Microwave Spectroscopic Data Research Articles

Tunable Spin Wave Propagation in YIG/Fe-Rh Stripe

Here, we present the results of an experimental and numerical study of controllable spin-wave propagation in the yttrium iron garnet stripe with an Fe-Rh slab. The transformation of spin-wave dispersion and transmission are observed by the focusing laser light on top of the Fe-Rh slab. It was shown that the geometry variation and design of the Fe-Rh slab significantly affect spin-wave propagation. The static internal magnetic field profile in the yttrium iron garnet is subject to position and the geometric parameters of the Fe-Rh slab. Additionally, the possibility of width mode filtering was shown for a surface magnetostatic spin wave by the means of micromagnetic simulation. The qualitative correspondence between the behavior of spin waves in the numerical simulation and microwave spectroscopy data was observed. The proposed structure can be used as a functional unit with the simultaneous frequency selective and spin-wave mode filtration regime in planar magnonic networks.

Fiberized Diamond-Based Vector Magnetometers

We present two fiberized vector magnetic-field sensors, based on nitrogen-vacancy (NV) centers in diamond. The sensors feature sub-nT/Hz magnetic sensitivity. We use commercially available components to construct sensors with a small sensor size, high photon collection, and minimal sensor-sample distance. Both sensors are located at the end of optical fibres with the sensor-head freely accessible and robust under movement. These features make them ideal for mapping magnetic fields with high sensitivity and spatial resolution (≤ mm). As a demonstration we use one of the sensors to map the vector magnetic field inside the bore of a ≥100 mT Halbach array. The vector field sensing protocol translates microwave spectroscopy data addressing all diamonds axes and including double quantum transitions to a 3D magnetic field vector.

Internal rotation and equilibrium structure of the 2-methyl-2-nitropropane molecule from joint processing of gas phase electron diffraction data, vibrational and microwave spectroscopy data, and quantum chemical calculation results

The structure and internal rotation of the 2-methyl-2-nitropropane molecule is studied by electron diffraction and quantum chemical calculations with the use of microwave and vibrational spectroscopy data. The electron diffraction data are analyzed within the general intramolecular anharmonic force field model and the quantum chemical pseudoconformer model, considering the adiabatic separation of the degree of freedom of large amplitude motion, i.e., the internal rotation of the NO2 group. The equilibrium eclipsed configuration of the C s symmetry molecule has the following experimental bond lengths and valence angles: r e(N=O) = 1.226//1.226(8) A, r e(C–N)//r e(C–C) = 1.520//1.515/1,521(4) A, ∠еC–C–N = = 109.1/106,1(8)°, ∠еO=N=O = 124.2(6)°, ∠eC–C–Havg = 110(3)°. The equilibrium geometry parameters are well consistent with MP2/cc-pVTZ quantum chemical calculations and microwave spectroscopy data. The thermally average parameters previously obtained within the small vibration model show a satisfactory agreement with the new results. The electron diffraction data used in this work do not allow a reliable determination of the barrier to internal rotation. However, at a barrier of 203(2) cal/mol, which is derived from the microwave study, it follows from the electron diffraction data that the equilibrium configuration must correspond to an eclipsed arrangement of C–C and N=O bonds, which is also consistent with the results of quantum chemical calculations of various levels.

Gas-Phase Structures of Ketene and Acetic Acid from Acetic Anhydride Using Very-High-Temperature Gas Electron Diffraction.

The gas-phase molecular structure of ketene has been determined using samples generated by the pyrolysis of acetic anhydride (giving acetic acid and ketene), using one permutation of the very-high-temperature (VHT) inlet nozzle system designed and constructed for the gas electron diffraction (GED) apparatus based at the University of Canterbury. The gas-phase structures of acetic anhydride, acetic acid, and ketene are presented and compared to previous electron diffraction and microwave spectroscopy data to show improvements in data extraction and manipulation with current methods. Acetic anhydride was modeled with two conformers, rather than a complex dynamic model as in the previous study, to allow for inclusion of multiple pyrolysis products. The redetermined gas-phase structure of acetic anhydride (obtained using the structure analysis restrained by ab initio calculations for electron diffraction method) was compared to that from the original study, providing an improvement on the description of the low vibrational torsions compared to the dynamic model. Parameters for ketene and acetic acid (both generated by the pyrolysis of acetic anhydride) were also refined with higher accuracy than previously reported in GED studies, with structural parameter comparisons being made to prior experimental and theoretical studies.

