摘要:

Solutions containing the sodium anion (Na-) were prepared by dissolving either NaK, NaRb or NaCs alloys in liquid 12-crown-4, 12C4. The23Na nuclear spin-lattice (T1n) and spin-spin (T2n) relaxation times of the N.M.R. signal originating from Na-have been measured as a function of temperature, concentration and counter-cation K+, Rb+or Cs+. The details of the inequality betweenT1nandT2nshown that the lifetime of Na-is limited by a two-step process. In the first step a strong complex of an alkali cation and 12C4 molecules dissociates to yield an uncomplexed cation to which one 3selectron from Na-is transferred in the second step. The23Na nuclear spin relaxation data are combined with the results of previous EPR and pulse radiolysis experiments to deduce both the reactions generating Na-as well as further equilibria involving both complexed and uncomplexed cations, solvated electrons and a variety of paramagnetic species containing an electron and a cation.

ISSN:0026-8976    

DOI:10.1080/00268979000100151

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A molecular beam of PbSe molecules was excited by the 4965 Å line emitted by a cw Ar+laser and the fluorescence spectrum was recorded. Five fluorescence series originating from thev′ = 9 level and one series originating from thev′ = 10 level of theA0+state were observed and analysed to yield improved isotopic vibrational constants for theX0+state. The observation of satellite lines due to inelastic collisions within the beam allowed also to determine the rotationalBconstant of thev′ = 10 level of theA0+state. Using a pulsed dye laser, lifetimes of thev′ = 9 and 10 levels of theA0+state and of thev′ = 1, 5, 6, 7 and 8 levels of theB1 state were measured. These lifetimes combined with calculated Franck-Condon factors allowed electronic transition moments for theA-XandB-Xtransitions to be determined.

ISSN:0026-8976    

DOI:10.1080/00268979000100161

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

We continue our development of group theory statistical mechanics applied to non-newtonian shear and elongational flow. We discuss some new aspects of shear flow discovered by non-equilibrium molecular dynamics, NEMD. We investigate the origins of time reversal asymmetry in newly discovered cross-correlation functions. Using the profile unbiased thermostat, PUT, shear flow algorithm we discover that the strong phase is stable in 3D, for typical system sizes considered by molecular dynamics. In addition, for thefirsttime we apply NEMD, to simultaneous shear and elongational non-newtonian flow. New equations of motion are constructed to enforce the elongational flow. We apply transient flows to a model Lennard-Jones liquid and monitor the thermodynamics and mechanical response, directly, and from transient time correlation functions. The value of the shear viscosity can be increased or lowered by the presence of simultaneous shear and elongational flow, in which the main velocity flow directions are perpendicular or parallel, respectively. A combination of shear and elongational flow can produce a heat flux, the thermal equivalent of the Weissenberg effect.

ISSN:0026-8976    

DOI:10.1080/00268979000100171

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The high resolution laser induced fluorescence spectrum of the 000S1(1A1) ←S0(1A1) electronic transition in 1,4-dimethylnaphthalene has been studied in a molecular beam. The residual Doppler width of 12 MHz allowed rotational resolution and the study of the effects of the internal rotation of the two methyl groups. All strong lines were assigned and the rotational constants in both the ground and excited electronic states were determined. The internal rotation of the two methyl groups manifests itself in the spectrum by a splitting of each rotational transition into three lines. The splitting of the lines is 40 ± 1 MHz and constant up toJ= 11 andK+1= 11. The intensity ratio of the lines is 1:2:1 within 10 per cent. No further splittings were observed in the investigated frequency range. It is shown that the spectrum is totally explained by the simple model of two independent internal rotors attached to an asymmetric rotor frame. The effect of the interaction of the two rotors is negligible with the present resolution as is the effect of the interaction between internal rotation and overall rotation. The measured splitting of 40 MHz yields information about the barriers to internal rotation in the two electronic states. With some assumptions a barrier height of 570 ± 10 cm-1in the excitedS1state is deduced.

