Dynamics of the 1 3 pi g state of K2 on helium nanodroplets

Fluorescence following optical excitation of the 1 3 sigma u+ state of K2 prepared on helium nanodroplets to the predissociative 1 3 pi g state yields molecular emission from both the (B)1 1 pi u and (A)1 1 sigma u+ K2 states as well as atomic emission from the expected 4 2P3/2, 1/2-->4 2S1/2 dissociation channel. A approximately 12 cm-1 red shift is observed in the molecular emission excitation spectrum compared to the atomic emission excitation spectrum. Time-correlated photon counting measurements demonstrate the rise time for both atomic and molecular products to be < 80 ps, independent of vibrational level excited. This lifetime is interpreted as the total depopulation time for the optically excited 1 3 pi g state, which is dominated by intersystem crossing at low vibrational energy and by predissociation at the highest vibrational level. It is deduced that the timescale for intersystem crossing must be of the order of 10 ps. Symmetry restrictions for the isolated K2 imply that the intersystem crossing from the 1 3 pi g state to the (B)1 1 pi u and (A)1 1 sigma u+ states must be induced by interaction with the helium nanodroplet.     

The dynamics of Br(2Pj) formation in the photodissociation of vinyl and perfluorovinyl bromides

The photodissociation dynamics of vinyl bromide and perfluorovinyl bromide have been investigated at 234 nm using a photofragment ion imaging technique coupled with a state-selective [2+1] resonance-enhanced multiphoton ionization scheme. The nascent Br atoms stem from the primary C-Br bond dissociation leading to the formation of C2H3(X) and Br(2Pj;j=1/2,3/2). The obtained translational energy distributions have been well fitted by a single Boltzmann and three Gaussian functions. Boltzmann component has not been observed in the perfluorovinyl bromide. The repulsive 3A'(n,sigma *) state has been considered as the origin of the highest Gaussian components. Middle translational energy components with Gaussian shapes are produced from the 1A"(pi,sigma*) and/or 3A"(pi,sigma*) which are very close in energy. Low-energy Gaussian components are produced via predissociation from the 3A'(pi,pi*) state. The assignments have also been supported by the recoil anisotropy corresponding to the individual components. It is suggested that intersystem crossing from the triplet states to the ground state has been attributed to the Boltzmann component and the fluorination reduces the probability of this electronic relaxation process.     

Charge-transfer processes in the assembly of Si(n)O(m) neutral clusters

The chemical bond formation in oxygen-rich Si(n)O(m) clusters was investigated by sampling the potential energy surface of the model systems SiO + SiO(2) → Si(2)O(3) and (SiO)(2) + SiO(2) → Si(3)O(4) along a two-dimensional reaction coordinate, by density functional theory calculations. Evidence for crossing between the weakly bound neutral-neutral (SiO)(n) + SiO(2) and the highly attractive ion-pair (SiO)(n)(+) + SiO(2)(-) surfaces was found. Analysis of frontier molecular orbitals and charge distribution showed that surface crossing involves transfer of valence electron charge from (SiO)(2) to SiO(2). The sum of the natural atomic charges over the (SiO)(n) and (SiO(2)) groups of the Si(n)O(m) cluster products, gave a net positive charge on the (SiO)(n) "core" and a net negative charge on the (SiO(2)) groups. This is interpreted as the "ion-pair memory" left on the Si(n)O(m) products by the charge-transfer mechanism and may provide a way to assess the role of charge-transfer processes in the assembly of larger Si(n)O(m) neutral clusters.     

Crossed beam studies of elementary reactions of N and C atoms and CN radicals of importance in combustion

The dynamics of some elementary reactions of N(2D), C(3P,1D) and CN(X2 sigma +) of importance in combustion have been investigated by using the crossed molecular beam scattering method with mass spectrometric detection. The novel capability of producing intense, continuous beams of the radical reagents by a radio-frequency discharge beam source was exploited. From angular and velocity distribution measurements obtained in the laboratory frame, primary reaction products have been identified and their angular and translational energy distributions in the center-of-mass system, as well as branching ratios, have been derived. The dominant N/H exchange channel has been examined in the reaction N(2D) + CH4, which is found to lead to H + CH2NH (methylenimine) and H + CH3N (methylnitrene); no H2 elimination is observed. In the reaction N(2D) + H2O the N/H exchange channel has been found to occur via two competing pathways leading to HNO + H and HON + H, while formation of NO + H2 is negligible. Formation of H + H2CCCH (propargyl) is the dominant pathway, at low collision energy (Ec), of the C(3P) + C2H4 reaction, while at high Ec formation of the less stable C3H3 isomers (cyclopropenyl and/or propyn-1-yl) also occurs; the H2 elimination channel is negligible. The H elimination channel has also been found to be the dominant pathway in the C(3P,1D) + CH3CCH reaction leading to C4H3 isomers and, again, no H2 elimination has been observed to occur. In contrast, both H and H2 elimination, leading in comparable ratio to C3H + H and C3(X1 sigma g+) + H2(X1 sigma g+), respectively, have been observed in the reaction C(3P) + C2H2(X1 sigma g+). The occurrence of the spin-forbidden molecular pathway in this reaction, never detected before, has been rationalized by invoking the occurrence of intersystem crossing between triplet and singlet manifolds of the C3H2 potential energy surfaces. The reaction CN(X2 sigma +) + C2H2 has been found to lead to internally excited HCCCN (cyanoacetylene) + H. For all the reactions the dynamics have been discussed in the light of recent theoretical calculations on the relevant potential energy surfaces. Previous, lower resolution studies on C and CN reactions carried out using pulsed beams are noted. Finally, throughout the paper the relevance of these results to combustion chemistry is considered.     

O+HCl→OH+Cl反应的立体动力学的准经典轨线研究

运用准经典轨线方法, 基于Peterson从头计算势能面对O+HCl→OH+Cl反应的立体动力学性质进行了研究. 讨论了在31.77和51.04 kJ/mol两种碰撞能情况下极化依赖的微分反应截面(2π/σ)(dσ₀₀/dω_t), (2π/σ)(dσ₂₀/dω_t), (2π/σ)(dσ₂₂₊/dω_t)和(2π/σ)(dσ_21-/dω_t)以及描述k-j′两矢量相关和k-k′-j′三矢量相关的分布函数P(θ_r)和P(φ_r). 计算得到的P(θ_r)分布表明, 产物分子的转动角动量j′具有强烈的取向分布, 并且产物转动角动量的取向效应对散射能的变化比较敏感. 而P(φ_r)的分布表明, 产物分子虽然具有沿着y轴的取向效应, 但是没有明显的定向效应.     

Experimental and theoretical study of the photodissociation reaction of thiophenol at 243 nm: intramolecular orbital alignment of the phenylthiyl radical

The photoinduced hydrogen (or deuterium) detachment reaction of thiophenol (C(6)H(5)SH) or thiophenol-d(1) (C(6)H(5)SD) pumped at 243 nm has been investigated using the H (D) ion velocity map imaging technique. Photodissociation products, corresponding to the two distinct and anisotropic rings observed in the H (or D) ion images, are identified as the two lowest electronic states of phenylthiyl radical (C(6)H(5)S). Ab initio calculations show that the singly occupied molecular orbital of the phenylthiyl radical is localized on the sulfur atom and it is oriented either perpendicular or parallel to the molecular plane for the ground (B(1)) and the first excited state (B(2)) species, respectively. The experimental energy separation between these two states is 2600+/-200 cm(-1) in excellent agreement with the authors' theoretical prediction of 2674 cm(-1) at the CASPT2 level. The experimental anisotropy parameter (beta) of -1.0+/-0.05 at the large translational energy of D from the C(6)H(5)SD dissociation indicates that the transition dipole moment associated with this optical transition at 243 nm is perpendicular to the dissociating S-D bond, which in turn suggests an ultrafast D+C(6)H(5)S(B(1)) dissociation channel on a repulsive potential energy surface. The reduced anisotropy parameter of -0.76+/-0.04 observed at the smaller translational energy of D suggests that the D+C(6)H(5)S(B(2)) channel may proceed on adiabatic reaction paths resulting from the coupling of the initially excited state to other low-lying electronic states encountered along the reaction coordinate. Detailed high level ab initio calculations adopting multireference wave functions reveal that the C(6)H(5)S(B(1)) channel may be directly accessed via a (1)(n(pi),sigma(*)) photoexcitation at 243 nm while the key feature of the photodissociation dynamics of the C(6)H(5)S(B(2)) channel is the involvement of the (3)(n(pi),pi(*))-->(3)(n(sigma),sigma(*)) profile as well as the spin-orbit induced avoided crossing between the ground and the (3)(n(pi),sigma(*)) state. The S-D bond dissociation energy of thiophenol-d(1) is accurately estimated to be D(0)=79.6+/-0.3 kcalmol. The S-H bond dissociation energy is also estimated to give D(0)=76.8+/-0.3 kcalmol, which is smaller than previously reported ones by at least 2 kcalmol. The C-H bond of the benzene moiety is found to give rise to the H fragment. Ring opening reactions induced by the pi-pi(*)n(pi)-pi(*) transitions followed by internal conversion may be responsible for the isotropic broad translational energy distribution of fragments.     

On the reversible O2 binding of the Fe-porphyrin complex

Electronic mechanism of the reversible O(2) binding by heme was studied by using Density Functional Theory calculations. The ground state of oxyheme was calculated to be open singlet state [Fe(S =1/2) + O(2)(S = 1/2)]. The potential energy surface for singlet state is associative, while that for triplet state is dissociative. Because the ground state of the O(2)+ deoxyheme system is triplet in the dissociation limit [Fe(S = 2) + O(2)(S = 1)], the O(2) binding process requires relativistic spin-orbit interaction to accomplish the intersystem crossing from triplet to singlet states. Owing to the singlet-triplet crossing, the activation energies for both O(2) binding and dissociation become moderate, and hence reversible. We also found that the deviation of the Fe atom from the porphyrin plane is also important reaction coordinate for O(2) binding. The potential surface is associative/dissociative when the Fe atom locates in-plane/out-of-plane.     

