摘要:

The Fourier transform infrared spectrum of C2D6(FWHM ≈ 0⋅0030 cm-1) has been investigated in the region of the ν6(A2u) and ν8(Eu) fundamentals, from 960 cm-1to 1180 cm-1. A strongx,yCoriolis interaction between ν6and ν8, withKlevel crossing, generates large displacements of the rotational components of both vibrational states, tuning them to additional local resonances in several spectral regions. Beyondlresonances with Δl= ±2, Δk= ∓ 1 within ν8, azCoriolis-type resonance of ν8+ ν4(A1u) and ν6occurs atK⩽6, and anx,yCoriolis-type resonance of ν8(- l, K-1) and ν3+ ν4(K) occurs atK= 7 and 8. A further coupling of ν8(+ l,K - 2) and ν3+ ν4(K) has been observed as well. The vibration-rotation constants of ν6, ν8and ν3+ ν4, and several interaction parameters, have been determined by the least-squares fit of the available data, with an overall standard deviation σ = 4. x 6 10-4cm-1in the fit of 1661 observed transition waveνmbers. A torsional splitting is observed only in the level ν8(-l,K= 8,J= 20), resonant with 2ν4+ ν9(-l,K= 11,J= 20) in which two torsional quanta ν4are excited. Many otherJcomponents of ν8(-l,K= 8) are broadened by this interaction. Rules on the symmetries of the allowed perturbing operators and of their torsional components inethane-like molecules are determined. In the high-barrier limit, we find it useful to factorize the torsional operators into functions of torsional coordinate and momentum operators and trigonometric functions of the torsional angle. Application of these rules to the coupling operators active in this spectrum is made.

ISSN:0026-8976    

DOI:10.1080/002689796173624

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Molecular dynamics simulations are performed on a periodic arrangement of 256 adamantane molecules interacting via a pairwise additive atom-atom potential. The low temperature phase is reproduced successfully. The transition from a tetragonal to a cubic unit cell is found between 380 K and 420 K with a first-order loss of long-range orientational order observed between 410 K and 420 K. A study of correlation between the orientations of neighbouring molecules shows that short-range orientational order persists dynamically above the phase transition, suggesting that in a real system the plastic phase is never truly disordered. On cooling,the reverse transitionfrom plastic to ordered tetragonal phase is found to occur at 340 K.

ISSN:0026-8976    

DOI:10.1080/002689796173633

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The exclusion of solvent from solute clusters provides an additional contribution to aggregation. A derivation of the well known equations for equilibrium aggregation is given, and an explicit expression for the solvent-exclusion effect is obtained for linear aggregates. The analytical result is shown to be in qualitative agreement with recent Monte Carlo simulations of model discotic solutions, which found a concentration dependence of the equilibrium constant. The latter behaviour is argued to stem from a peculiarity in the simulation protocol, namely that the total pressure was fixed, which means that the solvent pressure must increase due to the decreased osmotic pressure at lower solute concentrations. Finite size effects are shown to have a small effect in the simulations. Two further contributions to the observed increased aggregation at low temperatures and concentrations are analysed. For intracolumn aggregation it is argued that it is more appropriate to use the length of the column rather than the volume of the system in the definition of the aggregation constant. The possibility is raised that the increased aggregation seen at low solute concentrations could manifest a type of phase transition, either to one-dimensional columns, driven by feedback between the solvent pressure and the number of aggregates, or to a solvent-depleted globule.

ISSN:0026-8976    

DOI:10.1080/002689796173642

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Molecular potential curves for many excited states of the Na2molecule are presently available for a wide range of internuclear distances, in the framework of a two-electron model potential method. The energies were obtained through an extensive configuration interaction procedure using Na+2orbitals, and the quality of the results was controlled by the accuracy of the wavefunctions of the molecular ion. In this work, computed potential energy curves and transition moments are presented for the ground, excited and Rydberg Σ, Π and Δ states of Na+2up to the Na(7i) + Na+ dissociation limit. The accuracy of the first excited states is checked by comparing with available experimental data. Figures are presented for the molecular quantum defects as a function of internuclear distance, showing an interesting pattern of pseudo-crossings.

ISSN:0026-8976    

DOI:10.1080/002689796173651

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The spectroscopic characteristics of the polarization of129Xe nuclei in Xe gas by spin exchange with optically pumped Rb atoms is examined in high magnetic field. The high field Zeeman effect provides the spectral dispersion necessary to separate the effects of different light polarizations and incident wavelengths on the pumping cycle. Indirect detection of the D1line in Rb using129Xe nuclear magnetic resonance in combination with direct optical detection indicates that conventional container construction significantly decreases the efficiency of the129Xe polarization. The decreased pumping efficiency is due to randomly polarized photons that can be eliminated by using containers with good optical quality windows. Study of these effects is facilitated by the large Zeeman shifts obtained with multi-tesla fields which resolve the D1multiplet structure even in the presence of the significant pressure-broadening incells with typical gas pressures of 0⋅1-1 atm.

ISSN:0026-8976    

DOI:10.1080/002689796173660

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Ab initio multireference configuration interaction calculations of the static dipole and quadrupole moments of CO2and N2as functions of the internuclear distances have been carried out using the multireference single and double excitation configuration interaction method (MRDCI). The results are compared with the outcome of Hartree-Fock calculations and help shed light on the effect of such moments on the low energy interaction of these molecules during scattering processes, and hence on their influence on the threshold behaviour of the inelastic cross-sections involving vibrational degrees of freedom.

ISSN:0026-8976    

DOI:10.1080/002689796173679

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A method is described for relating the energy level correlation diagrams introduced by Renner to the angular momentum 'sawtooth' correlation diagrams constructed by Jungen and Merer. In order to do this new spin-orbit coupling versions of the diagrams are introduced for the strictly linear and bent-linear behaviour, and a version of the linear 'sawtooth' diagram is constructed. Finally the effects of vibrational resonances are introduced to modify the interference effects seen in the 'sawtooth' diagrams. The diagrams are constructed using an extension of the calculation method first introduced by Barrow, Dixon and Duxbury to allow <Lz> to be obtained.

ISSN:0026-8976    

DOI:10.1080/002689796173688

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Pair contributions to the polarizability of argon are calculatedab initio. A large basis set, including diffuse orbitals, is employed. Correlation effects are included using second-order Møller–Plesset perturbation theory. The results are used to compute moments of the polarized and depolarized collision-induced light scattering spectra, and second dielectric, refractivity and Kerr virial coefficients. Some discrepancies with experiment are found, but overall the agreement is satisfactory.

ISSN:0026-8976    

DOI:10.1080/002689796173697

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We study the stability, energetics and dynamics of small model hydrogen fluoride clusters (HF)nusing isoergic molecular dynamics simulations. The largest Lyapunov exponent is computed over the energy range when the clusters melt, and is found to be more useful in defining the onset of melting than Lindemann's index. We also examine the power spectrum of potential energy fluctuations of clusters in the liquid state, which show 1/fdependence over a smaller frequency range than rare-gas clusters of comparable size.

ISSN:0026-8976    

DOI:10.1080/002689796173705

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The melting of structure I methane clathrate hydrate has been investigated usingNVTmolecular dynamics simulations, for a number of potential energy models for water and methane. The equilibrated hydrate crystal has been heated carefully from 270 K, in steps of 5 K, until a well defined phase instability appears. At a density of 0⋅92 g cm-3, an upper bound for the mechanical stability of the methane hydrate lattice over a timescale of 11 nanoseconds is 330 K. Finite size effects have been investigated by simulating systems of 1 and 8 units cells of methane hydrate. The properties of the melted system upon cooling are examined.

ISSN:0026-8976    

DOI:10.1080/002689796173714

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor