The microwave spectrum of phosphabutadiyne, H---CC---CP

A detailed rotational analysis of the microwave spectrum between 26.5 and 40 GHz of phosphaethene, CH₂=PH, has been carried out. This molecule is the simplest member of a new class of unstable molecules—the phosphaalkenes. The species can be produced by pyrolysis of (CH₃)₂PH, CH₃PH₂ and also somewhat more efficiently from Si(CH₃)₃CH₂PH₂. Full first-order centrifugal distortion analyses have been carried out for both ¹²CH₂³¹PH and ¹²CH₂³¹PD yielding: A₀ = 138 503.20(21), B₀ = 16 418.105(26), and C₀ = 14 649.084(28) MHz for ¹²CH₂³¹PH. The 1₀₁-0₀₀ μ_A lines have also been detected for ¹³CH₂PH, cis-CDHPH and trans-CHDPH. These data have enabled an accurate structure determination to be carried out which indicates: r(H_cC) = 1.09 ± 0.015 Å, (H_cCP) = 124.4 ± 0.8°; r(H_tC) = 1.09 ± 0.015 Å, (H_tCP) = 118.4 ± 1.2°; r(CP) = 1.673 ± 0.002 Å, (HCH) = 117.2 ± 1.2°; r(PH) = 1.420 ± 0.006 Å, (CPH) = 97.4 ± 0.4°. The dipole moment components have been determined as μ_A = 0.731 (2), μ_B = 0.470 (3), μ = 0.869 (3) D for CH₂PH; μ_A = 0.710 (2), μ_B = 0.509 (10), μ = 0.874 (7) D for CH₂PD.     

The microwave spectrum, structure, chlorine nuclear quadrupole coupling constants, dipole moment, and centrifugal distortion constants of dichlorosilane

The microwave spectra of three isotopic species of dichlorosilane, SiH₂Cl₂, in its ground vibrational state, have been measured in the frequency region 8–40 GHz. The spectra have yielded values for the rotational constants, centrifugal distortion constants, and chlorine nuclear quadrupole coupling constants, as well as the molecular dipole moment, 1.13 ± 0.02 D. The molecule has C_2v symmetry, and the bond lengths and angles r(Si---Cl=2.033±Å, r(Si---H)=1.480±0.015Å, (Cl---Si---Cl)=109°43′±20±, (H---Si---H)=111°18′±40′ The centrifugal distortion constants have been compared with those calculated using a published force field.     

Rotational Spectra of CH2DCCH and CH3CCD: Experimental and ab Initio Equilibrium Structures of Propyne

The ground state rotational spectra of CH₂DCCH and CH₃CCD (main species and ¹³C-substituted species) have been measured up to 470 GHz. Accurate rotational and centrifugal distortion constants have been determined. r₀, r_s, r_ε,I, and r^ρ_m, structures of propyne have been calculated. The ab initio structure has also been calculated using three different methods (SCF, MP2, and QCISD) and two basis sets (DZP and TZ2P). Offsets have been derived empirically using molecules containing structural units present in propyne and whose equilibrium structures have been determined previously. A near-equilibrium structure has been estimated to be acetylenic r(C---H) = 1.061 (1) Å, r(CC) = 1.204 (1) Å, r(C---C) = l.458 (2) Å, methyl r(C---H) = 1.089 (1) Å, and (CCH) = 110.7 (5)°.     

The methyl bromide molecule: A critical consideration of perturbations in spectra

This work gives an extensive critique of studies on methyl bromide and all its isotopic varieties with special stress on their rotational, vibrational, and rovibrational spectra. The rotational constants of more than 40 vibrational states of CH₃Br and 20 of CD₃Br, as well as of the ground states of all varieties, were critically examined and corrected where needed. An almost complete set of harmonic and anharmonic constants for CH₃Br was derived. From the set of rotation-vibration interaction constants, new accurate equilibrium constants A_e and B_e have been evaluated for CH₃⁷⁹Br, CH₃⁸¹Br, CD₃⁷⁹Br, CD₃⁸¹Br, from which the following equilibrium structure is obtained: r_e(C---H) = 1.0823 Å; r_e(C---Br) = 1.9340 Å; α(HCH) = 111.157°.     

