Chemical Physics Letters (v.351, #5-6)

Effect of surface roughness on diffusion limited reactions, a multifractal scaling analysis by Ajay Chaudhari; Ching-Cher Sanders Yan; Shyi-Long Lee (341-348).
Eley-Rideal diffusion limited reactions (DLR) were performed over different rough surfaces generated by Rain model. Multifractal scaling analysis has been carried out on the reaction probability distribution to investigate the effect of surface roughness on the chemical reactions. The results are compared with the DLRs over surface of diffusion limited aggregation (DLA).

Luminescence anisotropy of functionalized carbon nanotubes in solution by Ya-Ping Sun; Bing Zhou; Kevin Henbest; Kefu Fu; Weijie Huang; Yi Lin; Shelby Taylor; David L Carroll (349-353).
Luminescence anisotropy of functionalized single-wall (SWNT) and multiple-wall (MWNT) carbon nanotubes in solution and in polymeric thin-film matrix was investigated. The results show that the absorption and emission dipole moments are intrinsically collinear, corresponding to the limiting positive anisotropy. The observation of strong luminescence polarization for the functionalized carbon nanotubes in room-temperature chloroform is consistent with the polymeric nature of these luminescent species; and the partial depolarization in solution is rationalized in terms of the flexibility of the nanotubes.

We study the exciton dynamics in ladder-type poly(p-phenylene) (LPPP) containing aggregate states under high electric field conditions. Time-resolved emission spectroscopy reveals a different dissociation behaviour of S1-intrachain excitons as compared to excitons located in aggregate states. No acceleration of the decay of aggregate excitons due to field-induced dissociation is found for electric fields up to 2×106 V/cm. The time-integrated photoluminescence quenching does not exhibit a strong spectral dependence and is completely due to the dissociation of initially excited S1-intrachain excitons.

Laser induced fluorescence spectroscopy of the HC4S and DC4S radicals by Masakazu Nakajima; Yoshihiro Sumiyoshi; Yasuki Endo (359-364).
Vibronic band systems for the HC4S and DC4S radicals were observed in supersonic jets for the first time by laser induced fluorescence (LIF) spectroscopy. The rotational structures of the bands were resolved by high-resolution scans. It was found that all the observed bands are 2Π3/2–2Π3/2 transitions. Band origins and effective rotational constants of the origin bands are determined to be T0=19 980.687(1) and B eff =0.046580(4)  cm −1 for HC4S, T0=20 034.8748(9) and B eff =0.044294(3)  cm −1 for DC4S. Ab initio calculations were carried out to interpret the vibronic transitions.

Disentangling the mystery of green bands of yttrium monohydride with the help of Stark spectroscopy by Zygmunt J. Jakubek; Benoit Simard; Walter J. Balfour (365-373).
YH molecules were produced by laser vaporizing yttrium in the presence of He doped with H2 or NH3. Stark spectra were recorded for four bands in the 19 300–19 800 cm−1 region at electrostatic fields up to 16 kV/cm. Stark measurements proved useful in establishing rotational and Ω quantum number assignments. The permanent electric dipole moments (in Debye) were measured to be: 1.569(64), 2.325(8), 3.316(11), 2.273(6), and 1.537(8) for the X 1Σ+ ground state and the 19 385, 19 746, 19 572, and 19 575 cm−1 excited states, respectively. Strong variation of the effective Ω quantum number with J was detected for the 19 572 cm−1 state.

The first and second generation of Fréchet-type dendrimer with a viologen core have been prepared; it has been observed that the association constant and the electron transfer quenching of these compounds with anthracene is modulated by the size of the polyether branches.

Mode-switching in the flow of water into a cup by Satoshi Nakata; Hiroyuki Kitahata; Akane Terada; Toyoki Matsuyama (379-384).
Mode-switching was investigated when water was poured into a cup. Three modes, i.e., accumulation flow (Mode I), scattering flow (Mode II), and oscillatory flow (Mode III), were regulated by the flow rate. The bifurcation flow rate at Mode I→II was different from that at Mode II→I , i.e., hysteresis in mode-switching was observed. Mode III was observed at Mode I  →  II. The bifurcation point changed depending on the radius of the water tube, and the water-hollow was an important factor in mode-switching. The mode-switching was reproduced by a numerical calculation including the double-minimum profile of the free energy and the flow rate.

Blue-light emission of nanocrystalline CaS and SrS synthesized via a solvothermal route by Chunrui Wang; Kaibin Tang; Qing Yang; Changhua An; Bin Hai; Guozhen Shen; Yitai Qian (385-390).
CaS and SrS nanocrystallites have been successfully synthesized via a solvothermal route by the reaction between XCl2 (X=Ca, Sr) and sulfur at relatively lower temperature for the first time. XS (X=Ca, Sr) nanocrystallites are efficient emission luminescence in comparison with that of bulk materials at room temperature. The emitted light of CaS and SrS nanocrystallites is yellow–green and blue, respectively.