Compound model-morphed potentials contrasting OC–79Br35Cl with the halogen bonded OC–35Cl2 and hydrogen-bonded OC–HX (X = 19F, 35Cl, 79Br)

A five-dimensional compound-model morphed (CMM) potential has been generated for the halogen bonded intermolecular interaction 16O12C–79Br35Cl based on a fit to the currently generated infrared and previously available microwave spectroscopic data. The experimentally determined blue frequency shift of the 16O12C stretching frequency on complexation with 79Br35Cl is found to be Δν=12.89643(28)cm−1 indicating a more strongly bound complex than in OC–35Cl2. Re center-of-mass to center-of-mass distance of 4.270(7)Å and dissociation energies De=778(70)cm−1 and D0=605(70)cm−1 are predicted from the CMM potential and also compared with the corresponding values of Re=4.742(3)Å and De=544(5)cm−1 and D0=397(5)cm−1 for 16O12C–35Cl2. The molecular dynamics, binding energy and other molecular parameters of OC–BrCl are also compared with the hydrogen bonded dimers OC–HX (X=F, Cl, Br) giving further insight into the characteristics of the complex.

Unraveling the internal dynamics of the benzene dimer: a combined theoretical and microwave spectroscopy study

We report a combined theoretical and microwave spectroscopy study of the internal dynamics of the benzene dimer, a benchmark system for dispersion forces. Although the extensive ab initio calculations and experimental work on the equilibrium geometry of this dimer have converged to a tilted T-shaped structure, the rich internal dynamics due to low barriers for internal rotation have remained largely unexplored. We present new microwave spectroscopy data for both the normal (C6H6)2 and partially deuterated (C6D6)(C6H6) dimers. The splitting patterns obtained for both species are unraveled and understood using a reduced-dimensionality theoretical approach. The hindered sixfold rotation of the stem can explain the observed characteristic 1 : 2 : 1 tunneling splitting pattern, but only the concerted stem rotation and tilt tunneling motion, accompanied by overall rotation of the dimer, yield the correct magnitude of the splittings and their strong dependence on the dimer angular momentum J that is essential to explain the experimental data. Also the surprising observation that the splittings are reduced by 30% for the mixed (C6D6)(C)(C6H6)(S) dimer in which only the cap (C) in the T-shaped structure is deuterated, while the rotating stem (S) monomer is the same as in the homodimer, is understood using this approach. Stark shift measurements allowed us to determine the dipole moment of the benzene dimer, μ = 0.58 ± 0.051 D. The assumption that this dipole moment is the vector sum of the dipole moments induced in the monomers by the electric field of the quadrupole on the other monomer yields a calculated value of μ = 0.63 D. Furthermore, the observed Stark behavior is typical for a symmetric top, another confirmation of our analysis.

ChemInform Abstract: Gas-Phase Structures of Ethynyl and Vinyl Pentafluorosulfur Derivatives: An Electron Diffraction and Microwave Spectroscopy Study

Abstract The gas-phase structures of ethynyl- and vinyl sulfur pentafluoride were determined by joint analyses of electron diffraction and microwave spectroscopic data. The following skeletal geometric parameters ( r z values with 3σ uncertainties) were obtained. SF 5 CCH: (SF) mean = 1.574 (1) A, ΔSF=(SF e SF a )=0.018 (14) A, SC=1.736 (6) A, CC=1.200 (7) A, F e SF a =88.9 (2)°; SF 5 CHCH 2 : (SF) mean 1.581 (1) A, ΔSF=0.020 (16) A, SC=1.787 (9) A, CC=1.337 (17) A, F e SF a =88.4 (3)° SCC=124.5 (15)°. In both compounds the equatorial SF bonds are longer than the axial ones, in accordance with the predicted “cis influence” in octahedral main group element compounds. The actual values for the bond length differences ΔSF, however, are poorly determined. The variation of the (SF) mean bond lengths between the ethynyl and vinyl derivatives can be rationalized by the different group electronegativities of these two substituents. The variation of the SC bond lengths reflects the different covalent radii of sp and sp 2 hybridized carbon atoms.