ISSN:0026-8976    

DOI:10.1080/00268979000100181

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The vertical excitation energies of thirty electronic states of TiH as well as the potential curves of all quartet and doublet states correlating with the first two channels Ti + H have been investigated by using extensive MRD-CI calculations. Based on the results for the transition energies and dipole transition moments, the known absorption bands extending from 18 200 to 21 300 cm-1(a strongest band near 18 870 cm-1assumed to be aX4Φ →4Δ transition) are assigned to transitions fromX4Φ into 14Γ (calculatedTvert= 17 420 cm-1) and into 44Δ (calculatedTvert= 19 440 cm-1), with possible contribution of the excitation 14Σ-→ 54Π (calculatedTvert= 17 500 cm-1). These strong (perpendicular) 8σ → 4π bands lie rather close to the measured excitation energies assigned to the dipole allowed high-intensity transition 4s→ 4pof the Ti atom. In addition the present study shows that two TiH bands of relatively high-intensity lie near 11 000 cm-1(i.e.X4Φ → 24Φ and 14Σ-→ 24Σ-), a prediction awaiting its experimental verification. The low-energy (parallel) 8σ → 6σ(3d) bands haveTevalues about 4500 cm-1higher than the equivalent 4s→ 3datomic transition. The term values for the first TiH Rydberg members4Φ and4Π (both 8σ → 5sstates lying slightly above 32 000 cm-1) compare well with the experimental 4s→ 5sterm values of the Ti atom. The analysis of the bonding in the 12Δ and 12Π states shows that these states have contributions from 3dσ (Ti), and as a consequence have shorter equilibrium distances than their quartet counterparts. States with sextet multiplicity are repulsive. The calculated dipole moment μ atR(TiH) = 3·47 a.u. for all bound states from channels I and II reveal a strong dependency of μ on the relative occupation of 6σ(3dσ) and 8σ, as pointed out by a low μ of 0·92 D for 14Δ (1δ6σ7σ28σ) and a high μ of 4·61 D for 24Δ (1δ3π27σ2). Between both extreme values, other examples are provided by μ = 1·90 forX4Φ (1δ3π7σ28σ) and μ = 2·83 D for 24Φ (1δ3π6σ7σ2).

ISSN:0026-8976    

DOI:10.1080/00268979000100191

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Ab initioSCF calculations of harmonic vibrational frequencies and I.R. and Raman intensities of the normal modes are reported for the H-bonded trimers: HCN … (HF)2, (HF)2… HCN, HF … HCN … HF, HCN … HF … HCN, HCN … HCN … HF and HF … HCN … HCN. Calculations with basis set of different levels, STO/4-31 G and D95, are presented. Rotational constants and one-electron properties are given and the assignments of the I.R. spectra discussed.

ISSN:0026-8976    

DOI:10.1080/00268979000100201

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A mixture of ψ components in an external field and interacting with potentials of 2, 3, …,n-bodies is considered. An exact equation for the entropy is derived. This equation gives the entropy as a sum of correlational contributions whose structure is increasingly complex. The first five terms are explicitly displayed.

ISSN:0026-8976    

DOI:10.1080/00268979000100211

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The Fisher-Kopeliovich generalized superposition approximation is applied to the entropy equation derived in the preceding paper. The free energy is written as a functional of the 1, 2, 3-body distribution functions and is minimized with the constraint that these distribution functions remain normalized. A system of integral equations is obtained which contains the HNC equation as a limiting case. An expression for the free energy of a homogeneous system is also obtained.

ISSN:0026-8976    

DOI:10.1080/00268979000100221

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The intensity of the central transition of a spin-3/2 system following excitation by two in-phase rf pulses is calculated using the fictitious spin-1/2 operator formalism. Measurement of this line intensity as a function of the duration of the second rf pulse enables the quadrupolar coupling to be determined. The method is illustrated with a study of7Li nuclei in a single crystal of LiTaO3. For polycrystalline samples the powder average is computed numerically in order to obtain the quadrupolar coupling constant and the asymmetry parameter.

ISSN:0026-8976    

DOI:10.1080/00268979000100231

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

We consider a fluid of oriented hard squares on a two-dimensional strip. When two squares cannot pass each other, the equilibrium behaviour is similar to that of repulsive cores on a line. However, when the strip is wide enough that two squares can pass, but not three, an exact solution shows that there is already an indication of a thermodynamic singularity coming into being at around 70 per cent of close packing volume.

ISSN:0026-8976    

DOI:10.1080/00268979000100241

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor