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     

Synthesis,Crystal Structures and Properties of Two Novel Co（Ⅱ） and Cd（Ⅱ） Complexes of N-AcetyI-L-glutamic Acid and Imidazole Ligands

Two novel complexes {[Co（A-glu）（Im）2]·0.5H2O}n （1） and [Cd（A-glu）（Im）3]n （2） （H2A-glu=N-acetyl-L-glutamic acid, Im=imidazole） have been synthesized from the reaction of H2A-glu with Co（CH3COO）2·4H2O or Cd（CH3COO）2·2H2O in the presence of Im. Both of the complexes display different coordination environment and similar one-dimensional chain structure. The magnetic susceptibility measurements for 1 show a weak antiferromagnetic interaction between two cobalt（Ⅱ） ions bridged by A-glu ligand. The complex 2 exhibits an intense fluorescent emission in solid state at room temperature.     

Facial selectivity of the (R)-1,3-dimethyl-1-cyclohexyl cation in the gas phase

The model reaction between the (R)-1,3-dimethyl-1-cyclohexyl cation (I) and methanol has been investigated under gas-phase radiolytic conditions (750 Torr; 25-120 degrees C) with the aim of evaluating the intrinsic factors that govern the facial selectivity of biased carbocations. The peculiarity of the experimental approach allows the formation of different CH(3) (18)OH.I ionic adducts. Subsequent conversion of these adducts to give the corresponding E/Z covalent products follows different reaction coordinates, which are characterized by their own activation parameters. On the grounds of density functional theory (DFT) results, several [CH(3)OH.I] structures have been located on the relevant potential-energy surface (PES). The experimental results point to a gas-phase facial selectivity, which is mainly governed by entropic factors that arise as a result of the occurrence of different noncovalent ion-molecule "facial adducts" (FA). The formation of FAs may also play an important role in both the reaction dynamics and the positional selectivity. The present results cannot be interpreted by any of the models based on solution-phase experiments.     

Extraction of kinetic information from single-molecule experiments.

We discuss two possible approaches for extracting kinetic information from single-molecule experiments. The first approach is based on computing correlation functions from measured fluorescence signals, and the second on studying the statistics of on and off times of the same fluorescence signal. We show that in both cases it is possible to extract kinetic information about the nature of intramolecular fluctuations of the single molecule. We show that for single-molecule kinetics the intramolecular fluctuations produce stochastic memory effects which lead to new dynamic features that do not exist in traditional chemical kinetics. In particular, we investigate a new type of chemical oscillations in correlation functions observed experimentally by Edman and Rigler (Proc. Natl. Acad. Sci. USA 2000, 97, 8266).     

Diffusion Monte Carlo study of correlation in the hydrogen molecule

The diffusion Monte Carlo (DMC) method shows that correlation in H₂ produces a set of three spatial changes: (i) an enhancement in the electron density distribution n( r ) in the left and right anti‐binding regions that include separately the immediate vicinity of each of the two nuclei, (ii) a reduction in n( r ) in the binding region intervening between the two nuclei as a counterbalance, and (iii) a concomitant increase in the equilibrium internuclear separation. It is stressed that the correlation energy E^c (= T^c + V^c) for diatomic molecules be defined by the difference in the total energy between the exact and the Hartree–Fock (HF) variational calculations that are performed at individually optimized internuclear separations. It is this definition that makes it possible to involve a significant contribution from a correlation‐induced change in the equilibrium internuclear separation as part of the correlation energy and to relate (i) and (ii) to (iii) in consistency with the electrostatic theorem. The present calculations fulfill the virial theorem to an accuracy of ?V/T = 2.00 for DMC and ?V^HF/T^HF = 2.000 for HF. The present correlation energy E^c = ?0.0408 hartree is not only in good agreement with the most accurate value previously reported, but also can be analyzed into all its components in accordance with the correlational virial theorem 2T^c + V^c = 0. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

DNAzyme amplification of molecular beacon signal

This paper reports an improved catalytic molecular beacon. Addition of the target oligonucleotide activates a DNA enzyme (DNAzyme), which, in turn, activates multiple copies of molecular beacons (MB) and gives rise to a strong fluorescence signal. In a previous design, the activated DNAzyme could oligomerize, especially dimerize, and result in inactivation of the DNAzyme. The current design avoids this problem, upon activated by the target DNA, the DNAzyme will stay constantly active. With the improved method, a detection of 10 pM DNA has been demonstrated, which is 1000 times more sensitive than the method previously reported.     

Quantum-chemical analysis of the CuCl2 molecule

This paper reports on quantum-chemical analysis of the linear structure of CuCl₂ by Hartree-Fock (HF) and density functional theory (DFT) methods and also by time-dependent HF (TD HF) and DFT (TD DFT) techniques. Using pure DFT exchange correlation functional (B3LYP) yields the best agreement with the experimental electronic spectra of CuCl₂. In this case, the odd electron is delocalized over the molecule, spin density on copper being 0.27. The ground state of the CuCl₂ molecule is ²Π_g with linear geometry.     

NMR Studies of Mixed-Ligand Lanthanide Complexes in Solution: Pseudorotation and Ring Inversion of 18-Crown-6 Molecule in Cerium Subgroup Chelates

¹H and ¹³C NMR measurements are reported for the CDCl₃ and CD₂Cl₂ solutions of [La(NO₃)₃(18-crown-6)] (I), [Pr(NO₃)₃(18-crown-6)] (II) and [Ce(NO₃)₃(18-crown-6)] (III) complexes. Temperature dependencies of the ¹H NMR spectra of II have been analyzed using the dynamic NMR methods for multi-site exchange. Two types of conformational dynamic processes in II were identified (the first one with activation enthalpy ΔH ^‡=26 ± 4 kJ/mol is conditioned by interconversion of complex enantiomeric form and pseudorotation of macrocycle molecule upon the C ₂ symmetry axis, the second one with ΔH ^‡=46 ± 5 kJ/mol is conditioned by macrocycle molecule inversion). Studies of the values of the lanthanide-induced shifts revealed that the structure of complexes in solution is similar to that reported for the complex I in the crystal state.This revised version was published online in July 2005 with a corrected issue number.     

MnIII2 (5-Rsaltmen)2NiII(pao)2(L)]2+: an S(T)=3 building block for a single-chain magnet that behaves as a single-molecule magnet

Mn(III)-Ni(II)-Mn(III) linear-type trinuclear complexes bridged by oximate groups were selectively synthesized by the assembly reaction of [Mn2(5-Rsaltmen)2(H2O)2](ClO4)2 (5-Rsaltmen2-=N,N'-(1,1,2,2-tetramethylethylene) bis(5-R-salicylideneiminate); R=Cl, Br) with [Ni(pao)2(phen)] (pao-=pyridine-2-aldoximate; phen=1,10-phenanthroline) in methanol/water: [Mn2(5-Rsaltmen)2Ni(pao)2(phen)](ClO4)2 (R=Cl, 1; R=Br, 2). Structural analysis revealed that the [Mn(III)-ON-Ni(II)-NO-Mn(III)] skeleton of these trimers is in every respect similar to the repeating unit found in the previously reported series of 1D materials [Mn2(saltmen)2Ni(pao)2(L1)2](A)(2) (L(1)=pyridine, 4-picoline, 4-tert-butylpyridine, N-methylimidazole; A=ClO4-, BF4-, PF6-, ReO4-). Recently, these 1D compounds have attracted a great deal of attention for their magnetic properties, since they exhibit slow relaxation of the magnetization (also called single-chain magnet (SCM) behavior). This unique magnetic behavior was explained in the framework of Glauber's theory, generalized for chains of ferromagnetically coupled anisotropic spins. Thus, in these 1D compounds, the [Mn(III)-ON-Ni(II)-NO-Mn(III)] unit was considered as an S(T)=3 anisotropic spin. Direct-current magnetic measurements on 1 and 2 confirm their S(T)=3 ground state and strong uniaxial anisotropy (D/k(B) approximately -2.4 K), in excellent agreement with the magnetic characteristic deduced in the study on the SCM series. The ac magnetic susceptibility of these trimers is strongly frequency-dependent and characteristic of single-molecule magnet (SMM) behavior. The relaxation time tau shows a thermally activated (Arrhenius) behavior with tau0 approximately 1x10(-7) s and Delta(eff)/k(B) approximately 18 K. The effective energy barrier for reversal of the magnetization Delta(eff) is consistent with the theoretical value (21 K) estimated from |D| S2T. The present results reinforce consistently the interpretation of the SCM behavior observed in the [Mn2(saltmen)2Ni(pao)2(L1)2](A)2 series and opens new perspectives to design single-chain magnets.