ChemInform Abstract: Gas-Phase Molecular Structure and Conformation of 3-Iodo-1-propene as Determined from Electron Diffraction and Microwave Spectroscopic Data

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Molecular structure and conformation of nitrobenzene reinvestigated by combined analysis of gas-phase electron diffraction, rotational constants, and theoretical calculations

The molecular structure and conformation of nitrobenzene has been reinvestigated by gas-phase electron diffraction (GED), combined analysis of GED and microwave (MW) spectroscopic data, and quantum chemical calculations. The equilibrium re structure of nitrobenzene was determined by a joint analysis of the GED data and rotational constants taken from the literature. The necessary anharmonic vibrational corrections to the internuclear distances (re − ra) and to rotational constants (Be(i) − B0(i)) were calculated from the B3LYP/cc-pVTZ quadratic and cubic force fields. A combined analysis of GED and MW data led to following structural parameters (re) of planar nitrobenzene (the total estimated uncertainties are in parentheses): r(C–C)av = 1.391(3) A, r(C–N) = 1.468(4) A, r(N–O) = 1.223(2) A, r(C–H)av = 1.071(3) A, \({\angle}\)C2–C1–C6 = 123.5(6)°, \({\angle}\)C1–C2–C3 = 117.8(3)°, \({\angle}\)C2–C3–C4 = 120.3(3)°, \({\angle}\)C3–C4–C5 = 120.5(6)°, \({\angle}\)C–C–N = 118.2(3)°, \({\angle}\)C–N–O = 117.9(2)°, \({\angle}\)O–N–O = 124.2(4)°, \({\angle}\)(C–C–H)av = 120.6(20)°. These structural parameters reproduce the experimental B0(i) values within 0.05 MHz. The experimental results are in good agreement with the theoretical calculations. The barrier height to internal rotation of nitro group, 4.1±1.0 kcal/mol, was estimated from the GED analysis using a dynamic model. The equilibrium structure was also calculated using the experimental rotational constants for nitrobenzene isotopomers and theoretical rotation–vibration interaction constants.

Microwave spectra and molecular structures of (Z)-pent-2-en-4-ynenitrile and maleonitrile.

Accurate equilibrium structures have been determined for (Z)-pent-2-en-4-ynenitrile (8) and maleonitrile (9) by combining microwave spectroscopy data and ab initio quantum chemistry calculations. The microwave spectra of 10 isotopomers of 8 and 5 isotopomers of 9 were obtained using a pulsed nozzle Fourier transform microwave spectrometer. The ground-state rotational constants were adjusted for vibration-rotation interaction effects calculated from force fields obtained from ab initio calculations. The resultant equilibrium rotational constants were used to determine structures that are in very good agreement with those obtained from high-level ab initio calculations (CCSD(T)/cc-pVTZ). The geometric parameters in 8 and 9 are very similar; they also do not differ significantly from the all-carbon analogue, (Z)-hex-3-ene-1,5-diyne (7), the parent molecule for the Bergman cyclization. A small deviation from linearity about the alkyne and cyano linkages is observed for 7-9 and several related species where accurate equilibrium parameters are available. The data on 7-9 should be of interest to radioastronomy and may provide insights on the formation and interstellar chemistry of unsaturated species such as the cyanopolyynes.

The determination of moisture in tobacco by guided microwave spectroscopy and multivariate calibration

The feasibility of using a general calibration model based on guided microwave spectroscopic (GMS) data for the determination of moisture in various tobacco types is described. Several calibration methods were used on this data; multivariate linear regression (MLR), partial least square (PLS), polynomial PLS ( n-PLS) and multi-layer feed-forward artificial neural networks (MLF) and the results are compared. Promising results (approximately 2% root mean squared validation error, for moisture levels between roughly 10 and 50%) were obtained. There was no significant difference between PLS and MLF predictions. It was found that the method is sensitive to the weight of the sample used, and that best results were obtained when weight is included as a variable, whereas the position of the sample in the field had little effect. The paper suggests several experimental adaptations to improve the data and thus increases the predictive ability of models based on this data.

Structural and conformational analysis of the isoelectronic isovalent molecules: (ethynylmethyl)cyclopropane and ethynylcyclobutane. A combined electron diffraction, rotational constants and ab initio study

The structures and conformations of gaseous isoelectronic and isovalent molecules (ethynylmethyl)cyclopropane (EMCP) and ethynyl-cyclobutane (ECB) have been determined by combined analysis of electron diffraction and microwave spectroscopic data. The refinement of the experimental data provided the geometrically consistent rav structure. The vibrational harmonic corrections necessary for the conversion of the rα0 structural parameters to the ra set appropriate for comparison with the diffraction data and the transformation of the observed rotational constants into Bz were derived from quadratic force fields MP2/6-31G∗∗ and HF/6-31G∗∗ for EMCP and ECB, respectively. The combined experimental data for EMCP are consistent with two stable conformers, the gauche and cis with the latter lower in energy than the former by about 0.92kJ/mol. This result is in fairly good agreement with the energy differences (ΔE=Ecis−Egauche) obtained from ab initio calculations at DFT (b3pw91/6-31G∗) (−0.68kJ/mol) and MP2/6-311++G(2d,p) (−1.78kJ/mol) levels of theory. HF/6-31G∗∗ calculations, however, predicted 1.5kJ/mol. The major bond distances (rav) and bond angles for the cis conformer obtained from least-squares analysis are: r(C1–C2)=1.509(9)Å,r(C2–C3)=1.517(14)Å,r(C–C)=1.450(13)Å,r(CC)=1.215(3)Å,r(〈C–H〉ring)=1.107(6)Å, ∠(C1–C4–C)=114.0(8)°, ∠(C4–C1(C1–C2–C3)ringplane=126.5(9)°, ∠(C4–C1–C2–C3)=110.4(19)°, ∠(C2–C1–C4–C5)=35.9(4)°.The combined study of ECB reveals that this molecule exists in axial and equatorial forms with the latter more stable in energy by about 4.0kJ/mol (corresponds to eq:ax=84:16) which is in excellent agreement with the values observed by means of microwave and vibrational spectroscopy. This result is also in good agreement with the ab initio calculations which were carried out using the methods: HF/6-31G∗∗, MP2/6-31G∗∗ and DFT (b3pw91/6-31G∗). These methods predicted the occurrence of the equatorial form to be 85, 81 and 88%. The most important structural parameters (rav) for the equatorial conformer obtained from the final refinement are: r(C1–C2)=1.555(16)Å,r(C–C)=1.452(8)Å,r(CC)=1.211(2)Å,r(〈C–H〉ring)=1.095(2)Å, ∠(C2–C1–C4)ring=88.0(16)°, ∠(C5–C1(C2–C1–C4)ring=132.3(17)°, puckering angle=29.2(99)°. For the axial conformer: ∠(C5–C1(C2–C1–C4)ring=124.6(50)° and the puckering angle=28.5(42)°.All uncertainties in parentheses include contributions resulting from the uncertainties of the fixed parameters. In both structural analyses of EMCP and ECB the C–CC–H chain was assumed to be linear which is supported by the ab initio calculations. Comparison of the structural parameters of the C–CC–H moiety in EMCP and ECB reveals that these are similar. This structural similarity is most likely based on the fact that these molecules are isoelectronic and isovalent.

Molecular structure of dichloroacetaldehyde oxime by gas-phase electron diffraction combined with microwave spectroscopy

The gas-phase structure of dichloroacetaldehyde oxime (Cl2CH–CHNOH, DCAO), was determined by gas-phase electron diffraction (GED) combined with microwave (MW) spectroscopic data. The nozzle temperature in the GED experiment was about 53°C. Structural constraints in the GED data analysis were obtained by the ab initio MO calculation of DCAO at the MP2/6-31G(d, p) level of theory. Vibrational amplitudes, shrinkage corrections for the data analysis of GED and vibrational corrections of the experimental rotational constants were calculated from the harmonic force constants given by normal coordinate analysis. The (E)-isomer with the dihedral angle of φ(ClCCN)=119.7(2)° was the dominant conformer. The MW spectroscopic investigation and the optimized structure in the ab initio calculations were consistent with the present result. The population of the dominant conformer was 80(1)%. The results of the data analysis indicated that there were two other conformers involved, whose conformations and populations were: (E)-isomer with one chlorine atom on the plane of the molecular skeleton (10(1)%) and (Z)-isomer with φ of about 105° (10(1)%). The principal bond distances and angles (rg/Å and ∠α/deg) of the dominant conformer, (E)-isomer, were: r(C–C)=1.497(8); r(CN)=1.281(4); r(C–Cl)=1.784(2); r(N–O)=1.415(4); ∠CCN=117.0(8); ∠CCCl=109.4(3); ∠CNO=111.1(5); and ∠NOH=97.2(50). The values in parentheses were three times the standard deviations.

Molecular structure and conformation of gaseous 3-amino-1-propanol from electron diffraction data and rotational constants

The molecular structure of gaseous 3-amino-1-propanol has been determined from electron diffraction and microwave spectroscopic data. Its conformation is gauche-gauche, forming an intramolecular hydrogen bond. The geometrical parameters of the skeleton are r g( C C) = 1.537(2) A ̊ , r g ( C O) = 1.425(3) A ̊ , r g ( C N) = 1.469(3) A ̊ , ∢ CCC = 113.2(3)° , ∢ CCO = 111.9(4)° , ∢ CCN = 112.0(4)° , ø(CCCO) = 72.1(8)°, and ø(CCCN) = − 57(2)°. The unsymmetrical deviations of the dihedral angles ø(CCCO) and ø(CCCN) from the normal gauche angle would be caused by the steric effect.

Rotational Isomers and Molecular Structures of (E)-Propionaldehyde Oxime as Studied from Electron Diffraction and Microwave Spectroscopic Data

Abstract The molecular structures of two rotational isomers (anticlinal and synperiplanar forms) of gaseous (E)-propionaldehyde oxime have been determined from electron diffraction and microwave spectroscopic data. The anticlinal form is more stable by 0.15 ± 0.10 kcal mol−1 than the synperiplanar form. The molecular parameters of the anticlinal form are rg(C1–C2) = 1.552(3) Å, rg(C2–C3) = 1.493(2) Å, rg(C3=N) = 1.284(2) Å, rg(N–O) = 1.429(2) Å, ∠C1C2C3 = 111.5(1)°, ∠C2C3N = 119.0(3)°, and ∠C3NO = 109.4(2)°. The ∠C2C3N, ∠C1C2C3, and rg(C3–N) values of the synperiplanar form (122.6(6)°, 112.6(6)°, and 1.291(3) Å, respectively) are not equal to those of the anticlinal form.

Determination of the quadrupole moment of the halogen nuclei (Cl,Br,I) from molecular data

The electric field gradients at the halogen nuclei in hydrogen halides are calculated by using the coupled cluster method for the treatment of the electron correlation, and the spin-averaged no-pair approximation for the evaluation of the relativistic contribution. Upon combining these results with microwave spectroscopic data for nuclear quadrupole coupling constants in HCl, HBr, and HI, the following values of the nuclear quadrupole moment of the halide nuclei are obtained: Q(35Cl) = 0.0816 barn, Q(79Br) = 0.2989 barn, and Q(127I) -0.651 barn. The present 'molecular' value of Q(35Cl) agrees with the latest 'atomic' data. The results obtained for 79Br and 127I strongly indicate that the current recommended standard values of their nuclear quadrupole moments need to be revised.

Molecular structure of 3-methylthiophene studied by gas electron diffraction combined with microwave spectroscopic data

The molecular structure of 3-methylthiophene ▪ has been determined by gas electron diffraction (GED) combined with microwave (MW) spectroscopic data. Ab initio calculations at the HF 3–21 G∗ level were carried out and used as structural constraints in the data analysis. The torsional vibration of the methyl group was treated as a large-amplitude motion. The structural parameters were determined to be: r g ( S C 2) = 1.719(2) A ̊ , r g ( C 2 C 3) = 1.370(3) A ̊ , r g ( C 3 C 6) = 1.497(6) A ̊ , r g ( C 2 H) = 1.101(5) A ̊ , ∠CSC = 91.6(2)°, ∠SC 2C 3 = 113.3(5)°, ∠SC 5C 4 = 111.3(3)°, ∠C 2C 3C 6 = 123.2(11)° and ∠C 3C 6H = 112(2)°. The values of r(SC 2) − r(SC 5) and r(C 2C 3) − r(C 4C 5) were fixed at the 3–21G∗ value of 0.002Å. Parenthesized values are the estimated limits of error (3σ) referring to the last significant digit.

Molecular structure of 3-methylthiophene studied by gas electron diffraction combined with microwave spectroscopic data

The molecular structure of 3-methylthiophene ▪ has been determined by gas electron diffraction (GED) combined with microwave (MW) spectroscopic data. Ab initio calculations at the HF/3–21G∗ level were carried out and used as structural constraints in the data analysis. The torsional vibration of the methyl group was treated as a large-amplitude motion. The structural parameters were determined to be: r g(SC 2) = 1.719(2) A ̊ , r g(C 2C 3) = 1.370(3) A ̊ , r g(C 3C 6) = 1.497(6) A ̊ , r g(C 2H) = 1.101(5) A ̊ , ∠CSC = 91.6(2)°, ∠SC 2C 3 = 113.3(5)°, ∠SC 5C 4 = 111.3(3)°, ∠C 2C 3C 6 = 123.2(11)° and ∠C 3C 6H = 112(2)°. The values of r(SC 2) - r(SC 5) and r(C 2C 3)- r(C 4 C 5) were fixed at the 3–21G∗ value of 0.002 Å. Parenthesized values are the estimated limits of error (3σ) referring to the last significant digit.

Molecular structure of 2-methylthiophene studied by gas electron diffraction combined with microwave spectroscopic data

The molecular structure of 2-methylthiophene has been determined by gas electron diffraction combined with microwave spectroscopic data. Ab initio calculations at treated as a large-amplitude motion. A C 6 H bond was found to be cis with respect to the C C bond in the equilibrium state. The structural parameter values with estimated error limits (3 σ) in parentheses are as follows: r g(S C 2) = 1.729(1) Å, r g(C 2 C 3) = 1.374(3) Å, r g(C 2 C 6) = 1.505(5) Å, r g(C 5 H = 1.096(5) Å, ∠CSC = 92.7(2)°, ∠SC 2C 3 = 110.5(4)°, ∠SC 5C 4 = 111.0(8)°, ∠SC 2C 6 = 121.4(6)°, t = 4(5)° where t is the tilt angle which is defined to be the angle between the C 3 axis of the methyl group and the C 2 C 6 bond. The values of r(S C 2) – r(S C 5), r(C 2 C 3 – r(C 4 C 5), r(C 3 H) – r(C 5 H), r(C 4 H) – r(C 5 H), r(C 6 H) − r(C 5 H), ∠C CH, ∠SCH and ∠HCH were taken from the HF/3-21G * calculations.

Molecular structure of 2-methylthiophene studied by gas electron diffraction combined with microwave spectroscopic data

The molecular structure of 2-methylthiophene ▪ has been determined by gas electron diffraction combined with microwave spectroscopic data. Ab initio calculations at the HF 3-21 G∗ level were carried out and used as an aid to the analysis. The torsional vibration of the methyl group was treated as a large-amplitude motion. A C 6H bond was found to be cis with respect to the CC bond in the equilibrium state. The structural parameter values with estimated error limits (3σ) in parentheses are as follows: r g ( S C 2) = 1.729(1) A ̊ , r g ( C 2 C 3) = 1.374(3) A ̊ , r g ( C 2 C 6) = 1.505(5) A ̊ , r g ( C 5 H) = 1.096(5) A ̊ , ∠CSC = 92.7(2)°, ∠SC 2C 3 = 110.5(4)°, ∠SC 5C 4 = 111.0(8)°, ∠SC 2C 6 = 121.4(6)°, t = 4(5)° where t is the tilt angle which is defined to be the angle between the C 3 axis of the methyl group and the C 2C 6 bond. The values of r(SC 2) − r(SC 5), r(C 2C 3) − r(C 4C 5), r(C 3H) − r(C 5H), r(C 4H) − r(C 5H), r( C 6 H) − r( C 5 b ̀ H) , ∠CCH, ∠SCH and ∠HCH were taken from the HF 3-21 G ∗ calculations.