Fundamental Wavenumbers Research Articles

Potential energy surface, effect of solvents in molecular level, experimental spectra (FTIR, Raman, UV–visible & NMR), electronic, and dynamics simulation of isobavachalcone –Anti tuberculosis agent

The spectroscopic characteristics, molecular structure, and biological characteristics of the Isobavachalcone (IBC) structure have been studied using computational techniques utilizing the usual B3LYP/6-311++G (d,p). PED (Potential Energy Distribution) is used throughout process of assigning the fundamental wave-numbers of IBC. In this work, we have reported the correlation between experimental and computed examination of molecular configuration, FT:IR & Raman, UV–Visible absorption, and NMR (Nuclear Magnetic Resonance) spectrum of the title compound. Potential energy scan (PES) analysis of IBC was enhanced in the initial stage with same basis set. FMO (Frontier Molecular Orbital), MEP (Molecular Electrostatic Potential), local reactivity and quantum chemical descriptors has also been analyzed. Furthermore, drug-likeness and ADMET predictions of the present ligand shows good pharmacological activity. ELF (Electron Localised Function), LOL (Localised Orbital Locator) and RDG (Reduced Density Function) enacted for both the gas and solvents phases. A docking simulation performed with the 2FUM receptor using the Auto Dock software showed that the IBC compound has inhibitory activity against Mycobacterium tuberculosis disease. All our results suggest that the IBC molecule could have a great effect in the treatment of tuberculosis disease. MD simulations been executed over 100 ns to predict the RMSD, RMSF, and the radius-of gyration analyses.

Structural, spectroscopic, molecular docking, ADME, molecular dynamics studies of Val-Trp dipeptide

Hypertension is a significant risk factor for various diseases, especially heart, brain, and kidney diseases. It is known that many peptides have the property of lowering blood pressure and determine as ACE inhibitors. The purpose of this study is to obtain information about the molecular structure of Val-Trp (L-valyl-L-tryptophan), which is one of the antihypertensive peptides, by molecular mechanical, quantum mechanical, and spectroscopic methods (FT-IR and Raman). Also, it is aimed to investigate the interactions of Val-Trp dipeptide with receptors related to hypertension and to determine the pharmacokinetic profile due to the potential of the peptide to be a drug candidate. The peptide structure was optimized by DFT/B3LYP/6-311++G(d,p) basis set, then vibrational wavenumbers, molecular electrostatic potential (MEP), HOMO-LUMO (highest occupied molecular orbital- lowest unoccupied molecular orbital), NBO (natural bond orbital) analyzes were performed. The assignment of fundamental theoretical vibration wavenumbers was carried out with potential energy distribution analysis (PED). After the structural analyzes of the peptide were performed, the interactions of the peptide with Angiotensin-converting enzyme (ACE), Angiotensin II Receptor Type 1 (AT1R) and Renin were investigated by molecular docking study. Then, the molecular dynamic (MD) simulation of the peptide-ACE complex with the best binding affinity in the molecular docking studies was carried out for 50 ns. ADME (absorption, distribution, metabolism, and excretion) analysis of Val-Trp dipeptide was performed. In support of the studies carried out, enlightening information about the feasibility of the antihypertensive drug of Val-Trp dipeptide with the help of the ADME profile was presented to the literature.Communicated by Ramaswamy H. Sarma

Structural, spectroscopic, in silico, in vitro and DNA binding evaluations of tyrosyl-lysyl-threonine

The main objective of the present study is to investigate the molecular structure and DNA binding interaction of the tyrosyl-lysyl-threonine (YKT) tripeptide, which has anticancer, antioxidant and analgesic properties, using various in silico (MD, QM, molecular docking), spectroscopic (UV, FT-IR, FTIR-ATR, Raman, gel electrophoresis) and in vitro (MCF-7 and HeLa cancer cell lines and BEAS-2B cell line) methods. The optimized geometry, vibrational wavenumbers, molecular electrostatic potential (MEP), natural bond orbital (NBO) and HOMO-LUMO (highest occupied molecular orbital- lowest unoccupied molecular orbital) calculations were carried out with Density Functional Theory (DFT) using B3LYP/6-311++G(d,p) basis set to indicate conformational, vibrational and intramolecular charge transfer characteristics. The assignment of all fundamental theoretical vibration wavenumbers was performed using potential energy distribution analysis (PED). DNA is a significant pharmacological target of drugs in several diseases such as cancer. For this reason, molecular docking calculation was used to elucidate the binding and interaction between YKT tripeptide and DNA at the atomic level. Also, the dynamic behaviors of YKT and DNA was examined using MD simulations. Besides, the interaction of YKT with DNA was experimentally examined by UV titration method and agarose gel electrophoresis method. Experimental results showed that YKT was intercalatively and electrostatically bound to CT-DNA (Calf thymus DNA) and cleavage pBR322 DNA in the presence of H2O2. The pharmacokinetic profile of YKT was also obtained. Cytotoxic effect of YKT was evaluated on MCF-7, HeLa and BEAS-2B cell lines. Hence, these studies about YKT tripeptide may pave the way for the development of various cancer drugs. Communicated by Ramaswamy H. Sarma

Influence of initial phase on subharmonic resonance in an incompressible boundary layer

The influence of the initial phase of fundamental and subharmonic waves on subharmonic resonance is investigated for an incompressible boundary layer with zero and adverse pressure gradients. Parabolized stability equation analyses are carried out for various combinations of the initial phases of fundamental and subharmonic waves. The amplification of subharmonic and higher modes is found to depend strongly on the initial phases, and this dependence is consistent with observations from previous experimental studies. There exists a certain combination of initial phases that leads to resonance or anti-resonance condition (i.e., maximum or minimum growth, respectively). For all combinations of the initial phases, the phase dependence appears to be a function of a single parameter that represents the initial phase difference between the fundamental and subharmonic waves. The amplification in the subharmonic resonant interaction depends on the initial phase difference rather than the individual initial phase of the fundamental or subharmonic wave. In the downstream direction, the phase difference changes from the initial value and eventually converges to a specific value approximately ranging from 80° to 90°, regardless of the initial phase difference. This transient behavior does not start until the subharmonic wave enters the parametric resonant stage, which yields double-exponential growth. The qualitative characteristic of the phase dependence remains unchanged for the fundamental frequencies and spanwise wavenumbers as well as for the pressure gradients studied. The method of analysis and results contribute to the physical foundations of controlling boundary-layer transition dominated by the subharmonic resonance.

Predicting OH stretching fundamental wavenumbers of alcohols for conformational assignment: different correction patterns for density functional and wave-function-based methods.

A model is presented for the prediction of OH stretching fundamental wavenumbers of alcohol conformers in the gas phase by application of a small set of empirical anharmonicity corrections to calculations in the harmonic approximation. In contrast to the popular application of a uniform scaling factor, the local chemical structure of the alcohol is taken into account to greatly improve accuracy. Interestingly, different correction patterns emerge for results of hybrid density functional (B3LYP-D3 and PBE0-D3) and wave-function-based methods (SCS-LMP2, LCCSD(T*)-F12a and CCSD(T)-F12a 1D). This raises questions about electronic structure deficiencies in these methods and differences in anharmonicity between alcohols. After its initial construction on the basis of literature assignments the model is tested with Raman jet spectroscopy of propargyl alcohol, cyclohexanol, borneol, isopinocampheol and 2-methylbutan-2-ol. For propargyl alcohol a spectral splitting attributed to tunneling is resolved. PBE0-D3 is identified as a well performing and broadly affordable electronic structure method for this model. A mean absolute error of 1.3 cm-1 and a maximum absolute error of 3 cm-1 result for 46 conformers of 24 alcohols in a 60 cm-1 range, when a single parameter is adjusted separately for each alcohol substitution class (methanol, primary, secondary, tertiary).

