Chemical Physics Letters (v.334, #4-6)

Triplet state properties of N-mTEG[60]fulleropyrrolidine mono and bisadduct derivatives by Konstantinos Kordatos; Tatiana Da Ros; Maurizio Prato; Sydney Leach; Edward J. Land; René V. Bensasson (221-228).
Laser flash photolysis and pulse radiolysis techniques were used to determine triplet state properties of N-mTEG[60]fulleropyrrolidine mono and bisadduct derivatives (FP) (mTEG=CH2CH2OCH2CH2OCH2CH2OCH3) in benzene. These properties include the triplet absorption spectra between 550 and 900 nm, quantum yields of triplet photosensitized singlet oxygen production (Φ Δ ) and triplet molar absorption coefficients (ε T) with the assumption that the quantum yield of triplet formation (Φ T) is equal to Φ Δ . Our results demonstrate that the triplet properties depend on the number of addends and the addition pattern.

Effects of ambient pressure on silicon nanowire growth by X.H. Fan; L. Xu; C.P. Li; Y.F. Zheng; C.S. Lee; S.T. Lee (229-232).
Growth of silicon nanowires (SiNWs) by thermal evaporation of SiO in a closed system was studied. The yield of SiNWs obtained in the present closed system was much higher than that from the previous open systems. As the ambient pressure increased, the yield of SiNWs decreased and the diameter of the SiNWs increased, but the surface of the SiNWs was roughened. Transmission electron microscopic examination showed that the originally smooth surface of SiNWs was roughened by the formation of Si nano-particles. The implication of these results on the growth mechanism of the SiNWs is discussed.

Azafullerene C59N, a stable free radical substituent in crystalline C60 by Ferenc Fülöp; Antal Rockenbauer; Ferenc Simon; Sándor Pekker; László Korecz; Slaven Garaj; András Jánossy (233-237).
Solid solutions of C59N azafullerene in C60 with concentrations of 10−5 to 10−4 were produced in large quantities in an electric gas discharge tube. C59N is a stable monomeric substituent molecule in crystalline C60. The isotropic 14N and 13C hyperfine coupling constants measured by electron spin resonance (ESR) are characteristic of the extent of delocalization of the charge over the cage and are a sensitive test of electronic structure calculations. The C59N reorientational activation energy measured below the face centered cubic (fcc) to simple cubic (sc) transition is 2300 K. This value is similar to that of the matrix C60 molecules, indicating that C59N–C60 intermolecular interactions are weak.

Metallic coverings of calcium on C60 by X.G. Gong; Vijay Kumar (238-244).
We present results of the electronic structure and stability of calcium coverings on C60 using a linear combination of atomic orbitals and the local density functional approximation. Calculations on Ca x C60 with x=12, 20 and 32 show partial charge transfer from calcium atoms to C60 and hybridization of the calcium and fullerene states. This leads to (i) a large binding energy of Ca on C60 which decreases with an increasing coverage and (ii) formation of a metallic shell on C60. The large abundance of the Ca32C60 complex is shown to be due to geometric factors in agreement with experiments.

A new amphiphilic Schiff base 2-hydroxy-5-nitro-N-benzylidene hexadecylamine (2H5NHDB) has been synthesized and its monolayer properties at the air/water interface have been studied. Surface pressure/molecular area (πA) and surface potential/molecular area (ΔVA) isotherms have been used to characterize the ligand and its complexation with nickel has been monitored using surface enhanced UV–Vis reflection spectroscopy at the gas/water interface. The complexation leads to either a shift or the appearance of new bands in the spectra. The preferred orientation and organization of the ligand into dimers at the air/water interface helps formation of stable nickel complexes. Sulfidation of the nickel complex (LB film) leads to uniform spherical clusters of nickel sulfide.

Rotational spectra and structure of the hydrogen-bonded complex oxetane⋯HCl by Sonia Antolı́nez; Juan C. López; José L. Alonso (250-256).
The hydrogen-bonded complex oxetane⋯HCl generated in a supersonic jet has been characterised by Fourier transform microwave spectroscopy. For the observed conformer the spectra of the four isotopic species C3H6O⋯H35Cl,C3H6O⋯H37Cl,C3H6O⋯D35Cl and C3H6O⋯D37Cl have been measured. Rotational data are consistent with a C s symmetry for the complex, with HCl lying in the symmetry plane bisector to the COC angle. The planar configuration of isolated oxetane has been reasonably elucidated to remain in the dimer, which implies that no significant change in the potential energy function of ring puckering motion of oxetane occurs upon complexation.

The synthesized titanium dioxide (TiO2) nanoparticle was found to enhance the formation of J-aggregate of water-soluble porphyrin, tetra (4-sulfonatophenyl) porphyrin dye, 5,10,15,20-tetraphenyl-21H, 23 H-porphine tetrasulfonic acid (TPPS). The forward and back electron transfers (ETs) between adsorbed TPPS and TiO2 nanoparticles were examined by picosecond single-photon timing and femtosecond transient absorption spectroscopy. The ultrafast back ET of ∼0.8 ps was observed both for the protonated monomer and the J-aggregate. The back ET almost completes within a few tens of picoseconds for the protonated monomer, while >1 ns is required for the J-aggregate. The difference has been interpreted in terms the hole delocalization and electronic coupling of the protonated monomer and J-aggregate adsorbed on TiO2 nanoparticles.

We report a solid-state 17 O NMR study of [α- 13 C,17 O ] benzamide. The orientations of the 17O electric-field-gradient and chemical shift tensors were determined from analysis of magic-angle spinning and stationary 17O NMR spectra. The largest electric-field-gradient component lies in the amide plane and perpendicular to the 13C–17O dipolar vector, whereas the intermediate electric-field-gradient component is along the CO bond. It is also found that the principal component of the 17O chemical shift tensor with the least shielding, δ 11, is approximately 18° off the CO bond and that the component with the most shielding, δ 33, is perpendicular to the amide plane. The present study confirms our earlier results of quantum chemical calculations.

Excited-state dynamics of rhodopsin probed by femtosecond fluorescence spectroscopy by Hideki Kandori; Yuji Furutani; Shoko Nishimura; Yoshinori Shichida; Haik Chosrowjan; Yutaka Shibata; Noboru Mataga (271-276).
Nonexponential fluorescence dynamics of bovine rhodopsin were measured at various wavelengths from 530 to 780 nm. No dynamic Stokes shift was detected but the fastest part of the fluorescence at both blue and red sides of the spectrum decayed faster than that at the center, which has led to the conclusion that the Franck–Condon state→fluorescence state conversion occurs within time-resolution of apparatus (<100 fs) owing to coupling with intra-chromophore high frequency modes and faster initial decay is due to sharpening of band shape caused by a decrease of amplitudes of hfm along the reaction coordinate of twisting.

A soft-landing experiment on organometallic cluster ions: infrared spectroscopy of V(benzene)2 in Ar matrix by Ken Judai; Kentaro Sera; Shin-ichi Amatsutsumi; Keiichi Yagi; Tomokazu Yasuike; Satoshi Yabushita; Atsushi Nakajima; Koji Kaya (277-284).
Vanadium (V)–benzene cluster ions, produced by laser ablation with reaction toward benzene vapor, were size-selected and deposited into a low-temperature Ar matrix. Infrared spectrum of V1(benzene)2 in the Ar matrix was measured after one-hour deposition with the deposition energy of 20 eV. The spectrum was in agreement with both the reported spectrum and our theoretical calculations, showing that (1) V1(benzene)2, prepared in the gas-phase reaction, takes a sandwich structure and that (2) the ions were soft-landed onto the Ar matrix and were neutralized by charge transfer from a metal substrate without fragmentation.

Structural characterization of 9-cyanoanthracene–water by rotational coherence spectroscopy by Kazuhiro Egashira; Yasuhiro Ohshima; Okitsugu Kajimoto (285-292).
Rotational coherence spectroscopy (RCS) has been applied to determine the rotational constants of the two isotopic species of the 9-cyanoanthracene (CNA)–water complex, CNA–H2O, and CNA–D2O. To support the experimental observation, DFT calculations at the B3LYP/6-31G(d, p) level have been also performed to identify several stable conformations. The structure of the complex is found to be such that water is hydrogen-bonded to the π-electrons of the cyano group of CNA. Geometrical parameters consistent with the experimental results are evaluated.

