On the equilibrium structure of MgC2 and AlC2

In order to find such unknown molecules as MgC₂ and AlC₂ in interstellar space, accurate calculations to determine the equilibrium structures of these molecules were carried out. The ab initio MCSCF and MRSDCI methods were employed in the calculations. MgNC whose rotational constant has been observed was used to check the reliability of the computational scheme. The predicted geometrical structures of MgC₂ and AlC₂ were equilateral triangles and their rotational constants were A_e = 51.55, B_e = 11.52 and C_e = 9.413 GHz for MgC₂ and A_e = 50.76, B_e = 12.00 and C_e = 9.705 GHz for AlC₂.     

Synthesis and the keto-enol equilibrium of 2-acyl lactams

Condensation of N-substituted lactams with carboxylic acid esters was studied. A wide range of substituted 2-acyl lactams with different ring sizes were synthesized. The structure of 2-acyl lactams (primarily, the ring size) was found to influence the keto-enol tautomerism.     

Rotational spectra and equilibrium structures of H2SiS and Si2S

The rotational spectra of two small silicon sulfides, silanethione H(2)SiS and the disilicon sulfide ring Si(2)S, have been detected in the centimeter band by Fourier transform microwave spectroscopy of a molecular beam; lines of H(2)SiS were also observed in the millimeter band up to 377 GHz in a glow discharge. Precise rotational and centrifugal distortionconstants have been determined for the normal and a number of the more abundant rare isotopic species of both closed-shell molecules. Theoretical equilibrium (r(e)) structures of H(2)SiS and Si(2)S were derived from coupled-cluster calculations that included triple and quadruple excitations, core correlation, and extrapolation to the basis-set limit. The r(e) structures agree to within 5×10(-4) A? and 0.1(°) with empirical equilibrium (r(e)(emp)) structures derived from the experimental rotational constants, combined with theoretical vibrational and electronic corrections. Both H(2)SiS and Si(2)S are good candidates for radioastronomical detection in the circumstellar shells of evolved carbon-rich stars such as IRC+10216, because they are fairly polar and are similar in composition to the abundant astronomical molecule SiS.     

Phase equilibrium in the Sb2Se3-Gd2Te3 system

The Sb₂Se₃-Gd₂Te₃ system was studied using differential thermal analysis, X-ray powder diffraction, and microstructure examination. This is a quasi-binary system. Sb₂Se₃-based solubility at 300 K is 10 mol % Gd₂Te₃. The eutectic contains 20 mol % Gd₂Te₃ and melts at 760 K. One incongruently melting compound (870 K) of composition GdSbTe_1.5Se_1.5 was found in the system.     

Infrared emission spectra and equilibrium structures of gaseous HgH2 and HgD2

A detailed analysis of the high-resolution infrared emission spectra of gaseous HgH2 and HgD2 in the 1200-2200 cm(-1) spectral range is presented. The nu3 antisymmetric stretching fundamental bands of 204HgH2, 202HgH2, 201HgH2, 200HgH2, 199HgH2, 198HgH2, 204HgD2, 202HgD2, 201HgD2, 200HgD2, 199HgD2, and 198HgD2, as well as a few hot bands involving nu1, nu2, and nu3 were analyzed rotationally, and spectroscopic constants were obtained. Using the rotational constants of the 000, 100, 01(1)0, and 001 vibrational levels, we determined the equilibrium rotational constants (B(e)) of the most abundant isotopologues, 202HgH2 and 202HgD2, to be 3.135325(24) cm(-1) and 1.569037(16) cm(-1), respectively, and the associated equilibrium Hg-H and Hg-D internuclear distances (re) are 1.63324(1) A and 1.63315(1) A, respectively. The re distances of 202HgH2 and 202HgD2 differ by about 0.005%, which can be attributed to the breakdown of the Born-Oppenheimer approximation.     

Counterpoise技术和He-H2O配合物的平衡几何

在得到MP4, SCF的关于总能量及结合能的四个势能面的基础上,着重分析了电子相关作用, 消除基函数超位误差的Counterpoise(CP)技术对van der Waals配合物He-H2O的平衡几何的影响并得到了更精确的平衡几何预测。     

Phase equilibrium in the As2S3-TlSe system

The interaction between the components of the As₂S₃-TlSe system has been studied using diffeential thermal analysis, powder X-ray diffraction, microstructure examination, and microhardness and density measurements. Two new quaternary compounds, TlAs₂S₃Se and Tl₃As₂S₃Se₃, are formed in the system. Both compounds may be prepared in a glassy state. They melt congruently at 350 and 280°C, respectively. The section As₂S₃-TlSe is a stable diagonal of the ternary reciprocal system As,Tl ‖ S, Se. The As₂S₃-base solid solution extends to 1.5 mol % TlSe. The extent of the TlSe-base solution is 5.2 mol % As₂S₃. Under slow cooling, the glass field in the system extends to 85 mol % TlSe; when the system is quenched to liquid nitrogen, the extent of the glass field is 100 mol % TlSe.     