3 µm Water vapor self- and foreign-continuum: New method for determination and new insights into the self-continuum

The H2O self- and foreign- in-band continua in the region 3400–3900 cm−1 were experimentally determined for 296 and 353 K from multispectrum fitting results of line parameters using the Hartmann-Tran line profile (HTP) and Rosenkranz line mixing. The continua were extracted from the baselines which were determined in the microwindow-based multispectrum fits. Continua were then obtained by simultaneous fitting of all baselines from measurements containing continuum information. The self-continuum at 296 K was determined from self-broadened measurements and agrees with that determined from air broadened measurements. The overall shape and strength of the new self-continuum agrees with the CAVIAR results between 3600 and 3800 cm-1 but differences exceed the stated uncertainties at higher and lower wavenumbers. Moreover, the new self-continuum is much smoother, has no gaps and is obtained with a high resolution of 2.4 cm−1. The self-continuum was fitted as sum of modeled bound and quasi-bound dimer spectra. From rotational constants, the bound dimer parallel and perpendicular band shapes of the near prolate symmetric top molecule were calculated and used as kernels to fit fundamental wavenumbers, relative band intensities and partitioning of parallel and perpendicular band type, while the integral of the band intensities of the four fundamentals was fixed to published experimental/theoretical data. A dimerization constant for the bound dimer of KDb = 0.026(2) atm−1 and the quasi-bound dimer of KDq = 0.044(5) atm−1 was derived from the fits.The foreign-continuum has no gaps, a spectral resolution of 6–16 cm−1, and is about 40% smaller than the MT_CKD3.2 continuum model. It has a distinctly different shape showing a pronounced P-Q-R branch structure. The foreign-continuum shape is narrower than the monomer band shape which is also true for the MT_CKD3.2 continuum model. The CAVIAR foreign-continuum is much noisier but on average is in good agreement with the new measurements.

A four-dimensional Numerov approach and its application to the vibrational eigenstates of linear triatomic molecules – The interplay between anharmonicity and inter-mode coupling

An adapted formulation of the grid-based Numerov approach to solve Schrödinger’s equation has been extended to four-dimensional systems and applied to problems in vibrational spectroscopy. The advantage of this novel implementation is that no approximations or assumptions with respect to the wavefunctions are required and the achieved accuracy at a given stencil size is only limited by the selected grid-spacing. To validate this approach the vibrational eigenstates and the corresponding wavenumbers of the linear molecules CO2, BeH2 and HCN were investigated. Based on a potential energy grid at CCSD(T)/cc-pVnZ (n = T, Q) level all fundamental wavenumbers could be reproduced with deviations of less than 1% of the experimental values. Furthermore, the hierarchical application of a one- to four-dimensional Numerov treatment provides detailed information about the increasing influence of inter-mode coupling in addition to the inherent account for anharmonic contributions. The associated vibrational states are eigenfunctions of the Numerov matrix eigenvalue problem. Since no vibrational basis functions have to be applied in this approach, the respective eigenstates are characterized using isosurfaces of the wavefunctions in the hyperplane x4=0. This enables the direct examination of the individual wavefunctions via suitable visualization tools and the assignment of the respective vibrational quantum numbers.

Spectral characterization, computed frequencies analysis and electronic structure calculations on (1E)[sbnd]N-hydroxy-3-(1H-imidazol-1-yl)-1-phenylpropan-1-imine: An oxime-bearing precursor to potential antifungal agents

(1E)N-Hydroxy-3-(1H-imidazol-1-yl)-1-phenylpropan-1-imine (H3IPI) is a precursor to potential antifungal agents and was subjected to experimental and simulated spectroscopic (UV, FT-IR, FT-Raman as well as 1H and 13C NMR) characterization. Density functional theory, Hartree-Fock fundamental wavenumbers and intensity of the modes are interpreted with the aid of structure optimizations and normal force field computations. The complete wavenumbers assignments of H3IPI were made on the basis of potential energy distribution of each vibrational mode. The electronic and excited state properties have been determined by time dependent-density functional theory method. The responsiveness parameters as chemical potential, global hardness, and electrophilicity index have also been calculated. The scaled B3LYP/6–311++G (d,p) calculations showed better coincidence with the experimental findings of H3IPI over the other computation method. Molecular electrostatic potential and thermodynamic properties of the title compound were also investigated. In addition, Mulliken and natural charges distribution, non-linear optics properties as well as natural bond orbital analysis of the title molecule were calculated and interpreted. Theoretical calculations of the NMR chemical shifts of H3IPI were carried out through GIAO method at B3LYP/6–311++G (d,p) level and the results were compared with the experimental values.

