ISSN:0026-8976    

DOI:10.1080/00268970009483365

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper draws attention to the advantages that would be obtained by adopting a new convention for the sign ofgfactors that would make thegfactor for electron spin a negative quantity (g≈ −2), rather than a positive quantity as generally adopted at present. The editors are aware that the proposal made in this paper concerning the conventional sign of thegfactor for electron spin will be seen by some readers as controversial. We have nonetheless agreed to publish this paper in the hope that it will stimulate discussion. The editors would welcome comments on this proposal in the form of short papers, which they will then be happy to consider for publication together at a later date.

ISSN:0026-8976    

DOI:10.1080/00268970009483366

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Gibbs ensemble Monte Carlo simulations of neon and argon have been performed with pair potentials taken from literature as well as with newab initiopotentials from just above the triple point to close to the critical point. The densities of the coexisting phases, their pair correlation functions, the vapour pressure and the enthalpy and entropy of vaporization have been calculated. The influence of the potential choice and of the addition of the Axilrod-Teller (AT) three-body potential on the above mentioned properties have been investigated. It turns out that an accurateab initiotwo-body potential in connection with the AT potential yields very good results for thermodynamic properties of phase equilibria.

ISSN:0026-8976    

DOI:10.1080/00268970009483367

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A low-field theory of nuclear spin relaxation in paramagnetic systems is developed, resulting in closed analytical expressions. We use the same approach as Westlund, who derived the low-field expression in the case ofS= 1 for a rhombic static zero-field splitting (ZFS). In the present paper we extend the derivation to includeS= 3/2, 2, 5/2, 3 and 7/2 for the case of an axial static ZFS, whereas onlyS= 3/2 is considered for a rhombic static ZFS. The slow-motion theory of nuclear spin relaxation in paramagnetic systems was recently generalized to account for arbitrary electron spinSand the calculations showed some unexpected features. Thus, one objective of the derivation of closed analytical low-field expressions is to provide a framework for physical explanation of slow-motion calculations. We find that the results of the low-field theory are, indeed, in good agreement with the slow-motion calculations in the case of slowly rotating complexes (e.g. metalloproteins). It is evident that the static ZFS influences the electron spin relaxation more markedly for higher spin systems than for S = 1. In fact, systems ofS= 2 andS= 3 show more similarities in the electron spin-lattice relaxation properties to half-integer spin systems than toS= 1 in the case of an axially symmetric static ZFS. These findings show the shortcomings of using Bloembergen-Morgan theory for the description of electron spin relaxation in the low-field limit and provide improved tools for the interpretation of experimental variable-field relaxation data.

ISSN:0026-8976    

DOI:10.1080/00268970009483368

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The electron density distribution ρ(r) generated by a DFT calculation was systematically studied by comparison with a series of reference densities obtained by wavefunction theory (WFT) methods that cover typical electron correlation effects. As a sensitive indicator for correlation effects the dipole moment of the CO molecule was used. The analysis reveals that typical LDA and GGA exchange functional already simulate effects that are actually reminiscent of pair and three-electron correlation effects covered by MP2, MP4, and CCSD(T) in WFT. Correlation functionals contract the density towards the bond and the valence region thus taking negative charge out of the van der Waals region. It is shown that these improvements are relevant for the description of van der Waals interactions. Similar to certain correlated single-determinant WFT methods, BLYP and other GGA functionals underestimate ionic terms needed for a correct description of polar bonds. This is compensated for in hybrid functionals by mixing in HF exchange. The balanced mixing of local and non-local exchange and correlation effects leads to the correct description of polar bonds as in the B3LYP description of the CO molecule. The density obtained with B3LYP is closer to CCSD and CCSD(T) than to MP2 or MP4, which indicates that the B3LYP hybrid functional mimics those pair and three-electron correlation effects, which in WFT are only covered by coupled cluster methods.

ISSN:0026-8976    

DOI:10.1080/00268970009483369

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In the present study, resolved OD EPR spectra were measured for the 431, 423, and 413levels of the Ã1Au00vibronic state. Values of the fine and hyperfine constants were estimated from an analysis of these spectra for the triplet rotational levels, coupled by the intramolecular interactions with the singlet levels studied. It was shown that the microwave power dependence differs significantly for different lines of the OD EPR spectrum. This difference can be explained by a model where the microwave field saturation effect is observed for different OD EPR lines at different power values of the microwave field. The decay profile can be fitted by a biexponential function in the presence of both magnetic and microwave fields. The observed data were analysed using the electron and nuclear spin decoupling mechanism in the limit of low level density.

ISSN:0026-8976    

DOI:10.1080/00268970009483370

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The rotation-vibration band of the weakly bound OCS-CO complex which corresponds to the carbon monoxide CO vibrational mode has been detected using a pulsed supersonic slit-jet expansion and a tunable infrared diode laser probe. The band was found to have a parallel (δKa= 0) structure, in good agreement with previous determinations of the structure of the complex. Its rotational structure appeared to be affected by numerous small (∼ 0.01 cm−1) perturbations in the upper state which probably are due to interactions with bound levels of a lower lying vibrational state of the complex. The band origin is located with a relatively small shift of + 1.23 cm−1from that of the free CO molecule.

ISSN:0026-8976    

DOI:10.1080/00268970009483371

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor