Microwave spectrum, molecular structure, dipole moment, and theoretical calculation of cyclopentanone oxime

The microwave spectra of cyclopentanone oxime (C₅H₈NOH) and its deuterated species (C₅H₈NOD) were observed in the frequency region from 9 to 40 GHz. Only a-type R-branch transitions were assigned in the vibrational ground and excited states. The rotational constants of normal species were determined to be A = 5870.80(33), B = 1917.021(8), and C = 1526.784(8) MHz in the vibrational ground state, and A = 5870.16(43), B = 1842.707(9), and C = 1479.401(9) MHz for deuterated species. The dipole moments were determined as μ_a = 0.80(10), μ_b = 0.20(10), and μ_c = 0.40(10) D. The ring-puckering vibrational states were observed up to v = 6. The vibrational mode was nearly harmonic. The fundamental frequency of the ring-puckering mode was found to be 70(20) cm⁻¹. The molecular structure of cyclopentanone oxime was determined to be a twisted configuration by comparing the observed and calculated rotational constants, planar moment of inertia, P_cc, and r_s coordinates of the hydroxyl hydrogen atom. On the molecular geometry, the bond angle, C₂C₁N₆ (Fig. 1), is larger than C₅C₁N₆ by ca. 6°, because of the steric repulsion between the methylene group of C₂ atom and hydroxyl group.     

Microwave spectra, molecular structure and theoretical calculation of two isotopic species of acetyl isocyanate CD3C(O)NCO and CH3C(O)NCO

The microwave spectra of two isotopic species of acetyl isocyanate, ¹³CH₃C(O)NCO and CD₃C(O)NCO, were observed in order to determine the r_o structure and confirmation of the molecular conformation. These isotopic species were prepared by reacting acetyl-2-¹³C-chloride or acetyl-d₃ chloride with sliver cyanate. The rotational spectra of A-level in 26.5-60.0 GHz region have been observed by Stark-modulated microwave spectrometer. Some absorption lines in E-level were observed in ¹³CH₃C(O)NCO. The rotational constants in the ground vibrational state were determined to be A = 10654.8(18), B = 2177.32(2), and C = 1827.65(2) MHz for ¹³CH₃C(O)NCO, and A = 9713.90(6), B = 2042.04(2), and C = 1722.78(2) MHz for CD₃C(O)NCO, respectively. The values of ΔI (= I_c − I_a − I_b) of the ¹³C species (−3.024(13) uŲ) and the d₃ species (−6.163(3) uŲ) indicate that the molecule has C_s symmetry. The r_s coordinates of the carbon atom in the methyl group were determined to be |a| = 2.183(3), |b| = 0.706(9), and |c| = 0.080(87) Å. The determined coordinates were in agreement with those calculated for the cis form, in which the carbonyl group is eclipsed by the NCO group. The six structural parameters of the cis form were adjusted by fitting to the observed rotational constants. The observed rotational constants of the cis form were in better agreement with those calculated using the QCISD/6-31G (d, p) level rather than those calculated using the MP2/6-31G (d, p) level. The barrier of internal rotation of the methyl group was determined as 4.283(16) kJ mol⁻¹ in ¹³CH₃C(O)NCO. The structural tendencies and the relationship between ∠RNC and ¹⁴N quadrupole coupling constants (χ_cc) were discussed.     

Reinvestigation of microwave spectrum, molecular structure, dipole moment, and theoretical calculation of s-trans (E)- and s-trans (Z)-acrylaldehyde oxime

