Experimental study of the energy dependence of the reaction rate coefficients of the reaction CH 3 + with N2O and NH3

The kinetics of the reaction of CH ₃ ⁺ ions with N₂O and NH₃ has been investigated in He and Ar buffers using Selected Ion Flow Drift Tube technique (SIFDT). Both studied reactions proceed with nearly collisional rate at near thermal energies. The rate coefficient of the reaction of CH ₃ ⁺ with N₂O is decreasing more than one order of magnitude (from 1.2×10^?9cm³s^?1 up to 8×10^?11cm³s^?1) with reactant ion/reactant neutral average centre-of-mass kinetic energy (E _r) increasing from near thermal up to 2 eV. The dominant product of this reaction is the isomer HCO⁺ (≥94%) and the minor product is CH₃O⁺. The reaction of CH ₃ ⁺ with NH₃ has two binary channels with the dominant product ion CH₂NH ₂ ⁺ (>70%) and the minor product ion NH ₄ ⁺ (≈10%) and three body association channel with product CH₃NH ₃ ⁺ (≈20% at 0.32 Torr). The rate coefficient of this reaction is decreasing nearly by one order of magnitude with increasingE _r from near thermal up to 0.8eV, forE _r>0.8 eV the rate coefficient increases with increasingE _r. The experimental results are interpreted in terms of a simple model assuming the reactions to proceed via the formation of long-lived collision complexes.     

Crystal structure of di-(L-serine) phosphate monohydrate [C3O3NH7]2H3PO4H2O

The crystal structure of di-(L-serine) phosphate monohydrate [C₃O₃NH₇]₂H₃PO₄H₂O is determined by single-crystal x-ray diffraction. The intensities of x-ray reflections are measured at temperatures of 295 and 203 K. The crystal structure is refined using two sets of intensities. It is established that, in the structure, symmetrically nonequivalent molecules of L-serine occur in two forms, namely, the monoprotonated positively charged molecule CH₂(OH)CH(NH₃)⁺COOH and the zwitterion CH₂(OH)CH(NH₃)⁺COO^?, which are linked with each other and with the H₂PO ^?₄ ion through a hydrogen-bond system involving water molecules.

     

PMR studies of molecular motions,phase transitions and quantum tunnelling in NH4SnCl3 and N(CH3)4SnCl3

Molecular reorientation and low temperature relaxation effects of NH⁺ ₄ ion and the effect of CH₃ substitution (in place of H) are investigated by proton spin lattice relaxation time (T₁) measurements at 10 MHz in NH₄SnCl₃ and N(CH₃)₄SnCl₃ in the temperature range 4.2 K upto the melting points of the compounds (? 440 K). Phase transitions around 360 K in NH₄SnCl₃ and around 361 and 116K in N(CH₃)₄SnCl₃ have been observed. In NH₄SnCl₃, the high temperature minimum at 330.5 K is attributed to the translational diffusion of the NH⁺ ₄ ions, while the other T₁, minima at 103.5, 60 and 50 K are ascribed to the reorientations of the NH⁺ ₄ ion about the C₂ and C₃ axes. The low temperature minimum at 13.5 K is attributed to rotational tunnelling of the NH⁺ ₄ ions. In N(CH₃)₄SnCl₃, in addition to the high temperature minima at 212.2 and 182.6 K due to N(CH₃)₄ tumbling and CH₃ reorientation, a temperature independent T₁ behaviour between 83 and 31 K is observed, below which T₁ decreases and tends to go through a minimum around 5 K. This low temperature minimum is attributed to rotational tunnelling of the CH₃ groups. The motional parameters and tunnel frequencies are estimated.     

PMR spin lattice relaxation by reorientational motions of NH3 and CH3 groups in some organic compounds

The spin-lattice relaxation times, T₁, of protons in o, m, p-phenylene-diamine dihydrochlorides C₆H₄(NH₂)₂·2HCl, phenylhydrazinium chloride C₆H₅NHNH₃Cl, hexaethylbenzene C₆(CH₂CH₃)₆, tetrabutylammonium bromide [CH₃(CH₂)₃]₄NBr, iodide [CH₃(CH₂)₃]₄NI, tetraheptylammonium bromide [CH₃(CH₂)₆]₄NBr and iodide [CH₃(CH₂)₆]₄NI powders have been measured between 400 and 100 K at 60MHz. The experimental results have been explained by considering the reorientational motions of ?NH₃⁺ and ?CH₃ groups about C₃ axes and their role of behaving as sinks to rapid spin diffusion of the ring protons of the phenylene and the methylene protons. The observed T₁, minima in all these substances turn out to be the measures of the ratios between the total number of protons and the number of reorienting ?NH₃⁺ or ?CH₃ protons. Therefore it has been concluded that the T₁, minima of ?NH₃⁺ and ?CH₃ groups, when obtainable can indicate their number present in a solid sample.     

Investigation of the kinetics of OH∗ and CH∗ chemiluminescence in hydrocarbon oxidation behind reflected shock waves

The temporal variation of chemiluminescence emission from OH^?(A² Σ ⁺) and CH^?(A² Δ) in reacting Ar-diluted H₂/O₂/CH₄, C₂H₂/O₂ and C₂H₂/N₂O mixtures was studied in a shock tube for a wide temperature range at atmospheric pressures and various equivalence ratios. Time-resolved emission measurements were used to evaluate the relative importance of different reaction pathways. The main formation channel for OH^? in hydrocarbon combustion was studied with CH₄ as benchmark fuel. Three reaction pathways leading to CH^? were studied with C₂H₂ as fuel. Based on well-validated ground-state chemistry models from literature, sub-mechanisms for OH^? and CH^? were developed. For the main OH^?-forming reaction CH+O₂=OH^?+CO, a rate coefficient of k ₂=(8.0±2.6)×10¹⁰ cm³?mol^?1?s^?1 was determined. For CH^? formation, best agreement was achieved when incorporating reactions C₂+OH=CH^?+CO (k ₅=2.0×10¹⁴ cm³?mol^?1?s^?1) and C₂H+O=CH^?+CO (k ₆=3.6×10¹²exp(?10.9 kJ?mol^?1/RT) cm³?mol^?1?s^?1) and neglecting the C₂H+O₂=CH^?+CO₂ reaction.     

Ion-molecular interactions in solutions of methanesulfonic acid in diethylamine according to IR spectroscopy data

The methanesulfonic acid (MSA)-diethylamine (DEA) binary liquid system is studied over the entire range of compositions at 30°C by using multiple frustrated total internal reflection IR spectroscopy. Solutions with acid: base equimolar ratio contain only 1 : 1 ion pairs. Upon adding the acid, a MSA molecule abstracts an anion from the 1 : 1 complex to produce a protonated DEA and an (H₃C(O₂)SO…H…OS(O₂)CH₃)⁻ anion with a strong H bond: (C₂H₅)₂(H)NH⁺ · OS(O₂)CH₃⁻ + HOS(O₂)CH₃ ↔ (C₂H₅)₂(H)NH⁺ + (H₃C(O₂)SO…H…OS(O₂)CH₃)⁻. This equilibrium is shifted to the left. The 1 : 1 complex is present in solutions even at an significant excess of the acid. To protonate the complex, it is required at least two MSA molecules. Under conditions of an excess of the base, DEA molecules do not solvate the 1 : 1 complex. The solution separates into two phases, composed of (C₂H₅)₂(H)NH⁺ · OS(O₂)CH₃⁻ complexes and pure DEA.     

Dielectric relaxation in ferroelectric (CH3)2NH2AL(so4)2 · 6H2O crystal

Abstract

This paper presents the results of the investigation of dielectric dispersion and ultrasonic velocity in the ferroelectric (CH₃)₂NH₂Al(SO₄)₂ · 6H₂O crystal. The crystal shows a critical slowing down process of polarization with an extremely long relaxation time of the dipole system (τ = 1.6 · 10^?7s at the phase transition point). The dielectric response over the frequency range up to 56 GHz in the paraelectric phase can be well described in terms of a monodispersive Debye-type formula. The activation energy of dipoles in the paraelectric phase is 0.11 eV = 8.5 kT_c . The results show that the proper ferroelectric phase transition is nearly critical and of the order-disorder type.     

Mössbauer effect studies on alkali tris (malonato) ferrates(III)

Mössbauer spectra of alkali tris(malonato) ferrates(III) i.e. M₃[Fe(C₃H₂O₄)₃].4H₂O(M=Li, Na, K, NH₄) at 298±2K display a single broad absorption band due to spin lattice relaxation effect. The isomer shift values indicate these complexes to be high spin with octahedral symmetry. The isomer shift shows a decreasing trend with the increase in electronegativity/polarizing power of the substituent cation (Li⁺, Na⁺, K⁺, NH₄ ⁺). A linear correlation between isomer shift values and the (Fe-O) stretching freguencies has also been observed.     

甲胺水合离子团簇的结构模型及红外光谱研究

本文利用量子化学计算方法，研究了甲胺和水复合离子团簇[(CH₃NH₂)(H₂O)_n]⁺的几何结构、能量和红外光谱，揭示了结构生长模型、氢键作用机制和质子转移机理. 研究结果表明，在[(CH₃NH₂)(H₂O)_n]⁺团簇中，甲胺甲基上的一个氢原子转移到氨基上，形成分子内质子转移的CH₂NH₃⁺离子核心结构模型，水分子作为氢键受体，与质子化氨基NH₃⁺形成氢键. CH₃NH₂⁺离子核心结构模型没有CH₂NH₃⁺离子核心结构模型稳定. 在团簇的红外光谱中，CH振动、自由NH振动、氢键结合的NH振动和OH振动模式在CH₃NH₂⁺和CH₂NH₃⁺两种离子核心结构模型的理论计算红外光谱中明显不同，因此可用于鉴别甲胺水合离子团簇的结构模型，有助于理解甲胺和水复合团簇的氢键网络结构.     

Millimeter- and submillimeter-wave length spectrum of the partially deuterated ammonias; A study of inversion,centrifugal distortion,and rotation-inversion interactions

Eighty-two new rotation-inversion transitions of the light asymmetric rotors NH₂D and ND₂H have been measured in the 80–600 GHz region by means of high resolution microwave techniques. Included among these transitions are several submillimeter R-branch transitions which make possible a calculation of both the rotational and distortion parameters which characterize the molecule. An accurate inversion Hamiltonian is developed and used as a preliminary step to a rotation-distortion treatment of the molecule. The spectrum of ND₂H reveals the existence of a rotation-vibration interaction which significantly alters the energy of a number of ground vibrational state levels. The results of an analysis technique which incorporates the effects of this perturbation as well as the inversion effects are presented. This procedure makes possible the analysis of all observed transitions to within experimental uncertainties as well as the accurate prediction of unobserved transitions. The rotational constants which result from this work are (MHz): For NH₂D, O⁺ vibrational state,a= 290 286.53 ± 0.21,B= 192 240.15 ± 0.42,C= 140 602.50 ± 0.42; for NH₂D, O^? vibrational state,a= 290 192.14 ± 0.21,B= 192 176.27 ± 0.42,C= 140 625.64 ± 0.42; for ND₂H, O⁺ vibrational state,a= 223 222.92 ± 0.18,B= 160 433.96 ± 0.17,C= 112 305.40 ± 0.17; for ND₂H, O^? vibrational state,a= 223 147.21 ± 0.14,B= 160 423.37 ± 0.13,C= 112 313.72 ± 0.13.     

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.     

Infrared laser spectroscopy of the CN free radical in a methane-nitrogen-hydrogen plasma

Many Pand R-branch lines of the fundamental bands of the ¹²C¹⁴N and ¹³C¹⁴N radicals in their ground (²Σ⁺) electronic state have been measured at high resolution by diode laser absorption spectroscopy. The radicals were generated in a 2.45 GHz planar microwave plasma in methane with varying proportions of N₂ and H₂. From a fit to the spectra the origins of the fundamental bands of the two isotopomers were determined to be 2042.42104(84) cm^?1 and 2000.084 70(30) cm^?1. The main product detected in the plasma by diode laser spectroscopy is HCN, with concentrations about three orders of magnitude higher than CN.     

New FIR laser lines from an optically pumped far-infrared laser with isotopic 13C16O2 pumping

A ¹³C¹⁶O₂ laser optically pumping a FIR laser has resulted in 17 new FIR cw emissions from 78.5 μm to 917 μm. The FIR media were: CD₃OD, CH₃OD, CD₃OH, NH₃ and ¹⁵NH₃. Interesting effects have been observed with a combination of NH₃ and CD₃OD resulting in a new FIR emission. Two new FIR emissions at 181.5 μm and 355.5 μm have been observed with a ¹²C¹⁶O₂ laser optically pumping CD₃OD.     

Anilinium Ions: Relations Between pK, σ and Intensity of the UV Transition

Spectroscopists have often assumed, based only on the UV spectrum of the anilinium ion (φNH₃ ⁺), that ammonium groups cannot bring a “mesomeric” effect upon π systems. This assumption^(1–3) which could be justified for the anilinium ion itself, whose OO band of the secondary transition (towards 260 nm) is very weak, has been unduly extended to all the ammonium groups. Actually, the interaction between a π system and (NX_aX_bX_c)⁺ groups has been studied by several authors^(4–8) and we have shown that contrary to what had been assumed by spectroscopists, such an interaction induces strong effects on the UV spectrum of the benzene chromophore^(9–11). Using the MNDO and the CNDO methods, we have studied the quantum factors which play a part in the long range interaction, between: an ω group X on the one hand, N on the other hand, and then φ, in φNH₂ ⁺CH₂X, φNH⁺ (CH₂X_a) CH₂X_b and φNH⁺ (C₂H₄)₂X.     

Electromagnetic wave absorption of polymeric nanocomposites based on ferrite with a spinel and hexagonal crystal structure

We have investigated composites designed for microwave absorption based on magnetic filler, composed of phases within the SrO-Fe₂O₃ system, embedded in a polyphenylene sulfide matrix with a concentration ratio of 80:20 by weight. The formation of the nanosized particles of SrFe₁₂O₁₉ and Fe₃O₄, as the principal magnetic phases was achieved via the co-precipitation of Sr²⁺/Fe³⁺ ions using different molar ratios. The various precursors obtained were calcined between 600 °C and 900 °C in air. The electromagnetic parameters of the composites were measured with a vector network analyzer at 400 MHz to 32 GHz. The results show that with a composite composed of a complex magnetic filler comprising the nanoparticles of two magnetically diverse phases, i.e., a spinel phase as the electromagnetic wave absorber in the lower GHz range and a hexagonal phase operating at a higher GHz range, above 32 GHz, a microwave absorber with an broad absorption range can be prepared.     

Synthesis, infrared and microwave absorbing properties of (BaFe12O19+BaTiO3)/polyaniline composite

The (BaFe₁₂O₁₉+BaTiO₃)/polyaniline composite was synthesized by in situ polymerization and introduced into epoxy resin and polyethylene to be a microwave and infrared absorber. The spectroscopic characterizations of the formation processes of (BaFe₁₂O₁₉+BaTiO₃)/polyaniline composite were examined using Fourier transform infrared, ultraviolet-visible spectrophotometer, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electron spin resonance. Microwave absorbing properties were investigated by measuring reflection loss in 2-18 and 18-40 GHz microwave frequency range using the free space method. Thermal extinction measurements in the 3-5 and 8-12 μm were done to evaluate the shielding effectivity of infrared. The results showed that a significant absorption frequency range shifting and thermal extinction could be obtained by adding polyaniline to the BaFe₁₂O₁₉+BaTiO₃ blend.     

Vibrational analysis of ethylamines: Trans and gauche forms

Starting from force constant values calculated by an ab initio MO method ($\text{4-31G(N}{}^1\text{)}$), and by adjusting the diagonal elements, a practical force constant matrix (F) has been reached which could explain the observed infrared and Raman spectra (in the frequency range lower than 2000 cm^?1) of the gauche form of the ethylamine CH₃CH₂NH₂ molecule and five isotopic species CH₃¹³CH₂NH₂, CH₃CH₂¹⁵NH₂, CH₃CD₂NH₂, CH₃CH₂ND₂, and CD₃CD₂NH₂. The F matrix for the trans form of ethylamine was constructed by transferring ab initio $\text{4-31G(N}{}^1\text{)}$ values and by revising diagonal elements with conversion factors whose values are equal to the corresponding values of gauche form. A nearly complete set of assignments was achieved of the vibrational bands of ethylamines, observed so far in the spectral range 2000–100 cm^?1. In matrix isolation spectroscopy, two bands assignable to the NH₂ wagging vibrations of gauche and trans forms have been found at 775 and 782 cm^?1, respectively, for CH₃CH₂NH₂. They are at 768 and 774 cm^?1, respectively, for CD₃CD₂NH₂. From the intensity changes of these bands observed on changing the nozzle temperature in the matrix formation, the energy difference ΔE (gauche-trans) of these two conformers has been estimated to be 100 ± 10 cm^?1.     

Infrared absorption of iodomethylperoxy (syn-ICH2OO) radical generated upon photolysis of CH2I2 and O2 in solid para-H2

Irradiation of a para-hydrogen (p-H₂) matrix containing diiodomethane (CH₂I₂) and O₂ at 3.2 K with light at 280 ± 20 nm, followed by annealing of the matrix at 4.0 K, yielded infrared (IR) absorption lines at 2982.4, 1408.9, 1231.8, 1226.5/1225.6, 1085.6, 917.7, 841.6/841.1, 550.5, and 490.2 cm^?1 that are assigned to the syn-iodomethylperoxy (syn-ICH₂OO) radical. Further irradiation of the matrix at 365 nm diminished these features. Experiments with CH₂I₂ and ¹⁸O₂ yielded lines of syn-ICH₂¹⁸O¹⁸O at 1407.3, 1228.1/1227.7, 1217.7/1217.0, 1031.5, 899.9/899.4, 836.7/836.0, and 473.6 cm^?1. The assignments are based on the photolytic behaviour and comparisons of observed vibrational wavenumbers, IR intensities, and ¹⁸O-isotopic shifts with those predicted with the B3LYP/aug-cc-pVTZ-pp method. The observation is consistent with a mechanism that, upon photolysis of CH₂I₂ at 280 nm, CH₂I was formed and subsequently reacted with O₂ to yield syn-ICH₂OO. Compared with the gaseous reaction CH₂I + O₂ → CH₂OO + I at low pressure, observation of ICH₂OO in a p-H₂ matrix instead of CH₂OO in the gaseous phase indicates that the excess energy of internally excited ICH₂OO, produced upon reaction of CH₂I + O₂, was rapidly quenched in the matrix so that ICH₂OO became readily stabilised without further decomposition to form CH₂OO + I.     

Nonlinear magnetic resonance in the (CH<Subscript>3</Subscript>NH<Subscript>3</Subscript>)<Subscript>2</Subscript>CuBr<Subscript>4</Subscript> crystal

The nonlinear microwave absorption in the (CH₃NH₃)₂CuBr₄ antiferromagnetic crystal is investigated experimentally. The temperature and angular dependences of the parameters of nonlinear resonance and the dependences of these parameters on the microwave pump power are analyzed. It is found that the nonlinear properties deteriorate with decreasing temperature and the linear and nonlinear contributions are competitive in character.     

The heat capacity of the layer compounds (CH3CH2CH2NH3)2MnCl4 and (CH3CH2CH2NH3)2CdCl4 from 10 K TO 300 K

The heat capacity of the layer compounds tetrachlorobis (n-propylammonium) manganese II and tetrachlorobis (n-propylammonium) cadmium II, (CH₃CH₂CH₂NH₃)₂MnCl₄ and (CH₃CH₂CH₂NH₃)₂CdCl₄ respectively, has been measured over the temperature range 10 K ?T ? 300 K.Two known structural phase transitions were observed for the Mn compound in this temperature region: at T = 112.8 ± 0.1 K (ΔH_t= 586 ± 2 J mol^?1; ΔS_t = 5.47 ± 0.02 J K^?1mol^?1) and at T =164.3 ± (ΔH_t = 496 ± 7 J mol^?1; ΔS_t =3.29 ± 0.05 J K^?1mol^?1). The lower transition is known to be from a monoclinic structure to a tetragonal structure, while the upper is from the tetragonal phase to an orthorhombic one. From comparison with the results for the corresponding methyl Mn compound it is deduced that the lower transition primarily involves changes in H-bonding while the upper transition involves motion in the propyl chain.A new structural phase transition was observed in the Cd compound at T= 105.5 ± 0.1 K (ΔH_t= 1472.3 ± 0.1 J mol^?1; ΔS_t = 13.956 ± 0.001 J K^?1mol^?1), in addition to two transitions that have been observed previously by other techniques. The higher of these transitions(T = 178.7 ± 0.3 K; ΔH_t = 982 ± 4 J mol^?1 ΔS_t = 6.16 ± 0.02 J K^? mol^?1) is known to be between two orthorhombic structures, while the structural changes at the lower transition (T= 156.8 ± 0.2 K; ΔH_t = 598 ± 5 J mol^?1, ΔS_t = 3.85 ± 0.03 J K^?1 mol^?1) and at the new transition are not known. It is proposed that these two transitions correspond respectively to the tetragonal to orthorhombic and monoclinic to tetragonal transitions in the propyl Mn compounds.In addition to the structural phase transitions (CH₃CH₂CH₂NH₃)₂MnCl₄ magnetically orders at t? 130 K. The magnetic contribution to the heat capacity is deduced from the heat capacity of the corresponding diamagnetic Cd compound and is of the form expected for a quasi 2-dimensional Heisenberg antiferromagnet.