Chemical Physics Letters (v.338, #4-6)

Conical intersections between electronic-state potential energy surfaces are known to provide extremely efficient pathways for fast dynamical molecular processes. In this Letter, we describe theoretical work which, for the first time, identifies the existence of such a feature in the field of long-range inter-molecular photo-initiated electron transfer. This is the process at the heart of many biological processes. A typical case is studied here: the donor–acceptor pair porphyrin–quinone, which forms the basis for photosynthesis. This discovery brings a new aspect to the treatment of this fundamental process.

Theoretical study of ZnO (1 0  1  0) and Cu/ZnO (1 0  1  0) surfaces by A. Beltrán; J. Andrés; M. Calatayud; J.B.L. Martins (224-230).
Periodic HF/6-31G and a hybrid density functional, B3LYP/6-31G, calculations have been carried out in order to determine the geometric and electronic structure of bulk ZnO. The lattice parameters, bulk modulus, charge distribution and band structure are reported. Surface energy and charge distribution of the ZnO (1 0  1  0) surface are obtained, while top site adsorption of Cu atoms on Zn or O atoms on the ZnO (1 0  1  0) surface are considered. Optimized distances, charge transfers, vibrational frequencies and binding energies associated with both types of adsorption processes are calculated. The theoretical results are compared with previous theoretical studies and available experimental data.

Highly ordered TiO2 nanowire arrays were prepared in anodic alumina membranes by anodic oxidative hydrolysis of TiCl3. The TiO2 nanowires are polycrystalline anatase-phase with uniform diameters around 50 nm and are composed of very small crystallites with diameters of about 2–4 nm. After annealing the crystallites grow to about 7 nm in diameters. At room temperature, Raman measurements of the TiO2 nanowire arrays show typical anatase TiO2 Raman spectra with significant broadening and shift, which can be attributed to phonon size confinement and oxygen deficiency.

The duals of the polyhedra for the deltahedral boranes B n H n 2− (n=6, 8, 10, 12) have the same geometries as those of symmetric skyrmions arising from the non-linear field theory of a system of interacting mesons and B= 1 2 (n+2) baryon (proton and/or neutron) sources within a nucleus. In the application of such a skyrmion model to the skeletal chemical bonding in deltahedral boranes, acetylenic HBBH units are considered to be the analogues of the mesons and the chemical interactions between the HBBH units necessary to construct deltahedra with even numbers of boron atoms are considered to be analogues of baryons.

Conductivity of fullerene-doped optical glasses by Heping Zeng; Zhenrong Sun; Yusaburo Segawa; Fucheng Lin; Sen Mao; Zhizhan Xu (241-246).
Appropriate amount doping of fullerenes caused insulating phosphate and fluorophosphate optical glasses to be conductive at room temperature. Microphotoluminescence measurements indicated the existence of ordered and disordered microstructures. A large number of fullerene-related medium-range microdomains aggregated as self-organized islands along the glass networks, and brought about connective tissues in the vitreous matrices for percolation migration of metal cations. The variation of microphotoluminescence induced by electric field presented us an indirect way to characterize the random activation, percolation migration, and retrap of metal cations near fullerene-related amorphous islands.

NMR spectroscopy of molecules oriented in liquid crystalline matrices provides information on the molecular structure and order parameters. Analyses of such spectra are generally carried out by numerical iterative calculations. The iterative analysis requires an initial estimate of proton–proton dipolar couplings. In the present study it is shown, for an AAMMX spin system, the two-dimensional HMQC experiment provides the magnitude of proton–proton dipolar couplings. In the case of an AAA″AX spin system the experiment provides the initial starting dipolar couplings values for the iterative analysis. The use of this experiment in combination with two-dimensional HSQC experiments has been demonstrated for the analyses of 1,1-difluoro-1,2-dibromoethane and p-dibromobenzene.

We report a simplified optical heterodyne detected transient grating setup consisting of a single diffractive optical element based on modifications of the arrangement used by Miller and co-workers [J. Phys. Chem. A, 103 (1999) 10619]. Our arrangement features ease of alignment, suppression of scattering and is free of pump–probe contamination in the detected transient grating signals. The capability of our arrangement is demonstrated by measurements on a non-resonant system, CS2, and a resonant system, malachite green in ethanol.