The spectroscopic constants of s-trans (E)-acrylaldehyde oxime of normal, CH₂CHCHNOH, and deuterated, CH₂CHCHNOD, species were refined by adding a-type R-branch transitions observed in the frequency range of 34-40 GHz in the ground vibrational state. For s-trans (Z) form, the spectroscopic constants of normal species were refined by refitting the reported frequencies with four b-type Q-branch transitions and those of deuterated species were determined by the least-squares fitting of the observed a-type R-branch transitions in the ground vibrational state. The spectroscopic constants of two isomers of normal species were also determined in the vibrationally excited states. The inertial defects (ΔI=I_c−I_a−I_b) of normal and deuterated species were determined to be −0.042(24) and −0.064(17) u Å² for s-trans (E)-1 form, and −0.0536(8) and −0.063(11) u Å² for s-trans (Z)-1 form, respectively. From the r_s coordinates of the hydroxyl hydrogen atom determined for s-trans (Z)-1 form, its OH bond was concluded to be at the trans position with respect to the CN double bond. The dipole moments of deuterated species of s-trans (E)-1 form and those of normal and deuterated species of s-trans (Z)-1 form were determined. The structural parameters of r(C₂C₃), ∠C₁C₂C₃, ∠C₂C₃N, and ∠C₃NO for s-trans (E)-1 and s-trans (Z)-1 forms were adjusted separately using to their rotational constants observed. It was found that the bond angle of ∠C₂C₃N in s-trans (Z)-1 form are much wider than that in s-trans (E)-1 form by about 10°. The difference between the observed and calculated (using MP2/6-311++G (d,p) level) rotational constants of s-trans (Z)-1 form was larger than that of s-trans (E)-1 form.     

Microwave spectrum and structure of furfural

The microwave spectrum of furfural was investigated in the frequency range 7 GHz-21 GHz and 49 GHz-330 GHz. The ground and first torsional state of trans-furfural and ground state of cis-furfural were assigned and analyzed. A total of 1720 rotational lines with J up to 100 and K_a up to 53 were assigned to the ground state of trans-furfural, 1406 rotational lines with J up to 100 and K_a up to 48 were assigned to the first torsional state of trans-furfural and 2103 rotational lines with J up to 90 and K_a up to 48 to the ground state of cis-furfural. Accurate sets of centrifugal distortion constants for both conformations have been determined for the first time. The spectra of all ¹³C and ¹⁸O singly substituted isotopic species were observed in natural abundance in the 7 GHz-21 GHz range. Molecular structure co-ordinates, bond lengths and angles of the Kraitchman substitution type (r_s) and pseudo-Kraitchman type (r_pKr) are derived from the isotopic studies.     

First-principles study of electronic structure and elasticity of UAlx (x=1,2,3) system

A detailed theoretical study of structural, electronic, and elastic properties of cubic UAl_x (x=1,2,3) is presented employing the pseudopotential plane-wave method based on density-functional theory. The structure parameters of these three compounds have been calculated within generalized gradient approximation (GGA) and local density approximation (LDA). The calculated results were compared with the experimental data and previous research. With the GGA approximation, the elastic constants, shear modulus, Young's modulus, and Poisson's ratio of UAl_x (x=1,2,3) are derived. According to the generalized mechanical stability criteria for cubic crystals, our calculation suggested that C15 UAl₂ and L12 UAl₃ are stable substance under hydrostatic pressures, but B2 UAl might be expected as a metastable compound, which is not reported in previous literature, and future experimental confirmation is needed. Furthermore, the calculated energy band structure and density of state (DOS) are found to be in good agreement with the theoretical values. Additionally, the charge density of these compounds have also been worked out and analyzed.     

Microwave spectrum of trans 3-fluorophenol in excited torsional states

The microwave rotational spectra of the trans conformer of 3-fluorophenol have been observed in excited torsional states and analyzed in the frequency range 12.0-43.0 GHz using conventional microwave and Radio-Frequency Microwave Double Resonance (RFMWDR) techniques. Analysis of the ground torsional state spectrum has been extended to higher rotational states. Least-squares analysis of three sets of rotational transitions yield rotational and centrifugal distortion constants for the ground and first two excited torsional states. A nonlinear behavior of the variation of inertial defect with the torsional quantum number was observed.     

