摘要:

High resolution (0.004cm-1instrumental bandwidth) interferometric Fourier transform infrared spectra of14ND3were obtained on a BOMEM DA002 spectrometer under essentially Doppler limited conditions. An analysis is reported of the ND3stretching fundamentals with band centres at [EQUATION]10(s←a) = (2420.056 ± 0.001)cm−1, [EQUATION]10(a←s) = (2420.650 ± 0.001)cm−1, [EQUATION]30(a←a) = (2563.8840 ± 0:0005)cm−1and [EQUATION]30(s←s) = (2563.9161 ± 0.0005)cm−1, with inversion tunnelling splittings Δ[EQUATION]1= 0.5412cm−1and Δ[EQUATION]3= 0.0209cm−1in the vibrationally excited levels. About 50 parameters of the effective Hamiltonian for this band system could be determined accurately. Assignments were established with certainty by means of ground state combination differences. The results are important for and are discussed in relation to the mode selective inhibition and promotion of inversion at the nitrogen atom by exciting ND stretching vibrations, and treatments of isotope e? ects on inversion of ammonia by means of effective Hamiltonians and true molecular Hamiltonians on high dimensional potential hypersurfaces.

ISSN:0026-8976    

DOI:10.1080/00268970050025457

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Accurate SCF and MP2 quartic property hypersurfaces have been computed for the energy, quadrupole moment and polarizability tensor of ethylene to obtain zero-point vibrational corrections to the properties. Coupled with accurate electrical properties computed at a high level correlatedregeometry, using a range of correlated methods, especially BD and BD(T), along with a number of purpose-built polarized basis sets, definitive estimates have been made of these properties that incorporate the effects of vibrational averaging. The effect of deuterium substitution on the properties was investigated, and the frequency dependence of the polarizability tensor was studied also. Careful attention has been paid to a critical comparison between these theoretical estimates and experimental measurements, and agreement between the two is shown to be exceptionally good. In particular, it is possible to resolve the disagreement between recent theoretical calculations and experimental measurements of the Cotton–Mouton constant. The results focus attention on both the general utility of the present method, and the necessity to allow for the effects of zero-point vibrational averaging when comparing theory with experiment, or even when comparing different theoretical results with one another using experiment as a benchmark.

ISSN:0026-8976    

DOI:10.1080/00268970050025466

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

SCF quartic property hypersurfaces have been computed for the energy, quadrupole moment and polarizability tensor of ethane via finite differences of analytical derivatives to obtain zeropoint vibrational corrections to the properties. Coupled with accurate electrical properties computed at a correlatedregeometry, using a range of correlated methods, especially BD and BD(T), excellent estimates of these properties have been obtained that incorporate the effects of vibrational averaging. The effect of deuterium substitution on the properties has been investigated, including the first known theoretical prediction of the dipole moment of CH3CD3, and the frequency dependence of the polarizability tensor and Rayleigh depolarization ratio have been examined. Careful attention has been paid to a critical comparison between these theoretical estimates and experimental measurements. Although the vibrational corrections are limited to SCF theory, and basis sets not as extensive as used in some studies of this kind, nevertheless the results can be compared quantitatively with experiment, and the agreement is found to be excellent. The results underline the necessity to allow for the effects of zero-point vibrational averaging when comparing theory with experiment, and suggest a viable approach for studies on larger molecules.

ISSN:0026-8976    

DOI:10.1080/00268970050025475

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Based on group theory and atomic and molecular reactive statics (AMRS), the ground state X3Σ−and excited state1Σ+of UO and their reasonable dissociation limits are derived successfully. Using the MP2 method with the relativistic e? ective core potential and valence electron basis set (5s4p3d4f)/[3s3p2d2f] for the U atom and basis set 6-311G* for the O atom, the present work has calculated the potential energy curves for the ground state Χ3Σ−and excited state1Σ+of UO. The equilibrium distance and dissociation energy are 0.1833 nm and 6.9241 eV for the Χ3Σ−state, and 0.1825 nm and 8.8756eV for the1Σ+state. Spectroscopic data are derived for the first time.

ISSN:0026-8976    

DOI:10.1080/00268970050025484

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Bromine oxides are of significant interest due to their importance in atmospheric chemistry. Density functional theory (DFT) methods have been used in conjunction with a DZP++ (double-ζ plus polarization with diffuse functions) basis set to study the molecular geometries and total energies of BrOnand BrO-n(n= 1-4). The adiabatic electron affinity (EAad), the vertical electron affinity (EAvert) of the bromine oxide and the vertical detachment energy (VDE) of each anion are reported. Harmonic vibrational frequencies and zero point energies are also reported. Five different DFT methods were employed for comparison. Among these, the BHLYP method predicts the geometries and the vibrational frequencies in best agreement with available experimental data, while the the other methods do better in predicting the limited number of energetic quantities determined observationally. The predicted adiabatic electron affinities are 2.38 eV (BrO, experiment 2.35 eV), 2.36 eV (BrO2), 3.35 eV (BrOO), 4.32 eV (BrO3), 2.91 eV (BrOOO) and 5.28 eV (BrO4). The electronic ground state of BrOO-is a triplet (3A") state. Predicted Br–;O bond distances range from 1.61 (BrO3) to more than 2 Å for Br...O2for the neutral molecules; and from 1.61 Å for BrO-to 1.82 Å for BrO-to more than 2 Å for Br-...O3among the anions. The BrOO isomer (Cssymmetry) is predicted to lie 17–18 kcal mol-1below the C2vsymmetry OBrO structure. The asymmetric3A"anion BrOO-analogously lies below OBrO-, in this case by 40–41 kcalmol-1. BrOOO (Cssymmetry) is predicted to lie 42-45 kcalmol-1 below the symmetric C3vBrO structure. Finally the asymmetric BrOOO- anion (C1symmetry) is predicted to lie 10-13kcal mol-1 below symmetric C3vBrO-3.

ISSN:0026-8976    

DOI:10.1080/00268970050025493

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A theoretical study has been made of the dependence of the1J(HD) coupling in HD on the interatomic distanceRin the presence of a static uniform magnetic fieldB0. The behaviour of all coupling terms arising from Ramsey's magnetic electron-nucleus interactions, Fermicontact (FC), spin-dipolar (SD) and paramagnetic (PSO) and diamagnetic (DSO) spin-orbital interactions is analysed qualitatively for largeR. It is concluded that the PSO, DSO and SD terms become negligibly small asRincreases. Detailed calculations were carried out for the FC term following two different approaches: detailed full CI calculations within a non-perturbative approach; and explicit diagonalization of the Hamiltonian operator restricted to the subspace spanned by the1Σ+;gand the3Σ+;ustates. Within the approximations considered, the FC term of1J(HD) is found to be independent ofB0and to increase by several orders of magnitude, in agreement with previous results by Bacskay, G. B., 1995,Chem. Phys. Lett.,242, 507, until a critical distanceR(B0) is reached, beyond which it almost vanishes. The quenching of the coupling atR(B0) is due to the splitting of the3Σ+;ustate in the presence of the fieldB0. The stronger the field the shorter isR(B0).

ISSN:0026-8976    

DOI:10.1080/00268970050025501

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The Lennard-Jones attractive and repulsive contributions of intermolecular forces (as separated in the Weeks-Chandler-Andersen (WCA) theory) to the pressure and chemical potential of coexisting vapour and liquid phases are obtained by using an equation of state recently proposed by us. Some comments are given about the computer simulation results obtained by Plackov and Sadus (1997,Fluid Phase Equilib.,134, 77) using the McQuarrie-Katz separation of the intermolecular potential.

ISSN:0026-8976    

DOI:10.1080/00268970050025510

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor