摘要:

A description is given of highly excited rotational and/or vibrational states of molecules in terms of localized vibrations or local modes. It is a didactic paper, making an attempt to unify the ideas and notations of the key publications on the subject in a manner that treats the vibrational and rotational motions equally and that demonstrates the importance of molecular symmetry. Emphasis is put on explaining the intimate relationship between local mode vibrations and the formation of both vibrational and rovibrational energy level clusters. In rovibrational cluster states, a molecule can sustain localized vibrations for very many vibrational periods, even with low vibrational excitation. Local mode behaviour is induced by both vibrational and rotational excitation. An important application of local mode theory is the derivation of relations between the effective rotation-vibration parameters for highly excited vibrational states of a molecule. It is shown here, using the H280Se molecule as example, that such relations are valid only for certain forms of the effective rotation-vibration Hamiltonian. Thus caution is required when the results of fittings to spectral data are compared with local mode theory.

ISSN:0026-8976    

DOI:10.1080/002689700413532

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The structure of a starlike molecule (SLM) fluid with four arms of different length is studied by applying the associative Percus–Yevick integral equation (IE) theory and canonical Monte Carlo (MC) simulations. In the IE study the SLM fluid is modelled by a fluid of hard spheres with four associative sites on each sphere while the MC has been performed for a freely-joined tangent hard sphere fluid. The total radial distribution functions have been calculated in both approaches for different volume fraction regimes and different arm lengths. It is shown that the associative IE theory predicts the structure of SLM fluid best for relatively long arms and at high densities. Additionally, the dependence of the SLM centre–centre correlations on the functionality and fluid particle density has been analysed using the MC results.

ISSN:0026-8976    

DOI:10.1080/002689700413541

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Wertheim's theory is used to determine the critical properties of chains formed bymtangent spheres interacting through the pair potentialu(r). It is shown that within Wertheim's theory the critical temperature and compressibility factor reach a finite non-zero value for infinitely long chains, whereas the critical density and pressure vanish asm-1.5. Analysing the zero density limit of Wertheim's equation or state for chains it is found that the critical temperature of the infinitely long chain can be obtained by solving a simple equation which involves the second virial coefficient of the reference monomer fluid and the second virial coefficient between a monomer and a dimer. According to Wertheim's theory, the critical temperature of an infinitely long chain (i.e. theΘtemperature) corresponds to the temperature where the second virial coefficient of the monomer is equal to 2/3 of the second virial coefficient between a monomer and dimer. This is a simple and useful result. By computing the second virial coefficient of the monomer and that between a monomer and a dimer, we have determined theΘtemperature that follows from Wertheim's theory for several kinds of chains. In particular, we have evaluatedΘfor chains made up of monomer units interacting through the Lennard-Jones potential, the square well potential and the Yukawa potential. For the square well potential, theΘtemperature that follows from Wertheim's theory is given by a simple analytical expression. It is found that the ratio ofΘto the Boyle and critical temperatures of the monomer decreases with the range of the potential.

ISSN:0026-8976    

DOI:10.1080/002689700413550

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We develop a method for treating an interface between coexisting fluid phases to study its structure and thermodynamical properties. Our approach includes calculated correlation functions. Approximations are intrinsically optimized. The method is successfully applied to the liquid vapour surface of a Lennard-Jones fluid, to the liquid–liquid interface of a demixing system and to the surface of a Stockmayer liquid towards vapour. In all cases we compare our results to simulations. The agreement with simulation results demonstrates the reliability of our approximations and shows that the technique we applied provides a powerful and robust method for studying inhomogeneous fluids.

ISSN:0026-8976    

DOI:10.1080/002689700413569

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Resonance Raman spectra have been obtained at four excitation wavelengths within the A-band ligand to metal charge transfer (LMCT) absorption oftrans-dichloro-bis(tricyclo-hexylphosphine) palladium(II) and a resonance Raman intensity analysis was done to elucidate the excited state structure relative to the ground state. Comparison of the present results fortrans-dichlorobis(tricyclohexylphosphine) palladium(II) with those previously reported fortrans-dichlorobis(triphenylphosphine) palladium(II) shows that the phenyl ligand appears to primarily affect the adjacent P-C vibrational reorganizational energy and does not significantly perturb the Pd-Cl or Pd-P vibrational reorganizational energies.

ISSN:0026-8976    

DOI:10.1080/002689700413578

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

GIAO calculations of the1H NMR chemical shifts for ethanol at the SCF and DFT levels of theory are presented. The importance of molecular geometry and basis set is discussed. Vibrational correction to the hydroxyl proton chemical shift is also considered in calculations for the monomer of ethanol. The final theoretical results for the monomer obtained at the optimized DFT/B3LYP/6-311G(d,p) geometry with the 6-311G++ (d,p) basis set for NMR are in very good agreement with gas phase experimental data. For the liquid phase ethanol the hydrogen bonding effects are taken into account by performing calculations on various clusters of ethanol. It is shown that inaccuracy due to molecular geometry and basis set in the monomer of ethanol is magnified significantly in calculations for its clusters. In this context the structure of liquid ethanol as predicted recently by quantum cluster equilibrium (QCE) theory is discussed.

ISSN:0026-8976    

DOI:10.1080/002689700413587

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The Fourier transform infrared spectrum of theυ3andυ9bands of methylene fluoride-d2(CD2F2) has been recorded with an unapodized resolution of 0.0024cm-1in the frequency range 970-1080cm-1. These two bands with band centres approximately 26 cm-1apart were mutually coupled by Coriolis interactions. By fitting a total of 1639 infrared transitions of bothυ3andυ9with a standard deviation of 0.00084cm-1S/S using a Watson'sA-reduced Hamiltonian in theIrrepresentation with the inclusion of a first orderc-type Coriolis resonance term, two sets of rovibrational constants forυ3= 1 andυ9= 1 states were derived. Theυ3band isB-type while theυ9 band isA-type with band centres at 1030.1573 ± 0.0003 and 1003.7435 ± 0.0001cm-1, respectively.

ISSN:0026-8976    

DOI:10.1080/002689700413596

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Quantum error correcting codes enable the information contained in a quantum state to be protected from decoherence due to external perturbations. Applied to NMR, this procedure does not alter normal relaxation, but rather converts the state of a 'data' spin into multiple quantum coherences involving additional ancilla spins. These multiple quantum coherences relax at differing rates, thus permitting the original state of the data to be approximately reconstructed by mixing them together in an appropriate fashion. This paper describes the operation of a simple, three-bit quantum code in the product operator formalism, and uses geometric algebra methods to obtain the error-corrected decay curve in the presence of arbitrary correlations in the external random fields. These predictions are confirmed in both the totally correlated and uncorrelated cases by liquid-state NMR experiments on13C-labelled alanine, using gradient-diffusion methods to implement these idealized decoherence models. Quantum error correction in weakly polarized systems requires that the ancilla spins be prepared in a pseudo-pure state relative to the data spin, which entails a loss of signal that exceeds any potential gain through error correction. Nevertheless, this study shows that quantum coding can be used to validate theoretical decoherence mechanisms, and to provide detailed information on correlations in the underlying NMR relaxation dynamics.

ISSN:0026-8976    

DOI:10.1080/002689700413604

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The laser-induced fluorescence spectra of the InCl molecule over the range 266.5–287.0nm and 332.0–373.0nm are reported and assigned to C1Π1-X1Σ+, B3Π1-X1Σ+, or A3Π0-X1Σ+transitions. It is the first time those radiative lifetimes of the C1Π1and B3Π1states have been measured by laser-induced fluorescence. The collision-free fluorescence radiative lifetime τ0= 353(7)ns and a quenching rate constantkQ= 1.985(0.010)x 10-10cm3molecule-1s-1are proposed for B3Π1and τ0= 11(1)ns for C1Π1states. From the radiative lifetime τ0and the Franck-Condon factors qv″v′for the v′ - v″ transitions, the electronic transition moments |Re|2of the B3Π1and C1Π1states have been obtained.

ISSN:0026-8976    

DOI:10.1080/002689700413613

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor