Radiative decay of the metastable quartet state of copperporphin

In CuP the low temperature luminescence originates from eight transitions between a quartet (M = ±3/2, ±1/2) and a doublet (M′ = ±1/2) with M and M′ denoting the (approximate) eigenvalues of the spin angular momentum S_z along the fourfold axis. Here we report (1) the selection rules governing the polarizations of the transitions; (2) the zero-field splitting ξ between the ±3/2 and ±1/2 components of the quartet for CuP in an n-octane crystal (ξ = 1·1 ± 0·2 cm^-1); (3) a photo-selection experiment on CuP in an isopentane glass from which it is concluded that the ratio of in-plane to out-of-plane polarization in the 0-0 band at 2·1 K amounts to an intensity ratio I _‖/I _⊥ ≈ 2. The implications of these results for the different SOC pathways are analysed.     

New evidence for supernarrow dibaryons production in pd interactions

The analysis of new experimental data, obtained at the Proton Linear Accelerator of INR, with the aim to search for supernarrow dibaryons in the pd↦ppX ₁ and pd↦pdX ₂ reactions is presented. Narrow peaks with an experimental width of 5 MeV at masses of 1904±2, 1926±2, and 1942±2 MeV have been observed in missing mass M _pX1 spectra. In the missing mass M _X1 spectra, the peaks at M _X1 = 966±2, 986±2, and 1003±2 MeV have been found. The analysis of the data obtained leads to the conclusion that the observed peaks in M _pX1 spectra are most likely supernarrow dibaryons, the decay of which into two nucleons is forbidden by the Pauli exclusion principle. An alternative interpretation of the spectra by assuming a decay of the supernarrow dibaryons in “exotic baryon states” with masses M _X1 is discussed. Received: 22 October 2001 / Accepted: 15 November 2001     

Reflection asymmetry in the structure and spectroscopy of224Ac

Minor changes in the assignments of gamma rays following the alpha decay of²²⁸Pa in two previous studies make possible a reinterpretation of²²⁴Ac into two alternative level schemes. The resulting level structures arise from the reflection asymmetric configurations π3/2^±(0.0 −0.3)−ν3/2^±(−0.1 0.6), π5/2^±(0.0 −0.2)±ν3/2^±(−0.1 0.6) and π5/2^±(0.0 −0.2)±ν1/2^±(0.2 −0.1 3) which give rise to eitherK=0^± or 1^±,K=4^±,K=2^± andK=3^± parity doublet bands. The bands with appreciable band structure, namelyK=0^± or 1^± andK=3^±, have average parity doublet splittings of 11.0 and 5.8 keV respectively. These are extremely small values and suggest that²²⁴Ac is the most octupole deformed nucleus studied thus far. A method of calculating the parity doublet splitting in odd-odd nuclei is suggested and tested for²²⁴Ac. It seems to work remarkably well. The systematics of the hindrance factors for the bands with extended band structures confirm their interpretations as band structures. Finally, the two alternative level schemes are analyzed in the framework of the axially-symmetric rigid rotor model including the Coriolis interaction.     

Conformational and structural studies of n‐propylamine from temperature dependent Raman and far infrared spectra of xenon solutions and ab initio calculations

The Raman and infrared spectra (4000 to 50 cm^–1) of the gas, liquid or solution, and solid have been recorded of n‐propylamine, CH₃CH₂CH₂NH₂. Variable temperature (−60 to −100 °C) studies of the Raman (1175 to 625 cm^–1) and far infrared (600 to 10 cm^–1) spectra dissolved in liquid xenon were carried out. From these data, the five possible conformers were identified and their relative stabilities obtained with enthalpy difference relative to trans–trans (Tt) for trans–gauche (Tg) of 79 ± 9 cm^–1 (0.9 ± 0.1 kJ/mol); for Gg of 91 ± 26 cm^–1 (1.08 ± 0.3 kJ/mol); for Gg′ of 135 ± 21 cm^–1 (1.61 ± 0.2 kJ/mol); for Gt of 143 ± 11 cm^–1 (1.71 ± 0.1 kJ/mol). The percentage of the five conformers is estimated to be 18% for the Tt, 24 ± 1% for Tg, 23 ± 3% for Gg, 18 ± 1% for Gg′ and 18 ± 1% for Gt at ambient temperature. The conformational stabilities have been predicted from ab initio calculations utilizing several different basis sets up to aug‐cc‐pVTZ from both second‐order Møller–Plesset (MP2, full) and density functional theory calculations by the Becke, three‐parameter, Lee–Yang–Parr method. Vibrational assignments were provided for the observed bands for all five conformers, which are supported by MP2(full)/6‐31G(d) ab initio calculations to predict harmonic force constants, wavenumbers, infrared intensities, Raman activities and depolarization ratios for both conformers. Estimated r₀ structural parameters were obtained from adjusted MP2(full)/6‐311+G(d,p) calculations. The results are discussed and compared with the corresponding properties of some related molecules. Copyright © 2012 John Wiley & Sons, Ltd.     

In situ confocal micro‐Raman spectroscopic investigation of rearrangement kinetics and phase evolution of UHMWPE during annealing

Ultrahigh molecular weight polyethylene was investigated using in situ confocal micro‐Raman spectroscopy during annealing at 110.0 °C. Based on the Raman spectra, crystalline, amorphous, and all‐trans noncrystalline fractions were recognized to evaluate rearrangement kinetics during isothermal annealing at 110.0 °C and phase evolution during cooling from 110.0 to 30.0 °C. For the crystalline fraction, a substantial increase from 0.600 ± 0.001 to 0.639 ± 0.008 was observed during the first 24.2 min of annealing; a very gradual increase from 0.639 ± 0.001 to 0.679 ± 0.001 occurred during the following 114.6 min. For the amorphous phase fraction, conversely, a sharp decrease from 0.240 ± 0.000 to 0.213 ± 0.004 was exhibited during the first 24.2 min of annealing, and then, a flat decrease happened from 0.213 ± 0.004 to 0.192 ± 0.001 as time expanded to 138.8 min. For the all‐tans noncrystalline fraction, a gradual decrease was shown from 0.160 ± 0.000 at 0.0 min to 0.128 ± 0.001 at 138.8 min. The rearrangement rate constant K was obtained to be 0.632 by an Avrami equation. During cooling from 110.0 to 30.0 °C, there were two phase evolution regions: region 1 from 110.0 to 90.0 °C and region 2 from 90.0 to 30.0 °C. The crystal lamella thickened faster in region 1 than in region 2. The amorphous layer continually decreased in content in the combined region of 1 and 2. The all‐trans noncrystalline phase obviously decreased in region 1 and then almost maintained a constant level in region 2. Copyright © 2014 John Wiley & Sons, Ltd.     

Raman and infrared spectra,conformational stability,vibrational assignment,barriers to internal rotation and ab initio calculations of but-2-enoyl chloride

The Raman (3500–10 cm⁻¹) and infrared (3200–50 cm⁻¹) spectra were recorded for the fluid and solid phases of but-2-enoyl chloride (crotonyl chloride), trans-CH₃CHCHCClO, where the methyl group is trans to the CClO group, and a complete vibrational assignment is proposed. These data were interpreted on the basis that the s-trans (anti) form (two double bonds oriented trans to one another) is the most stable form in the fluid phases and the only conformer remaining in the solid state. The asymmetric torsional fundamental of the more stable s-trans and the higher energy s-cis (syn) form were observed at 97.5 and 86.9 cm⁻¹, respectively. From these data the asymmetric potential function governing the internal rotation about the C C bond was determined. The potential coefficients are V₁ = −111 ± 2, V₂ = 1860 ± 48, V₃ = 6 ± 2, V₄, = −43 ± 24 and V₆ = −22 ± 6. The s-trans to s-cis and s-cis to s-trans barriers were determined to be 1890 and 1785 cm⁻¹, respectively, with an enthalpy difference between the conformers of 105 ± 52 cm⁻¹ [300 ± 149 cal mol⁻¹ (1 cal = 4.184 J)]. Similarly, the barrier governing internal rotation of the CH₃ group for the s-trans conformer was also determined to be 912 ± 30 (2.61 ± 0.09 kcal mol⁻¹) from the torsional fundamental observed in the far-infared spectrum of the gas. All these data were compared with the corresponding quantities obtained from ab initio Hartree–Fock gradient calculations employing the RHF/3–21G*, RHF/6–31G* and/or MP2/6–31G* basis sets. These results were compared with the corresponding quantities for some similar molecules.     

Zeeman spectroscopy of the 4 Eu → 2 B 1g phosphorescence of copper porphin in an n-alkane single crystal

The phosphorescence spectrum of the metastable ⁴ E_u state of copper porphin in single crystals of n-octane (C₈) and n-decane (C₁₀) has been studied between 2·3 and 35 K, with and without a magnetic field B. The crystal field splitting between the orbital components observed at 35 K is δ = 30·3 ± 0·3 (C₈), 13·8 ± 0·2 cm^-1 (C₁₀). From the Zeeman shifts we derive the effective orbital angular momentum Λ′ = 0·8 ± 0·2 (C₁₀), the spin-orbit coupling parameter |Z′| = 1·5 ± 1·0 cm^-1 (C₁₀), the spin-spin dipolar interaction parameters D = -0·1 ± 0·2 cm^-1 (C₈, C₁₀) and |E| = 0·31 ± 0·03 cm^-1 (C₈, C₁₀), and the g-factors g _∥ = 2·14 ± 0·04 (C₈, C₁₀) and g _⊥ = 2·00 ± 0·03 (C₈, C₁₀).     

The keto-enol equilibrium in substituted acetaldehydes: focal-point analysis and ab initio limit

High-level ab initio electronic structure calculations up to the CCSD(T) theory level, including extrapolations to the complete basis set (CBS) limit, resulted in high precision energetics of the tautomeric equilibrium in 2-substituted acetaldehydes (XH₂C-CHO). The CCSD(T)/CBS relative energies of the tautomers were estimated using CCSD(T)/aug-cc-pVTZ, MP3/aug-cc-pVQZ, and MP2/aug-cc-pV5Z calculations with MP2/aug-cc-pVTZ geometries. The relative enol (XHC?=?CHOH) stabilities (ΔE _{e,CCSD(T)/CBS}) were found to be 5.98?±?0.17, ?1.67?±?0.82, 7.64?±?0.21, 8.39?±?0.31, 2.82?±?0.52, 10.27?±?0.39, 9.12?±?0.18, 5.47?±?0.53, 7.50?±?0.43, 10.12?±?0.51, 8.49?±?0.33, and 6.19?±?0.18?kcal?mol^?1 for X?=?BeH, BH₂, CH₃, Cl, CN, F, H, NC, NH₂, OCH₃, OH, and SH, respectively. Inconsistencies between the results of complex/composite energy computations methods Gn/CBS (G2, G3, CBS-4M, and CBS-QB3) and high-level ab initio methods (CCSD(T)/CBS and MP2/CBS) were found. DFT/aug-cc-pVTZ results with B3LYP, PBE0 (PBE1PBE), TPSS, and BMK density functionals were close to the CCSD(T)/CBS levels (MAD?=?1.04?kcal?mol^?1).     

Isotope effects on the degree of order and the deuterium quadrupole coupling constants,as measured by N.M.R. of oriented benzene-d 1, 1,4-benzene-d 2 and 1,3,5-benzene-d 3

Proton and deuteron magnetic resonance spectra of benzene-d ₁, 1,4-benzene-d ₂ and 1,3,5-benzene-d ₃, oriented in various liquid crystal solvents have been analysed. Isotope effects on the degree of order have been measured. The ratios of S-values in the benzene plane are found to be S_xx/S_zz =1·0201 ± 0·0009 in benzene-d ₁ and 1·0389 ± 0·0004 in 1,4-benzene-d ₂ with the deuterons substituted on the z-axis. Deuteron quadrupole coupling constants of 190·4 ± 1·2 kHz and 192·4 ± 1·2 kHz have been obtained for 1,4-benzene-d ₂ and 1,3,5-benzene-d ₃.     

Directional correlation studies in the decay of177gLu

Directional gamma-gamma correlations of the strong 208.4–112.9 keV and of the weak 71.6–249.7 keV cascade transitions in the decay of^177gLu have been measured. The correlation coefficientsA ₂₂=?0.208±0.012 of the strong andA ₂₂=?0.105±0.005 of the weak cascade have been determined. The mixing ratioE2/M1 of ?3.7±0.3 for the 112.9 keV transition and theM2/E1 of ?0.0173±0.0065 for the 71.6 keV transition have been obtained. The deducedM2 admixture in the 71.6 keV transition is in good agreement with the theoretical estimates of Weisskopf and of Nilsson.

