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141.
142.
The Fourier transform gas-phase infrared spectra of the v 10 and v 11 bands of natural CH2=CHCl have been measured with a resolution of 0.005 cm?1 in the frequency range 820–1010 cm?1. These vibrations of symmetry species A″ give rise to c-type bands and the transitions observed are characterized by δK a = ±1 and δK c = 0, ±2. Both J and K structures have been resolved in different subbranches and about 1800 (J ≤ 64, K a ≤ 13) and 2800 (J ≤ 72, K a ≤ 14) transitions for the v 10 and v 11 fundamentals, respectively, have been identified for the 35Cl isotopomer. Combined analysis of the assigned data with the available ground state constants allowed the determination of the band origins, rotational and centrifugal distortion parameters for the v 10 = 1 and v 11 = 1 excited states of CH2=CH35Cl isotopic species. The molecular constants obtained account for slight perturbations in the v 10 vibrational level. 相似文献
143.
A method to obtain (approximate) analytical expressions for the radial distribution functions in a multicomponent mixture of additive hard spheres that was recently introduced is used to obtain the direct correlation functions and bridge functions in these systems. This method, which yields results practically equivalent to the generalized mean spherical approximation and includes thermodynamic consistency, is an alternative to the usual integral equation approaches and requires as input only the contact values of the radial distribution functions and the isothermal compressibility. Calculations of the bridge functions for a binary mixture using the Boublik-Mansoori-Carnahan-Starling-Leland equation of state are compared to parallel results obtained from the solution of the Percus-Yevick equation. We find that the conjecture recently proposed by Guzman and del Rio (1998, 98, Molec. Phys., 95, 645), stating that the zeros of the bridge functions occur approximately at the same value of the shifted distance for all pairs of interactions, is at odds with our results. Moreover, in the case of disparate sizes, even the Percus-Yevick bridge functions do not have this property. It is also found that the bridge functions are not necessarily non-positive. 相似文献
144.
A multi-reference configuration interaction (MRCI) method is described, which is devised for the calculation of interaction energies of van der Waals complexes and applied to calculating the HeNe potential energy curve. The MRCI calculations make use of a generalized Pople-correction in order to account for the lack of size consistency. The orbital space is partitioned into three subspaces: the first active space (AS1), which contains the strongly occupied orbitals; the second active space (AS2), which contains the main intra-correlating orbitals; and the external space (ES). It is shown that, to keep the error below ± 0.2 K in the excitation scheme and the active orbital space it is sufficient to include only σ-orbitals in AS2 and to use an excitation scheme (labelled Qq-MRCI) that encompasses only up to quadruply excited configurations. The final active orbital space (AS2) turned out to be 2s(He), 2pσ(He), 3s(Ne), 3σ(Ne) and 3dσ(Ne). Other MRCI variants, in which most or all quadruply excited configurations were deleted from the CI expansion (Qt- and Tt-MRCI), were found to be inadequate. Using the Qq-MRCI scheme together with a 197-orbital ‘interaction optimized’ basis set (IO197), the MRCI interaction energy at R = 5.7 a0 was calculated to be -21.12K. The corresponding values at the MP4 and CCSD(T) levels of theory are -20.06 K and -20.99 K, respectively, indicating that the MP4 method is inappropriate for highly accurate calculations on this system. Fitting the calculated data using a generalized Morse function, including an additional C6/R6 term to account for a correct long-range behaviour of the potential, the MRCI well depth was calculated to be -21.16K at Req = 5.73a 0. The MRCI and CCSD(T) potentials have the same quality and are found to be in good agreement with the Hartree-Fock dispersion (HFD-B) potential of Keil, M., Danielson, L. J., and Dunlop, P. J., 1991, J. Chem. Phys., 94, 296. It is concluded that, for basis IO197, the CCSD(T) method is sufficiently accurate for calculating the HeNe interaction. To recover the small, missing contributions (a few tenths of a Kelvin), MRCI should be used. 相似文献
145.