We have encapsulated ZnII tetraphenylporphyrin (ZnIITPP) into MCM-41 and CuIIAlMCM-41. Raman and UV–Vis spectroscopic investigations allow us to conclude that ZnIITPP in MCM-41 is oxidized to a considerable extent. This is consistent with the well-known fact that the mesoporous silicate framework in MCM-41 plays the role of a good electron acceptor. Central metal ion exchange of ZnIITPP encapsulated into CuIIAlMCM-41 gives CuII tetraphenylporphyrin (CuIITPP) with almost unit transformation efficiency. We will discuss the interesting reaction which occurred in nanometer-sized pores in terms of the characteristics of the mesoporous silica and the nature of the encapsulated ZnIITPP.

A phase transition in H2O due to a high electric field close to an electrode by I. Danielewicz-Ferchmin; A.R. Ferchmin (397-402).
In this study a phase transition in H2O due to an applied very high local electric field E at ambient conditions is predicted. We analyse the equation of state and behaviour of entropy. For E=109   V m −1 some characteristic features of local electrostriction pressure Π and of entropy change ΔS as a function of the field strength E are noted. These features are interpreted as testifying to a phase transition: water in low field → H2O in high field (or, in other words, H2O compressed by the field). A consistency of the present results with recent off-specular surface X-ray scattering studies is discussed.

A novel motif of the cytosine tetrad: a theoretical study by Jiande Gu; Jerzy Leszczynski (403-409).
We report here the quantum chemical prediction of a new motif of the C-tetrad. The revealed H-bonding pattern of this tetrad conformer is different from that assumed on the base of the NMR experiment. The present study has predicted the small cavity pattern in which the four non-hydrogen-bonded amino protons point to the center of the tetrad. They are accessible to stack over the O6 atoms of the successive guanine tetrads. Both of the amino protons interact weakly with the N1 atom of the neighboring base. The stabilization energy of the C-tetrad is predicted to be 56.41 kcal/mol at the B3LYP/6-311G(d,p) level.

A modified Oregonator model subject to colored noise is investigated. As the model system locates in the dynamical region of period-1 oscillation, the flow rate is modulated by exponential Gaussian colored noise. The signal-to-noise ratio (SNR) as a function of the noise intensity shows the nonmonotonic behavior, indicating occurrence of explicit internal signal stochastic resonance (EISSR). The colored noise can weaken EISSR, and the maximum effect of EISSR is shifted to lower noise intensity with the increment of the correlation time. The SNR also shows resonance behavior with the variation of the correlation time as the noise intensity is fixed.

Possibility of quantum effect in micropore filling of Ne on AlPO4-5 by H. Tanaka; M. El-Merraoui; T. Kodaira; K. Kaneko (417-423).
Adsorption isotherms of neon at 27, 30, and 33 K on aluminophosphate AlPO4-5 were measured. The experimental adsorption isotherms and isosteric heat of adsorption for neon on AlPO4-5 were compared with those calculated from the density functional theory (DFT) treating the classical Lennard-Jones systems. The classical DFT results exhibited the first layer filling on the pore wall and the second filling in the center of the pore. However the experimental isotherms showed only one layer transition, suggesting that quantum contributions cannot be neglected for neon adsorption on the micropores of AlPO4-5 at low temperatures.

Electronic g-tensors obtained with the mean-field spin–orbit Hamiltonian by Olav Vahtras; Maria Engström; Bernd Schimmelpfennig (424-430).
The accuracy of the atomic mean-field approximation (AMFI) to the spin–orbit interaction Hamiltonian is evaluated for the paramagnetic contribution to electronic g-tensors. A variety of different substances are tested for this purpose for restricted open-shell Hartree–Fock and multi-configuration self-consistent field wave functions. In most cases the introduced error is significantly lower than errors of wave function parameterization. Considering the substantial computational savings, it is argued that the mean-field approximation is warranted given the resolution available in current electron spin resonance experiments.

Hyperpolarizability β of fused-ring molecules tetra-substituted by two ortho-positioned donor (D)–acceptor (A) were studied for three types of C2v isomers, using simplified sum-over-states (SOS) calculation, missing-orbital analysis (MOA), and homologous substitution model. The model is comprised of two molecules, one di-substituted by two D's, the other by two A's at the sites homologous as a whole to tetra-substitution. Ortho1-type with two D–A pairs at molecular x-edges showed larger β zxx than that of the model, exhibiting charge-transfer (CT), nevertheless all isomer types could show CT enhancement according to resonant structures. The substitution model successfully described qualitatively magnitudes and signs for β for all isomers.

A quantum propagation method in D-dimensional problem (D=1,3,5,…,) based on the Liouville coupling equation is considered. The evolution operator U=exp(−iHt/ℏ) for the Hamiltonian H=H 0+V with a discrete spectrum is expressed in terms of the unperturbed operator U (0)=exp(−iH 0 t/ℏ) that has well-defined matrix elements. Comparison with the existing methods (Lanczos propagation and Chebychev series) displays the advantages of the new approach.

