Microwave spectrum,centrifugal distortion constants,dipole moment and quadrupole coupling constants of pentafluoropyridine

Pentafluoropyridine has been analysed in the frequency range of 8 to 18 GHz at dry ice temperature, using a conventional 100 kHz Stark modulated microwave spectrometer. The rotational constants and centrifugal distortion constants are A = 1481.539 ± 0.003 MHz, B = 1075.348 ± 0.004 MHz and C = 623.101 ± 0.001 MHz; and d_J = ?0.39 ± 0.06 kHz, d_JK = 1.86 ± 0.27 kHz, d_K = 0.70 ± 0.1 kHz, d_EJ = (0.3 ± 0.03) × 10^?6 and d_EK = (?1.5 ± 0.2) × 10^?6. The electric dipole moment has been found to be 0.98 ± 0.08 D and the values of the quadrupole coupling constants are x_aa = 1.94 ± 0.22 MHz, x_bb = ?4.08 ± 0.06 MHz and x_cc = 2.14 ± 0.22 MHz. A simple analysis based on Townes and Dailey theory points to a considerable increase in the π-electron density and excess charge on the nitrogen site.     

Microwave spectroscopic study on the molecular structure and the quadrupole coupling constants of thionyl chloride

Microwave spectra of thionyl chloride, SO³⁵Cl₂ and SO³⁵Cl³⁷Cl, in the frequency range 8–25 GHz have been analyzed. The rotational constants have been obtained from the low J transition frequencies. The r_S coordinates of Cl atoms and the r_o structure have been evaluated with some assumptions: r(S-O) = 1.435 ± 0.011± Å, r(S—Cl) = 2.072 0.005 Å, ∠ OSCl = 108.00 ± 0.06°, ∠ ClSCl = 97.15 ± 0.30°. Nuclear quadrupole coupling constants have been obtained for the SO³⁵Cl₂, species: x_aa = ?25.02 ± 0.04 MHz, x(_bb = ?0.25 ± 0.04 MHz, X_cc = 25.27 ± 0.08 MHz, and X_zz = ?96.75 MHz. The values obtained are compared with those of other workers.     

The determination and assignment of a complete 14N quadrupole coupling tensor in liquid solution

¹⁴N line splittings in the spectrum of nitrobenzene (neat liquid) and metadinitrobenzene (dissolved in benzene), induced by an external electric field, have been used to determine the complete ¹⁴N quadrupole coupling tensor of these substances. Assuming that both molecules are rigid and planar, and that the quadrupole coupling tensors at the ¹⁴N nuclei are identical, the principal components in a local reference frame (x′, y′, z′) are (eQ/h)V_x′ x′ = ±0.34 MHz (eQ/h)V_y′_y′= ±1.18 Hz and (eQ/h)V_z′_z′ = ±1.52. The z′-direction is parallel to the CN bond and the y?direction is perpendicular to the plane of the nitrogroup. With these data the asymmetry parameter η = 0.55.     

Microwave spectrum of N2D4, 14N quadrupole coupling constants,and the barrier to inversion of the amino group

The microwave spectrum of N₂D₄ has been observed and analyzed. Based on five low-J rotational transitions the effective rotational constants are: A = 74712.9 ± 1.9 MHz, B = 18500.42 ± 0.46 MHz, and C = 18439.91 ± 0.46 MHz. The quadrupole coupling constants of the ¹⁴N nuclei are X_aa = 4.23 ± 0.04 MHz, X_bb = 1.98 ± 0.05 MHz, and X_cc = ?2.25 ± 0.05 MHz. Using the observed ground state inversion splittings for N₂D₄ and N₂H₄ the barrier to inversion of a single amino group is computed to be 5.00 kcal mol^?1.     

