The heat capacity of the layer compounds (CH3CH2CH2NH3)2MnCl4 and (CH3CH2CH2NH3)2CdCl4 from 10 K TO 300 K

The heat capacity of the layer compounds tetrachlorobis (n-propylammonium) manganese II and tetrachlorobis (n-propylammonium) cadmium II, (CH₃CH₂CH₂NH₃)₂MnCl₄ and (CH₃CH₂CH₂NH₃)₂CdCl₄ respectively, has been measured over the temperature range 10 K ?T ? 300 K.Two known structural phase transitions were observed for the Mn compound in this temperature region: at T = 112.8 ± 0.1 K (ΔH_t= 586 ± 2 J mol^?1; ΔS_t = 5.47 ± 0.02 J K^?1mol^?1) and at T =164.3 ± (ΔH_t = 496 ± 7 J mol^?1; ΔS_t =3.29 ± 0.05 J K^?1mol^?1). The lower transition is known to be from a monoclinic structure to a tetragonal structure, while the upper is from the tetragonal phase to an orthorhombic one. From comparison with the results for the corresponding methyl Mn compound it is deduced that the lower transition primarily involves changes in H-bonding while the upper transition involves motion in the propyl chain.A new structural phase transition was observed in the Cd compound at T= 105.5 ± 0.1 K (ΔH_t= 1472.3 ± 0.1 J mol^?1; ΔS_t = 13.956 ± 0.001 J K^?1mol^?1), in addition to two transitions that have been observed previously by other techniques. The higher of these transitions(T = 178.7 ± 0.3 K; ΔH_t = 982 ± 4 J mol^?1 ΔS_t = 6.16 ± 0.02 J K^? mol^?1) is known to be between two orthorhombic structures, while the structural changes at the lower transition (T= 156.8 ± 0.2 K; ΔH_t = 598 ± 5 J mol^?1, ΔS_t = 3.85 ± 0.03 J K^?1 mol^?1) and at the new transition are not known. It is proposed that these two transitions correspond respectively to the tetragonal to orthorhombic and monoclinic to tetragonal transitions in the propyl Mn compounds.In addition to the structural phase transitions (CH₃CH₂CH₂NH₃)₂MnCl₄ magnetically orders at t? 130 K. The magnetic contribution to the heat capacity is deduced from the heat capacity of the corresponding diamagnetic Cd compound and is of the form expected for a quasi 2-dimensional Heisenberg antiferromagnet.     

The heat capacity of the layer compound tetrachlorobis (methylammonium) manganese—II (CH3NH3)2MnCl4, from 10 to 300k

The heat capacity of the layer compound, tetrachlorobis (methylammonium) manganese II, (CH₃NH₃)₂MnCl₄, has been measured over the range 10K <T<300K. In this region, two structural phase transitions have been observed previously by other techniques: one transition is from a monoclinic low temperature (MLT) phase to a tetragonal low temperature (TLT) phase, and the other is from TLT to an orthorhombic room temperature (ORT) phase. The present experiments have shown that the lower transition (MLT→TLT) occurs at T = 94.37±0.05K with ΔH_t = 727±5 J mol^?1 and ΔS_t = 7.76±0.05 J K^?1 mol^?1, and the upper transition (TLT→ORT) takes place at T = 257.02±0.07K with ΔH_t = 116±1J mol^?1 and ΔS_t = 0.451±0.004 J K^?1mol^?1. These results are discussed in the light of recent measurements on (CH₃NH₃)₂CdCl₄, and also with regard to a recent theoretical model of the structural phase transitions in compounds of this type.In addition to the structural phase transitions, (CH₃NH₃)₂MnCl₄ also undergoes magnetic ordering at T < 150K. The magnetic component to the heat capacity, as deduced from a corresponding states comparison of the heat capacity of the present compound with that of the Cd compound, is shown to be consistent with the behaviour expected for a quasi 2-dimensional Heisenberg antiferromagnet.     

