The Enfrared Spectra of tris (Methyl Methylphosphonate) Iron(III), Tris (Ethyl Ethylphosphonate) Iron(III), and Tris (Isopropyl Methylphosphonate) Iron(III)

The literature contains few references to the reactions of phosphonate esters with iron salts. Guilbault et al. ¹ recently studied the infrared spectrs of diisopropyl methylphosphonate (DIMP) and dimethyl methylphosphonate (DIMP) chemisorbed on solid FeCl ³ and made infrared band assignments. We wish to report the results of a study of the products of the homogeneous reaction of DIMP, DMMP and diethyl ethylphosphonate (DEEP) with ferric chloride. On the basis of elemental analysis and infrared absorption data, the products isolated were identified as tris (methylmethylphosphonate) iron (III), tris (ethyl ethylphosphonate) iron (III), and tris (isopropyl methylphosphonate) iron (III).     

Structural studies on banana oil,isoamyl acetate,by means of microwave spectroscopy and quantum chemical calculations

The rotational spectrum of isoamyl acetate, H₃C–COO–(CH₂)₂–CH(CH₃)₂, has been recorded and assigned using a molecular beam Fourier transform microwave (MB-FTMW) spectrometer in the frequency range of 3–26.5?GHz. One conformer has been observed. By comparing the spectroscopic data with the quantum chemical data, it was found that the conformer observed does not have C_s symmetry. The rotational and centrifugal distortion constants were determined. The barrier to internal rotation of the acetate methyl group was found to be 93.98?cm^?1. Due to the high number of the conformers, a systematic nomenclature will be presented.     

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.     

Fourier Transform Microwave Spectrum and ab Initio Study of Dimethyl Methylphosphonate

The rotational spectrum of dimethyl methylphosphonate (DMMP) has been studied using a pulsed molecular beam Fourier transform microwave spectrometer. The spectrum is complicated by the internal rotation motions of the three methyl tops in the molecule as well as an interconversion motion of the two methoxy groups. Here, we present the microwave spectrum, the ab initio calculations, and the assignment of the rigid-rotor A-symmetry state of the molecule. The rotational constants for this state are A=2828.753(2) MHz, B=1972.360(3) MHz, and C=1614.267(2) MHz. In the following paper, a group theoretical analysis is developed for DMMP. The observed conformation of the molecule has no point-group symmetry and all three electric-dipole selection rules are active, with c-type transitions being the most intense. Ab initio calculations were carried out at both the Hartree-Fock 6-31G* and MP2/6-311G* levels of theory. These calculations indicate that two low-energy conformations are possible separated by energies of less than 170 cm⁻¹. Furthermore, the calculated lowest energy conformer is in agreement with the one observed experimentally. The relative energies of the two low-energy conformers rise from 34 cm⁻¹ at the HF level to 170 cm⁻¹ at the MP2 level.     

Interaction of diethyl aniline methylphosphonate with DNA: Spectroscopic and isothermal titration calorimetry

In this study the diethyl aniline methylphosphonate (DAM) was synthesized, the interaction of DAM with ct-DNA has been investigated by fluorescence spectra, UV spectra, molecular modeling and isothermal titration calorimetry (ITC). The binding constant of DAM to ct-DNA calculated from both isothermal titration calorimetry and fluorescence spectra were found to be in the 10⁴ M⁻¹ range. According to the ethidium bromide displacement studies, UV spectra and isothermal titration calorimetry experimental results, it can be concluded that DAM is an intercalator that can slide into the G-C rich region of ct-DNA. Furthermore, the results obtained from molecular modeling corroborated the experimental results obtanied from spectroscopic and ITC investigations. At the same time, fluorescence spectra suggested that the mechanism of the interaction of DAM to ct-DNA was a static enhancing type. ITC data showed that ct-DNA/DAM binding is enthalpy controlled.     