2-Pyridinethiol/2-pyridinethione tautomeric equilibrium. A comparative experimental and computational study

The gas phase and solvent dependent preference of the tautomerization between 2-pyridinethiol (2SH) and 2-pyridinethione (2S) has been assessed using variable temperature Fourier transform infrared (FTIR) experiments, as well as ab initio and density functional theory computations. No spectroscopic evidence (nu(S)(-)(H) stretch) for 2SH was observed in toluene, C(6)D(6), heptane, or methylene chloride solutions. Although, C(s)() 2SH is 2.61 kcal/mol more stable than C(s)() 2S (CCSD(T)/cc-pVTZ//B3LYP/6-311+G(3df,2p)+ZPE), cyclohexane solvent-field relative energies (IPCM-MP2/6-311+G(3df,2p)) favor 2S by 1.96 kcal/mol. This is in accord with the FTIR observations and in quantitative agreement with the -2.6 kcal/mol solution (toluene or C(6)D(6)) calorimetric enthalpy for the 2S/2SH tautomerization favoring the thione. As the intramolecular transition state for the 2S, 2SH tautomerization (2TS) lies 25 (CBS-Q) to 30 kcal/mol (CCSD/cc-pVTZ) higher in energy than either tautomer, tautomerization probably occurs in the hydrogen bonded dimer. The B3LYP/6-311+G(3df,2p) optimized C(2) 2SH dimer is 10.23 kcal/mol + ZPE higher in energy than the C(2)(h)() 2S dimer and is only 2.95 kcal/mol + ZPE lower in energy than the C(2) 2TS dimer transition state. Dimerization equilibrium measurements (FTIR, C(6)D(6)) over the temperature range 22-63 degrees C agree: K(eq)(298) = 165 +/- 40 M(-)(1), DeltaH = -7.0 +/- 0.7 kcal/mol, and DeltaS = -13.4 +/- 3.0 cal/(mol deg). The difference between experimental and B3LYP/6-311+G(3df,2p) [-34.62 cal/(mol deg)] entropy changes is due to solvent effects. The B3LYP/6-311+G(3df,2p) nucleus independent chemical shifts (NICS) are -8.8 and -3.5 ppm 1 A above the 2SH and 2S ring centers, respectively, and the thiol is aromatic. Although the thione is not aromatic, it is stabilized by the thioamide resonance. In solvent, the large 2S dipole, 2-3 times greater than 2SH, favors the thione tautomer and, in conclusion, 2S is thermodynamically more stable than 2SH in solution.     

Infrared emission spectra and equilibrium bond lengths of gaseous ZnH2 and ZnD2

A detailed analysis of the high resolution infrared emission spectra of gaseous ZnH2 and ZnD2 in the 800-2200 cm(-1) spectral range is presented. The nu3 antisymmetric stretching fundamental bands of 64ZnH2, 66ZnH2, 67ZnH2, 68ZnH2, 64ZnD2, 66ZnD2 and 68ZnD2, as well as several hot bands involving nu1, nu2 and nu3 were rotationally analyzed, and spectroscopic constants were obtained. Rotational l-type doubling and l-type resonance, local perturbations, and Fermi resonances were observed in the vibration-rotation bands of both ZnH2 and ZnD2, and equilibrium vibrational frequencies (omega1, omega2 and omega3) were estimated. Using the rotational constants of the 000, 100, 01(1)0 and 001 vibrational levels, the equilibrium rotational constants (B(e)) of 64ZnH2 and 64ZnD2 were determined to be 3.600 269(31) cm(-1) and 1.801 985(25) cm(-1), respectively, and the associated equilibrium bond lengths (r(e)) are 1.524 13(1) angstroms and 1.523 94(1) angstroms, respectively. The difference between the r(e) values of 64ZnH2 and 64ZnD2 is about 0.01%, and is mainly due to the breakdown of the Born-Oppenheimer approximation.     

Liquid-vapor equilibrium of dilute aqueous solutions of ethanol and 2-propanol

An automated vapor pressure apparatus has been used to obtain highly precise values of the total pressure and composition of aqueous solutions of ethanol and of 2-propanol in the water-rich region at 25 and 35°C. From these results, values of the partial pressures and fugacities of the components and osmotic coefficients have been inferred. Interaction virial coefficients derived from the present results are compared with interaction parameters previously reported for alcohol molecules in dilute aqueous solution. A discussion is given of the relative importance of hydrophobic effects and hydrogen-bonding in producing the unusual thermodynamic properties of aqueous alcohol solutions.     

Exchange equilibrium in the H-sulfocationite KU-2 × 8-phenylalanine-histidine system

The equilibrium properties of the joint sorption of phenylalanine and histidine on KU-2 × 8 sulfocationite from mixed solution were studied. The effect of the ratio between the concentrations of the amino acids in the solution on their sorption characteristics was reveled. The coefficients of separation and distribution of the amino acids between the sorbent and solution phases were determined.     

cis-trans-and Intramolecular enol-enolic equilibrium of β-ketoaldehydes

Tautomerism of aromatic β-ketoaldehydes p-XPhCOCH₂CHO ( 1 , X = NMe₂, OMe, Me, H, Br, NO₂), aliphatic β-ketoaldehydes and benzoylacetaldehyde RCOCH₂CHO ( 2 , R = Me, i-Bu, t-Bu, Ph), RCOCH(Me)CHO ( 3 , R = Me, Et, i-Pr) and methyl 2-formylpropionate MeOCOCH(Me)CHO ( 4 ) has been studied by the ¹H NMR technique. In basic solvents both cis- and trans-enol forms of these compounds co-exist. trans-Enolisation, which occurs exclusively at the formyl group, is most favoured in compound ( 4 ) and least favoured in compounds ( 1 ) and ( 2 ). The increasing electron-attracting property of the substituent X in the aromatic β-ketoaldehydes ( 1 ), as well as increasing solvent basicity in the series propanediol-1, 2-carbonate, acetone < dimethylformamide < dimethylacetamide < pyridine, also shifts the equilibrium towards the trans-enol form. The trans-enol form is absent in aprotic solvents of low basicity such as CCl₄, C₂HCl₃ and toluene. The thermodynamic parameters of the cis-trans-enol (C ? T) and cis-enol-enolic (C ? C') equilibria have been estimated from the temperature dependences. The transition from the cis-to the trans-enol form is accompanied by an entropy decrease of about 10 cal mol^?1 degree^?1. Nevertheless the trans-enol form is stabilised due to its lower enthalpy. The cis-trans-enol equilibrium is determined by the relative strength of the intramolecular hydrogen bond in the cis-enol form and the intermolecular hydrogen bonds with basic solvent molecules of the trans-enol form. The enthalpy difference of the two cis-enolic forms does not exceed 1.0 kcal/mol, in rough agreement with the data calculated by the CNDO/2 approximation. Polar solvents favour the hydroxymethyleneketone form (C) for both groups of compounds 2 and 3 . The content of the hydroxymethyleneketone form is about the same within series 2 where R = Me, i-Bu, Ph and is a little higher for the t-Bu derivative. A decrease of temperature only slightly shifts the equilibrium of compounds 1 and 2 to the hydroxymethyleneketone form, while in the case of 2-methyl-β-ketoaldehydes (3) this effect is markedly pronounced.     

Rate coefficients and equilibrium constant for the CH2CHO + O2 reaction system

The kinetics of the CH2CHO + O2 reaction was experimentally studied in two quasi-static reactors and a discharge flow-reactor at temperatures ranging from 298 to 660 K and pressures between 1 mbar and 46 bar with helium as the bath gas. The CH2CHO radicals were produced by the laser-flash photolysis of ethyl vinyl ether at 193 nm and by the reaction F + CH3CHO, respectively. Laser-induced fluorescence excited at 337 or 347.4 nm was used to monitor the CH2CHO concentration. The reaction proceeded via reversible complex formation with subsequent isomerization and fast decomposition: CH2CHO + O2 <= => O2CH2CHO --> HO2CH2CO --> products. The rate coefficients for the first and second steps were determined (k1, k-1, k2) and analyzed by a master equation with specific rate coefficients from the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Molecular and transition-state parameters were obtained from quantum chemical calculations. A third-law analysis led to the following thermodynamic parameters for the first step: Delta(R)S degrees 300K(1) = -144 J K(-1) mol(-1) (1 bar) and Delta(R)H degrees 300K(1) = (-101 +/- 4) kJ mol(-1). From the falloff analysis, the following temperature dependencies for the low- and high-pressure limiting rate coefficients were obtained: k1(0) = 5.14 x 10(-14) exp(210 K/T) cm(-3) s(-1); k1(infinity) = 1.7 x 10(-12) exp(-520 K/T) cm(-3) s(-1); and k2(infinity) = 1.3 x 10(12) exp[-(82 +/- 4) kJ mol(-1)/RT] s(-1). Readily applicable analytical representations for the pressure and temperature dependence of k1 were derived to be used in kinetic modeling.     

On the mechanism of proton transfer in the 2-hydroxypyridine α 2-pyridone tautomeric equilibrium

The saddle point for the proton transfer involved in the equilibrium 2-hydroxypyridine α 2-pyridone has been calculated in a 3-21G basis to be 206 kJ mol^?1 above the lactim form, for a unimolecular mechanism. This barrier is estimated to be reduced to 46 kJ mol^?1 in the self-associated dimer.     

O2/CO2循环燃烧方式下矿物元素蒸发特性的热力学研究

运用热力学平衡计算方法（F*A*C*T）对O2/CO2循环燃烧方式下矿物元素的蒸发特性进行了研究，并采用高温热天平进行了实验验证。结果表明，各矿物元素蒸发的主要形态分别是Na(K)Cl(g), FeO(g)和SiO(g)，反应气氛和温度对矿物元素蒸发形态和蒸发率有明显影响。O2/CO2循环燃烧方式下矿物元素的蒸发率均小于常规空气燃烧，尤其是还原性气氛中，当温度为2400 K时，常规空气燃烧矿物总蒸发率为9.65％，而O2/CO2循环燃烧方式矿物元素总蒸发率仅为4.46％。实验值比计算值略高，但主要趋势相同。