Pulsed dephotolysis in emulsion nanocrystals of silver halides: I. Recombination processes at early stages of photolysis

Early stages of formation of few-atom clusters of photolytic silver in AgBr nanocrystals are studied using the pulsed dephotolysis technique. It is shown that dephotolysis is characterized by a clearly pronounced dependence on the pulse duration of nonactinic and actinic radiations, the highest efficiency of dephotolysis being achieved for nanosecond pulses. The rate constant of recombination of free electrons with captured holes is determined (κ_p = (6 ± 1) × 10^?9 cm³ s^?1) and the dependence of the recombination rate on the level of excitation is found. The maximum recombination rate for the highest excitation level is found to be V _p ^max = 10⁹ s^?1 and the surface concentration of recombination centers is determined to be N _r = (2 ± 0.5) × 10¹¹ cm^?2.     

Intensities and half-widths at different temperatures for the 201III←000 band of CO2 at 4854 cm−1

Measurements made at temperatures of 197, 233, and 294°K of the absolute intensities and self-broadening coefficients for the vibration-rotation lines of the 201_III←000 band of the ¹²C¹⁶O₂ molecule, are reported. From these measurements, values have been derived for the vibration-rotation interaction factor (F_VR), the purely vibrational transition moment (|R(O)|), and the intensity (S_Band). The results are: E_VR(m) = 1+(2.2±0.7)×10^?3m+(5.6±1.6)×10^×5m², |R(0)| = (2.064±0.017)×10^?3 debye, S_Band = 21,329±69 cm^?1km^?1atm^?1_STP. The results for the self-broadening coefficients are presented in the text.     

High-precision evaluation of the magnetic moment of the helion

NMR spectra of samples containing a mixture of hydrogen deuteride HD with pressure of about 80 atm and helium-3 with partial pressure of about 1 atm are analyzed. The ratio of the resonance frequencies of the nuclei, F(³He)/F(H₂), is determined to be 0.761786594(2), which is equal to the magnetic moment of the helion (bound in a helium atom) in the units of the magnetic moment of a proton (bound in molecular hydrogen). The uncertainty of two digits in the last place corresponds to a relative error of ??[F(³He)/F(H₂)] = 2.6 × 10^?9. The use of the known calculated data on the shielding of nuclei in the helium-3 atom (??(³He) = 59924(2) × 10^?9) and on the shielding of protons in hydrogen (??(H₂) = 26288(2) × 10^?9) yields a value of ??(³He)/?? _p = ?0.761812217(3) for the free magnetic moment of the helion in the units of the proton magnetic moment.     

High resolution Raman spectroscopy of gases with laser sources. The rotational spectrum of cyanuric fluoride-C3N3F3

The pure rotational Raman spectrum of cyanuric fluoride vapor was photographed using a high resolution plane grating spectrograph. The spectrum was excited with the $\text{λ = 4880}\text{A}\text{?}$ radiation emitted by a single-mode argon-ion laser. Two sets of molecular constants were determined from the R and S branches. The preferred results are those determined from the S-branch data. These are: B₀ = 0.0655954 ± 14 × 10^?7 cm^?1, D_J = (2.52 ± 0.17) × 10^?9 cm^?1 and H_J = (?1.59 ± 0.59) × 10^?14 cm^?1, where the uncertainties are one standard deviation. Possible effects of line shifts due to unresolved K structure and the presence of hot bands on the accuracy of the values of the molecular constants are discussed. The B₀ value is compared to the rotation constant computed with the structural parameters determined with the electron diffraction technique; the agreement between these two rotation constants is only fair.     

Absolute intensity measurements of the CO2 bands 401III←000 and 411III←010

The absolute intensities of the transitions 401_III←000 and 411_III←010 of CO₂ have been measured from spectra obtained under high resolution. Both the vibration-rotation line intensities and the integrated band intensities are reported. The rotationless transition moment of 401_III←000 is deduced and a vibration-rotation interaction factor F(m) = 1+(4.92×10^?4)m+(4.4×10^?7)m² is determined. The values obtained are: S_Band(401_III←000) = (25.54±0.22)×10^?5 cm^?2atm_{(293 K)}^?1, |R₀₀₀^401_III| = (1.87±0.02)×10^?4D, and S_Band(411_III←010) = (1.83±0.13)×10^?5 cm^?2atm_{(293 K)}^?1.     

