Chemical Physics Letters (v.370, #3-4)

Intramolecular vibrational redistribution of CH2I2 dissolved in supercritical Xe by K. Sekiguchi; A. Shimojima; O. Kajimoto (303-308).
Intramolecular vibrational energy redistribution (IVR) of CH2I2 in supercritical Xe has been studied. The first overtone of the C–H stretching mode was excited with a near infrared laser pulse and the transient UV absorption near 390 nm was monitored. Signals showed a rise and decay profile, which gave the IVR and VET (intermolecular vibrational energy transfer) rates, respectively. Solvent density dependence of each rate was obtained by tuning the pressure at a constant temperature. The IVR rate in supercritical Xe increased with increasing solvent density and asymptotically reached a limiting value. This result suggests that the IVR process of CH2I2 in condensed phase is a solvent-assisted process.

The low-frequency spectra of simple liquids have been studied with a stimulated Raman gain technique using tunable picosecond pulses in the mid-infrared region. The obtained results on CS2, CCl4, C2Cl4 and CDCl3 are rescaled to reduced Raman spectra, which are a representation of the low-frequency density of states of these liquids, weighted by the corresponding intermolecular polarizability. This thermal ‘bath’ is believed to accept or provide small portions of energy during vibrational relaxation processes. The technique demonstrated here has a large potential for time-resolved studies of vibrational relaxation and related phenomena.

Ab initio study on the mechanism of the HCO+O2→HO2+CO reaction by Mónica Martı́nez-Ávila; Julio Peiró-Garcı́a; Vı́ctor M Ramı́rez-Ramı́rez; Ignacio Nebot-Gil (313-318).
The gas-phase reaction HCO+O2→CO+HO2 has been investigated by means of ab initio calculations. The mechanism can proceed through either a direct hydrogen abstraction or addition of O2 to the formyl radical. The energy barriers calculated at the QCISD(T)/6-311G(2df,2p) level of theory upon QCISD/6-311G(d,p) optimized structures are, respectively, of 2.98  kcal mol −1 for the direct abstraction and of 2.26  kcal mol −1 for the addition. Thus, the results obtained show that there is not a dominant pathway in the HCO+O2 reaction under atmospheric conditions of temperature and pressure.

Influence of geometry on light harvesting in dendrimeric systems by Jonathan L. Bentz; Fatemeh Niroomand Hosseini; John J. Kozak (319-326).
The exact analytic expression for the mean time to trapping (or mean walklength) for a particle (electron/exciton) performing a random walk on a finite dendrimer lattice with a trap at the center of the dendrimer was obtained. Exact analytic expressions have also been obtained for articulated/extended dendrimeric systems. The full dynamical behavior was determined for each case studied via numerical solution of the stochastic master equation, and the results obtained were shown to be a direct consequence of the structural properties of the dendrimeric system. These studies are linked to the behavior observed in experiments on light harvesting in dendrimeric supermolecules.

Starting from a compact and accurate explicitly correlated wave function a systematic study of two-body properties in both position and momentum space has been performed for the He atom. A systematic comparison with the values obtained from both a multi-configuration Hartree–Fock and a Hylleraas (when available) wave function is performed. The wave function and the different expectation values are obtained by using the variational Monte Carlo method. The quality of both the wave function and the methodology used are analyzed and discussed.

Large-scale synthesis of uniform urchin-like patterns of Bi2S3 nanorods through a rapid polyol process by Guozhen Shen; Di Chen; Kaibin Tang; Fanqing Li; Yitai Qian (334-337).
A rapid and convenient polyol method has been developed to synthesize uniform urchin-like patterns of Bi2S3 nanorods in ethylene glycol at 197 °C for 30 min. X-ray diffraction pattern indicates that the obtained sample is orthorhombic phase Bi2S3. Scanning electron microscopy images and transmission electron microscopy images reveal that it is produced as uniform urchin-like pattern with spherical symmetry. The individual Bi2S3 nanorods is about 50 nm in diameter. The solvent and the S source material, thiourea, are of great importance on the final urchin-like structures.

For the straight-forward decomposition of the correlation contributions to intermolecular interaction energies in localized orbitals, the dependence on orbital localization is investigated. It is found that from the six classes of excitations intra-molecular contributions, as well as one ionic configuration and the basis set superposition error are very sensitive to the localization in the virtual orbital space, whereas the other three terms are less affected. An invariance of the individual contributions with respect to orbital rotations within the monomer spaces is formulated, which restricts the dependence of results on arbitrary orbital rotations and permits significant speed-ups, at least in Møller–Plesset second-order perturbation theory.

Shape resonance of the ethylene anion stabilized in a molecular trap by Iwona Anusiewicz; Piotr Skurski (345-352).
The possibility of stabilizing an electronically metastable anion in a molecular trap is studied using ab initio electronic structure methods. The 2 B 2g   C 2 H 4 d-wave shape resonance state is used as the metastable anion solute, and a pair of inwardly oriented LiCN molecules (NCLi⋯LiCN) is used as a molecular trap. Although the global minimum of the C2H4+2LiCN+e system is the (LiCN)2 anion with a weakly (van der Waals) bound C2H4 molecule, it was found that for the (NCLi⋯LiCN) trap at its local minimum geometry, the 2 B 2g state becomes electronically stable and is the ground state of the system. It is also found that, in this model trap, three other (excited) anionic states are bound ( 2 A g , 2 B 1u , and 2 B 2u ). Detailed numerical results are presented for the (NCLi⋯H2CCH2⋯LiCN) species (i.e., the trapped ethylene anion) whose vertical electron detachment energy is 2.97 eV at the CCSD(T) level with the augcc-pVDZ basis sets.

Methods for calculations of intermolecular potentials following the local density approximation (LDA) have earlier been considered, especially for inert gas atom – inert gas atom interactions using the so-called electron gas density functional (EGDF) model. In this Letter some density gradient corrections are discussed and new results are presented. The general conclusion based on the results in the present report seems to be that the EGDF method gives surprisingly good numerical results in the LDA limit for calculations of intermolecular potentials. Corrections due to density gradients contribute only small changes in the sum of the density functional terms considered for the total energy in the EGDF method, but they contribute important corrections to the kinetic energy and to the exchange energy separately.

The barrier to inversion of ammonia by Céline Léonard; Stuart Carter; Nicholas C Handy (360-365).
A six-dimensional analytic potential energy surface for NH3 has been obtained using ab initio CCSD(T) data. The variational method has been used to determine its vibrational energy levels. The parameters in the surface which describe inversion have been refined such that the vibrational levels for inversion give best agreement with observation. Nearly all the fundamentals and overtones of the refined surface then agree with observation to within 1 cm−1. The barrier to inversion is found to be 1769 cm−1. This is compared with other computed estimates of 1766 and 1777 cm−1 which appear in the literature.

Water was adsorbed prior to and after admission of D atoms to HOPG surfaces which essentially consisted of graphite (0 0 0 1) patches. After formation of a water monolayer at 100 K or a compact assembly of ice crystallites at 120 K adsorption of D on graphite was completely suppressed. Likewise, an adsorbed monolayer of water or ice crystals on D covered graphite (0 0 0 1) surfaces prevents abstraction of D by gaseous H atoms. Since icy mantles are expected to exist on interstellar grain particles, the results suggest that H by H abstraction reactions on graphitic particles proposed as origin of molecular hydrogen in the interstellar medium must be reconsidered.

Accurate three-dimensional quantum-mechanical (QM) scattering calculations have been performed for the S(1 D)+H 2→SH+H reaction at a collision energy of 2.24 kcal/mol. The shape of the rotational distribution and the forward/backward symmetry found in the total differential cross section (DCS) are characteristic of an insertion reaction. The QM DCS agrees with the experimental angular distribution. QM calculations show the bimodal behaviour of the experimental product translational energy distribution, in contrast with recent quasi-classical trajectory calculations.

Observations of electric field-gradient induced birefringence (the Buckingham effect) in gaseous N2 over a range of temperature (≈293–412 K) and pressure (up to ≈2000 kPa) are reported. Analysis of the data shows that the temperature-independent contribution to the effect is not negligible, and values of the molecular hyperpolarizability, B, and quadrupole moment, Θ, are derived. In the case of the quadrupole moment, the experimental value [Θ=(−4.97±0.16)×10−40   C m 2] and a state-of-the-art ab initio value [Θ=(−4.93±0.03)×10−40   C m 2] due to Halkier, Coriani and Jørgensen [Chem. Phys. Lett. 294 (1998) 292] are in excellent agreement.

Photoinduced absorption (PIA) spectroscopy was used to investigate dye-sensitized electrodes and solar cells under illumination conditions comparable to sunlight. In the absence of redox electrolyte, cis-Ru(dcbpy)2(NCS)2-sensitized nanostructured TiO2 films show a long-lived photoinduced charge-separation (oxidized dye molecules/injected electrons in TiO2), with a lifetime of about 10−3 s under full sun illumination. The PIA spectrum of a complete dye-sensitized cell is due to electrons in TiO2 and iodine radicals (I2 ) in the electrolyte. The lifetime of this charge-separated state at open-circuit conditions was determined to be 0.15 s (0.27 sun illumination).

Complex formation between DNA and dodecyl-dimethyl-amine-oxide induced by pH by A. Bonincontro; S. Marchetti; G. Onori; A. Santucci (387-392).
Dodecyl-dimethyl-amine-oxide (DDAO) is an amphiphile that may exist either in a neutral or cationic protonated form depending on the pH of aqueous solutions. Thus it realizes ionic or non-ionic micelles of easily controlled composition. These micelles, partially charged, realize an efficient support on which DNA can be linked in a controlled manner. In this Letter we report a study on DNA/DDAO complex formation using two physical techniques, dielectric spectroscopy (DS) and circular dichroism (CD). At pH 8, where the micelle is in a neutral state, no formation of a complex DNA/DDAO is evident. At pH 7, where the degree of ionization of the micelle is very low, the formation of the complex has been observed by the two techniques. Coherent results on the formation of the complex as a function of DDAO concentration and its influence on DNA conformation are presented.

Controlled non-classical photon emission from single conjugated polymer molecules by Christopher W. Hollars; Stephen M. Lane; Thomas Huser (393-398).
Photon pair-correlation spectroscopy was used to study the photoluminescence of single, isolated chains of the conjugated polymer MEH-PPV (poly[2-methoxy,5-(2-ethyl-hexyloxy)-p-phenylene-vinylene]). The chain conformation of these multichromophoric molecules was controlled by varying solvent polarity to result in either tightly folded collapsed chain or extended chain structures. We demonstrate, that the polymer conformation has strong influence on the quantum optical nature of the single chain photon emission. Polymers in the collapsed-chain conformation exhibit the non-classical phenomenon of photon antibunching in contrast to extended-chain structures. Analysis of the second-order correlation function provides a quantitative measure of the number of active emitter sites.

In this Letter, the stress transfer properties between single-/multi-walled nanotubes and polymer matrix are theoretically studied through the uses of local density approximation, elastic shells and conventional fibre pullout models. Several parameters such as the wall thickness, Young’s modulus, nanotubes’ volume fraction and chiral vectors of the nanotubes were considered in the study. According to the analytical results, it was found that the maximum shear stress, at the bond interface between the nanotubes and matrix, increases with increasing the nanotubes’ wall thickness of nanotube/polymer composites. Besides, the stress transfer length of zigzag nanotube is comparatively shorter than those of the armchair and chiral nanotubes.

A simple quantum mechanical/molecular mechanical (QM/MM) model for methanol by Joseph A. Morrone; Mark E. Tuckerman (406-411).
Mixed quantum mechanical/molecular mechanical (QM/MM) models, in which one part of a system is treated at an ab initio level while the rest is described by an empirical force field, are becoming increasingly popular. In this Letter, we describe a simple QM/MM model for methanol (CH3OH) in which the OH constitutes the ab initio region and is treated within a density functional representation, while the methyl group, the MM region, is treated using the AMBER force field. The model is used to study the structure of the bulk liquid and is shown to compare favorably with the experimental structure.

We carry out calculations of selected transition metal–oxygen molecules within density functional theory, post-Hartree–Fock, and quantum Monte Carlo (QMC) methods. Transition metal–oxygen systems have competing electron correlation and exchange effects and require accurate treatment of both of these effects. We analyze the biases of the mentioned methods and their impacts on the electronic structure. We evaluate binding energies and compare the accuracy of various approaches including single and multi-reference trial wave functions in QMC.

Concerning the stability of dichlorodiazene by Gregory S. Tschumper; Michael C. Heaven; Keiji Morokuma (418-424).
The stability of N2Cl2 with respect to dissociation into N2+2Cl has been investigated using ab initio electronic structure techniques. Triple-ζ basis sets with d- and f-functions were required to obtain qualitative agreement between multi-reference and highly-correlated single reference methods regarding the stability of the cis- and trans-isomers. The CCSD(T) method predicts a barrier to dissociation of 7–8  kcal mol −1 for the two isomers. CASPT2 barrier heights are substantially smaller (⩽1.5  kcal mol −1 ), indicating that these species are barely bound.

Photoelectron spectroscopic study of iodine- and bromine-treated indium tin oxides and their interfaces with organic films by X.H. Sun; L.F. Cheng; M.W. Liu; L.S. Liao; N.B. Wong; C.S. Lee; S.T. Lee (425-430).
Work function variations of indium tin oxide (ITO) treated with solutions of iodine and bromine as well as bromine vapor were studied by ultraviolet and X-ray photoelectron spectroscopies. Interfaces between the treated ITO and NPB were also investigated. Treatments by iodine and bromine solutions, and bromine vapor led to work function increase by as much as 0.6, 0.7, and 0.9 eV, respectively. After the halogen treatments, the hole-injection barrier for the NPB/ITO contact was remarkably decreased. A light-emitting device fabricated with bromine vapor-treated ITO as anode clearly demonstrated better hole injection at the ITO/NPB interface and a lower drive voltage.

Controlled step-by-step dissociation of single iodobenzene molecules has been performed at Cu(1 1 1) step-edges using tunneling electrons from a scanning tunneling microscope (STM) tip at 12 K. We show that the threshold tunneling electron energies to break a single bond inside a polyatomic molecule can be determined by using I–V spectroscopy of single molecules. Electron energies of 1.5±0.1 eV are necessary to break the σ C–I bond. This selective bond breaking procedure is possible due to the inherent bond energy differences inside the molecule. It requires electron energies of 3.1±0.1 eV or higher to further disrupt the π ring.

We made the first observation of transient vibrational spectra of both adsorbate and adsorbent at molecule-adsorbed surface using a two-color infrared picosecond laser system. The transient measurements were carried out on the CO-adsorbed surface hydroxyl group (OD) of DM-20 zeolite by pumping the CO stretching mode (2175 cm−1) or OD stretching mode (2470 cm−1) and probing over the CO and OD stretching region (2000–2700 cm−1). The T 1 lifetime for OD was 5.8 ps and that for CO was 540 ps. By comparison with other CO-adsorbed systems, vibrational relaxation mechanisms of CO on various surfaces are discussed. We also found evidence of energy flows from the vibrational mode of the adsorbent (OD stretching) to that of the adsorbate (CO stretching) via van der Waals interaction.

The recently developed plane wave packet method is applied to the F + HD reaction on the Stark–Werner potential surface, yielding converged differential cross-sections (d.c.s.) over the collision energy range E=0–0.15 eV. A wave packet ‘movie’ is obtained showing how the HF product scatters into space. Two direct and two time-delayed mechanisms are observed. One of the latter corresponds to a recently observed Feshbach resonance. The movie is related to the energy-dependent d.c.s. by a time-dependent d.c.s., which reveals quantum interference between the direct and time-delayed mechanisms.

The density functional theory methods are used to calculate the equilibrium molecular structures and vibrational spectra of helical H(CH2CH2O) n H (OEG) oligomers (n=4–7) at a level of precision that has not been accomplished before. The largest deviation between experimentally observed frequencies, obtained from infrared reflection–absorption spectra of OEG-monolayers on gold, and calculated, single molecule frequencies (unscaled), is slightly above 2%. Moreover, the most intense peak in the CH2-stretching region at about 2890 cm−1, commonly regarded as a trademark of the OEG helical conformation, is reassigned in this study to the asymmetric CH2-stretching mode.

Infrared spectrum of a spiropyran, 1,3-dihydro-1,3,3-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2-[2H]indole], in a low-temperature argon matrix was measured with a Fourier transformed infrared spectrophotometer. The conformation of this spiropyran was determined by comparison of the observed spectrum with a spectral pattern obtained by the density-functional-theory calculation. This conformation differs from the optimized geometry derived from an HF/6-31G* calculation. The conformations of a merocyanine produced from the spiropyran upon UV irradiation were also determined by the same method.

An experimental and theoretical investigation of the triple fragmentation of CFClBr2 by photolysis near 250 nm by Nathan L. Owens; Klaas Nauta; Scott H. Kable; Naomi L. Haworth; George B. Bacskay (469-477).
Photodissociation of CFClBr2+→CFCl has been shown to occur for λ<274 nm (436±2  kJ mol −1 ). G3 Ab initio calculations were performed to provide estimates of Δ f H for CFClBr2, CFClBr, and CFCl, which were calculated to be −188±5, −43±5 and +30±5  kJ mol −1 , respectively. The dissociation energies (0 K) for sequentially breaking the C–Br bonds were calculated to be 257±5 and 183±5  kJ mol −1 , respectively. The energy required to break both C–Br bonds was calculated to be 440±5  kJ mol −1 , in excellent agreement with the experimental appearance threshold for CFCl. From the experimental appearance threshold, Δ f H (CFClBr2) is estimated to be −184±5  kJ mol −1 .

We report a systematic investigation of the adiabatic electron affinities (EA) of BO, NO and O2 using a specifically adapted massively parallel version of the configuration-selective configuration interaction method (MRCI) which permits the explicit treatment of the most important triple and quadruple excitations (TQ). We find the EA(BO)=2.52  eV , EA(NO)=0.015  eV and EA(O 2)=0.39  eV in good agreement with experimental results. We elucidate the physical mechanism that is responsible for the failure of standard MRCI to quantitatively describe the EA of oxygen containing molecules.

Spectral difference between nanocrystalline and bulk Y2O3:Eu3+ by Hongshang Peng; Hongwei Song; Baojiu Chen; Shaozhe Lu; Shihua Huang (485-489).
In this Letter spectral difference between nanocrystalline yttria doped with europium (Y2O3:Eu3+) and the bulk ones was reported. Besides a 580.6-nm line similar to that in the bulk Y2O3:Eu3+, a new broad excitation line at 579.9 nm was observed in the nanocrystals (NCs). The lifetime of the 579.9-nm line became slightly shorter than that of the 580.6-nm line. The 579.9-nm line was attributed to the Eu3+ ions near the surface of the NCs. Due to numerous surface defects, the crystal field on the surface degenerated, leading the energy levels of the electrons in 4f state to shift.

An extensive ab initio direct molecular dynamics simulation of the reaction of C+ colliding with water with a relative kinetic energy of 0.62 eV has been performed. Energy and gradient evaluations were done at the MP2/6-31+G* level. 579 trajectories comprised the study, enough to calculate a reliable distribution of product kinetic energies and product angular distribution. These were found to agree well with experiment, and this agreement supports the mechanistic conclusions drawn in a smaller previous study of the reaction.

A new approach to heteronuclear dipolar recoupling in solid-state NMR which combines symmetry-based, γ-encoded dipolar recoupling with off-resonance rf irradiation is described. By irradiating the two spin species with offsets of equal magnitude but opposite sign, the dipolar scaling factor may be increased while using lower rf field strengths than under on-resonance conditions. Larger scaling makes the experiment less susceptible to relaxation, while released rf field requirements facilitate combination with fast magic-angle spinning while maintaining efficient 1 H decoupling. Furthermore, homonuclear dipolar couplings may be suppressed by adjusting the off-resonance irradiation to the Lee–Goldburg condition.

Rotational cooling and translational trapping during the thermal evaporation of free nitrogen clusters by Gregor Jundt; Holger Vach; Nihed Chaâbane; Quentin Brulin; Gilles H. Peslherbe (504-509).
Thermal evaporation of free nitrogen clusters is investigated using molecular dynamics simulations. Energy distributions of molecules evaporating from (N2)64 clusters at initial temperatures between 50 and 190 K are reported. Rotational energy distributions always follow single temperature Boltzmann distributions. The resulting rotational temperatures first increase with cluster temperature and then saturate at about 87 K. For the translation, Maxwell–Boltzmann distributions permit an adequate description for initial cluster temperatures above 90 K where the resulting translational temperatures roughly correspond to the initial cluster temperatures. For lower cluster temperatures, however, non-thermal behavior is observed and attributed to a velocity-dependent recapture of the slowest evaporating molecules.

Equilibrium geometries, electron affinities and dissociation energies of W2, W2 , W3 and W3 clusters and harmonic vibrational frequencies of W2 and W2 clusters were studied by density functional methods B3LYP, B3PW91, BLYP, BHLYP, B3P86 and MPW1PW91. The results indicate that singlet state is the ground state for W2 cluster, and doublet for W2 cluster. For W3 and W3 clusters, triplet with D3h symmetry and doublet with C2v symmetry are the ground state, respectively. Comparing among different methods, the results indicate that the calculated quantities, such as electron affinity and dissociation energy, are sensitive to the methods used and cluster size.

Doppler-free multi-photon ionization: a proposal for enhancing ion images by Andrew E. Pomerantz; Richard N. Zare (515-521).
We report on the use of Doppler-free 2+1 resonance enhanced multi-photon ionization (REMPI) to probe H atoms resulting from HBr photolysis at 243 nm. The Doppler-free technique allows almost all H atoms to be ionized at a single probe wavelength, regardless of their lab-frame velocities. This technique yields a significant enhancement in ionization efficiency of the product while leaving the background ionization essentially unaffected. We point out the utility of this technique for the ion imaging of reaction products.

Cubic nitride boron (c-BN) films have been prepared on polished single crystal Si(1 1 1) surface at room temperature (25 °C) by radio frequency plasma enhanced pulsed laser deposition (RF-PEPLD), assisted with substrate negative bias. Components, structure and surface morphology of the deposited films were identified by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The growth mechanism of c-BN phase upon RF-PEPLD is discussed in detail, and the experimental evidence indicates that two deposition parameters, i.e., RF plasma power and substrate negative bias, played the key roles in the growth of the resulted c-BN films at room temperature.

Testing the morphed potential of Ar:HBr using frequency and phase stabilized FASSST with a supersonic jet by S.P. Belov; B.A. McElmurry; R.R. Lucchese; J.W. Bevan; I. Leonov (528-534).
The lowest frequency Σ bending vibration of Ar:HBr has been recorded using frequency and phase stabilized Fast Scan Submillimeter Spectroscopic Technique (FASSST) coaxially with a supersonic jet. The fitted band origin was ν 0=329611.4482(16) MHz, the excited stated rotational constant was B=1236.41359(22) MHz, the distortion constants were D J =0.0124740(36) MHz and H J =−2.503(17)×10−6 MHz and the quadrupole constants were χ aa =260.9552(79) MHz and D χ =−0.03174(35) MHz for Ar: H 79 Br . Corresponding values have also been determined for the Ar: H 81 Br isotopomer. χ aa and D χ are compared with values predicted from a recently determined morphed potential of Ar:HBr.