Microwave absorption properties of rod-shaped Co-Ni-P shells prepared by metallizing Bacillus

The rod-shaped Co-Ni-P shells were prepared by metalling Bacillus. The microstructures and composition of the shells were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive analysis (EDS). The electromagnetic parameters were measured by the coaxial line method in the frequency of 2-18 GHz. It was found that the Bacillus were successfully coated with Co-Ni-P, and the inner structure of the shells are hollow in structure. The shells exhibit excellent microwave absorption properties in 5-17 GHz frequency. The microwave reflection loss is above −10 dB in 5.38-16.6 GHz frequency. The maximum microwave reflection loss reaches −35.83 dB at 9.12 GHz for samples thickness 2.4 mm, and the widest bandwidth for microwave reflection loss above −10 dB is about ∼5.32 GHz for samples thickness 2.0 mm. These results confirm the feasibility of applying Bacillus as biotemplates for fabrication of the metallic shells as lightweight microwave absorption materials are very promising for applications.     

Microwave structural studies of organoselenium compounds 1. Microwave spectra, molecular structure, and methyl barrier to internal rotation of dimethyl diselenide

The rotational spectra of nine isotopomers of dimethyl diselenide, CH₃SeSeCH₃, have been measured with a molecular-beam Fourier transform microwave spectrometer. The spectra were complex due to the presence of many isotopomers in natural abundance and the splitting caused by the interactions with two methyl internal rotors. The spectra were assigned and fit to experimental precision to an effective rotational Hamiltonian for molecules with two periodic internal motions. The spectra of the symmetric isotopomers are consistent with a C₂ equilibrium structure. The rotational constants were used to determine the r_s structure of the C-Se-Se-C frame with the results r(SeSe)=2.306(3) Å, r(SeC)=1.954(6) Å, ?(CSeSe)=99.8(2)°, ?(CSeSeC)=85.2(1)°. A barrier to internal rotation of the methyl groups of 395 ± 2 cm⁻¹ was derived from the internal rotation splittings.     

Vibrational spectroscopy of trans and cis deuterated formic acid (HCOOD): Anharmonic calculations and experiments in argon and neon matrices

The absorption spectra of trans and cis conformers of deuterated formic acid (HCOOD) isolated in argon and neon matrices are analyzed in the mid-infrared and near-infrared spectral regions (7900-450 cm⁻¹). Vibrational excitation by narrow-band IR radiation is used to convert the lower-energy trans conformer to the higher-energy cis form. A large number of overtone and combination bands are identified. The results of anharmonic vibrational calculations (CC-VSCF) for both conformers are reported and compared to the experimental spectra.     

Rotational spectrum and structure of asymmetric dinitrogen trioxide, N2O3

The rotational spectra of the ground vibrational state and the ν₉ = 1 torsional state have been reinvestigated and accurate spectroscopic constants have been determined. The torsional frequency, ν₉ = 70(15) cm⁻¹, has been determined by relative intensity measurements. The assignment of the infrared spectrum has been slightly revised and an accurate harmonic force field has been calculated. The equilibrium structure has been determined using different, complementary methods: experimental, semi-experimental and ab initio, leading to r(NN) = 1.870(2) Å, in particular.     

Microwave spectrum of isotopic species of urea (NH2)2CO

We report new microwave measurements for the (¹⁵NH₂)₂CO and (¹⁴NH₂) (¹⁵NH₂)CO isotopologues of urea. The spectra were recorded between 5 and 20 GHz with our MWFT spectrometer coupled to a newly built heated nozzle. A new centrifugal distortion analysis was performed for the (¹⁵NH₂)₂CO species including all available data. For the (¹⁴NH₂) (¹⁵NH₂)CO species the hyperfine structure was recorded for the first time.     

Spectroscopic and theoretical evidence for the photoinduced twisted intramolecular charge transfer state formation in N,N-dimethylaminonaphthyl-(acrylo)-nitrile

The phenomenon of excited state twisted intramolecular charge transfer (TICT) process in N,N-dimethylaminonaphthyl-(acrylo)-nitrile (DMANAN) has been reported on the basis of steady-state absorption and fluorescence spectroscopy in combination with quantum chemical calculations. The absorption and fluorescence characteristics of DMANAN in solvents of different polarity reveal the presence of a single species in the ground state which forms the intramolecular charge transfer state upon photoexcitation. The observed dual fluorescence is assigned to a high-energy emission from the locally excited or the Franck-Condon state and the red-shifted emission from the charge transfer (CT) state. In polar protic solvents, hydrogen-bonding interaction on CT emission has been established from the linear dependency of the position of the low-energy emission maxima on hydrogen-bonding parameter (α). The experimental findings have been correlated with the theoretical results based on TICT model obtained at density functional theory (DFT) level. The theoretical potential energy surface for the first excited state along both the donor and acceptor twist coordinates in the gas phase obtained by time dependent density functional theory (TDDFT) method and in polar solvent by time dependent density functional theory-polarized continuum model (TDDFT-PCM) method predicts well the experimental spectral properties.     

Theoretical study of the new compound VO2 (D)

The structural feature and the electronic properties of the newly synthesized compound VO₂ (D) are theoretically studied. Our calculations reveal that all of the V ions in VO₂ (D) form two types of chains. One of the chains contributes to the electronic states near the Fermi level, but the other one almost does not yet. Such discrepancy is attributed to the different strength of the VO bonds belonging to the different chains. Furthermore, it is found that one type of the VV chains characters the antiferromagnetic feature, whereas the other one is almost non-magnetic. So, the compound VO₂ (D) is of one-dimensional antiferromagnetic ordering. In addition, we propose that the structural transition from VO₂ (D) to the rutile-type VO₂ (R) is driven by three vibrational modes. The transition temperature is estimated to be about 600 K, being consistent with experiment.     

Dispersed fluorescence spectroscopy of S0 vibrational levels in formaldehyde-d

High resolution dispersed fluorescence (DF) spectra of excited vibrational levels in S₀ HDCO up to 10 000 cm⁻¹ energy were recorded in a free-jet expansion. Excitation to the 0₀₀ rotational level in 4⁰ and 4¹ S₁ HDCO yielded pure vibrational spectra that are free from rotational congestion. The 162 transitions (133 unique vibrational levels) assigned in these spectra have been fit to a multiresonant Hamiltonian model, which includes harmonic frequencies , anharmonic constants (x_ij), and resonance constants (K). The assigned vibrational states were fit to the model with a standard deviation of 4.02 cm⁻¹. Extensive vibrational mixing is observed throughout the spectra. Six harmonic constants, eight anharmonic constants, and four resonance constants (K_44,1, K_66,1, K_44,66, and K_33,5) were determined experimentally. The 18 experimentally determined spectroscopic constants, with the exception of and K_66,1, were found to agree within 6 cm⁻¹ of ab initio calculated values.     

The millimeter- and submillimeter-wave spectrum of the trans-gauche conformer of diethyl ether

The results of a first investigation of the rotational spectrum of the trans-gauche conformer of diethyl ether are reported. Two spectrometers have been used to measure the spectrum in the millimeter-wave and submillimeter-wave regions and a total of 1090 absorption line frequencies in the range 108-366 GHz were obtained and analyzed. Of these lines, 902 were measured with a spectrometer employing the fast scan submillimeter spectroscopic technique (FASSST) at Ohio State and the remaining 188 were measured with the phase-lock two-loop system (PLL) in Warsaw. The spectrum was fit to within experimental accuracy with the use of the A-reduced Watson Hamiltonian. Based on relative intensity measurements, the percentage of diethyl ether at room temperature in the trans-gauche conformer was found to be 30.5(13)%, in good agreement with prior spectroscopic values and an ab initio determination based on an energy difference of 5.40 kJ mol⁻¹ (452 cm⁻¹) between the excited trans-gauche and ground trans-trans conformers. This work also stimulated a critical evaluation of the data acquisition and calibration procedure of the FAAAST spectrometer, the results of which will be discussed.     