Deduction of the conformation of short chain luminescent conjugated polymers from single molecule photophysics by J.D. White; J.H. Hsu; W.S. Fann; Shu-Chun Yang; G.Y. Pern; S.A. Chen (263-268).
The fluorescent transient of single polymers of a PPV derivative, poly(2,5-dioctyloxy p-phenylene vinylene) (DOO-PPV) spin-cast in polystyrene matrix is observed. Having the polymer with low-defect density and length close to its persistent length, the effect of defects on conformation can be investigated. Independent chromophores align in the majority of cases suggesting that the polymer maintains a rod-like structure in the absence of defects. Non-aligned chromophores are the result of defects that introduce `kinks' in the polymer conformation.

Experimental observation of nonlinear circular dichroism in a pump–probe experiment by H. Mesnil; M.C. Schanne-Klein; F. Hache; M. Alexandre; G. Lemercier; C. Andraud (269-276).
We present experimental evidence of nonlinear optical activity in a time-resolved pump–probe experiment carried out in a liquid of chiral molecules. By modulating the polarization of the probe or of the pump, we measure a variation of the circular dichroism (CD) induced by the pump. Application of these techniques to time-resolved spectroscopy of excited molecules is discussed.

Infrared water recombination lasers by E.A. Michael; C.J. Keoshian; D.R. Wagner; S.K. Anderson; R.J. Saykally (277-284).
Extensive mid-infrared lasing action by water molecules is observed in a supersonic plasma expansion contained inside an optical supercavity. An ion–electron dissociative recombination mechanism is proposed, that may also be relevant to atmospheric and astrophysical environments.

Non Franck–Condon effects in the photoionization of molecular nitrogen to the N 2 +   A   2Π u state in the 19–34 eV photon energy region by Jaume Rius i Riu; A. Karawajczyk; M. Stankiewicz; K. Yoshiki Franzén; P. Winiarczyk; L. Veseth (285-290).
Photoionization to the N 2 +   A   2Π u state is studied using photoelectron spectroscopy. Experimentally, vibrational branching ratios for the v =0–3 levels obtained for the first time in the 20–34 eV region, show strong non Franck–Condon effects around 22 eV. Using ab initio many body perturbation theory, branching ratios for ionization to the A   2Π u state are calculated. This study indicates that the Franck–Condon breakdown in the photoionization of the N2u electron is due to autoionization from Rydberg and valence states of N2.

We have investigated the chemical dynamics of Mg+-acetaldehyde bimolecular complexes following Mg+-centered (3p←3s) excitation. Non-reactive dissociation to Mg+ is the dominant decay channel. However, excitation in the 3pσ(A)←3sσ(A) band also results in reactive dissociation to MgH+, MgCHO+, and MgCH3 + products, showing a clear σ-like electronic orbital alignment preference for chemical quenching. Isotope substitution shows reaction involves a direct attack on the aldehydic C–H or C–C bonds; the relative product branching indicates that the probabilities for C–H and C–C bond cleavage are comparable.

The 266 nm photodissociation of gaseous C6H5NO has been studied by monitoring the nascent NO ( X 2Π v″=0–3) product using the single-photon laser-induced fluorescence technique. The rotational-state distributions of the nascent NO photofragment have been measured and can be characterized by Bolzmann temperatures. The vibrational-state and Λ-doublet populations were also determined. Energy disposal into the internal degrees of freedom of NO ( X 2Π) photofragment is about 18% of the total available energy. Some planarity in the fragmentation process was observed.

The stabilization of active oxygen species by Pt supported on TiO2 by Hisahiro Einaga; Atsushi Ogata; Shigeru Futamura; Takashi Ibusuki (303-307).
Pt/TiO2 was active for the oxidation of CO to CO2 in the dark at ambient temperature after UV irradiation. Pure TiO2 was inactive and the presence of Pt supported on TiO2 was indispensable for the reaction. Based on the ESR study, it was found that Pt deposited on TiO2 stabilized the O and O3 species photoformed on the TiO2, and they were responsible for the CO oxidation.