GABRELLIA CAPECCHI DARIO DE FAZIO GAIA GROSSI LEONARDO PERONCELLI NASEEM RAHMAN 《Molecular physics》2013,111(5):443-453
Adiabatic energy levels for two prototypical reactions, F + H2 → HF + H and He + H+ 2 → HeH+ + H, are analysed by means of statistical tests. These levels result from quantum mechanical calculations of dynamics based on the hyperspherical approach, and are given as a function of the total inertia of the system measured by the hyperradius ρ The nearest neighbour level spacing distributions of Brody and of Berry and Robnik, the spectral rigidity δ3 of Dyson and Mehta and the correlation coefficient are reported, together with other properties, such as variance, skewness and kurtosis of the distributions. Trends are studied as a function of ρ, proposed as a natural control variable. For low ρ, which correspond to the transition state, evidence is found of Wigner-like behaviour, which is interpreted as the signature of quantum chaos. On the passage of the systems through intermediate ρ a mixture of Wigner- and Poisson-like behaviour emerges. The situation for high ρ where reactants and products of the reactions are well separated, is characterized by a tendency towards regular Poisson-like behaviour. A comparison between the two investigated systems shows that the chaotic regime in the transition state region is more pronounced for the He reaction, which proceeds through a deep well and whose dynamics are characterized by a rich resonance pattern. 相似文献
146.
E. SICILIA G. DE LUCA S. CHIODO N. RUSSO P. CALAMINICI A. M. KOSTER 《Molecular physics》2013,111(12):1039-1051
Density functional calculations of the electric field gradient tensor at the nitrogen nucleus in 13 test molecules, containing 14 nitrogen sites, have been performed using the linear combination of Gaussian-type orbital Kohn-Sham density functional theory (LCGTO-KSDFT) approach. Local and gradient corrected functionals were used for all-electron calculations. All the molecular structures were optimized at their respective levels of theory with extended basis sets. Calibrated 14N nuclear quadrupole moments were obtained through a fitting procedure between calculated electric field gradients and experimental nuclear quadrupole coupling constants of the test set of molecules for each basis set and functional considered. With these calibrated 14N nuclear quadrupole moments, the nuclear quadrupole coupling constants of the following selected systems were determined: fluoromethylisonitrile, pyridine, pyrrole, imadazole, pyrazole, 1,8-bis(dimethyl-amino)naphthalene, cyclotetramethylenetetranitramine, cocaine and heroin. 相似文献
147.
Raphael Kruse 《BIT Numerical Mathematics》2012,52(1):109-140
The focus of this article lies on the bistability of multistep methods applied to stochastic ordinary differential equations.
Here bistability is understood in the sense of F. Stummel and leads to two-sided estimates of the strong error of convergence.
It is shown that bistability can be characterized by Dahlquist’s strong root condition. The main ingredient of the stability
analysis is a stochastic version of Spijker’s norm. 相似文献
148.
149.
Jennifer S. Teichert Florian M. Kruse Oliver Trapp 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(29):10049-10052
It is assumed that RNA played a key role in the origin of life, and the transition to more complex but more stable DNA for continuous information storage and replication requires the development of a ribonucleotide reductase to obtain the deoxyribonucleotides from ribonucleotides. This step, as well as an alternative path from abiotic molecules to DNA‐based life is completely unknown. Shown here is the formation of deoxyribonucleosides under relevant prebiotic conditions in water in high regio‐ and stereoselectivity, from all canonical purine and pyrimidine bases, by condensation with acetaldehyde and sugar‐forming precursors. Thus, a continuous path to deoxyribonucleosides, starting from simple, prebiotically available molecules has been discovered. Furthermore, the deoxyapionucleosides (DApiNA) were identified as a potential DNA progenitor. The results suggest that the DNA world evolved much earlier than previously assumed. 相似文献
150.
Bob D. Guenther Paul W. Kruse 《International Journal of Infrared and Millimeter Waves》1986,7(8):1091-1109
A brief report on the results of a workshop concerning submillimeter wave detection held September 34, 1985. 相似文献