Vibrational transitions in hydrogen bonded bimolecular complexes – A local mode perturbation theory approach to transition frequencies and intensities

The local mode perturbation theory (LMPT) model was developed to improve the description of hydrogen bonded XH-stretching transitions, where X is typically O or N. We present a modified version of the LMPT model to extend its application from hydrated bimolecular complexes to hydrogen bonded bimolecular complexes with donors such as alcohols, amines and acids. We have applied the modified model to a series of complexes of different hydrogen bond type and complex energy. We found that the differences between local mode (LM) and LMPT calculated fundamental XH-stretching transition wavenumbers and oscillator strengths were correlated with the strength of the hydrogen bond. Overall, we have found that the LMPT model in most cases predicts transition wavenumbers within 20cm−1 of the experimental values.

Influence of three-dimensional wall roughness on the transition of a finite Stokes layer

A finite Stokes layer with a large half-width over three-dimensional wall roughness is numerically simulated by solving the perturbation equations. Simulations are conducted for different parameters that affect the shape of the wall roughness, e.g., streamwise wave number, spanwise wave number and the amplitude of the roughness. The calculations are performed at a Reynolds number of Rδ=600, which represents the transitional Reynolds number observed in experimental cases. The onset of the transition is shown to be highly correlated with the amplitude of pre-existing two-dimensional waves. It is found that the critical amplitude of the two-dimensional wave is approximately 1% of the velocity amplitude of the external flows. Moreover, the results indicate that the appearance of the transition is also affected by the fundamental wave numbers.

Resolution of Incident and Reflected Components of Nonlinear Regular Waves

The method of Lin and Huang [Lin and Huang [2004] “Decomposition of incident and reflected higher harmonic waves using four wave gauges,” Coast. Eng. 51 (5), 395–406.] (LH) is improved for resolution of incident and reflected strongly nonlinear regular waves in shallow waters with measurements of four stationary wave gauges. For first harmonics, wavenumbers, amplitudes and initial phases are obtained by using a nonlinear least squares method. For higher harmonics, wavenumbers of free and bound modes are determined from linear dispersion relation and multiple of first-harmonic wavenumbers, respectively, and the other unknowns are solved by using a linear least squares method. Auto-correlation function is used to determine fundamental wave period for gaining a good performance of Fourier transform. The efficiency and accuracy of the present method are demonstrated by using artificial data and numerical flume data. It is also demonstrated that the present method is less sensitive to signal noise and gauge spacings. Comparison between the present method and the LH method indicates the necessity of employing nonlinear method in determining fundamental wavenumbers of nonlinear shallow-water waves. Finally, the present method is extended to account for obliquely-incident waves. Sensitivity tests indicate the robustness of the extended method with respect to incident angles. Relative position of gauges in the array for avoiding singularity is suggested.

Vibrational, NMR and UV–Visible spectroscopic investigation, VCD and NLO studies on Benzophenone thiosemicarbazone using computational calculations

In order to explore the unbelievable NLO property of prepared Benzophenone thiosemicarbazone (BPTSC), the experimental and theoretical investigation has been made. The theoretical calculations were made using RHF and CAM-B3LYP methods at 6-311++G(d,p) basis set. The title compound contains CS ligand which helps to improve the second harmonic generation (SHG) efficiency. The molecule has been examined in terms of the vibrational, electronic and optical properties. The entire molecular behavior was studied by their fundamental IR and Raman wavenumbers and was compared with the theoretical aspect. The molecular chirality has been studied by performing vibrational circular dichroism (circularly polarized infrared radiation). The Mulliken charge levels of the compound ensure the perturbation of atomic charges according to the ligand. The molecular interaction of frontier orbitals emphasizes the modification of chemical properties of the compound through the reaction path. The enormous amount of NLO activity was induced by the Benzophenone in thiosemicarbazone. The Gibbs free energy was evaluated at different temperature and from which the enhancement of chemical stability was stressed. The VCD spectrum was simulated and the optical dichroism of the compound has been analyzed.

Structural investigation of a self-assembled monolayer material 5-[(3-methylphenyl) (phenyl) amino] isophthalic acid for organic light-emitting devices

The molecular structure and vibrations of 5-[(3-methylphenyl) (phenyl) amino] isophthalic acid (MePIFA) were investigated by infrared and Raman spectroscopies, UV–Vis, 1H and 13C NMR spectroscopic techniques and NBO analysis. FT-IR, FT-Raman and dispersive Raman spectra were recorded in the solid phase. 1H and 13C NMR spectra and UV–Vis spectrum were recorded in DMSO solution. HOMO–LUMO analysis and molecular electrostatic potential (MEP) analysis were performed. The theoretical calculations for the molecular structure and spectroscopies were performed with DFT (B3LYP) and 6-311G(d,p) basis set calculations using the Gaussian 09 program. After the geometry of the molecule was optimized, vibration wavenumbers and fundamental vibration wavenumbers were assigned on the basis of the potential energy distribution (PED) of the vibrational modes calculated with VEDA 4 program. The total (TDOS), partial (PDOS) density of state and overlap population density of state (OPDOS) diagrams analysis were made using GaussSum 2.2 program. The results of theoretical calculations for the spectra of the title compound were compared with the observed spectra.

Infrared and Raman spectra, conformations, quantum chemical calculations and spectral assignments of 1-methyl-1-silacyclohexane

Raman spectra of of 1-methyl-1-silacyclohexane as a liquid were recorded at 293K and depolarization data obtained. Additional Raman spectra were recorded at various temperatures between 293 and 143K, and intensity changes with temperature of certain Raman bands were detected. A supercooled liquid appeared after slow cooling, but an amorphous phase was observed after shock freezing to 78K. After annealing, first a plastic phase and subsequently a crystal were observed. In the crystalline phase spectral shifts and some vanishing bands were observed.The infrared spectra of the vapor and liquid were studied at ambient temperature and the solid sample investigated at 78K. Negligible spectral changes ocurred at 78K compared with the fluid state, but after annealing to ca. 170K an apparent crystal was formed and a few bands vanished and others were shifted.The compound exists in two conformers, equatorial (e) and axial (a) in the liquid, amorphous and plastic phases, but only the e-conformer was present in the crystal. The experimental results suggest that the e-conformer has 0.6kJmol−1 lower energy than a in the liquid.B3LYP calculations with various basis sets gave a conformational enthalpy difference ΔH (a–e) around 2.4kJmol−1 while G3 model chemistry gave 0.6kJmol−1. Infrared and Raman intensities, polarization ratios and vibrational frequencies for the e and a conformers were calculated. The fundamental wavenumbers were also derived in the anharmonic approximation in B3LYP/cc-pVTZ calculations. A relative deviation of 0.94% and 1.31% between the observed and calculated wave numbers for the 57 modes of the e-and a-conformers, respectively, was obtained.

Accurate ab initio potential energy surface and vibration‐rotation energy levels of hydrogen peroxide

The accurate ground-state potential energy surface of hydrogen peroxide, H(2)O(2), has been determined from ab initio calculations using the coupled-cluster approach in conjunction with the correlation-consistent basis sets up to septuple-zeta quality. Results obtained with the conventional and explicitly correlated coupled-cluster methods were compared. The core-electron correlation, scalar relativistic, and higher-order valence-electron correlation effects were taken into account. The adiabatic effects were also discussed. The vibration-rotation energy levels of the H(2)O(2), D(2)O(2), and HOOD isotopologues were predicted, and the experimental vibrational fundamental wavenumbers were reproduced to 1 cm(-1) ("spectroscopic") accuracy.

Conformational and structural studies of cyclobutylsilane from temperature dependent infrared spectra of xenon solutions and ab initio calculations

The infrared spectra (3500–220cm−1) in the gas phase of cyclobutylsilane, c-C4H7SiH3 has been recorded. Variable temperature (−65 to −100°C) studies of the infrared spectra (3500–400cm−1) dissolved in liquid xenon have been carried out. From these data, both the equatorial and axial conformers have been identified and their relative stability obtained. The enthalpy difference has been determined from 15 band pairs to be 67±7cm−1 (0.81±0.08kJmol−1) with the equatorial conformer the more stable form. The percentage of the axial conformer is estimated to be 42±1% 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 MP2(full) and density functional theory calculations by the B3LYP method. By utilizing previously reported microwave rotational constants along with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r0 parameters have been obtained for both conformers. The determined heavy atom distances (Å) for the equatorial [axial] form are Si–Cα=1.879(3) [1.884(3)], Cα–Cβ, Cβ′=1.562(3) [1.561(3)], Cγ–Cβ, Cβ′=1.551(3) [1.553(3)] and angles in degrees (°) ∠SiCαCβ=118.6(5) [113.2(5)], ∠CβCαCβ′=88.2(5) [88.4(5)], ∠CαCβCγ=87.8(5) [88.9(5)], ∠CβCγCβ′=88.9(5) [89.0(5)] and a puckering angle of 29.0(5) [23.5(5)]. Support for the vibrational studies have been provided from MP2(full)/6-31G(d) ab initio calculations to predict harmonic force constants, fundamental wavenumbers, infrared intensities, Raman activities and depolarization ratios for both conformers. The results are discussed and compared to the corresponding properties of some related molecules.

Structure and conformation studies from temperature dependent infrared spectra of xenon solutions and ab initio calculations of cyclobutylgermane

The infrared spectra (3500–220cm−1) of cyclobutylgermane, c-C4H7GeH3 have been recorded of the gas. Also variable temperature (−65 to −100°C) studies of the infrared spectra (3500–400cm−1) of the sample dissolved in liquid xenon were recorded and both the equatorial and axial conformers were identified. The enthalpy difference has been determined from 10 band pairs 8 temperatures to give 112±11cm−1 (1.34±0.13kJmol−1) with the equatorial conformer the more stable form. The percentage of the axial conformer present at ambient temperature is estimated to be 37±1%. From ab initio calculations conformational stabilities have been predicted from both MP2(full) and density functional theory calculations from a variety of basic sets. The r0 structure parameters have been obtained for both conformers from the previously reported rotational constants from the three isotopologues. The determined heavy atom distances for the equatorial [axial] form are (Å) Ge–Cα=1.952(3) [1.950(3)], Cα–Cβ,Cβ′=1.557(3)[1.565(3)], Cγ–Cβ,Cβ′=1.551(3) [1.551(3)] and angles in degrees (°) ∠GeCαCβ=118.6(5) [113.4(5)], ∠CβCαCβ′=88.3(5)[88.0(5)], ∠CαCβCγ=87.8(5) [88.8(5)], ∠CβCγCβ′=88.7(5)[89.0(5)] and a puckering angle of 29.1(5) [25.1(5)]. Data from ab initio calculations were used to predict vibrational harmonic force constants, fundamental wavenumbers, infrared intensities, Raman activities and depolarization ratios for both conformers. The results are compared to the corresponding properties of some related molecules.

Vibrational spectra, conformations, quantum chemical calculations and spectral assignments of 1-chloro-1-silacyclohexane

The infrared spectra of 1-chloro-1-silacyclohexane have been studied as a vapour and liquid at ambient temperature and as amorphous and annealed crystalline solids at 78K. Various infrared bands present in the vapour and liquid states vanished in the crystalline state upon cooling. Raman spectra of the liquid were recorded at 293K and polarization data obtained. Additional Raman spectra were recorded at various temperatures between 293 and 163K, and intensity changes with temperature of certain Raman bands were detected. A crystalline phase was observed around 140K, leading to spectral shifts and a number of vanishing bands.The compound exists in two conformers, equatorial (e) and axial (a) in the fluid phases, but only the a-conformer was present in the crystal. The experimental results suggest that the a-conformer has 2.8kJmol−1 lower enthalpy than e in the liquid, leading to 69% of the a conformer at 293K.B3LYP calculations with various basis sets and the G3 model chemistry gave conformational energy difference ΔE (e−a) in the range 0.4–1.4kJmol−1. Infrared and Raman intensities, polarization ratios and vibrational frequencies for the e and a conformers were calculated. The fundamental wavenumbers were also derived in the anharmonic approximation in B3LYP/cc-pVTZ calculations, a relative deviation of less than 2% between the observed and calculated wave numbers for the 48 modes of the e- and a-conformers was obtained.

TRANSVERSE OSCILLATIONS OF A LONGITUDINALLY STRATIFIED CORONAL LOOP SYSTEM

Collective transverse coronal loop oscillations seem to be detected in observational studies. In this regard, Luna et al. modeled the collective kink-like normal modes of several cylindrical loop systems using the T-matrix theory. This paper investigates the effects of longitudinal density stratification along the loop axis on the collective kink-like modes of the system of coronal loops. The coronal loop system is modeled as cylinders of parallel flux tubes, with two ends of each loop at the dense photosphere. The flux tubes are considered as uniform magnetic fields, with stratified density along the loop axis which changes discontinuously at the lateral surface of each cylinder. The MHD equations are reduced to solve a set of two coupled dispersion relations for frequencies and wavenumbers, in the presence of a stratification parameter. The fundamental and first overtone frequencies and longitudinal wavenumbers are computed. The previous results are verified for an unstratified coronal loop system. Finally, we conclude that an increased longitudinal density stratification parameter will result in an increase of the frequencies. The frequency ratios, first overtones to fundamentals, are very sensitive functions of the density scale height parameter. Therefore, stratification should be included in dynamics of coronal loop systems. For unstratified coronal loop systems, these ratios are the same as monoloop ones.

Conformational stability from variable temperature infrared spectra of xenon solution, r0 structural parameters, and vibrational assignment of fluorocyclohexane

The infrared spectra (3500–300 cm −1) of the gas and xenon solutions of fluorocyclohexane have been recorded. By the utilization of nine different temperatures of nine conformer pairs the enthalpy difference between the more stable chair-equatorial conformer and the chair-axial form was determined to be 48 ± 5 cm −1 (137 ± 14 cal/mol). The ab initio predicted values ranged from 121 cm −1 with the chair-axial conformer more stable from the MP2(full)/6-311G(d,p) calculations to 24 cm −1 with the chair-equatorial form more stable with diffuse functions. The r 0 structural parameters have been obtained from predicted parameters from ab initio MP2(full)/6-311+G(d,p) calculations adjusted to fit the previously reported microwave determined rotational constants. The determined heavy atom structural parameters for the equatorial[axial] conformer are: the distances (Å) C 1–C 7,8 = 1.533(3)[1.531(3)], C 7,8–C 13,14 = 1.543(3)[1.538(3)], C 4–C 13,14 = 1.518(3)[1.520(3)], C 4–F 6 = 1.404(3)[1.410(3)] and angles in degrees ∠C 1C 7,8C 13,14 = 111.0(5)[111.2(5)], ∠F 6C 4C 13,14 = 108.7(5)[107.9(5)] and τC 8C 1C 7C 13 = 55.9(10)[55.9(10)]. The harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational frequencies have been obtained for both conformers from MP2(full)/6-31G(d) ab initio calculations. With two scaling factors of 0.88 for the C–H stretches and 0.9 for the remaining ones, the fundamental wavenumbers have been predicted and along with the depolarization values and infrared band contours (B-type for A″ modes) a complete vibrational assignment has been made for both conformers. The results are discussed and compared to the corresponding properties of some similar molecules.