Rotational spectra, conformational structures, and dipole moments of thiodiglycol by jet-cooled FTMW and ab initio calculations

The rotational spectra of three low-energy conformers of thiodiglycol (TDG) (HOCH₂CH₂SCH₂CH₂OH) have been measured in a molecular beam using a pulsed-nozzle Fourier-transform microwave spectrometer. To determine the likely conformational structures with ab initio approach, conformational structures of 2-(ethylthio)ethanol (HOEES) (CH₃CH₂SCH₂CH₂OH) were used as starting points together with the consideration of possible intramolecular hydrogen bonding in TDG. Three lower-energy conformers have been found for TDG at the MP2=Full/6311G** level and ab initio results agree nicely with experimentally determined rotational constants. In addition, Stark measurements were performed for two of the three conformers for dipole moment determinations, adding to our confidence of the conformational structure matches between experimental observations and ab initio calculations. Of the three lower-energy conformers, one displays a compact folded-like structure with strong hydrogen bonding between the two hydroxyl groups and the central sulfide atom. Two other conformers have relatively open chain-like structures with hydrogen bonding between each of the hydroxyl groups to the central sulfur atom, of which one has pure b-type dipole moment according to the ab initio results.     

A Far-Infrared Study of the Structures of Tris(Methyl Methyl Phosphonate) Iron(III), Tris(EthylEthylphosphonate) Iron(III), and Tris(IsopropylMethylphosphonate) Iron(III)

In articles by Kokalas et al.^1,2 studies were made of the interaction of FeCl₃ with diisopropyl methylphosphonate (DIMP), diethyl ethylphosphonate (DEEP), and dimethyl methyl phosphonate (DMMP) and structures were proposed for the reaction products. When the reactions are run under much milder conditions, there is much evidence^3–5 to support a different mechanism than that proposed by Kokalas and an altogether different structure of the complexes formed. In the structures proposed by Kokalas et al. the iron atom is surrounded by six oxygen atoms and these are the only bonding atoms to the iron. But on the other hand, in donor-acceptor complexes as are formed in chemisorption reactions,^3–5 some of these sites are filled by chloride ions and this difference should be ascertained quite easily by far-infrared spectroscopy. It was the purpose of this study to look at the far-infrared data and either further substantiate the structures proposed or to propose new ones.     

Two conformers of ethyl pivalate studied by microwave spectroscopy

The rotational spectra of two conformers of ethyl pivalate, (CH₃)₃C-COO-C₂H₅ have been recorded by molecular beam FT microwave spectroscopy. The analysis yielded a set of three rotational constants and five quartic centrifugal distortion constants for each conformer. The conformers were identified by comparing the experimental rotational constants with those obtained by ab initio calculations at MP2/6-311++G∗∗ level. One conformer has C_s symmetry, the other one forms a pair of enantiomers with C₁ symmetry. Additionally, the torsional potentials of the tert-butyl group and of the methyl groups were obtained by ab initio methods.     

乙醚团簇的激光电离质谱及从头计算

应用激光多光子电离质谱与超声脉冲分子束技术研究了乙醚团簇，实验中观测到乙醚的碎片离子以及强度较小的(E)H⁺，(E)^＋₂和(E)₂H⁺(E代表CH₃CH₂OCH₂CH₃)，没有发现更大尺寸的团簇离子.结合从头计算理论，在B3LYP/6-311++G(d,p 关键词： 乙醚团簇 偶极-偶极相互作用 从头计算     

Millimeter-wave spectrum and ab initio DFT calculation of the C-gauche conformer of allyl isocyanate

The analysis of the ground state rotational spectrum of the C-gauche conformer of allyl isocyanate has been extended up to the frequency range of 100.0 GHz. A detailed centrifugal distortion analysis has been carried out using previously reported and newly measured transition frequencies. More accurate values of the rotational and centrifugal distortion constants are presented. Quantum chemical calculations at DFT levels of theory using large basis sets b3lyp/6-311G(d, p), have also been made to compute rotational constants, dipole moments and potential energies for different conformers of this molecule. Finally, different bond lengths and centrifugal distortion constants for the C-gauche conformer have been computed.     

Rotational spectra, conformational structures and dipole moments of 2-(ethylthio)ethanol by jet-cooled FTMW and ab initio calculations

The rotational spectra of three low-energy conformers of 2-(ethylthio)ethanol also known as ethyl 2-hydroxyethylsulfide or hydroxyethyl ethyl sulfide (HOEES), together with the monosubstituted ¹³C and ³⁴S isotopic forms of the two lowest energy conformers, have been measured in a molecular beam using a pulsed-nozzle Fourier-transform microwave spectrometer. To search for the likely conformational structures, ab initio calculations were performed at the MP2/6-31G* level for reduced dimensionality potential energy mapping and at the MP2=FULL/6-311G** and B3LYP=FULL/6-311G** levels for full structural optimization and electronic energy calculations of possible lower energy conformers. In all, five low-energy conformers, each of C₁ point group symmetry, were located in the ab initio search with complete information obtained on rotational constants, dipole moments, and structures. Rotational constants for three of the conformers agree well with the experimental observations, leaving the other two with no experimental partners. The three having experimental matches display relatively open “chain-like” structures corresponding to TG-, and GG-like forms, while the two with no experimental matches display relatively closed or “folded” structures with significantly different rotational constants. Although results using different ab initio level theories with and without zero point energy corrections alter the conformer energy ordering slightly, the no-match conformers always stay in the lower energy group, leaving an unsolved question as to why these lower energy conformers with “folded-like” structures were not observed in the jet-cooled FTMW spectra.     

Millimeter wave spectrum of glycine

We present new investigations of the millimeter wave spectra of the two lowest-energy conformers of glycine (NH₂CH₂COOH). Measurements of these spectra have been carried out between 75 and 260 GHz using the millimeter-wave spectrometer in Kharkov. The new data set involves rotational transitions with J up to 44 and K_a up to 15 for conformer I and transitions with J up to 43 and K_a up to 14 for conformer II. This represents a more than twofold expansion both in the frequency range and J quantum-number range in comparison with previous investigations. The improved sets of spectroscopic parameters obtained for both conformers provide accurate transition frequencies for the key lines necessary for radio astronomy searches for interstellar glycine.     

Experimental and computational study of diethyl sulfide pyrolysis and mechanism

The pyrolysis of diethyl sulfide (C₂H₅SC₂H₅), a simulant for mustard chemical warfare agents, was studied in a turbulent flow reactor with extractive gas composition analysis by GC/MS and FTIR. Experiments were performed at approximately atmospheric pressure for four different temperatures between 630 and 740 °C with maximum residence times between 0.06 and 0.08 s. Temperature and species profiles were obtained on the centerline of the reactor. The mixing characteristics in the reactor were determined by using carbon monoxide as a tracer. 80% destruction of diethyl sulfide was observed for the experiment at the temperature of 740 °C and the residence time of 0.06 s. The following species were quantified: diethyl sulfide, ethylene, methane, ethane, acetylene, carbon disulfide, and thiophene. In addition, ethanethiol, methyl thiirane CH₃-(Cy-CH-CH₂-S), ethyl methyl disulfide, and diethyl disulfide were identified but not quantified. A light yellow solid containing sulfur condensed in sampling probes. Thermochemical properties for all species and a detailed mechanism were developed for modeling the reaction system. Thermodynamic and kinetic parameters were based on density functional theory and ab initio calculations using isodesmic work reactions for enthalpies. Kinetic parameters for chemical activation and unimolecular dissociation reactions were determined with multi frequency quantum RRK analysis for k(E) and master equation for fall-off. Important reactions were identified by sensitivity analysis and reaction pathway analysis of the mechanism. Model predictions show overall good agreement with experiment.     

Rotational spectrum of trans-trans diethyl ether in the ground and three excited vibrational states

We report the results of a comprehensive reinvestigation of the rotational spectrum of diethyl ether based on broadband millimetre-wave spectra recently recorded at The Ohio State University and in Warsaw, covering the frequency region 108-366 GHz. The data set for the ground vibrational state of trans-trans diethyl ether has been extended to over 2000 lines and improved spectroscopic constants have been determined. Rotational spectra in the first excited vibrational states of the three lowest vibrational modes of trans-trans-diethyl ether, ν₂₀, ν₃₉, and ν₁₂ have been assigned. The v₂₀ = 1 and v₃₉ = 1 states are near 100 cm⁻¹ in vibrational term value and are coupled by a strong c-axis Coriolis interaction, which gives rise to many spectacular manifestations in the rotational spectrum. All of these effects have been successfully fitted for a dataset comprising over 3000 transitions, leading to precise determination of the energy difference between these states, (ΔE/hc)=10.400222(5) cm⁻¹. A newly developed software package for assignment and analysis of broadband spectra is described and made available.     

Organic compounds in the C3H6O3 family: Microwave spectrum of cis-cis dimethyl carbonate

Geometry optimization calculations on 13 members of the C₃H₆O₃ family of organic species have been carried out to determine their relative binding energies. Dimethyl carbonate [(CH₃)₂CO₃] is one of the lower energy species in this family, which includes the C₃-sugars 1,3-dihydroxyacetone and glyceraldehyde. The microwave spectrum of dimethyl carbonate has been measured over the frequency range 8.4-25.3 GHz with several pulsed-beam Fourier-transform microwave spectrometers and from 227 GHz to 350 GHz with direct absorption spectrometers. The spectrum of the lowest-energy cis-cis conformer of dimethyl carbonate has been assigned, and ab initio electronic structure calculations of the three possible conformers have been performed. Stark effect measurements were carried out on the cis-cis conformer to provide accurate determinations of the dipole moment components.     

Etching reaction of methylchloride molecule on the GaAs (0 0 1)-2 × 4 surface

Adsorption process of methylchloride (CH₃Cl) on the GaAs (0 0 1)-2 × 4 surface was studied by a scanning tunnelling microscopy (STM) measurement. The arsenic rich 2 × 4 surface, which was prepared by molecular beam epitaxy (MBE), was exposed to a supersonic molecular beam of CH₃Cl with a kinetic energy of 0.06 eV. New bright spots appeared on the CH₃Cl exposed surface. They were largely observed at the “B-type” step edge and divided into two types according to their locations. It was suggested that new spots were due to weakly adsorbed CH₃Cl molecules without any dissociation. The adsorption mechanism of CH₃Cl molecule was also studied by an ab initio Hartree-Fock calculation, which explained the experimental results well.     

Analysis of the rotational spectrum of pyruvonitrile up to 324 GHz

The room-temperature rotational spectrum of pyruvonitrile (acetyl cyanide, CH₃COCN) was measured up to 324 GHz, and additional measurements were also made in supersonic expansion in the region 7-19 GHz. The available data sets for the A and E torsional sublevels were extended to over 1200 transitions, J = 65 and K_a = 38 for the ground vibrational state, and to comparable numbers of transitions for first excited states of the methyl torsional mode ν₁₈, and the in-plane CCN bending mode ν₁₂. The collected experimental measurements were fitted with several different computer programs for dealing with the effects of methyl torsional motion on the rotational spectrum and many spectroscopic constants have been determined. The experimental results are discussed in detail and are augmented by ab initio computations. Stark effect measurements in supersonic expansion were used to precisely determine the electric dipole moment of pyruvonitrile, ∣μ_a∣ = 2.462(2) D, ∣μ_b∣ = 2.442(2) D, μ_tot = 3.468(2) D. Pyruvonitrile, as an 8-atom molecule with a sizable dipole moment, is a possible candidate for astrophysical detection and the present work provides the laboratory data necessary for that purpose.     

Microwave spectrum, tunneling motions, and quadrupole coupling hyperfine structure of ethylene diamine

New transitions are measured in the microwave spectrum of two conformers of the non-rigid ethylene diamine (CH₂NH₂-CH₂NH₂) molecule using both molecular beam Fourier transform and stark modulation spectroscopy. Ab initio calculations are carried out to obtain geometries and energies for several stationary points of the potential energy surface and to gain quantitative information on the tunneling paths along which the molecule tunnels. The microwave data are reproduced using an IAM-like approach which accounts for the rotational dependence of the tunneling splitting corresponding to the interconversion large amplitude motion. For one of the conformers, the results of this analysis are consistent with the ones obtained through ab initio calculations. Hyperfine patterns are analyzed with the help of a theoretical approach accounting for the large amplitude motion effects and for hyperfine matrix elements within and between tunneling sublevels.     

Methyl torsional state analysis of the jet-cooled microwave spectrum of N-acetylglycine

The microwave spectrum of N-acetylglycine was obtained using a NIST Fourier-transform microwave spectrometer equipped with a heated, pulsed-nozzle source. One conformer has been identified and its spectrum assigned. The conformer has C_S point group symmetry and an intramolecular hydrogen bond between the carbonyl and amide groups of the 5-membered glycine unit. Internal rotation of the methyl rotor group leads to splitting of the rotational lines into A and E symmetry tunneling states. The ¹⁴N nuclear-quadrupole hyperfine structure verifies the rotational and internal-rotor state assignments. The V₃ barrier of 57.5(1) cm⁻¹ and the angles between the C₃ axis of the methyl rotor and the principal inertial axes are in best agreement with the calculated values for the lowest energy conformer of the four conformers predicted at the MP2/6-311++G(d,p) level of theory.     

Analysis and fit of the Fourier-transform microwave spectrum of the two-top molecule N-methylacetamide

The jet-cooled Fourier-transform microwave spectrum of N-methylacetamide (CH₃NHC(O)CH₃), a molecule containing two methyl tops with relatively low barriers to internal rotation, has been recorded and fit to nearly experimental uncertainty. Measurements were carried out between 10 and 26 GHz, with the nitrogen quadrupole splittings resolved for many transitions. The permutation-inversion group for this molecule is G₁₈ (not isomorphic to any point group), with irreducible representations A₁, A₂, E₁, E₂, E₃, and E₄. One of these symmetry species and the usual three asymmetric rotor quantum numbers J_KaKc were assigned to each torsion-rotation level involved in the observed transitions. F values were assigned to hyperfine components, where . Transitions involving levels of A₁ and A₂ species could be fit to an asymmetric rotor Hamiltonian. The other transitions were first fit separately for each symmetry species using a Pickett-like effective rotational Hamiltonian. Constants from these fits show a number of additive properties which can be correlated with sums and differences of effects involving the two tops. A final global fit to 48 molecular parameters for 839 hyperfine components of 216 torsion-rotation transitions involving 152 torsion-rotation levels was carried out using a newly written two-top computer program, giving a root-mean-square deviation of observed-minus-calculated residuals of 4 kHz. This program was written in the principal axis system of the molecule and uses a free-rotor basis set for each top, a symmetric-top basis set for the rotational functions, and a single-step diagonalization procedure. Such an approach requires quite long computation times, but it is much less prone to subtle programming errors (a consideration felt to be important since checking the new program against precise fits of low-barrier two-top molecules in the literature was not possible). The two internal rotation angles in this molecule correspond to the Ramachandran angles ψ and φ often defined to describe polypeptide folding. Barriers to internal rotation about these two angles were found to be 73 and 79 cm⁻¹, respectively. Top-top coupling in both the kinetic and potential energy part of the Hamiltonian is relatively small in this molecule.