Upconversion excitation of Cr3+ 2 E emission in Y3Ga5O12 codoped with Cr3+ and Yb3+ by S. Heer; M. Wermuth; K. Krämer; H.U. Güdel (293-297).
The 2 E→4 A 2 emission of Cr3+ in crystals and glasses is of great importance in science and technology. We report a new excitation mode for this emission in Y3Ga5O12 (YGG) codoped with Cr3+ and Yb3+. It is based on an upconversion mechanism using 2 F 5/2 of Yb3+ as an intermediate state. Excitation in the near-IR at 969.6 nm leads to visible luminescence around 700 nm at low temperature. In YGG:2%Cr3+,1%Yb3+ at 15 K and for a laser power of 150 mW the efficiency of the process is 5.5%. From its time dependence the upconversion mechanism is found to be dominated by an energy transfer step: Two excited Yb3+ ions simultaneously transfer their 2 F 5/2 excitation to Cr3+.

Fabrication and optical absorption of ordered indium oxide nanowire arrays embedded in anodic alumina membranes by Maojun Zheng; Lide Zhang; Xinyi Zhang; Jun Zhang; Guanghai Li (298-302).
Ordered semiconductor In2O3 nanowire arrays embedded in anodic alumina membranes were fabricated by electrodeposition and oxidizing methods. The X-ray diffraction and transmission electron microscopy indicate that the In2O3 nanowires with polycrystalline structure are uniformly assembled into the hexagonally ordered nanochannels of the anodic alumina membranes. The optical absorption band edge of In2O3 nanowires array exhibits a marked red shift with respect to that of the bulk In2O3, and depends on the post-heat treatment temperature. This is attributed to the oxygen vacancy in In2O3 nanowires and the interface interactions between the anodic alumina membranes and the In2O3 nanowires.

Predicting polarizabilities and lifetimes of excitons on conjugated polymer chains by J.-W. van der Horst; P.A. Bobbert; P.H.L. de Jong; M.A.J. Michels; L.D.A. Siebbeles; J.M. Warman; G.H. Gelinck; G. Brocks (303-308).
The properties of excitons on three different conjugated polymers in solution are investigated both experimentally and theoretically. The theoretical description of the excitons is obtained by solving the electron-hole Bethe–Salpeter equation (BSE) for the polymers, starting from a calculation within density-functional theory. The calculated radiative lifetimes and polarizabilities of the excitons are compared with experimental results from time-resolved fluorescence decay and flash-photolysis microwave conductivity measurements. The quantitative agreement demonstrates the predictive power of the theoretical approach.

The temperature rise induced by illumination in a (YAl3(BO3)4) crystal activated with Nd3+ luminescent ions has been measured under spontaneous and stimulated emission conditions. Due to the low-quantum efficiency (18–26%) of the Nd3+ ion in this crystal, a remarkable temperature decrease (13° at 150 mW of absorbed pump power) is observed when switching from spontaneous to stimulated emission. This `thermal cooling' can also be used to estimate the B Einstein coefficient. The value we have obtained, B=2.3×1014   m 3   J −1   s −1 for the main laser transition, is in good agreement with those reported by other methods.

We have considered the dendrimer supermolecule as comprised of two-level systems as monomer units on the nodes of a Cayley tree. Each unit undergoes dissipation and driving by an external laser field along with nearest neighbour interaction among the monomer units. We have studied the steady-state absorption spectra. The effects of Cayley tree geometry on the spectral properties are investigated through the intensity and width of the spectra. The origin of the enhanced energy transfer mechanism of the extended dendrimer in comparison to the compact one is explained.

The correlation factor in the explicitly correlated wave function for the ground state of the helium atom has been analyzed. The general structure of the correlation factor (including its angular dependency) in the region of small r 12 has been obtained. The `extent of non-sphericity' of the correlation factor, g(r 1,r 2,r 12), is proportional to the first derivative of logarithm of the `coalescence function' h(r)=g(r,r,0).

Dissociative recombination of antiprotonic atomcules p ̄ He + with positronium: towards antihydrogen synthesis? by Sébastien Sauge; Pierre Valiron; István Mayer (330-336).
We investigate the reactive association of metastable antiprotonic helium `atomcules' ([ p ̄ He +]nl ) with positronium(Ps). In the framework of the Born–Oppenheimer approximation, we further discuss the evolution and stability of the intermediate complex (α, p ̄ , e+, 2e) using a classical trajectory approach for treating the nuclei (α, p ̄ ). We predict two possible channels for the atomcule–Ps reaction depending upon the atomcule principal quantum number n:n ⩾ 38 states dissociate to H ̄ , whereas, n<38 states form a new class of metastable atomcules, which could be confirmed by laser spectroscopy. The present work illustrates the pertinence of simple chemical physics concepts to the study of exotic processes involving antimatter.

Further investigation on the validity of Stokes–Einstein behaviour at the molecular level by Regula Walser; Berk Hess; Alan E. Mark; Wilfred F. van Gunsteren (337-342).
Stokes–Einstein behaviour at the molecular level is investigated by simulating water at different temperatures and by simulating `water' models with different mass distributions. When combining Stokes' law for the viscosity with Einstein's formula for the diffusivity, an expression for the product of these quantities is obtained, which shows that the product of diffusivity and viscosity should be independent of the mass distribution and positively proportional to the temperature. Using both, equilibrium and non-equilibrium simulation techniques to compute the viscosity slight deviation from Stokes–Einstein behaviour was found for the `water' models and temperatures investigated. Non-equilibrium simulation seems to yield systematically lower values for the viscosity than the equilibrium simulation.

A novel simulation method for unbinding a ligand from its receptor is described. It requires no prior knowledge of the unbinding trajectory and has atomic resolution. It places forces of equal magnitude but opposite directions on the two molecules, and lets the system locate an unbinding trajectory. The mutual repulsion method has been applied successfully to the bovine serum retinol-binding protein / retinol complex. A change in water structure has been observed during the unbinding process. The free energy change of unbinding has also been evaluated, and the value compares favourably with the experimental result.

An ab initio quartic force field calculated from a cc-pVTZ basis set at CCSD(T) level of theory is used to compute the vibrational energy levels of diphosphorus oxide, P2O, in the range 200–2000  cm −1 . The most important vibrational configurations, constructed from harmonic vibrational wavefunctions, selected by an iterative process by means of a variational perturbational method are diagonalized. The results show a good agreement with the most reliable experimental values such as ν 3, the ν 1+ν 3ν 1 hot band and two postulated Fermi resonances and predict unobserved overtones and combinations bands in the medium IR region.

Phase shift cavity ring-down measurement of C–H (Δv=6) vibrational overtone absorptions by Ernest K Lewis; Dovie Reynolds; Xiaochuan Li; Geraud de Villele; Charles Leduc; David L Cedeño; Carlos Manzanares I (357-364).
Phase shift cavity ring-down absorption spectroscopy with a continuous laser is used to measure the absorption coefficients and integrated cross-sections for the Δv=6 C–H stretching overtones of C2H4,C2H6,C3H8, n-C4H10, and n-C5H12. The absorption spectrum is obtained by measuring the magnitude of the phase shift that an intensity modulated continuous laser beam experiences upon passing through an optical cavity. Sensitive absorption detection (10−6   cm −1 ) on gas-phase samples is demonstrated.

Theoretical Gibbs free energy study on UO2(H2O) n 2+ and its hydrolysis products by Satoru Tsushima; Tianxiao Yang; Atsuyuki Suzuki (365-373).
Hydration of uranyl ion (UO2 2+) in aqueous system was investigated using hybrid density functional theory B3LYP method. Gibbs free energies and solvation energies for different UO2(H2O) n 2+ (n=4, 5, and 6) (including the first and the second solvation shell) clusters were calculated. Polarized continuum model (PCM) was used to calculate the solvation energy. The results show that the hydration number of UO2 2+ in liquid phase is 5. The hydrolysis reactions of UO2(H2O)5 2+ were investigated. The temperature and pressure effects on the reaction energies were studied. It was found that temperature and pressure significantly changed the equilibrium constants of hydrolysis reactions.

Dipole-bound anion of 1,3-butanediol. Ab initio and Rydberg electron transfer spectroscopy study by S Carles; C Desfrançois; J.P Schermann; A.F Jalbout; Ludwik Adamowicz (374-380).
Rydberg electron transfer spectroscopy (RET) has been used to determine the dipole-bound (DB) electron affinity (EA) of 1,3-butanediol and a single spectral feature was obtained corresponding to the EA value of 8±1 meV. A series of high-level ab initio calculations were also carried out for this system. They revealed an interesting configuration landscape of the 1,3-butanediol DB anion with four minima corresponding to different configurations. All four configurations can be responsible for the single RET spectral peak.

Can NO2 + exist in bent or cyclic forms? by A.K Füzéry; R Burcl; L.L Torday; P Császár; O Farkas; A Perczel; M.A Zamora; J.G Papp; B Penke; P Piecuch; I.G Csizmadia (381-386).
Calculations of NO2 + at HF, CBS-4, CASSCF, MBPT(2), MBPT(3), and MBPT(4) theory levels, using 3-21G and 6-31G(d) basis sets, found two C2V structures along with the linear geometry. Computations using MBPT(2) and CCSD(T) approaches and the aug-cc-pvtz basis set confirmed these results. Harmonic vibrational frequency calculations, performed with MBPT(2) and CCSD(T) theories, indicated that the linear structure was the global minimum while one of the bent structures (∠ONO=80°) was a higher energy local minimum. The second C2V structure (∠ONO=45°) exhibited a large imaginary vibrational frequency along the asymmetric stretching (B2) mode, indicating its saddle point nature.

The effects of anisotropic hyperfine interactions on the recombination reactions of spin correlated radical pairs in a weak applied magnetic field are discussed in the context of the radical pair mechanism (RPM). Model calculations are presented for radical pairs containing a single spin-1/2 nucleus with an axial or rhombic coupling to one of the unpaired electrons. The so-called low field effect (LFE) and various resonances in the magnetic field effect (MFE) are calculated. Approximate analytical expressions are given for the field positions of the resonances which are shown to arise from energy level crossings.

The zeroth-order regular approximation (ZORA) to the Dirac Hamiltonian and the Douglas–Kroll–Hess Hamiltonian (DKH) in their scalar-relativistic formulation have been implemented in a density functional code. The two approaches are compared on the same footing, i.e., using the same exchange-correlation functionals, basis sets and grids for numerical integration. The monohydrides, monooxides and monofluorides of La, Lu, Ac and Lr have been selected for a calibration study. Both methods yield very consistent results for bond lengths, binding energies and vibrational constants. Comparison is also made to experimental data as well as other relativistic all-electron and pseudopotential results.

The frequency-dependent dipole polarizabilities are calculated for the five lowest states 31S; 41S; 31P; 33P and 43S of Mg by using our time-dependent gauge invariant method (TDGI). Estimations of the long-range dispersion coefficients for all the first-molecular states dissociations of Mg2 are proposed. Accuracy of the results is checked through the calculations obtained from a length, a velocity and a mixed approach in the formulation of the oscillator strengths and the corresponding dynamic dipole polarizabilities. In all cases, the length results appear as a reference for the comparison with some previous works concerning the ground state. The long-range coefficients reported for almost all the low-lying states are new and predict a repulsive interaction between the 41S states.

The interaction of halogen atoms with the p(2 × 1)-Ag(1 1 0) surface has been studied by using the pseudopotential total energy method based on density functional theory (DFT). Adsorption properties of halogen atoms at several possible sites on p(2 × 1)-Ag(1 1 0) are presented. Our results show that adsorption energies decrease from F to I. The most stable adsorption site for all halogen atoms is the short bridge (SB) site. The adsorption of halogen can greatly affect both the structural and electronic properties of the surface.

In a recent Letter, M. Rode et al. [Chem. Phys. Lett. 314 (1999) 326] claim the incapability of the coupled cluster singles and doubles model including connected triple excitations to describe the intermolecular interaction in the CO dimer. We have investigated the problem and found several facts in favor of the coupled cluster singles and doubles model including connected triple excitations being accurate even for the CO dimer.

In an earlier Letter [Chem. Phys. Lett. 314 (1999) 326] we pointed out that the CCSD(T) method lacks some terms necessary for an accurate computation of the CO–CO interaction. In a Comment by Pedersen et al. [Chem. Phys. Lett. 304 (2000) 419] this finding is contested. In the present Reply we show that Pedersen et al. missed the main point of our argument.

Author index (426-433).