Heat capacities and volumes of transfer of cholesteryl oleyl carbonate into various solvents

Heat capacities C _p and volumes V have been obtained at 25°C for the transfer of cholesteryl oleyl carbonate (ChOC) from a reference solvent, the highly-branched alkane 2,2,4,4,6,8,8-heptamethylnonane into various solvents. These include normal, branched, and cyclic alkanes as well as the pure cholesteric ChOC. V and most C _p are associated with the change of environmental free volume during the transfer process and are predicted by the Prigogine-Flory theory. However, for n-alkane solvents with more than twelve carbons, C _p is large, positive, and unattributable to free volume changes. It is consistent with a restriction of alkane segmental motion by the ChOC. The same mechanism has been proposed to explain an antiplasticization effect of ChOC on transitions in polymers.     

Three-dimensional quantum dynamics study of vibrational predissociation of HeI_2 van der Waals molecule for low vibrational excitation using the time-dependent wave packet method

Three-dimensional quantum mechanical calculations for vibrational predissociation of HeI2(B) van der Waals molecules are presented using the time-dependent wave packet technique within the golden rule approxima tion.The total and partial decay widths,lifetimes,rates and their dependence on initial vibrational states were obtained for HeI2 at low initial vibrational excited levels.Our calculations show that the calculated tota decay widths,lifetimes and rates agree well with those extrapolated from experimental data available The predicted total decay widths as a function of initial vibrational states exhibit highly nonlinear behavior.The very short propagation time (less.than 1 ps) required in the golden rule wave packet calculation is determined by the duration time of the final state inter-action between the fragments on the vibrationally deexcited adiabatic potential surface.The final state interaction between the fragments is shown to play an important role in determining the final rotational distri     

Laser two-photon ionization of organic molecules in dielectric liquids

The ionization threshold of fluoranthene and of TMPD in n-pentane was determined by laser two-photon ionization (TPI) and found to be 4.50 ± 0.05 and 3.88 ± 0.05 eV respectively. For both molecules the TPI spectra show distinct structure due to autoionization. For fluoranthene the TPI spectrum suggests that the molecule dissociates via the first excited singlet state.     

N-苯基苯二甲酰亚胺和2-苯基喹噁啉晶态分子动力学行为研究

本文在晶体结构分析的基础上, 对二个芳香杂环高聚物模型化合物N-苯基苯二甲酰亚胺和2-苯基喹噁啉分子的原子热振动参数进行分析, 结果表明N-苯基苯二甲酰亚胺晶态分子基本上为刚性分子, 而2-苯基喹噁啉分子的热振动应包含分子内取代苯基的内旋转运动, 其平均平方振幅为53(25) deg~2。     

A one-step conversion of isoquinolinium salts into naphthalene derivatives1

Berberine chloride (1) upon treatment with NaOAc-Ac₂O yields naphthalene derivatives 4 and 5 In like fashion, 8 gives naphthalene 10; isoquinoline methiodide leads to β-naphthyl acetate; and 12 provides 14. The reaction has been extended to the 3-carbonyl pyridinium series where 3-acetylpyridine methiodide and 3-pyridinecarboxaldehyde methiodide furnish lactones 16 and 17, respectively. All these transformations proceed by initial nucleophilic attack of the acetic anhydride anion on the immonium carbon atom.     

Dielectric and13C NMR studies of the carbon monoxide clathrate hydrate

The structure I clathrate hydrate of carbon monoxide has been studied using dielectric measurements and¹³C NMR spectroscopy. Broad, weak dielectric absorption curves with maxima at 2.2–3.8 K yieldE _a = 0.14 kJ mol^–1 for the average Arrhenius activation energy associated with the reorientation of the low polarity guest. Except for H₂S this represents the fastest reorienting polar guest known among the clathrate hydrates. The low temperature dielectric absorption curves can best be fitted with a Cole-Davidson asymmetric distribution of relaxation times and activation energies (with = 0.06 at 4 × 10⁶ Hz), which at 10⁷ Hz has been resolved into a double symmetric distribution of discrete relaxation times for CO in the small and large cages. The cross-polarization magic angle spinning¹³C NMR spectra indicate identical chemical shifts for CO in the small and large cages, in contrast to other hydrates. The static spectra show that the CO molecules undergo anisotropic reorientation in the large cages and that there is still considerable mobility at 77 K. One possible model for the anisotropic motion has the CO rapidly moving among sites over each of the 14 faces of the cage with the CO axis orientated towards the cage centre. The cage occupancy ratio at 220 K, _s/ _L = 1.11, indicates slightly greater preference of CO for the small cage.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.     

A characterization of brownian motion in a lipschitz domain by its killing distributions

Let (Y _t, Q^x) be a strong Markov process in a bounded Lipschitz domainD with continuous paths up to its lifetime , and let (X _t, P^x) be a Brownian motion inD. IfY _– exists in D andQ ^x(Y_– C)=P^x(X_– C) for all Borel subsetsC of D and allx, thenY is a time change ofX.     

Probability theory and polymer physics

This study applies the theory of stochastic processes to the equilibrium statistical physics of polymers in solution. The topics treated include random copolymers and randomly branching polymers, with self-consistent mean field effects. A new and more natural way of dealing with Boltzmann weighting is discussed, which makes it possible from the beginning of a calculation to consider only the physical polymer conformations. We also show that in general the random copolymer problem can be reduced to the ordinary polymer problem, and treat the self-consistent field problem for a general branching polymer.     

Theoretical Study of Rotational Isomerism in Ethyl Pseudohalides

The structure and conformational stability of ethyl pseudohalides CH₃CH₂ — XCN (X = O, S, Se) were investigated using ab initiocalculations at the MP2 level of theory with a triple- basis set augmented with polarization and diffusion functions. Full optimization was performed on the minimum energy structures as well as on the transition state forms. The relative stabilities of rotational conformers were calculated at the MP4 level using MP2 optimized reference geometries. The nature of all considered stationary points was verified by calculation of the harmonic vibrational frequencies. The calculated bond lengths, bond angles, dipole moments, and rotational constants of optimized global minima structures agree very well with the corresponding experimental data obtained from microwave spectroscopic studies. Also, available experimental frequencies are in good accord with the theoretical values. For ethyl cyanate CH₃CH₂ — OCN, the antiperiplanar (trans) form is predicted to be more stable than the synclinal (gauche) form, and the synperiplanar (cis) form corresponds to the transition state. For both ethyl thiocyanate CH₃CH₂ — SCN and ethyl selenocyanate CH₃CH₂ — SeCN, the gaucheform is the global minimum while the trans-conformer is a local minimum and the cis-form is a transition state.     

Random walk in an inhomogeneous medium with local impurities

In spite of Sinai's result that the decay of the velocity autocorrelation function for a random walk on ^d (d=2) can drastically change if local impurities are present, it is shown that local impurities can not abolish weak convergence to the Brownian motion if d2.