1,721,018 research outputs found
An improved anharmonic force field of difluoromethanimine, F2C=NH
No full textThe anharmonic force field of difluoromethanimine, F2C=NH. has been reinvestigated theoretically using a coupled-cluster singles and doubles approach, augmented for structural optimization and harmonic force field by a contribution of connected triple excitations, CCSD(T). The cubic and quartic force constants have been obtained by numerical derivatives computed from analytical quadratic force constants calculated by second-order Moller-Plesset perturbation theory, MP2. The quadratic force constants and the equilibrium structure of F2C=NH have then been scaled by a global least-squares fitting procedure to the spectroscopic data and parameters experimentally determined for this molecule. This force field, obtained in the internal coordinates space and therefore valid for all isotopmers of difluoromethanimine. yields a complete set of spectroscopic molecular constants providing a critical assessment of the experimental rotational and centrifugal distortion constants fundamentals. overtones, and combination bands determined so far for F2C=NH. In addition, the final force field can he used to make predictions of all important vibrational and rotational parameters which should he accurate and useful for new spectroscopic investigations, (C) 2002 Elsevier Science (USA)
Esercizi di Chimica Fisica
No full textEsercizi svolti di termodinamica, termochimica, elettrochimica e cinetica chimica
Acid–base logarithmic diagrams with computer algebra systems
No full textThe pH of any polyprotic weak and strong acid (or base) can be calculated employing the logarithmic concentration diagram. The aim of this text is to introduce a joint approach of algebraic, as used in textbook, and graphical method. The logarithmic diagrams provide an easy insight into the acid–base systems. The mathematical complexities are overtaken using a Computer Algebra System program, which is also exploited to draw the dia- grams. Examples of the use of the program are given together with the code employed
The energetics and structural properties of HCNN and HNCN and their related cations and anions from ab initio calculations
No full text
Anharmonic force fields of bromofluoromethane
No full textHigh-level ab initio calculations with relatively large basis sets are reported for bromofluoromethane, CH2BrF. Correlated harmonic and anharmonic force constants are obtained from several levels of theory including second-order Moller-Plesset perturbation and coupled cluster CCSD(T). Density functional theory and to be more precise the B3LYP functional, is also employed. Results are used to determine a number of anharmonic molecular properties, including vibration-rotation interaction constants, vibrational anharmonicity constants, fundamental vibrational frequencies, sextic centrifugal distortion constants and rotational constants which include zero-point corrections. Good agreement with available experimental data is found combining coupled cluster CCSD(T) optimized geometry and harmonic force field with cubic and quartic force constants obtained at MP2 level of theory, a cost-effective computation in terms of time. Moreover, transformations of the force. elds in mass-independent internal coordinate force constants suitable for other isotopologues of CH2BrF are also investigated
Exploring the reaction of iodine with α-diazo esters
No full textIn this paper we describe the unprecedented reaction between alpha-diazo esters 1 and iodine. The reaction, carried out in the presence of aqueous NaHCO3, afforded the Z-isomer of the corresponding unsaturated-2-iodo ester 8. The configuration of compounds 8 was determined using the 3J(C-H) coupling between carbonyl carbon atom and alkene proton. Mechanistic considerations accounting for the observed phenomena and including quantum chemical calculations are proposed
High-resolution analysis of the nu(4) absorption band of (CH2BrF)-Br-79
No full textThe gas-phase infrared spectrum of the fundamental band of CH 79BrF was recorded in the 1010 –1116 cm1 wavenumber 42
79
region using a TDL spectrometer. In this first high-resolution investigation of the synthesized
Br isotopic form, more than
10 200 transitions of this a/b-hybrid band centered at 1068.5385 cm
1
were assigned and, using the Watson’s A-reduced
Hamiltonian in the Ir-representation, a reliable set of molecular constants for the excited state v 1 was determined. From
4
ground state combination differences having rotational quantum numbers J and Ka up to 97 and 21, respectively, improved and extended ground state rotational and centrifugal distortion constants were calculated as well. Comparison between the observed and calculated band intensities in appropriate regions of the spectrum gave an estimate of the transition dipole- moment ratio along the a and b axes as a/b 2.0 0.2, in agreement with the predicted theoretical value of 1.99
The anharmonic force field of (cis)-1-chloro-2-fluoroethylene
No full textA comprehensive anharmonic vibrational analysis of cis-1-chloro-2-fluoroethylene and its isotopomers has been performed on the basis of a complete ab initio quartic force field constructed by means of second-order Moller-Plesset perturbation theory (MP2) and the coupled-cluster singles and doubles approach, augmented for structural optimization and harmonic force field by a contribution of connected triple excitations (CCSD(T)). The theoretical force field was scaled by global least-squares fitting to all spectroscopic data and parameters experimentally determined for this molecule. This final force field, employing standard perturbation theory, yields a complete set of spectroscopic molecular constants providing a critical assessment of experimental rotational and centrifugal distortion constants, fundamentals, overtones, and combination bands determined over many years. Effects of Fermi and Darling-Dennison resonances were included by matrix diagonalization
The reaction between ethanedioyl (oxalyl) dihalides and Ag2C2O4: a route to Staudinger's elusive ethanedioic (oxalic) acid anhydride
No full textEthanedioic (oxalic) acid anhydride 1 was prepared for the first time and its dimeric cyclic nature established by spectroscopic and chemical evidence. The strong instability of 2-chloro-2-oxoethanoic acid 3 was incidentally observed. The chemical behaviour of 1 with MeOH and CH2N2 was investigated
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