We perform a block-averaging and extrapolation analysis of fast-switching free-energy difference (ΔF) estimates for a computer-modeled, fully solvated ethane↔methanol transformation. The results suggest that the analysis can greatly reduce the `finite-sampling error' in ΔF estimated from a small number of very fast switches. This error, which can be many times k B T, is the difference between an estimate based on a finite amount of data and that from an infinite data set; it is inherent in the ΔF calculations. Our blocking/extrapolation procedure appears to be particularly useful for broad, non-Gaussian distributions of data which typically produce large finite-sampling errors.

Linear relationships between acidity and stability in mono- and hexahydrated metal ions: a computational study by Philip George; Jenny P. Glusker; Mendel Trachtman; Charles W. Bock (454-458).
Linear relationships have been established between the dissociation enthalpies of the monohydrates of Li+, Na+, K+, Be2+, Mg2−, Ca2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Al3+, Sc3+, Ti3+, V3+, Mn3+, Fe3+ and Ga3+ calculated at the MP2(FULL)/6-311++G**//MP2(FULL)/6-311++G** level, the hexahydrates of Na+, K+, Mg2+, Ca2+, Mn2+, Zn2+, Al3+, Sc3+, Fe3+ and Ga3+ calculated at the MP2(FULL)/6-311++G**//HF/6-311++G** level, and experimentally reported pK a values for the first ionization of the corresponding aqua-ions. In contrast to the results of Chang and Wang [Chem. Phys. Lett. 286 (1998) 46], we find that the 3+ ion hexahydrates are more (not less) stable than the 2+ ion hexahydrates.

The present study suggests that the thermal decomposition of 5-nitro-1-hydrogen-tetrazole might be the main contribution to the N2 releasing process of 5-nitro-tetrazole's decomposition. Three reaction channels of 5-nitro-1-hydrogen-tetrazole were revealed in ab initio molecular dynamics (MD) simulations. The direct ring rupture of N1–N2 bond breaking has the lowest energy barrier at the first reaction step and is expected to dominate the thermal decomposition. Hydrogen-transfer leading process has a relatively higher energy barrier for the first step. However, the proton-transfer rate could increase dramatically due to the quantum tunneling effect. The direct ring-opening reaction through the C5–N4 bond breaking is less important for its very high activation energy.

The time dependent-density functional theory (TD-DFT) has been applied to study the photoionization from the two symmetry resolved initial states (1σg and 1σu) of the core N 1s in N2. The results are compared with very recent experimental data and with previous ab initio calculations. The calculated intensity ratio is in excellent agreement with the experiment and performs better than previous calculations. Good quantitative results are also obtained for the absolute partial cross-section. The calculated asymmetry parameters are also predicted to be very different in the two contributions, so a new experiment to investigate the angular distribution of the photoelectron is suggested.

Fragment molecular orbital method: use of approximate electrostatic potential by Tatsuya Nakano; Tsuguchika Kaminuma; Toshiyuki Sato; Kaori Fukuzawa; Yutaka Akiyama; Masami Uebayasi; Kazuo Kitaura (475-480).
Recently, we have proposed the fragment molecular orbital (FMO) method; an approximate MO method for calculating large molecules such as proteins. The method has been shown to reproduce ab initio total energies and geometries of molecules in good accuracy. The most time consuming part in the method, the calculations of environmental electrostatic potentials, were speeded up by employing the Mulliken approximation for two-electron integrals and a fractional point charge approximation. Numerical calculations on several polypeptides revealed that the approximations brought no significant loss of accuracy in the total energy of molecules and were of practical use.

Conformational analysis of 2,2-bithiophene (BT) under the influence of an electric field (EF) constructed by point charges has been performed by using semi-empirical Austin Model 1 (AM1) and Parametric model number 3 (PM3) calculations. When the EF perpendicular to the molecular conjugation chain is applied, both AM1 and PM3 calculations show an energy increase of the anti-conformation. AM1 predicts that the global minimum shifts to syn-conformation when the EF strength is larger than a critical value, and PM3 predicts that the local minimum in anti-conformation vanishes. This kind of EF effect has been ascribed to the EF and dipole moment interaction.

Calculations of third-order optical properties of titanyphthalocyanine polymorphs by D.-S. Wu; W.-D. Cheng; H. Zhang; J.-T. Chen (486-494).
We report the dynamic third-order nonlinear optical susceptibilities χ (3) using the INDO/SDCI method coupled with the SOS method for the different forms of PcTiO films. The calculated values of χ (3) at a low frequency are found to decrease in the order α-PcTiO>Y-PcTiO>β-PcTiO, and well corresponded to the varied trends in the measurements. A low space symmetrical structure of α-PcTiO film has the largest magnitude of χ (3), which is the contribution from the intermolecular interaction. The electron transfers from macrocycle π orbitals to metal Ti 3d orbital make a substantial contribution to the third-order NLO response for the PcTiO.

Author Index (495-503).