Doppler-limited dye laser excitation spectroscopy of DCF

The dye laser excitation spectrum of the vibronic transition of DCF was observed between 17 200 and 17 400 cm⁻¹ with the Doppler-limited resolution. DCF was produced by the reaction of microwave-discharged CF₄ with CD₃F. The observed spectra, which were found to be nearly free of perturbations, were assigned to 858 transitions of the K′_a − K″_a = 4−5, 3−4, 2−3, 1−2, 0−1, 1−0, 2−1, 3−2, 3−3, 2−2, 1−1, 0−0, 2−0, and 0−2 subbands, and were analyzed to determine the rotational constants and centrifugal distortion constants for both the and à states. The rotational constants of DCF thus determined were combined with those of HCF to calculate the structural parameters for this molecule: r(C---H) = 1.138 Å, r(C---F) = 1.305 Å, and HCF = 104.1° for the ground state, and r(C---H) = 1.063 Å, r(C---F) = 1.308 Å, and HCF = 123.8° for the excited à state.     

Sulfur dioxide: Rotational constants and asymmetric structure of the state

Eight bands of the 2350 Å system of sulfur dioxide have been rotationally analyzed as A-type transitions of a prolate asymmetric rotor, confirming that the electronic transition is ¹B₂ ← ¹A₁[2b₁(π^*) ← 1a₂(π)]. The electronic energy and rotational constants of the 0-0 band are, in cm⁻¹: These constants correspond to the average structure r₀ = 1.560 Å and θ₀ = 104.3°. However, the vibrational structure can only be satisfactorily accounted for on the hypothesis of a double-minimum potential in the antisymmetrical stretching coordinate Q₃, the energies of the fundamental levels in the three modes of the B₂ state being: (100), 960 cm⁻¹; (010), 377 cm⁻¹; and (001), 220 cm⁻¹ The (001) level is not observed in the spectrum but can be calculated from the distortion constants and inertial defect of the rotational analysis: the level (002) = 561 cm⁻¹, obtained directly from the vibrational structure, establishes that there is strong, positive anharmonicity in the first three levels of this vibration, as required by the assumption of a double-minimum potential function. Preliminary values are reported for the barrier to the symmetrical configuration, V/hc 100 cm⁻¹, and for the difference in bond distances in the equilibrium configuration, Δr0.12 Å. Coon and his co-workers have previously considered the possible asymmetry of this state but the Q₃ inversion barrier obtained by them, 656 cm⁻¹, is much higher than in the present work, and reasons for this are discussed.     

The microwave spectrum of 1-phosphabut-3-ene-1-yne, CH2=CHCP

The new molecule 1-phosphabut-3-ene-1-yne, CH₂=CHCP, produced by pyrolyzing prop-1-ene-3-phosphorus dichloride, CH₂=CHCH₂PCl₂, was detected by microwave spectroscopy. The analysis of the rotational transitions indicates that the molecule is planar with constants: A₀ = 46 694(24), B₀ = 2807.7100(21), and C₀ = 2645.8356(21) MHz. These rotational constants indicate that the structure of the vinyl group is essentially the same as that in CH₂=CHCN and CH₂=CHCCH; r(C---C) = 1.432 Å and (C=C---C) = 123.9°. The dipole moment parameters are μ_A = 1.181(2), μ_B = 0.074(1), and μ = 1.183(2) D. The vibrational satellite spectra for the C---CP bending modes indicate that ν₁₁(a′) = 184 ± 30 cm⁻¹ and ν₁₅(a″) = 263 ± 30 cm⁻¹.     

Microwave spectrum and structure of ethylene ozonide: Effects of large axes rotations in structure calculations

Rotational spectra for 14 isotopic species of ethylene ozonide have now been assigned. The consistency of the Kraitchman substitution structure was checked by calculating the O_p---O_p bond distance six ways; the values ranged from 1.458 to 1.502 Å. This variation was attributed to an amplification of residual vibrational effects by large axes rotations upon isotopic substitution. Estimates of errors produced from this effect were made and a procedure was developed for choosing r_s parameters in which the effect is minimized. This gave the following ring parameters: d(CO_e) = 1.416 Å, d(CO_p) = 1.412 Å, d(OO) = 1.461 Å, <CO_eC = 104.8°, <O_eCO_p = 105.5°, <CO_pO_p = 99.3°.     

Isotope and Hyperfine Structure in the "Orange" System of FeO: Evidence for Two Δi Excited States

The orange system of FeO has been reinvestigated using low-temperature molecular beam laser-induced fluorescence spectra, obtained by supersonic jet cooling. Two new weak bands have been found, and analyses of some of the previously known bands extended. Measurements of the ⁵⁴Fe-⁵⁶Fe isotope shifts have been made for most of the bands, and the hyperfine structure of the low-J lines has been recorded for two of the strongest bands of ⁵⁷FeO. The isotope shifts are consistent with the presence of two ⁵Δ_i-⁵Δ_i transitions lying within 1000 cm⁻¹; the origins of the Ω = 4 spin components lie at 5583 and 6110 Å, respectively. The hyperfine patterns and the spin-orbit structure indicate that the upper state electron configurations are (3dδ)³ (3dπ)² (3dσ)¹, (D⁵Δ_i, 5583 Å) and O(2pπ)³ (4sσ)¹ (3dδ)³(3dπ)³, (D′⁵Δ_i, 6110 Å). The bond length in the D′ state (r₀ = 1.654 Å) has been obtained from a deperturbation of the 6110 Å band; it is only 0.035 Å longer than in the ground state, which indicates that electron promotion between the two π orbitals, nominally O(2pπ) and Fe(3dπ), has only a small effect on the strength of the bonding. The new isotope data still do not clarify the vibrational assignments of the higher levels, which are disorganized by extensive electronic perturbations.     

Fe3O4(111) termination of α-Fe2O3(0001)

Scanning tunnelling microscopy (STM) has been used to investigate the structure formed on an α-Fe₂O₃(0001) substrate after argon ion bombardment and annealing in 1 × 10⁻⁶ mbar of O₂ at 1000 K. The STM images recorded at positive sample bias reveal an hexagonal array, with a distance between (Fe) atoms of 6.0 ± 0.1 rA and steps in multiples of 4.8 Å. These results are consistent with formation of an Fe₃O₄(111) epitaxial layer terminating in a monolayer of Fe atoms.     

The microwave spectrum and structure of carbonyl fluoride

The ground state microwave rotational spectra of four isotopic species of carbonyl fluoride have been measured between 18 GHz and 77 GHz, and analyzed to obtain the quartic and some sextic centrifugal constants. The rotational constants have been used to obtain a r₀ structure and, using a harmonic force field, a r_z structure is also obtained: r_z(C---F) = 1.3166 (10) Å, r_z(C---O) = 1.1700 (26) Å.These values are considerably more precise than those of the previously estimated average structure.     

The microwave spectrum and rotational structure of the Δ and Σ electronic states of sulfur monoxide

The spectrum of ¹Δ and ³Σ SO has been studied in the millimeter and submillimeter region of the microwave spectrum. This expanded spectral coverage has made possible the measurement of twenty-two previously unobserved transitions, several of which are necessary for an accurate calculation of the energy levels. As a result, it is now possible to calculate the rotational transitions between energy levels for which J ≤ 10 in both the ground ³Σ electronic state and the excited ¹Δ electronic state to an accuracy comparable to that of the microwave measurements themselves ( 1 MHz). Among the molecular constants calculated are; for the ¹Δ state: B₀ = 21 295.405 MHz, D₀ = 0.0350 MHz, ω_e = 1108 cm⁻¹, and r₀ = 1.4920 Å; and for the ³Σ state: B₀ = 21 523.561 MHz, D₀ = 0.03399 MHz, λ₀ = 158 254.387 MHz, γ₀ = −168.342 MHz, ₀ = 0.305 MHz, r₀ = 1.4840 Å, B_e = 21 609.552 MHz, λ_e = 157 779.2 MHz, and r_e = 1.4811 Å.     

A mixed spectral and finite difference model to study baroclinic annulus waves

A mixed spectral and finite difference model to study finite amplitude baroclinic waves in a differentially heated rotating annulus is presented. The model consists of the full Navier-Stokes equations and the heat equation. The field variables f = f(r, φ z; t) are decomposed into zonally averaged components f_o(r, z; t) and eddy components f(r, φ, z; t), the latter being periodic in f and represented in terms of Fourier series. The unknowns f_o(r, z; t) and f^{c, s}(r, z; t), which are Fourier amplitudes of f′(r, φ, z; t) are governed by two-dimensional primitive equations with the addition of source terms. These equations are solved semi-implicitly by the alternating direction implicit method on variable grids.A simplified model with two Fourier components which permits self-interaction of the chosen wave and the interaction of the wave and the mean fields had been used to repeat a computation done by G. P. Williams, who used a fully three-dimensional finite difference algorithm. We can reproduce almost all of Williams' results in 1/20 of the computing time with the present model. It only requires 1/30 the additional computer storage of Williams' finite difference model over the axisymmetric problem.The potential of the present model for investigation of multiwave interaction as well as the advantages and disadvantages of the two different approaches is discussed.     

High-resolution infrared and millimeterwave spectra of the v3=1 vibrational state of NF3 at 907 cm

The ν₃^±1 perpendicular band of ¹⁴NF₃ ( cm⁻¹) has been studied with a resolution of 2.5 × 10⁻³ cm⁻¹, and 3682 infrared (IR) transitions (J_max=55, K_max=45) have been assigned. These transitions were complemented by 183 millimeterwave (MMW) rotational lines (J_max=25, K_max=19) in the 150–550 GHz region (precision 50–100 kHz). The kl=+1 level reveals a strong A₁/A₂ splitting due to the l(2,2) rotational interaction (q=−4.05 × 10⁻³ cm⁻¹) while the kl=−2 and +4 levels exhibit small A₁/A₂ splittings due to l(2,−4) and l(0,6) rotational interactions. All these splittings were observed by both experimental methods. Assuming the v₃=1 vibrational state as isolated, a Hamiltonian model of interactions in the D reduction, with l(2,−1) rotational interaction (r=−1.96 × 10⁻⁴ cm⁻¹) added, accounted for the observations. A set of 26 molecular constants reproduced the IR observations with σ_IR=0.175 × 10⁻³ cm⁻¹ and the MMW data with σ_MMW=134 kHz. The Q reduction was also performed and found of comparable quality while the QD reduction behaved poorly. This may be explained by a predicted Coriolis interaction between v₃=1 and v₁=1 (A₁, 1032.001 cm⁻¹) which induces a slow convergence of the Hamiltonian in the QD reduction but has no major influence on the other reductions. The experimental equilibrium structure could be calculated as: r_e(N–F)=1.3676 Å and (FNF)=101.84°.     

New ferromagnetic La3Co2TaO9 double perovskite: Structural and magnetic properties

The new double perovskite La₃Co₂TaO₉ has been prepared by a solid-state procedure. The crystal and magnetic structures have been studied from X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD) data. Rietveld refinements were performed in the monoclinic space group P2₁/n. The structure consists of an ordered array of alternating B′O₆ and B″O₆ octahedra sharing corners, tilted along the three pseudocubic axes according to the Glazer notation a⁻b⁻c⁺. Rietveld refinements show that at RT the cell parameters are a=5.6005(7) Å, b=5.6931(7) Å, c=7.9429(9) Å and β=89.9539(7)°, and the refined crystallographic formula of this “double perovskite” can be written as La₂(Co)_2d(Co_1/3Ta_2/3)_2cO₆. Magnetization measurements and low-temperature NPD data show that the perovskite is a ferromagnet with T_C=72 K. At high T it follows the Curie–Weiss law with an effective magnetic moment of 3.82μ_B per Co ion which is very close to spin only Co²⁺ (HS).     

Electrical and mechanical properties of proton conducting SrCe0.95Yb0.05O3 − α

Yb³⁺-doped ceramic strontium cerate of exactly the composition SrCe_0.95Yb_0.05O_{3 − α} was prepared, having a relative density of 99.0 (± 0.3%). Great care was taken to obtain homogeneous, carbonate free material. Analysis are made of the X-ray powder diffraction pattern of the as-prepared dense ceramic, resulting in the orthorhombic unit cell parameters a = 6.997(2) Å, b = 12.296(3) Å, c = 8.588(2) Å, Z = 8 and d_x = 5.806(2) g cm⁻³. Bending strength values of the ceramic in non-proton and proton conducting state are found to be 177 and 194 MPa respectively. The ceramic kept under proton conducting conditions for 500 h at 300 °C to 800 °C in a N₂ flow containing 155 mbar water vapour and 245 mbar H₂, have shown to remain chemically and structurally stable. Impedance spectroscopy measurements of the bulk conductivity of the proton conducting ceramic revealed an activation energy of 53.2 kJ mol⁻¹ and a preexponential factor of 359.1 (Ω cm)⁻¹ K. In the non-proton conducting state the ceramic is mainly oxygen ion vacancy conducting, which indicates that charge compensation on substituting Yb⁺³ in SrCeO₃ takes place by oxygen ion vacancies.     

Rotational absorption spectrum of methylene fluoride in the 20–100 cm region

The pure rotational spectrum of CH₂F₂ was recorded in the 20–100 cm⁻¹ spectral range and analyzed to obtain rotation and centrifugal distortion constants. Analysis of the data yielded rotation constants: A = 1.6392173 ± 0.0000015, B = 0.3537342 ± 0.00000033, C = 0.3085387 ± 0.00000027, τ_aaaa = −(7.64 ± 0.46) × 10⁻⁵, τ_bbbb = −(2.076 ± 0.016) × 10⁻⁶, τ_cccc = −(9.29 ± 0.12) × 10⁻⁷, T₁ = (4.89 ± 0.20) × 10⁻⁶, and T₂ = −(1.281 ± 0.016) × 10⁻⁶cm⁻¹.     

The structure of H2CSe from microwave spectroscopy

The microwave spectra of six isotopic species of selenoformaldehyde, H₂¹³C^78,80Se, D₂C^78,80Se, and DHC^78,80Se have been assigned. The resultant rotational constants, together with those of previous work yield the following substitution structure: r(C=Se) = 175.31 pm, HCH = 117.93°, and r(C---H) = 109.04 pm. This structure is compared with the equilibrium structure derived from ab initio calculations. The fundamental vibrational frequencies and centrifugal distortion constants of H₂C⁸⁰Se have been calculated.     

The rotational-vibrational spectra of HNCS and DNCS : An analysis of the high resolution spectra

Ro-vibrational spectra of HNCS and DNCS have been obtained in the spectral range 300–4000 cm⁻¹ with a practical resolution limit of 0.06 cm⁻¹ in the region 350–1200 cm⁻¹ and 0.15 cm⁻¹ in the region 1200–4000 cm⁻¹. The observed fine structure permitted definitive assignments for some of the ^PQ_K, ^QQ_K, and ^RQ_K branches in both molecules, and yielded sets of rotational constants in substantial agreement with those obtained from recent microwave and far-infrared studies. Precise estimates of the band origins have been obtained and there is evidence of second-order Coriolis coupling between the three bending modes in each molecule. The isolation of the out-of-plane bending modes has lead to a re-assignment of ν₃, ν₄, ν₅, and ν₆ for each molecule. The band origins, uncorrected for Coriolis interaction, are for HNCS and DNCS, respectively. v₁:3538.6 ±0.3, 2644.5±0.5cm⁻¹;v₂:1989.0 ±0.3, 1944.3±0.5cm⁻¹;v₃:857.0 ±0.6, 851.0±0.1cm⁻¹;v₄:615.0 ±0.5, 549.1±0.2cm⁻¹;v₅:469.2 ±0.1, 365.8 ±0.2cm⁻¹;v₆:539.2 ±0.5, 481.0±0.1cm⁻¹;     

The 2ν8 Band of CH3CN

The overtone band 2ν⁰₈ of CH₃CN around 720 cm⁻¹ has been measured on a Bruker Fourier transform spectrometer at a resolution of 0.003 cm⁻¹. Only the parallel band was observed, but due to the l(2, 2) resonance, ΔK = −2 lines leading to the v₈ = 2, l₈ = −2 levels with K = 1-3 could be seen. More information for the l₈ = ±2 component of the vibrational state v₈ = 2 was evaluated from the hot band 2ν^±2₈ - ν^±1₈. Altogether more than 1000 lines were assigned. In the fit pure rotational lines from literature were also combined. Among the results the anomalous A₀ - A′ values 4.6722(13) × 10⁻³ cm⁻¹ for the 2ν⁰₈ band and 7.0324(32) × 10⁻³ cm⁻¹ for the 2ν^±2₈ band are striking.