Formation of vinylidene and vinylene by selective reactivity of Si(1 0 0)2 × 1 towards iso, cis and trans isomers of dichloroethylene

The room temperature (RT) chemisorption of three (iso, cis and trans) isomers of dichloroethylene (DCE) on Si(1 0 0)2 × 1 have been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Unlike ethylene, the lack of molecular desorption features in the TPD data effectively rules out the cycloaddition adsorption mechanism for all three isomers. XPS spectra show that cis- and trans-DCE adsorb dissociatively on the 2 × 1 surface in equal proportion as mono-σ bonded 2-chlorovinyl and di-σ bonded vinylene adspecies, which could be produced by dechlorination mechanisms involving the proposed tri-atom π-complex and diradical intermediates, respectively. Acetylene (m/z 26) evolution from 2-chlorovinyl adspecies at 590 K and vinylene at 750 K are also observed for both cis- and trans-DCE, further confirming the common adsorption mechanisms for these geometrical isomers and the relative stabilities of the adspecies. In contrast, only vinylidene adspecies is found for iso-DCE, which indicates that the high ionicity of the CCl₂ group favours the diradical dechlorination mechanism. The single m/z 26 desorption peak for iso-DCE adspecies observed at a higher temperature (780 K) than cis and trans isomers is consistent with the higher adsorption energy of vinylidene than vinylene on Si(1 0 0) obtained in our ab initio calculations. The different relative locations of the Cl atoms in these isomers therefore play a crucial role in controlling the adsorption and thermal evolution on Si(1 0 0)2 × 1. The selective reactivity of the 2 × 1 surface towards these isomers can be used to generate vinylene or vinylidene templates from their corresponding adspecies.     

Luminescent properties of KGd1−x(WO4)2:Eux and KGd1−x(WO4)2−y(MoO4)y:Eux phosphors in UV-VUV regions

KGd_1−x(WO₄)_2−y(MoO₄)_y:Eu³⁺_x(0.1?x?0.75, y=0 and 0.2) phosphors are synthesized through traditional solid-state reaction and their luminescent properties in ultraviolet (UV) and vacuum ultraviolet (VUV) regions are investigated. Under 147 nm excitation, these phosphors show characteristic red emission with good color purity. In order to improve their emission intensity, the MoO₄²⁻ (20 wt%) is introduced into the anion of KGd_1−x(WO₄):Eu³⁺_x. The Mo⁶⁺ and Eu³⁺ co-doped KGd(WO₄)₂ phosphors show higher emission intensity in comparison with the singly Eu³⁺-doped KGd(WO₄)₂ in VUV region. The chromaticity coordination of KGd_0.45(WO₄):Eu³⁺_0.55 is (x=0.669, y=0.331), while that of KGd_0.45(WO₄)_1.8(MoO₄)_0.2:Eu³⁺_0.55 is (x=0.666, y=0.334) in VUV region.     

Structural and Torsional Properties of o-Cresol and o-Cresol-OD as Obtained from Microwave Spectroscopy and ab Initio Calculations

The microwave spectra of o-cresol and of o-cresol-OD were assigned using molecular beam Fourier transform microwave (MB-FTMW) spectrometers in the frequency range of 3-40 GHz. Two conformers of o-cresol were measured where the hydroxy group is syn with respect to the methyl group in one case and anti in the other. The transitions of both conformers were split due to internal rotation of the methyl group. For syn-o-cresol we found the rotational constants A=3249.45242(18) MHz, B=2202.02546(18) MHz, C=1323.66277(16) MHz, and the barrier to internal rotation of the methyl group V₃=7.912(46) kJ mol⁻¹. In the case of anti-o-cresol A=3273.80084(18) MHz, B=2196.26747(18) MHz, C=1325.36424(22) MHz, and V₃=4.4256(14) kJ mol⁻¹ was obtained. Moreover we were able to determine the quartic centrifugal distortion constants, the angle between the internal rotor axes, and the inertial a axes, and, for the deuterated species, additionally the deuterium nuclear quadrupole coupling constants.