     

Observation of the 7 MeV excited spin-flip and non-spin-flip partners in 16 ΛO by γ -ray spectroscopy

We have observed three γ -ray transitions in _Λ ¹⁶ O from both 7MeV excited spin-flip and non-spin-flip partners ( 2^-, 1^- ₂ to the ground-state doublet ( 1^- ₁, 0^- via the ¹⁶O(K ^-,π^-) reaction. The 7MeV excitation energies of the spin-doublet members ( 2^-, 1^- ₂ were determined to be 6784±4±4 keV and 6562±1±2 keV, respectively, and thus the spacing was obtained to be 222±4±5 keV. This is the first observation of the spin-flip state directly populated by the ( K ^-,π^- reaction. Moreover, such directly populated spin-flip and non-spin-flip partners were resolved for the first time.     

ESR and optical study of Cu2+-doped bis-(5,5′-diethylbarbiturato)bis picoline Zn(II)

ESR studies were conducted on Cu²⁺-doped bis-(5,5′-diethylbarbiturato)bis picoline Zn(II). Two Cu²⁺ lattice sites, Cu²⁺(I) and Cu²⁺(II), were identified. These sites exhibit two sets of four hyperfine lines in all directions. The g factor and hyperfine splitting were calculated from ESR absorption spectra: g_x ?=?2.0201?±?0.002, g_y ?=?2.0900?±?0.002, g_z ?=?2.1634?±?0.002, A_x ?=?(30?±?2)?×?10^?4?cm^?1, A_y ?=?(40?±?2)?×?10^?4?cm^?1 and A_z ?=?(154?±?2)?×?10^?4?cm^?1. It was found that Cu²⁺ enters the lattice substitutionally. The ground-state wavefunction of the Cu²⁺ ion in this lattice was determined from the spin Hamiltonian constants obtained from the ESR studies. With the help of an optical absorption study, the nature of the bonding in the complex is also discussed.     

A high resolution FTIR spectroscopic study of the hydrogen-bonded heterodimer H3N−HCN

The spectrum of the symmetric top, hydrogen-bonded heterodimer H₃N?HCN has been recorded between 2900 and 3200cm^?1 using a high resolution FTIR spectrometer. The more intense bands are associated with the ν₂ (H?CN stretch) vibration and include hot bands associated with the low frequency modes ν₅, ν₂ and ν₁₀. Weaker difference bands of the type ν₂+(n?1) ν5?nν₅ are also observed. Analysis of the bands yields values for the band origins: ν2/0=3110·5±0·2cm^?1 and ν5/0=140±5cm^?1 and the anharmonicity constants: x _2,10=12·7±0·5cm^?1, x _2,9≈x _2,5=23±3cm^?1 and x _5,10=?5±2cm^?1. The lifetime in ν₂ with respect to vibrational predissociation, estimated from the width of the sharpest observed feature, is 100?200 ps but there is some indication that this lifetime may decrease at high J.     

Thermal depolarisation current study of electron irradiated fluorinated ethylene propylene

Thermally stimulated current (TSC) studies have been reported in the co-polymer of tetrafluoro ethylene and hexafluoropropylene films. Depolarisation current peaks are obtained atα ₁,α ₂ andβ relaxation temperatures of the polymer and the detrapping process is explained on the basis of its molecular motion. A cross-over electron energy of 18 keV is observed where the nature of TSC spectra undergoes a remarkable change. This is explained in relation to the surface states in FEP. Five groups of trapping levels, 0.25±0.08, 0.57±0.10, 1.07±0.1, 1.3±0.25 and 2.3±0.4 eV are obtained.     

On the calculation of the orientational correlation parameter g 2

The g ₂ factor for a model of liquid carbon disulphide has been calculated by molecular dynamics simulation. The values of g ₂ for the model at three points along the orthobaric curve are: 1·17 ± 0·04 (298 K), 1·27 ± 0·03 (245 K), 1·39 ± 0·06 (193 K). These values are in good agreement with available experimental values. By calculating g ₂ in shells of cubic symmetry it is found that the value of g ₂ is determined by the orientational correlation of a molecule with neighbours within a few (two to three) molecular diameters. Spurious orientational correlations are introduced by the periodic boundary conditions and the calculation of collective correlation functions by averaging over the whole cube is shown to be unreliable. A theoretical calculation of g ₂ using RISM + SSA fails to reproduce the state dependence of the g ₂ values calculated from the simulation. This failure is not due to the small differences between the simulation and RISM g _αβ(r) for r < 4·5 Å but to inaccuracies in the SSA in the intermediate region r ～ 6 Å.     