Hydrated structure of Nph(H2O)2 was investigated using infrared (IR) spectroscopy. Among OH stretching vibrations, three π-hydrogen bonds to anionic naphthalene ring, namely ionic π-hydrogen (iπH) bonds, and an interwater hydrogen bond were observed. It allowed us to elucidate the geometrical structure of Nph(H2O)2. The unstable naphthalene bare anion was stabilized through the iπH bonds with the water dimer on its ring, forming the one-sided structure. Besides, the intensity of the aromatic CH stretching modes was found to be enhanced upon the electron attachment without significant lowering of their frequencies.

Langmuir film behaviors of dendrons at water–air interface by Shi-Zhao Kang; Sai-Long Xu; Guojun Deng; Peng Wu; Qinghua Fan; Chen Wang; Lijun Wan; Chunli Bai (542-547).
The film behaviors of a series of dendrons (G2, G3 and G4) on pure water subphase were investigated on a Langmuir–Blodgett trough. Moreover, the in situ observation of the film morphology and the film formation process was performed by using Brewster angle microscopy (BAM). The results indicate that the dendrons all can form solid monolayer on water surface, and the stability and reversibility of monolayer decrease as the generation of dendron increases. These phenomena may be mostly ascribed to the spatial interaction between molecules.

Adsorption and decomposition pathways for ICN on Si(1 0 0)-(2×1) by Evgueni B. Kadossov; P. Rajasekar; Nicholas F. Materer (548-554).
The adsorption and surface reactions of ICN on the Si(1 0 0)-(2×1) surface are studied using ab initio quantum calculations on model dimer clusters. ICN can physisorb via a dative bond through the N atom. This species can further react to form either a dissociated state through I–CN bond cleavage or a stable side-on intermediate by reacting across the dimer bond. There are two important differences between the ICN adsorption process and that of HCN. Unlike HNC, the INC dative bonded structure is not stable. Next, there is no transition state between the side-on adsorbed ICN and INC species.

Using molecular dynamics simulations, we explore the mechanism that may underlie the type of folding transitions observed experimentally in anhydrous proteins. Recent relaxation studies of a partly unfolded α-helical bundle suggest an approach to simulating cycles of folding/re-unfolding transitions. Here, we provide evidence that such processes may be general, by uncovering a similar relaxation pattern in lysozyme, a more flexible α/β protein. We find that, while refolding is initiated by partial polymer collapse, the reversible re-unfolding of compact nonnative structures proceeds as a correlated transition not unlike the direct unfolding of lysozyme from its native state.

The non-adiabatic transitions between the first-tier E and D ion-pair states of iodine molecule induced by collisions with Ar atom are investigated using first-order semiclassical perturbation theory. PES’s and diabatic couplings between electronic states are obtained in analytical form by the first-order perturbation theory-diatomics-in-molecule method. Electronic and vibrationally inelastic rate constants and product state distributions are calculated and compared with available experimental data.

We study the low-lying two-photon excited states in nonlinear optical processes in poly(p-phenylene vinylene) (PPV) and its derivatives. We find that, within the Pariser–Parr–Pople (PPP) model, the mAg state in (unsubstituted) PPV is exactly the lowest two-photon excited state (i.e., the 21 A g + state). Due to the breaking of charge-conjugation symmetry, the 2Ag in substituted PPVs, originating from the 11 A g , is weakly two-photon allowed, while the mAg has its origin from the 21 A g + , hence giving a strong peak in the two-photon absorption spectra.

The geometric derivatives of the static and dynamic electric dipole polarizability have been calculated at the all-electron Dirac–Hartree–Fock level for the dihalogen molecules F2, Cl2, Br2, and I2 and for the hydrogen halides HF, HCl, HBr, and HI. A comparison with the non-relativistic Hartree–Fock values shows that the relativistic corrections tend to be larger for the geometric derivatives of the polarizabilities than for the polarizabilities. The frequency dispersion of the corrections due to relativity is significant for the molecules containing bromine and iodine. As expected, for the same molecules relativistic effects are sizable, and they improve the agreement between theory and experiment for the electric dipole polarizabilities. In the case of the Raman scattering cross sections, only a few experimental data are available. In general the relativistic effects are in this case within the range of the experimental error.