and density is shown. We have also measured the absolute Raman scattering cross section of the 665 cm^?1 line of UF₆ by the substitution technique and obtained a value of 1.02±0.09×10^?29 cm²/sterad at 488 nm. Measurements of the line position and the depolarization ratio of this line are also reported.     

Coherent Stokes and anti-Stokes Raman spectra of the ν1 (A1) and ν2 (E) bands of SF6 and UF6

Coherent Stokes and anti-Stokes Raman scattering are used to study the ν₁ and ν₂ spectral band profiles of UF₆ and SF₆. Most of the observed SF₆ “hot” bands are assigned, leading to evaluations of the anharmonicity constants X_ij: X₁₂ = ?(2.80 ± 0.30) cm^?1, X₁₄ = ?(1.00 ± 0.15) cm^?1, X₁₅ = ?(1.00 ± 0.15) cm^?1. For UF₆, a tentative assignment of the “hot” bands is made: X₁₂ = ?(1.80 ± 0.30) cm^?1, X₁₃ = ?(1.60 ± 0.30) cm^?1, X₁₄ = ?(0.20 ± 0.10) cm^?1, X₁₅ = ?(0.25 ± 0.10) cm^?1, and X₁₆ = ?(0.10 ± 0.05) cm^?1. Parameters such as the vibration-rotation coupling constants are determined. For SF₆: α = (7 ± 2) × 10^?5 cm^?1 for the ν₂ band and α = ?(1.02 ± 0.01) 10^?4 cm^?1 for the ν₁ band. The calculated spectral profiles of the coherent Stokes or anti-Stokes spectra, which are in good agreement with experimental results, give values for the resonant and nonresonant parts of the susceptibility in both molecules. They also show, in some cases, the influence of neighboring combination bands.     

Theory of self-locking phenomena in the pressure broadened three-mode He-Ne laser

Taking account of pressure broadening the coefficients in Lamb's third-order amplitude and phase determining equations for three modes are evaluated in the Doppler limit, and comparison is made with other theories. After expanding the coefficients to first order in the detuning ε from the linecenter an expression is presented for the frequency range where mode locking will occur. Using experimental data of several authors for the 6328 Å Ne-transition numerical values are obtained for the pressure dependent decay rates Υ _a , Υ _b , of the upper and lower laser level and the linewidth Υ _ab ^′ , viz.:Υ _a =17.7+(12.6±0.6)P _He, Υ _b =8.3+(12.6±0.6)P _He, and Υ _ab ^′ =13.0+(91±6)P _He MHz, whereP _He is measured in torr.     

Mössbauer studies of dilute Au:Er alloys: Obervation of hyperfine structure of ground and excited CEF levels

The hyperfine structure of dilute ¹⁶⁶Er impurities in Au has been investigated between 1.8 and 60 K by Mössbauer spectroscopy. The hyperfine spectrum of the Γ₇ electronic ground state is clearly observed below 4.2 K while at higher temperatures there is an indication of the contribution from the excited CEF-states Γ⁽¹⁾₈ and Γ₆. Using Hirst's relaxation theory for the Γ₇ ground state the magnetic hyperfine coupling constant A=(247±3) MHz and the exchange coupling constant J_sf=(0.10±0.02)eV were derived. A quadruple coupling constant B of about 1 MHz was estimated from the hyperfine pattern of the Γ⁽¹⁾₈ quartet.     

Plasmon dispersion in Beryllium

We have measured the plasmon dispersion in polycrystalline Beryllium at wave vectors up tok=1.29 Å^?1 with electron energy loss spectroscopy. The plasmon energy is 18.8±0.1 eV, the fitted quadratic dispersion coefficient is α=0.36±0.03 for 0<k<1.29 Å^?1 and α _L =0.52+0.04 fork<0.55 Å^?1. We compare our results with the plasmon dispersion in other simple metals and point out discrepancies with the theories of the homogeneous electron gas.     

Neutron diffraction determination of the magnetic structures of NpCo2Si2 and NpCu2Si2

A small polycrystalline ingot sample of NpCo₂Si₂ (weight ≈ 1.5 g) has been studied by neutron diffration between 2 and 160 K on the multi-detector D1B of ILL, Grenoble. At 100 K, the crystal structure is body-centered tetragonal (space group 14/mmm) with a = 3.886 Å and c =9.649 Å. Below T_N = (44 ± 2) K, seven superlattice lines are observed which correspond to a simple tetragonal lattice with lattice constants as above. They are consistent with a type I antiferromagnetic structure of the Np (2a) sublattice, with (001) ferromagnetic sheets coupled antiferromagnetically according to the sequence +-+-. At 6 K, the neptunium moment obtained from the diffracted intensities is: (1.48 ± 0.20)_μuB, and makes an angle 52° ± 15° with the c axis. The cobalt moment is certainly smallet than 0.3_μuB. The Np moment correlates well with the ²³⁷Np hyperfine field deduced from Mos?sbauer spectroscopy; the sublattice magnetization-temoperature curve follows very well the $\text{J=}\text{1}\text{2}$ brillouin curve. The magnetism is therefore probably of lovalized character in this compound. An isomorphous sample of NpCu₂Si₂ (a = 3.990 Å c = 9.920 Å) was shown to be ferromagnetic below (41 ± 2) K, with the Np moment [1.5 ± 0.2)_μuB] aligned along the c axis.     

Excitation of projectile Rydberg states in the collisions Be+-He and Mg+-He, 10–75 keV

The photoabsorption coefficient of molecular oxygen has been measured at 1215.70 Å and in the ranges 1205 Å–1214 Å and 1218 Å–1225 Å with an average resolution of ±0.015 Å. The light source in this experiment was the Doppler shifted radiation obtained from Stark quenching of a metastable hydrogen beam with energies between 2 keV and 60 keV. Using observation angles of 45°, 90°, and 135° with respect to the beam the above mentioned tuning ranges are obtained. Our data join smoothly to those of Ogawa [1] in the range 1214 Å–1218 Å and are in fair agreement with earlier measurements in other laboratories. Analytical expressions for the absorption coefficient for use in geophysical applications are presented for the whole wavelength range 1205 Å–1225 Å. Rotational structure of the absorption coefficient in the range 1220 Å–1223 Å arising from the 3-0 band of theα ¹ ∑ _u ⁺ -X ³ ∑ _g ^? forbidden transition in molecular oxygen is clearly resolved in the present measurements. A transition probability ofA=4×10⁴ s^?1 is obtained for this system. A careful study of a possible pressure dependence of the absorption coefficient was made. Except from the region were rotational line absorption occurs and the single point at 1215.70 Å no measurable effect was found for pressures below 100 Torr.     

Raman scattering cross section and density measurements of UF6

We have applied laser Raman scattering to the measurement of the density of UF₆ vapor. A linear relation between scattering intensity and density is shown. We have also measured the absolute Raman scattering cross section of the 665 cm⁻¹ line of UF₆ by the substitution technique and obtained a value of 1.02±0.09×10⁻²⁹ cm²/sterad at 488 nm. Measurements of the line position and the depolarization ratio of this line are also reported. Work supported by the U. S. Energy Research and Development Administration.     

Non-cubic Mn2+-centers in BaF2

The EPR spectra of thermally treated BaF₂: Mn samples is reported. After thermal annealing at 900 K a trigonal Mn²⁺ center with g=2.000±0.005, |D|=2725±40MHz, |A|=265±10MHz, $\text{D}\text{A}\text{>0}$, is observed. Annealing at 1200 K produces an orthorhombic Mn²⁺ center with g=2.00±0.01, |D|=2430±40MHz, |E|=570±20MHz, |A|=265±10MHz, $\text{D}\text{A}\text{<0}$. The superhyperfine (SHF) structures due to interactions with the neighbouring fluorines indicates that the trigonal manganese interacts with four fluorines, three of them equivalent. The orthorhombic Mn²⁺ shows interaction with four equivalent fluorine nuclei.     

Metal-insulator transition in the mercury-xenon system

A gradual conductivity transition as the atomic composition (X) of Hg/Xe samples is varied at 6 K has been observed. The temperature coefficient of the conductivity (TCC) follows the power law TCC α (X₀ ? X)^{2.4 ± 0.4} with X₀ = 0.790 ± 0.005, the conductivity at X₀ being 400 ± 50 (Ω-cm)^-1. The gradual conductivity transition is interpreted in terms of a Mott-Anderson metal-nonmetal transition smeared out by thermally activated hopping.