Hydrogen bond studies

The deuteron magnetic resonance spectra from partially deuterated single crystals of NaHC₂O₄. H₂O have been studied. The quadrupole coupling tensors for stationary deuterons are determined at about 25°C. The quadrupole coupling constants and the assymmetry parameters η of the tensors for the two deuterons in the water molecule are, 235·2 ± 1·9 and 228·5 ± 1·6 kHz, and 0·09 ± 0·01 and 0·13 ± 0·01, respectively. The principal axes corresponding to the largest components both deviate by 0·9 ± 0·5° from their respective O-H directions. For one of the tensors this angular displacement is in the plane of the H₂O molecule and towards the other O-H direction. The displacement for the other tensor is out of the plane of the H₂O molecule.     

Kinetics of the gas‐phase homogeneous unimolecular elimination of selected ethyl esters of 2‐oxo‐carboxylic acids

The gas‐phase elimination kinetics of selected ethyl esters of 2‐oxo‐carboxylic acid have been studied over the temperature range of 270–415 °C and pressures of 37–114 Torr. The reactions are homogeneous, unimolecular, and follow a first‐order rate law in a seasoned static reaction vessel, with an added free radical suppressor toluene. The observed overall and partial rate coefficients are expressed by the following Arrhenius equations:

• Ethyl oxalyl chloride
• log k_overall (s^?1) = (13.22 ± 0.45) ? (179.4 ± 4.9) kJ mol^?1 (2.303 RT)^?1
• Ethyl piperidineglyoxylate
• log k_(CO2) (s^?1) = (12.00 ± 0.30) ? (191.2 ± 3.9) kJ mol^?1 (2.303 RT)^?1
• log k_(CO) (s^?1) = (12.60 ± 0.09) ? (210.7 ± 1.2) kJ mol^?1 (2.303 RT)^?1
• log k_t(overall) (s^?1) = (12.22 ± 0.26) ? (193.4 ± 3.4) kJ mol^?1 (2.303 RT)^?1
• Ethyl benzoyl formate
• log k_(CO2) (s^?1) = (12.89 ± 0.72) ? (203.8 ± 9.0) kJ mol^?1 (2.303 RT)^?1
• log k_(CO) (s^?1) = (13.39 ± 0.31) ? (213.3 ± 3.9) kJ mol^?1 (2.303 RT)^?1
• log k_t(overall) (s^?1) = (13.24 ± 0.60) ? (205.8 ± 7.6) kJ mol^?1 (2.303 RT)^?1

The kinetic and thermodynamic parameters of these reactions, together with those reported in the literature, lead to consider three different mechanistic pathways of elimination. Copyright © 2010 John Wiley & Sons, Ltd.     

Anharmonic resonances between the v 1 + v ±1 6, v 3 + v ±1 5 + 2v 0 6 and v 3 + v ∓1 5 + 2v ±2 6 vibrational bands of CH3 79Br

The 22 K sub-bands, belonging to the v ₁ + v ^±1 ₆, v ₃ + v ^± ₅ + 2v ⁰ ₆ and v ₃ + v ^±1 ₅ + 2v ^±2 ₆ rovibrational bands of monoisotopic CH₃ ⁷⁹Br, have been identified. An RMS standard deviation of about 0·020 cm^-1 has been achieved by a least squares fit over 619 lines belonging to these 22 sub-bands. For this purpose, a model taking into account (a) anharmonic resonances between (i) v ₁ + v ^±1 ₆, and v ₃ + v ^±1 ₅ + 2v ⁰ ₆, (ii) v ₁ + v ^±1 ₆ and v ₃ + v ^?1 ₅ + 2v ^±2 ₆ and (iii) v ₃ + v ^±1 ₅ + 2v ⁰ ₆ and v ₂ + 2v ₃ + v ^±1 ₅ and (b) Coriolis resonances between the v ₂ and v ₅ modes, was used.     

Phase transition in the ternary fluorides Li3Alf6 and Li3CrF6

The phase transitions of two ternary fluorides have been reinvestigated by thermal and X-ray diffraction analyses. Four phase transitions have been detected at T ₁ = 483 ± 5 K, T ₂ = 548 ± 5 K, T ₃ = 765 ± 5 K and T ₄ = 867 ± 5 K for Li₃AlF₆. Only two transformations occurred at T ₁ = 550 ± 5 K and T ₂ = 660 ± 10 K for Li₃CrF₆. Dielectric and optical measurements performed respectively on ceramics and single crystals revealed a ferroelectric behaviour coupling partially with ferroelastic coupling for the two investigated fluorides.