Resonance Raman and density functional study of the A-band absorption of C5H5[WCCPh]O2 by Yung Fong Cheng; David Lee Phillips; Guo Zhong He; Chi-Ming Che; Yun Chi (308-316).
Resonance Raman spectra including absolute Raman cross-section measurements and density functional theory (DFT) calculations were performed to study the A-band absorption of C5H5[WCCPh]O2. The three most intense Franck–Condon active modes, the nominal WO stretch, CC stretch and CC stretch, show noticeable intensity in their overtones as well as their combination bands with each other. This is consistent with the changes in the HOMO–LUMO electron densities obtained from the DFT calculations. This suggests that the excited-state experiences significant structural changes simultaneously in the WO, CC and CC groups and the charge transfer is delocalized in the electronic transition.

Emission of SH radicals in solid krypton: mixed quantum-classical molecular dynamics simulations by Denis A Firsov; Bella L Grigorenko; Alexander V Nemukhin; Leonid Yu Khriachtchev; Markku O Räsänen (317-322).
Direct simulations of the specific features in the A2 Σ +(v =0)→X2 Π emission of SH radicals in solid krypton, namely, the appearance of two bands with different lifetimes, are carried out by using mixed quantum-classical molecular dynamics (MD). More evidence is provided to support the assignment of these two bands to different trapping sites of electronically excited SH in krypton, including estimates of the radiative lifetimes. The higher-energy emission with a shorter lifetime corresponds to a site with relatively free movement of SH(A) inside the lattice. The emission at longer wavelengths and with longer lifetime originates from a site where one of the matrix atoms is attached to the guest molecule forming a transient complex SH(A)·Kr inside the solvation shell.

A significant portion of the energy functional of the one-particle reduced density matrix (1-RDM) is elucidated through geminal functional theory (GFT) [D.A. Mazziotti, J. Chem. Phys. 112 (2000) 10125]. We optimize the functional through an iterative solution of the 1,3-contracted Schrödinger equation (1,3-CSE). The method yields energies which are (i) above the true energy, (ii) more accurate than Hartree–Fock, and (iii) exact for a general family of correlated Hamiltonians. By applying a learning algorithm to these results, we determine correlation energies within 10% for atoms and molecules.

Computer simulations of one- and two-color experiments in above threshold dissociation (ATD) are reported for the first heteronuclear alkali ion LiNa+. We focus on the 12Σ+→12Π→4,52Σ+ process, with dissociation to Li++Na(3p) or Li(3s)+Na+. The product yields are determined by the presence of an avoided crossing between the 4 and 52Σ+ potential curves, according to the frequency and delay of the second laser pulse.

NMR implementation of a building block for scalable quantum computation by D.E. Chang; L.M.K. Vandersypen; M. Steffen (337-344).
We report the implementation of the central building block of the Schulman–Vazirani procedure for fully polarizing a subset of two-level quantum systems which are initially only partially polarized. This procedure consists of a sequence of unitary operations and incurs only a quasi-linear overhead in the number of quantum systems and operations required. The key building block involves three quantum systems and was implemented on a homonuclear three-spin system using room temperature liquid-state nuclear magnetic resonance (NMR) techniques. This work was inspired by the state initialization challenges in current NMR quantum computers but also shines new light on polarization transfer in NMR.

The effect of the so-called change of picture for operators in approximate relativistic theories on the second-order properties arising from some external perturbation, is considered. By means of the direct perturbation theory the general formula for the lowest-order relativistic correction to second-order properties is derived. The term which arises from the change of picture for the external perturbation operator is identified and evaluated for dipole and quadrupole polarizabilities. For the 1s1/2 state of the hydrogen-like ions this term is found to bring about 16% and 7% of the total lowest-order irelativistic correction to the dipole and quadrupole polarizabilities, respectively. This finding is discussed in terms of its importance for long range interactions between heavy systems.

The protonation of nitric acid by a proton has been studied by ab initio direct molecular dynamics (MD) simulation. Energies of important structures on the potential surface were calculated by the G2MP2 method. Four intermediates and four transition state structures have been identified. All four reactive intermediates were found to play significant roles in the mechanism of reaction, but the dominant channel is HNO3+H+→NO2 ++H2O. Reaction energies for reaction to form each of the possible products range from −150 to −180 kcal/mol.

MP2/6-311++G ∗∗ calculations were performed on HF⋯H2O, HF⋯NH3, HF⋯LiH, (H 2 O)2, (HCOOH)2,C 2 H 2⋯H 2 O , H 2 O⋯NH 3, (C 2 H 2)2 complexes to characterise different hydrogen bonds; typical as O–H⋯O and O–H⋯N, weak like C–H⋯O and C–H⋯π, dihydrogen bonds, etc. For such heterogeneous samples a new measure of hydrogen bond strength was introduced. The Bader theory was also applied to characterise hydrogen bonds.

A Gaussian-3 investigation of N7 isomers by Xin Wang; Anmin Tian; N.B Wong; Chi-Kin Law; Wai-Kee Li (367-374).
A Gaussian-3 investigation is carried out to examine the isomers of N7 clusters. Twelve species are found, five of which are reported for the first time, including the most stable isomer, I. Isomer I, with Cs symmetry, consists of a five-membered ring and an N2 side-chain. Natural bond orbital analysis is also carried out to study the bonding of the isomers. It is found that the stability of some of the more stable isomers is enhanced by conjugation or hyperconjugation.

A new approach to the bond-breaking problem is proposed. Both closed and open shell singlet states are described within a single reference formalism as spin-flipping, e.g., α  →  β , excitations from a triplet (M s=1) reference state for which both dynamical and non-dynamical correlation effects are much smaller than for the corresponding singlet state. Formally, the new theory can be viewed as an equation-of-motion (EOM) model where excited states are sought in the basis of determinants conserving the total number of electrons but changing the number of α and β electrons. The results for two simplest members of the proposed hierarchy of approximations are presented.

Kinematic rotations in RRKM theory by L. Bonnet; J.C. Rayez (385-388).
It is shown that kinematic rotations allow the generation of variable canonical coordinate systems making the application of RRKM theory relatively simple with respect to existing methods.

Partial multidimensional grid generation method for efficient calculation of nuclear wavefunctions by Tzvetelin Iordanov; Salomon R. Billeter; Simon P. Webb; Sharon Hammes-Schiffer (389-397).
A partial multidimensional grid generation method for the efficient calculation of nuclear wavefunctions is presented. This method substantially decreases the number of potential energy calculations by avoiding this calculation for grid points with high potential energy. The application of this method to the calculation of three-dimensional hydrogen nuclear wavefunctions for hydride transfer in the enzyme liver alcohol dehydrogenase is presented. The results indicate that the partial multidimensional grid generation method is nearly as accurate as and significantly faster than the standard full grid method.

Possibility of the magnetic field effect on the thermal decomposition of N2O: molecular dynamics simulation by Osamu Takahashi; Naotake Kurushima; Akio Kawano; Ko Saito (398-406).
Molecular dynamics (MD) model calculations for the thermal decomposition of N2O with external magnetic field were performed. The effect of external magnetic field was modeled by parameterization of the interaction term between the singlet and triplet potential surfaces. It was suggested that the increase of the rate constant by external magnetic field could be explained by means of the increase of interaction term which is dependent on the angle of the Jacobi coordinate.

Ab initio g-tensor calculations of hydrogen bond effects on a nitroxide spin label by Maria Engström; Rikard Owenius; Olav Vahtras (407-413).
Hydrogen bonding effects on the electron paramagnetic resonance (EPR) g-tensor of a nitroxide spin label was investigated by quantum chemical calculations. The restricted open-shell Hartree–Fock (ROHF) linear response method with the atomic mean field approximation (AMFI) was used in the calculations. The results show that hydrogen bonding reduces the g-tensor component directed along the NO bond, g xx . This decrease is traced to higher excitation energy and lower spin–orbit coupling and angular momentum matrix elements for the n–π* excitation. The calculations show that the g-tensor is practically invariable when hydrogen bonding was modeled with methanol instead of water.

Author Index (414-420).