Chemical Physics Letters (v.345, #5-6)

Observation and identification of the molecular triplet in C60 thin films by G Chambers; A.B Dalton; L.M Evans; H.J Byrne (361-366).
The excited state properties of C60 thin films have been probed at 77 K using Raman spectroscopy. The change in the Raman, A 2g mode of C60, whose position is largely independent of temperature was monitored as a function of the excitation intensity at 514.5 nm. This mode, normally positioned at 1469 cm−1, was seen to shift to a lower Raman frequency with increasing laser intensity. Two excited state species have been identified. The first, at 1466 cm−1, has been associated with the molecular triplet of C60, while the second species, at 1463 cm−1, has been speculated to be an excited state co-operative in the solid.

Electronic structures of gold nanowires by Akira Hasegawa; Kazunari Yoshizawa; Kazuyuki Hirao (367-371).
The electronic properties of the 7-1 structure of a gold nanowire, which is the simplest structure among possible helical multi-shell nanowires, are examined. Density of states (DOS) and crystal orbital overlap population (COOP) analyzes at the extended Hückel level of theory show that the contribution of the inner gold-atom row to the electric conduction and structural strength is small. The outer tube is responsible for both the structural stability and the electric conduction. The gold atoms of the nanowire are charged when the nanowire has an inner row. There is a wavy negative charge distribution in the outer tube when the outer tube has a helical structure.

Micro-Raman investigation of GaN nanowires prepared by direct reaction Ga with NH3 by J Zhang; X.S Peng; X.F Wang; Y.W Wang; L.D Zhang (372-376).
Ordered crystalline GaN nanowires embedded in the nanochannels of anodic alumina membrane (AAM) were achieved by direct reaction Ga with NH3. The impact of reaction temperatures on Raman spectroscopic properties of GaN nanowires is investigated. X-ray diffraction and transmission electron microscopy (TEM) observations demonstrate that the crystalline GaN nanowires have hexagonal wurtzite structure. The hexagonal wurtzite structure GaN nanowires prepared at 960 °C are about 40 nm in diameter and up to several hundreds of micrometers in length.

Microstructures of gallium nitride nanowires synthesized by oxide-assisted method by W.S. Shi; Y.F. Zheng; N. Wang; C.S. Lee; S.T. Lee (377-380).
Gallium nitride (GaN) nanowires were synthesized using the recently developed oxide-assisted method by laser ablating a target of GaN mixed with gallium oxide (Ga2O3). Transmission electron microscopic characterization showed that GaN nanowires were smooth and straight with a core-sheath structure of 80 nm in average diameter and tens of micrometers in length. Both hexagonal and cubic structured GaN nanowires were produced. The growth mechanism was discussed.

Study of laser action of Coumarine-153 incorporated in sol–gel made silica/poly(propylene oxide) nanocomposite gels by Elias Stathatos; Panagiotis Lianos; Urska Lavrencic Stangar; Boris Orel (381-385).
Coumarin-153 (C-153) has been incorporated by the sol–gel method into transparent nanocomposite matrices made by using a precursor composed of a poly(propylene oxide) (PPO) chain covalently linked by urea bridges with two end triethoxysilane groups. The solid gels can be used without any further treatment as active components in a dye laser, providing a rather wide range of laser emission. This range is further widened by exploiting the solvatochromic effect of coumarin and the different polarity of the solubilization sites provided by nanocomposites of various PPO chain sizes.

Energy transfer in nanostructured oligothiophene inclusion compounds by G. Bongiovanni; C. Botta; G. Di Silvestro; M.A. Loi; A. Mura; R. Tubino (386-394).
Resonant energy transfers from terthiophene (T3) to quinquethiophene (T5) oligomers embedded in the nanochannels of perhydrotriphenylene (PHTP) crystals are studied by cw and femtosecond spectroscopy. The stringent geometry imposed by the host results in a very peculiar supramolecular organization of the guest molecules consisting of parallel linear arrays of chromophores. This provides a unique opportunity to make a quantitative analysis of the energy transfer phenomena and in particular to distinguish between heterotransfers and homotransfers. The experimental data fitted by a suitable theoretical analysis indicate that homotransfers become important in the long time dynamics and that the heterotransfer rate is satisfactorily described by the analytical solution obtained by assuming a continuous intermolecular spacing.

A new highly selective calix[4]arene-based fluorescent probe for Ca2+ by Huibiao Liu; Yan Xu; Baolong Li; Gui Yin; Zheng Xu (395-399).
A new calix[4]arene Schiff Base with two anthracenes has been synthesized; Investigation of its photo-physical and complexing properties towards alkali and alkaline earth metal ions reveals a high selectivity for Ca2+ in MeCN–ethanol mixtures.

Modifications to the satellite-transition magic angle spinning (STMAS) experiment for obtaining high-resolution NMR spectra of quadrupolar nuclei are discussed. A phase-modulated `shifted-echo' STMAS experiment that yields pure absorptive lineshapes is presented and shown to be compatible with the `split-t 1' technique used in multiple-quantum (MQ) MAS NMR to reduce the duration of t 2 acquisition and avoid shearing the final two-dimensional spectrum. The application of STMAS to nuclei with spin greater than I=3/2 is also considered, the dispersion of isotropic shifts achieved by STMAS and MQMAS are compared, and the effects of anisotropic `cross-term' broadening mechanisms on linewidths in `isotropic' STMAS spectra are discussed.

Photophysical properties of dibenzotropylium cation incorporated within acidic ZSM-5 zeolite by Marı́a Luz Cano; Michelle N. Chrétien; Hermenegildo Garcı́a; J.C. Scaiano (409-414).
Dibenzotropylium ion (DT+) has been generated as an indefinitely persistent species within the channels of ZSM-5 in its H+-form. Diffuse reflectance laser flash photolysis has allowed detection of a transient (two bands: 300 nm, sharp and ∼440 nm broad) decaying in the μs time-scale that has been assigned to the corresponding triplet excited state. The tight fit of DT+ within the straight channels (5.2×5.7  A ̊ 2 ) of ZSM-5 and the presence of coadsorbed water explain why the DT+ triplet excited state is not quenched by oxygen but interacts with triethylamine, which is highly water-soluble. In the latter case, formation of a new transient compatible with DT (λ max=270 and 350 nm) through electron transfer from the amine to DT+ triplet is observed.

We studied the photodissociation of water-clustered HNO3 molecules at 193 nm, a process relevant in atmospheric chemistry, by generating water clusters by adiabatic expansion and doping them with HNO3 using the pickup method. The nascent OH(X 2Π) photofragments were probed by LIF, and the rotational state distribution in the exclusively produced vibrational ground state determined. These experiments were complemented by corresponding ones with argon and methanol clusters. The average cluster size was estimated to be n∼200–800 depending on the compound. The results of this study are compared with those previously obtained from the photodissociation of the HNO3 monomer.

Pure long-range ion-pair Cs2 molecules by T Ban; H Skenderović; R Beuc; I Krajcar Bronić; S Rousseau; A.R Allouche; M Aubert-Frécon; G Pichler (423-428).
We performed absorption measurements in dense cesium vapor, around the Cs second principal series lines (6s→7p). Three satellite bands peaking at 454.3, 459.1 and 471.6 nm are found. New ab initio Cs2 potential curves calculated with the inclusion of the spin–orbit interaction are used for the identification and simulation of the observed satellite bands. The 454.3 and 459.1 nm satellite bands stem from avoided crossings of long-range ion-pair potential curves with long-range covalent potential curves associated with various asymptotes. Semiclassical spectral simulations of these ion-pair satellite bands show satisfactory agreement with measured spectra.

The luminescence of PbS nanoparticles embedded in sol–gel silica glass by Ping Yang; Chun Feng Song; Meng Kai Lü; Xin Yin; Guang Jun Zhou; Dong Xu; Duo Rong Yuan (429-434).
PbS nanoparticles embedded in a novel silica glass have been achieved in the present study by sol–gel processing. Their fluorescence properties have been evaluated and compared with those of un-doped glass. A novel luminescent phenomenon has been observed from the composite of PbS nanoparticles and the sol–gel silica glass. The photoluminescence (PL) spectrum of the composite consists of two emission peaks (440 and 605 nm). The Pb2+ ions in the sol–gel silica glass show sharp emission band. This novel luminescence from the samples is assigned to the composite structure of PbS nanoparticles and porous silica glasses.

Theoretical study on the kinetics and mechanism of the hydrogen atom abstraction reactions of CF3O+H2O and CF3OH+OH by Katarzyna Brudnik; Jerzy T. Jodkowski; Emil Ratajczak; Ramaiyer Venkatraman; Andrzej Nowek; Richard H. Sullivan (435-444).
Quantum mechanical ab initio calculations have been performed at various levels of theory to study kinetics of the reactions leading to formation/decay of CF3OH in the gas phase. It is shown that two considered reactions i.e., CF3O+H2O (reaction ) and CF3OH+OH proceed via formation of intermediate complexes. Mechanism of the reactions appears to be more complex, and may consist of three consecutive processes. Calculated rate constants are in excellent agreement with available experimental data. Derived expressions: k1=2.5×10−13×(T/300)1.4×exp(−3130/T)  cm 3   molec −1   s −1 and k−1=1.9×10−12×(T/300)1.0×exp(−3650/T)  cm 3   molec −1   s −1 allow a description of the kinetics of the reactions under investigation in the temperature range 300–1000 K.

Atomic and bond properties within the atoms in molecules (AIM) approach have been computed for a series of 52 alkyl diethers of formula CH3(CH2) n O(CH2) l O(CH2) m CH3 on HF/6-31++G**//HF/6-31G* electron distributions. The results indicate that the mutual influence of oxygen atoms is negligible when they are separated by more than three methylene groups, and that 13 different approximate transferable oxygen atoms can be considered in alkyl diethers. The regression analysis indicates that the atomic population, and remaining non-energetic properties of the different transferable oxygens for l>3 agree within the statistical error with those for the corresponding alkyl monoethers.

We explore a statistical-theoretic origin of the linear surprisal theory with respect to final energy disposals to a given vibrational (rotational or translational) mode in chemical reaction dynamics under a fixed total energy. As a consequence of a variational statistical theory, exponential distributions inherent in the linear surprisal theory, along with the necessity of the so-called prior distribution, arise quite naturally from a standard statistical rate expression without information theoretic reasoning or the maximum entropy principle (MEP).

Bound and quasibound states of HeH2 + and its isotopomers by B. Maiti; N. Sathyamurthy (461-470).
Bound and quasibound states of HeH2 + and its isotopic variants have been computed on the recently reported ab initio potential energy surface by Palmieri et al. [Mol. Phys. 98 (2000) 1835] using a time-dependent wave packet methodology. It is shown for the first time that the lowest energy bound states for HeH2 + and HeD2 + in three dimensions are doublets, with a splitting of 7.0 and 4.8 cm−1, respectively. Such a finding has profound implications for the interpretation of microwave and other spectra for the system.

Unidirectional wave propagation in one spatial dimension by Ágota Tóth; Dezső Horváth; Kenichi Yoshikawa (471-474).
The propagation of chemical waves in the model of the light-catalyzed Belousov-Zhabotinsky (BZ) reaction with asymmetric illumination has been studied numerically in a one-dimensional environment. The asymmetric distribution of light intensity is sufficient to yield unidirectional wave propagation in wide parametric domains. Depending on the excitability and the diffusion coefficient of the catalyst, two types of chemical diode exist with opposite directionality.

Highly accurate treatment of electron correlation in polymers: coupled-cluster and many-body perturbation theories by So Hirata; Ireneusz Grabowski; Motoi Tobita; Rodney J. Bartlett (475-480).
A series of accurate and size-extensive ab initio wavefunction-based methods, i.e., coupled-cluster (CCD, CCSD, LCCD, ACCD, QCISD, and LCCSD) and many-body perturbation theories [MBPT(2) and MBPT(3)], are formulated and implemented for infinitely extended one-dimensional lattices (polymers), by taking account of the periodic boundary conditions. We present the results of initial benchmark calculations and also investigate the spatial spread of electron correlation by plotting the atomic-orbital-based t 1- and t 2-amplitudes with respect to a unit cell parameter n. The two-electron integrals and t 2-amplitudes decay as n −1 and n −3, leading to the n −3 convergence of the lattice summations for correlation energies.

Magnetic excitations of Co2 dimer by G.L. Gutsev; S.N. Khanna; P. Jena (481-489).
The electronic and geometrical structure of the ground and excited states of Co2 and Co2 has been calculated using the density functional theory with two generalized gradient approximations for the exchange-correlation potential. The computed electron affinity of Co2 ( 5Δ g ) is in good agreement with experiment. For each permitted spin multiplicity, Co2 possesses several states having close bond lengths and/or total energies. It is found that Co2 possesses an antiferromagnetic singlet state which is inaccessible by excitations from the triplet states but could be reached through magnetic de-excitations.

On the performance of energy-consistent spin–orbit pseudopotentials: (111)H revisited by Michael Dolg; Hermann Stoll; Michael Seth; Peter Schwerdtfeger (490-496).
A new two-component relativistic pseudopotential (PP) of the energy-consistent (EC) variety, adjusted to multi-configuration Dirac–Hartree–Fock (MCDHF) data, is presented for the superheavy element 111 and is applied in correlated valence ab initio calculations, with and without inclusion of spin–orbit (SO) coupling, to the determination of spectroscopic constants of the element 111 monohydride. Good agreement with a recent study by Han and Hirao [Chem. Phys. Lett. 328 (2000) 453] is found, and it is concluded that a direct two-component PP fit is superior to a previously practiced two-step (scalar-relativistic/SO) adjustment procedure. We estimate the molecular constants of element 111 monohydride to be R e=1.529 Å, D e =2.83  eV and ω e =2642  cm −1 .

Adiabatic electron affinity (EA) of the CH2Br radical and vibrational frequencies and inversion barrier of the corresponding anion CH2Br have been calculated using ab initio coupled cluster and hybrid density functional methods with large basis sets up to the augmented correlation-consistent polarized quadruple-zeta (aug-cc-pVQZ) level. The effect of systematic basis set expansion on the calculated EA of CH2Br and inversion barrier of CH2Br has been investigated with the two theoretical approaches. Electron localization function (ELF) topological analysis of the CH2Br/CH2Br system is performed to enlighten the process of electron attachment to CH2Br to form CH2Br.

The MRSDCI/CIS study of excited electronic states of the SF2 radical by Y.-J. Liu; M.-B. Huang; X. Zhou; S. Yu (505-511).
The vertical (T v) and adiabatic (T 0) excitation energies for singlet electronic excited states of the SF2 radical have been calculated by using the multireference single and double excitation configuration interaction (MRSDCI) method and aug-cc-pVTZ basis sets augmented by Rydberg functions. The MRSDCI T v calculations indicate that the X 1 A 1 , 11 A 2 , 11 B 1 , 21 B 1 , 21 A 2 , 21 A 1 , 31 B 1 , 41 B 1 , 31 A 1 , and 11 B 2 states are the 10 lowest-lying singlet states. Based on the MRSDCI//CIS T 0 calculations (using CIS optimized geometries for excited states), the A, B, C, E, F, G, H, and I states of SF2 are assigned to 11 B 1 , 21 B 1 , 31 B 1 , 21 A 2 , 21 A 1 , 31 A 1 , 41 B 1 , and 11 B 2 , respectively.

Relationship between scanning near-field optical images and local density of photonic states by Gérard Colas des Francs; Christian Girard; Jean-Claude Weeber; Alain Dereux (512-516).
From numerical calculations based on Green's dyadic formalism, we show that a scanning near-field optical microscope (SNOM) working with a point-like illuminating probe delivers images that contain features directly related to the local density of photonic states (LDOS). More precisely, an unambiguous identification of the partial LDOSs (x, y or z polarized) can be made in the SNOM images when the solid angle of detection reaches 2π sr.

We report a new three-dimensional ab initio potential energy surface of the first excited singlet (11A′′) state of HCN. More than one thousand potential points have been calculated at the multi-reference configuration interaction level employing a large basis set. Variational calculations of the predissociative resonances of both HCN and DCN are performed on the three-dimensional spline fitted potential energy surface, which yield both positions and widths. Fairly good agreement with experiment confirms the accuracy of our new potential energy. These resonances provide valuable information on the photodissociation dynamics of HCN/DCN in the 11A″ state.

The X1 Σ + state of the 40 Ar 1 H + and 40 Ar 2 D + was explored with an ab initio molecular orbital (MO) study (MP4, basis set 6-311++G(3df, 3pd), followed with SDQ): E Total =−527.182 771 62 hartree at R e =1.2767  A ̊ (Exp. 1.280 3730(11)); D e =33 509.189  cm −1 ; μ=1.9283  D . The potential energy (PE) follows a Morse curve with r 2=0.9993. Vibrational term values are G 0(ArH+)=1374.95 (ArD+: 964.83)  cm −1 and G 1(ArH+)=4038.13 (ArD+: 2788.47)  cm −1 . Rotational constant B=315.406 897 GHz for 40 Ar 1 H + and 161.70 GHz for 40 Ar 2 D + (Exp. 158.702 3259(55) GHz). The energy level diagram and the electron density contours are discussed.

Density functional studies on aniline dimer cations by Norifumi Yamamoto; Kazuhiko Ohashi; Kazuyuki Hino; Hironobu Izutsu; Koichi Mogi; Yoshiko Sakai; Hiroshi Sekiya (532-538).
The structures of aniline dimer cation are investigated by the density functional theory calculations at the B3LYP/cc-pVDZ level. We obtained two stable conformational isomers which have `NH⋯N' or `NH⋯π' hydrogen bond. The NH⋯N isomer is more stable by 2.50  kcal mol −1 . The calculated infrared spectra suggest that the NH stretching vibrations due to the two isomers are overlapped in the experimental spectrum [Chem. Phys. Lett. 323 (2000) 43].

Author Index (539-548).