Observation of the radiative transition ψ → γE(1420)

We have observed a radiative transition from the ψ to a state decaying into K_SK^±π^?, with mass M = 1.44_?0.015^+0.01 GeV/c² and width Γ = 0.05_?0.02^+0.03 GeV/c². We tentatively identify this state as the E(1420). Assuming that this state is an isospin singlet, we have determined the branching fraction product $\text{B(ψ → γ}\text{E}\text{) × B(}\text{E}\text{×}\text{K}\text{K}\text{π) = (3.6 ± 1.4) × 10}{}^{\mathrm{?3}}$.     

Lifetime and absolute transition probabilities of the 2p 10(3 S 1) level of NeI by beam-gas-dye laser spectroscopy

The lifetime of the 2p ₁₀(³ S ₁) level in the NeI 2p ⁵3p configuration has been measured by means of the cascade-free two-step excitation technique of beam-gas-dye laser spectroscopy. The lifetime determined is τ=(25.43±0.09) ns, where the uncertainty quoted corresponds to one standard deviation. By using the same excitation technique the absolute transition probabilities of all fine-structure transitions from 2p ₁₀ to the four levels 1s _i(i=2?5) in the 2p ⁵3s configuration have been measured, too. The high level of experimental accuracy attained enables a comparative evaluation of the theoretical methods used in the literature to calculate the radial and angular parts of the transition integrals.     

The effect of air impurities on pure neon luminescence

The luminescence decay curves of the 2p ₁ level of the NeI atom (the transition 3p??[1/2]₀?3s??[1/2] ₁ ^° , ?? = 585.2 nm) and the B ²?? _u ⁺ level of the N ₂ ⁺ molecule (the transition B ²?? _u ⁺ (?? = 0)?X ²?? _g ⁺ (??? = 0), ?? = 391.4 nm) in pure and air-containing neon are measured. The gas was excited by electron beam pulses (E _e = 150 keV, ?? = 5 ns, I _max = 500 A). It is shown that the molecular gases contained in air strongly quench the long-lived component of neon luminescence exciting due to dissociative recombination of Ne ₂ ⁺ molecular ions. The relative light yield at a wavelength of 585.2 nm as a function of the partial pressure of air in neon is determined to be ?? = (1+ 2??p)^?1, where p is the air pressure in Torr.     

Growth and spectroscopic studies of NaLa(MoO4)2:Tm3+ crystals: A new promising laser material

Single crystals of scheelite-like disordered double molybdate NaLa(MoO₄)₂ doped with thulium ions with dopant concentrations of 3.0 × 10¹⁹ and 1.2 × 10²⁰ cm^?3 are grown by the Czochralski method. Spectral and luminescent studies of crystals grown are performed in wavelength ranges of 800 nm (the transitions ³ H ₆?³ H ₄) and 2 μm (the transitions ³ H ₆?³ F ₄), including the measurements of the polarized absorption and luminescence spectra of these crystals and the decay kinetics of their excited states. A model that satisfactorily describes the decay kinetics of the luminescence from the ³ H ₄ level taking into account cross-relaxation interactions is proposed. The prospects for the use of these crystals as active media in two-micrometer solid-state lasers are discussed.     

Line strengths,spin-splittings,and forbidden transitions in the (101) band of 14N16O2

Measurements of line strengths in the (101) and (111)-(010) bands of ¹⁴N¹⁶O₂ have been made at a resolution of 0.02 cm^?1 in the region 2863 to 2934 cm^?1. The strength data in the (101) band were analyzed to determine a vibrational band strength and coefficients of the F factor. Each subband for K_?1 ≤ 9 was analyzed separately and all the F-factor coefficients in terms of the rotational quantum number, N, were found to be too small to be of significance. However, F was found to be dependent on K_?1 and the experimentally determined subband strengths were least-squares fitted to the expression S_v⁰·F, where S_v⁰ = 68.3 cm^?2 atm^?1 at 296 K and F = 1 + (2.899 × 10^?3)K_?1 + (4.08 × 10^?3)K_?1² ? (2.34 × 10^?4)K_?1³. The integrated strengths for the (101) and (111)-(010) bands were found to be 70.9 ± 2.3 and 2.7 ± 0.3 cm^?2 atm^?1 at 296 K, respectively. Also included in this study are measurements of line center positions in the two bands and spin-splittings in the (101) band. Recent frequency measurements of lines with K_?1 ≤ 8 in the (101) band have been made at a resolution of 0.0033 cm^?1 by V. Dana and J. P. Maillard (J. Mol. Spectrosc.71, 1–4) (1978)) for the region above 2889 cm^?1 and our values are in excellent agreement with theirs. Separations of the split lines measured in this work (K_?1 ≤ 10) agree well with calculated values using expressions which include the η_aaaaK_?1⁴ term with η′_aaaa = ?1.70 ± 0.15 × 10^?4 cm^?1 as derived for the (101) state. Three forbidden (ΔN ≠ ΔJ, ΔK_?1 = 0) transitions in the (101) band were observed with their identifications based on the agreement between measured and calculated line positions and strengths.     

Measurement of Ar(I) and Ar(II) transition probabilities in LTE ARC plasmas

The transition probabilities of two Ar(I) lines and one Ar(II) line have been measured in emission on wall-stabilized argon arc plasmas (0·5×10⁵?p, Nm^-2?3×10⁵; 10,000?T, K?20,000; 10²²?N_e, m^-3?5×10²³) using the “method of best fit (MBF)”. The results (without line-wing correction) are for Ar(I) at 714·7 nm, A_nm=5·66×10⁵ s^-1±5%; for Ar(I) at 430·0 nm, A_nm=3·40×10⁵ s^-1±5%; for Ar(II) at 480·6 nm, A_nm=8·82×10⁷ s^-1±7%. These values were not influenced by deviations from LTE, which have been observed at electron number densities n_e?10²³ m^-3. The small uncertainties were achieved after careful corrections of different sources of error.     

Laser photoluminescence spectra of the M+S2− species in solid argon at 12K

Matrix reactions of alkali metal atoms with S₂Cl₂ and photolyzed H₂S samples have been examined by laser excitation at 457.9 nm. The strong photoluminescence spectrum from 12 300 to 18 300 cm^?1 exhibited vibrational spacings near 550 cm^?1. Observation of the same ZPL spectrum with two different precursors identified the carrier as Na⁺S₂^?. The vibrational numbering was made possible by the Na⁺³²S³⁴S^? species in natural abundance and from a 33% ³⁴S-enriched sample of S₂Cl₂. The spectroscopic constants ν₀₀ = 19 990 ± 10 cm^?, ω₀″ = 586 ± 2 cm^?1 and ω₀x₀″ = 2.8 ± 0.2 cm^?1 are in excellent agreement with those reported for S₂^? in alkali halide crystals at low temperature.     

Spin-spin interaction of Dy3+ ions in KY(WO4)2

The spin-spin interaction of Dy³⁺ ions in a KY(WO₄)₂ single crystal is investigated by electron paramagnetic resonance (EPR) spectroscopy at a temperature of 4.2 K and a frequency of 9.2 GHz. The EPR spectra of ion pairs located in different coordination shells are analyzed. It is revealed that the considerable contribution to the spin-spin interaction of the nearest neighbor ion pair nn is made not only by the magnetic dipole-dipole interaction but also by the isotropic exchange interaction with the parameter I _nn = (+601 ± 17) × 10^?4cm^?1. The exchange interaction in pairs of more widely spaced ions is substantially weaker: I _5n = (?38 ± 3) × 10^?4cm^?1 and I _9n = (+18 ± 4) × 10^?4cm^?1. For the other ion pairs, the magnetic dipole-dipole interaction dominates. It is found that the EPR spectra of single ions and ion pairs exhibit a superhyperfine structure associated with tungsten nuclei.     

Excitation of the 3p3Πu level of H2 by electron impact; pressure effects

The excitation cross-section of the 3p³Π_u level of H₂ has been measured for electrons from energy threshold to 100 eV. We compare the intensities of the emitted lines to the Balmer lines whose excitation cross-sections from H₂ are known. The effects of dissociation, cascade, polarisation and pressure are discussed. The maximum excitation cross-section is found to be 3·30 × 10^-18 cm² ± 50% at 22·5 eV.     

Chemisorption of H2 on W(100): Absolute sticking probability,coverage, and electron stimulated desorption

Measurements of both the absolute sticking probability near normal incidence and the coverage of H₂ adsorbed on W(100) at ~ 300K have been made using a precision gas dosing system; a known fraction of the molecules entering the vacuum chamber struck the sample crystal before reaching a mass spectrometer detector. The initial sticking probability S₀ for H₂/W(100) is 0.51 ± 0.03; the hydrogen coverage extrapolated to S = 0 is 2.0 × 10¹⁵ atoms cm^?2. The initial sticking probability S₀ for D₂/W(100) is 0.57 ± 0.03; the isotope effect for sticking probability is smaller than previously reported. Electron stimulated desorption (ESD) studies reveal that the low coverage β₂ hydrogen state on W(100) yields H⁺ ions upon bombardment by 100 eV electrons; the ion desorption cross section is ~ 1.8 × 10^?23 cm². The H⁺ ion cross section at saturation hydrogen coverage when the β₁ state is fully populated is ? 10^?25 cm². An isotope effect in electron stimulated desorption of H⁺ and D⁺ has been found. The H⁺ ion yield is ? 100 × greater than the D⁺ ion yield, in agreement with theory.     

Infrared rotation-vibration spectra of ethane: The perpendicular band, ν7, of C2H6

The study of the gas-phase infrared spectrum of C₂H₆ in the region of the perpendicular CH-stretching band, ν₇, near 3000 cm^?1 is extended for the ΔK = + 1 subbands as far as K = 20. The spectral resolution of ～0.030 cm^?1 is increased to ～0.015 cm^?1 by deconvolution. The earlier investigation of this band for KΔK = +9 to ?5, is repeated with greater accuracy, providing more reliable ground-state constants (cm^?1): B₀ = 0.663089 ± 24, D₀^J = (0.108 ± 4) × 10^?5, D₀^JK = (0.50 ± 7) × 10^?5. The molecular constants (cm^?1) for the ν₇ fundamental are B₇ = 0.66310 ± 3, A₇ = 2.682, ν₀ = 2985.39, ζ₇ = 0.128. A discussion of resonance effects in this band, in particular x-y-Coriolis and Fermi resonance, is given.     

Dipolar studies in CaF2 with Ce3+

Dielectric relaxation in CaF₂ doped with various amounts of Ce³⁺ (0·01 to 1·0 mol%) was measured. The value of the activation energy for orientation of the dipoles {Ce³⁺-F^? interstitial} was determined to be H = (0·46 ± 0·01) eV. The frequency factor was found to have the value τ_o = (5 ± 1) × 10^?15 sec, giving for the vibrational frequency of the interstitial the value ν_o = (5 ± 1) × 10¹³ sec^?1.The number of dipoles contributing to the dielectric loss peak was determined to be between 10¹⁷ and 8 × 10¹⁷ cm^?3 for the different doping amounts of Ce³⁺. Optical absorption measurements showed the existence of large aggregate bands. We could verify that there exists a second-order reaction of aggregation, which is responsible for the non-linearity found between optical absorption at 305 nm and the nominal concentration of Ce³⁺ in the samples. On the other hand, if we assume that the centers which contribute to optical absorption at 305 nm are those also responsible for the relaxation peak, we find that the number contributing to each process is not the same. We can define an interaction radius R as the minimum separation between two dipoles allowing them to contribute to the relaxation peak. From our experimental data R ? 3·8 × 10^?7 cm.     

The analysis of symmetric rotor Raman spectra: The pure rotational spectrum of 11BF3

The pure rotational Raman spectrum of ¹¹BF₃ has been photographed. Great care was taken in the analysis to consider all the unresolved components under each observed Raman line profile. If this is ignored, systematic errors result. The final set of molecular constants obtained was B₀ = 0.34502(±3 × 10^?5)cm^?1, D_J = 4.38(±0.10) × 10^?7cm^?1, and D_JK = ?9.1(±1.0) × 10^?7cm^?1.