The molecular Zeeman effect in HCP,HCN, and HCCBr and a comparison with similar molecules

The molecular Zeeman effect has been observed in the J = 0 → 1 ΔM = 0, and ± 1 transitions in H¹²CP, D¹²CP, H¹²C¹⁵N, H¹²C¹²C⁷⁹Br, and H¹²C¹²C⁸¹ Br giving the molecular g-values, magnetic susceptibility anisotropies, and corresponding molecular quadrupole moments. The results are g_⊥(HCP) = ?0.0430 ± 0.0010, g_⊥(DCP) = ?0.0353 ± 0.0010, x_⊥ - x_| = (8.4 ± 0.9) × 10^?6 erg/G² mole and Q_|(HCP) = (4.4 ± 1.2) × 10^?26 esu; g_⊥(HC¹⁵N) = ?0.0904 ± 0.0003, x_⊥ - x_| = (7.2 ± 0.4) × 10^?6 erg/G² mole, and Q_|(HC¹⁵N) = (3.1 ± 0.6) × 10^?26 esu; g_⊥(HCC⁷⁹Br) = ?0.00395 ± 0.00032, g_⊥(HCC⁸¹Br) = ?0.00388 ± 0.00014, x_⊥ - x_| = (9.5 ± 0.9) × 10^?6 erg/G² mole, and Q_| = (8.5 ± 1.1) × 10^?26 esu. The results in HCN agree very well with an earlier prediction of the magnetic properties. The new results presented here are compared to other members in the acetylene and cyanide series of molecules and we conclude that the sign of the g-value in acetylene should be positive.The deuterium nuclear quadrupole coupling constant was also determined in DCP to be x_D = 233 ± 40 kHz.     

Angular distribution for the major photoelectron bands of nitrogen below 45 eV binding energy

High-resolution optically detected magnetic resonance (ODMR) and optically detected electron—electron double resonance (ODEEDOR) have been performed on the lowest excited triplet states of pyrazine-h₄ and pyrazine-d₄, as dilute guests in polycrystalline benzene and cyclohexane host matrices. Computer simulated spectra have been fitted to those experimentally observed, using a spin hamiltonian which takes into account the ¹⁴N and ¹H (or ²D) nuclei of the pyrazine guest molecule. Good agreement is obtained when one ¹⁴N nuclear quadrupole energy difference, |ε_y^N - ε_z^N| ? 1.3 MHz, and the remaining component, |ε_x^N| = 0.6 ± 0.2 MHz for pyrazine-d₄ in benzene-d₆.     

Molecular Zeeman effect of 3-oxetanone and 3-methylene oxetane,and the comparison of the magnetic-susceptibility anisotropies,molecular quadrupole moments,and other magnetic parameters with other four-membered rings

The molecular Zeeman effect is reported for 3-oxetanone and 3-methylene oxetane at fields near 20000 G. The results for 3-oxetanone are molecular g-values: g_aa = ?0.1059 ± 0.0008, g_bb = ?0.0581 ± 0.0004,g_cc = ?0.0437 ± 0.0004, magnetic susceptibility anisotropies:2x_aa -x_bb - x_cc = (9.6±0.5) x 10^?6 erg/G²mole, 2x_bb - x_aa - x_cc = ?(7.8±0.6) x 10^?6 erg/G²mole, and molecular quadrupole moments: Q_aa = ?(12.8±0.8) x 10^?26 esu cm,Q_bb = (7.9±0.8) x 10^?26 esu cm, and Q_cc = (4.9±0.8) x 10^?26 esu cm. For 3-methylene oxetane, the results are g_aa = ?0.0510 ± 0.0018, g_bb = ?0.0435 ± 0.0010, g_cc = ?0.0313 ± 0.0010, 2x_aa - x_bb - x_cc = ?(10.9±0.5) x 10^?6 erg/G² mole, 2x_bb - x_aa - x_cc = (2.3±0.9) x 10^?6 erg/G² mole, Q_aa = -?5.4±1.0) x 10^?26 esu cm, Q_bb = (5.1 ± 1.2) x 10^?26 esu cm, and Q_cc = (0.2±1.5) x 10^?26 esu cm. The bulk magnetic susceptibility for 3-oxetanone was measured to be x = 1/2 (x_aa+x_bb+x_cc) = ?(30.6±1.5) x 10^?6 erg/G² mole. The out-of-plane minus average in-plane magnetic-susceptibility anisotropies in four-membered rings show larger paramagnetism than predicted on the basis of localized group susceptibility anisotropies. This effect is discussed and a possible explanation presented.     

L-band parallel mode epr. measurement of quadrupole coupling through direct observation of secondary transitions

An L-band (1–2 GHz) EPR spectrometer with static and oscillating magnetic fields parallel is used to obtain quadrupole coupling information through direct measurement of secondary (Δm_s = ±1, Δm₁, = ∓1) transitions. Spectra and interpretations are presented for a test case, ⁶³Cu/Pd(acac)₂ powder, for which QD = 9±1 MHz and QE = 0.6 MHz are obtained.     

Correlation of crystal structures with electric field gradients in the fluorite- and pyrochlore-type compounds in the Gd2O3-ZrO2 system

Correlation of crystal structure with electric field gradient (EFG) in the fluorite- and pyrochlore-type compounds in the Gd₂O₃-ZrO₂ system Gd_xZr_1−xO_2−x/2 with 0.18?x?0.62 were investigated by ¹⁵⁵Gd Mössbauer spectroscopy, powder X-ray diffraction and point-charge model (PCM) calculation. An intermediate ordered pyrochlore phase forms for 0.45?x?0.55, sandwiched with a disordered fluorite phase for 0.18?x<0.45 and 0.55<x?0.62. Some ¹⁵⁵Gd Mössbauer parameters, especially the quadrupole coupling constant (e²qQ), were found to exhibit a characteristic maximum around the ideal-pyrochlore Gd₂Zr₂O₇ (x=0.50) composition. The validity of the proposed pyrochlore-based structural model was examined by comparing the experimental values of EFG at the Gd sites with those calculated by the PCM calculations.     

Microwave spectrum of aminoborane,BH2NH2

The unstable species aminoborane, BH₂NH₂, has been identified as a reaction product of ammonia with diborane by microwave spectroscopy. The rotational constants determined are A = 138212 ± 4 MHz, B = 27487.83 ± 0.10 MHz and C = 22878.44 ± 0.11 MHz for ¹¹BH₂NH₂ and A = 138199 ± 6 MHz, B = 28420.36 ± 0.11 MHz and C = 23520.78 ± 0.12 MHz for ¹⁰BH₂NH₂. The dipole moment is 1.844 ± 0.015 D.     

Microwave spectrum,conformation, intramolecular hydrogen bond,dipole moment, 14N quadrupole coupling constants and centrifugal distortion of 2flu

Microwave spectra of CH₂FCONH₂, CH₂FCOND(1)H(2), CH₂FCONH-(1)D(2), and CH₂FCOND₂ are reported. The stable form of the molecule is shown to possess a planar FCCONH₂ skeleton, with two out-of-plane hydrogens. The C-F and CO bonds are trans to one another and a weak intramolecular hydrogen bond is formed between the fluorine atom and the nearest amide group hydrogen atom stabilizing the identified rotamer. Other conformations are not present in concentrations exceeding 10% of the total. Nine vibrationally excited states were assigned. Six of these were attributed to the C-C torsional mode and one to the lowest in-plane bending mode. The first excited state of -NH_z out-of-plane deformation mode was tentatively assigned. Relative intensity measurements yielded 114±14 cm^?1 for C-C torsional mode and 239±20 cm^?1 for the in-plane bending mode. The dipole moment was determined asμ_a = 1.27±0.01 D, μ_b = 1.67±0.02 D, and μ_tot = 2.10±0.02 D, while the ¹⁴N quadrupole coupling constants were found to be χ_aa = 1.6±0.2 MHz, χ_bb = 1.6±0.2 MHz and χ_cc = ?3.2±0.3 MHz.     

Microwave spectrum and structure of CF3OOCl

The microwave spectrum of chloroperoxytrifluoromethane has been recorded from 12.5 to 40.0 GHz. Only a-type transitions were observed. The R-branch assignments have been made for both the CF₃OO³⁵C1 and CF₃OO³⁷Cl species for the ground vibrational state. The rotational constants are: A=4808± 12, B=1318.55±0.02, C=1278.28±0.02 MHz for the ³⁵CI species, and A=4748±300,B=1285.28±0.96, C=1246.80±0.96 MHz for the ³⁷Cl species. From a diagnostic least-squares adjustment to fit the six rotational constants the following structural parameters were obtained: r(C-0)=1.377±0.03 Å, r(O-O)=1.445± 0.049 Å, r(Cl-O)=1.69±0.04 Å, ∠COO=108.1±4.2°, ∠ClOOC=99.5±2.0°, and ∠tilt = 6.0±0.9° with reasonable assumptions for the three other structural parameters. The relatively large uncertainty in these structural parameters results from the large uncertainty in the A rotational constants. These parameters are compared to the corresponding ones in some other peroxides. The quadrupole coupling constants have been obtained and are discussed.     

Microwave spectrum of 1,2,4-trifluorobenzene

The microwave spectrum of 1,2,4-trifluorobenzene has been observed in the range 12.5–18.0 GHz and 21.5–25.3 GHz at dry-ice temperature and assigned up to angular momentum state J = 39. The ground state rotational constants and the five quartic centrifugal distortion constants thus obtained are (in MHz): à = 3084.0037 ± 0.0108, B? = 1278.3614 ± 0.0062, C? = 903.6989 ± 0.0108, d_j = ( ?4.599 ± 0.621) · 10^?4, d_jk = (5.9757 ± 1.1586) · 10^?3, d_k = (11.4923 ± 2.0886) · 10^?3, d_wj = (4.0 ± 1.0) · 10^?7, d_wk=(?5.8± 1.1) · 10^?6.The small value of Δ = 0.029 (amu Ų) shows that the molecule is planar and an r₀ - structure using a regular hexagonal benzene ring with the bond lengths C-C = 1.397 Å, C-H = 1.084 Å and C-F = 1.312 Å, reproduces the rotational constants.     

Homogeneity range of neodymium manganite in air

The solubility boundaries for Nd₂O₃ and manganese oxides in NdMnO_{3 ± δ} have been determined by X-ray powder diffraction analysis of homogeneous phases and heterogeneous compositions of the general formula Nd_{2 ? x} Mn _x O_{3 ± δ} (0.90 ≤ x ≤ 1.20; Δx = 0.02) prepared by ceramic technology from constituent oxides in air in the temperature range 900–1400°C. The results are presented in the form of a fragment of the Nd-Mn-O phase diagram in air. It is suggested that the Nd₂O₃ solubility in NdMnO_{3 ± δ} is due to crystal defects and the solubility of manganese oxides is in addition due to the disproportionation reaction 2Mn³⁺ = Mn²⁺ + Mn⁴⁺ and the subsequent partial substitution of divalent for tervalent manganese ions in the cuboctahedral positions of the perovskite-like crystal lattice. To verify this suggestion, it is necessary to systematically study the oxygen nonstoichiometry δ in Nd_{2 ? x} Mn _x O_{3 ± δ} as a function of x and synthesis temperature and structurally study this oxide with these parameters being varied.     

The 99Ru Mössbauer spectrum of β-RuCl3

The ⁹⁹Ru nuclear quadrupole interaction in β-RuCl₃ can be related to the large trigonal distortion at the ruthenium site. The ratio of the quadrupole moments has been determined to be Q_e/Q_g = +3.06 ± 0.10, and it is confirmed that Q_c and Q_g are both positive.     

Thermodynamics of solid solution formation in NiOMgO and NiOZnO

High-temperature calorimetric measurements of the enthalpies of solution in molten 2PbO · B₂O₃ of (Ni_xMg_1?x)O and (Ni_xZn_1?x)O permit the calculation of the enthalpy of the zincite to rocksalt transformation in ZnO, and the enthalpies of mixing, relative to rocksalt standard states, in the two solid solution series. The enthalpy of the zincite to rocksalt transformation is 24,488 ± 3,592 J mole^?1 with a corresponding positive entropy change of 0.48 ± 3.3 J K^?1 mole^?1. The small positive entropy change for the transformation necessitates a very flat and perhaps negative $\text{dP}\text{dT}$ slope for the phase boundary. Both solid solutions, when referred to rocksalt standard states, show negative enthalpies of mixing. For (Ni_xMg_1?x)O the negative enthalpies of mixing are fitted by a subregular model, where ΔH_mix = X_AX_B(BX_A + AX_B), with A = ?21,971 ± 4,953 J mole^?1 and B = ?5103 ± 1151 J mole^?1. The associated negative excess entropies of mixing, calculated from the heats of mixing and previously measured activity-composition relations, are similarly modeled with A = ?10.7 J K^?1 mole^?1 and B = + 1.1 J K^?1 mole^?1. Negative enthalpies of mixing in (Ni_xZn_1?x)O conform to a regular solution model with W = ?13520 ± 5581 J mole^?1. The negative enthalpies of mixing are interpreted in terms of a tendency toward ordering in the solid solutions, the proposed ordering scheme finding support in spectroscopic, structural, and magnetic data. These tendencies toward order are used to explain observed phase relations and thermodynamic properties in some other systems containing a transition metal cation and another ion of similar size, namely carbonates, hydrated sulfates and the systems CuOMO (M = Mg, Co, Ni).     

The rotational spectrum,nuclear spin—spin coupling,nuclear quadrupole coupling,and molecular structure of KrHF

Rotational spectra have been assigned for the ⁸²Kr, ⁸³Kr, ⁸⁴Kr, and ⁸⁶Kr isotopic species of the KrHF and KrDF van der Waals molecules by using pulsed microwave Fourier transform spectroscopy in a Fabry—Perot cavity with a pulsed supersonic nozzle molecular source. The rotational, centrifugal distortion, nuclear spin—spin, and nuclear quadrupole coupling constants are used to determine the structure and obtain intramolecular potential binding information. The ⁸³Kr nuclear quadrupole coupling constants are 10.28 ± 0.08 MHz and 13.83 ± 0.13 MHz for KrHF and KrDF respectively. The electric field gradient at the krypton nucleus is calculated from the coupling constant and the known nuclear quadrupole moment and explained by Sternheimer shielding and formation of the van der Waals bond. There is a negligible charge transfer in the KrHF bond.     

Ruthenium-99 Mössbauer spectra of some nitrido complexes of Ru(VI)

The quadrupole splittings found in the ⁹⁹Ru Mössbauer spectra of (Bu₄ⁿN)[RuNCl₄ and (Ph₄As)[RuNBr₄] at 4.2 K are the largest yet observed for this isotope. The six component lines are almost resolved, and lead to new estimates for the ratio of the nuclear quadrupole moments of Q_e/Q_g = +2.82 ± 0.09 and for the E2/M1 mixing ratio of δ² = 2.64 ± 0.17. By contrast, the spectrum of Cs₂[RuNCl₅] has a much smaller quadrupole splitting and a more negative isomer shift. These differences can be interpreted empirically in terms of the asymmetric occupation of the 4d orbitals. The new data confirm an earlier deduction that both Q_e and Q_g are positive.     

Doppler-free rotational spectrum of methyl iodide. Nuclear quadrupole,spin-rotation and nuclear shielding tensors of iodine

The ground-state microwave spectrum of methyl iodide has been measured between 59 and 240 GHz with a molecular beam spectrometer and by use of the Lamb dip method. The following molecular parameters have been accurately determined: B = 7501275.70(2) kHz; D_J = 6.3070(2) kHz; D_JK = 98.762(3) kHz; H_J = ?0.0051(6) Hz; H_JK = 0.04(2) Hz; H_KJ 4.51(3) Hz; eq. Q = ?1934.136 (5) MHz; C_⊥= ?17.40(6) kHz; C_| = ?19.4(5) kHz; x_J = ?1.41(4) kHz; x_K = ?38(1) kHz and x_d = 26.2(6) kHz. The last three constants characterize the interaction of centrifugal distortion with quadrupole coupling. The data are used to determine the elements of the iodine nuclear magnetic shielding tensor. Comparisons of the shielding are made for molecules which contain one iodine atom.     

Étude en ondes millimétriques des variétés isotopiques en 13c et 18o de la molécule de trioxane: Structure de la molécule

The rotational spectra of the molecules (¹³CH₂O)(¹²CH₂O)₂ and (CH₂¹⁸O) (CH₂¹⁶O)₂ have been investigated in the region 30–290 GHz. The rotational constants determined are (MHz):A = 5271.106±0.007, B = 5176.405 ±0.007, C = 2904.376±0.34 for the former, andA = 5267.34±0.3, B = 508I.106±0.3, C = 2872.378± 10 for the latter molecule.The parameter C of the parent molecule (CH₂O)₃ has been determined: 2933.95 ±0.34 MHz. With the value A = B = 5273.258 ±0.002 for the parent molecule the following structural parameters were determined: r(C-O) = 1.4205± 0.005 Å, ∠COC = 109.5±0.5°, ∠OCO = 112±0.5°.