Electron correlation in the GK state of the hydrogen molecule

The second excited (1)Sigma(g)(+) state of the hydrogen molecule, the so-called GK state, has a potential energy curve with double minima. At the united atom limit it converges to the 1s3d configuration of He. At large internuclear distances R, it dissociates to two separated atoms, one in the ground state and another in the 2p excited state. Radial pair density calculations and natural orbital analyses reveal unusual effect of electron correlation around the K minimum of the potential energy curve. As R>2.0 a.u., a natural orbital of sigma(u) symmetry joins the two natural orbitals of sigma(g) symmetry at smaller R. The average interelectronic distance decreases as the internuclear distance increases from R=2.0 to 3.0 a.u. Around R=3.0 a.u. the singly peaked pair density curve splits into two peaks. The inner peak can be attributed to the formation of the ionic electron configuration (1s)(2), where both 1s electrons are on the same nucleus. As the two 1s electrons run into different nuclei, one of the two 1s electrons is promoted to the 2p state, which results in the outer peak in the pair density curve. The Rydberg 1s2p configuration persists as the nuclei stretch, and becomes dominant at large R where four natural orbitals, two of sigma(g) and two of sigma(u) symmetry, become responsible.     

Photodissociation dynamics of CH(2)Br(2) near 234 and 267 nm

The photodissociation dynamics of CH(2)Br(2) was investigated near 234 and 267 nm. A two-dimensional photofragment ion velocity imaging technique coupled with a [2+1] resonance-enhanced multiphoton (REMPI) ionization scheme was utilized to obtain the angular and translational energy distributions of the nascent Br ((2)P(3/2)) and Br* ((2)P(1/2)) atoms. The obtained translational energy distributions of Br and Br* are found consist of two components which should be come from the radical channel and secondary dissociation process, respectively. It is suggested that the symmetry reduction from C(2v) to C(s) during photodissociation invokes a non-adiabatic coupling between the 2B(1) and A(1) states. Consequently, the higher internal energy distribution of Br channel than Br* formation channel and the broader translational energy distribution of the former are presumed correlate with a variety of vibrational excitation disposal at the crossing point resulting from the larger non-adiabatic crossing from 2B(1) to A(1) state than the reverse crossing. Moreover, the measured anisotropy parameter beta indicate that fragments recoil along the Br-Br direction mostly in the photodissociation.     

Vibrational spectroscopy and state-specific dissociation dynamics for vinyl chloride cation in the B state

C(2)H(3)(35)Cl+ in the ground vibronic state was generated by one-photon mass-analyzed threshold ionization spectrometry, and its photodissociation in the 461-406 nm range was investigated. Ionization energy to the ground state of C(2)H(3)(35)Cl+ was 10.0062 +/- 0.0006 eV while its B state onset was higher by 2.7456 +/- 0.0003 eV. A vibrational spectrum of the cation in the B state obtained by recording the product ion yield as a function of wavelength was analyzed by referring to the quantum chemical results at the TDDFT/B3LYP/6-311++(df,pd) level. Analysis of product time-of-flight profiles recorded with different laser polarization angles showed that the dissociation pathway for the cation in the B state changed with the vibrational energy, from internal conversion to X and statistical dissociation therein to curve crossing to C and repulsive dissociation therein. B --> C curve crossing seemed to occur along a direction close to the C-Cl bond stretch.     

Rotational state-resolved reaction cross section in the reactions of state-selected CH with NO and with O2

A pure and highly intense state-selected pulsed supersonic CH(X (2)Pi) radical beam source was developed by use of the C((1)D)+H(2) reaction with the combination of the state selection and purification by an electrostatic hexapole field. Under the beam-cell condition, the elementary reactions of CH+NO and CH+O(2) were studied by using this state-selected CH beam. NH(A (3)Pi) [and NCO(A (2)Sigma(+))] formations and OH(A (2)Sigma(+)) formation were directly identified in the elementary reaction of CH+NO and CH+O(2), respectively. For the CH+NO reaction, the relative branching ratio sigma(NCO*)sigma(NH) of NCO(A (2)Sigma(+)) formation to NH(A (3)Pi) formation was determined to be 0.35+/-0.15. The state-selected reaction cross sections were determined for each rotational state of CH. In the CH+NO reaction, a remarkable rotational state dependence of the reactive cross section was revealed, while the CH+O(2) reaction showed little rotational state dependence.     

Quantitative determination of 1sigma(g)+ and 1delta(g) singlet oxygen in solvents of very different polarity. General energy gap law for rate constants of electronic energy transfer to and from O2 in the absence of charge transfer interactions

The quenching of excited triplet states of sufficient energy by O2 leads to O2(1sigma(g)+) and O2(1delta(g)) singlet oxygen and O2(3sigma(g)-) ground-state oxygen as well. The present work investigates the question whether in the absence of charge transfer (CT) interactions between triplet sensitizer and O2 the rate constants of formation of the three different O2 product states follow a generally valid energy gap law. For that purpose, lifetimes of the upper excited O2(1sigma(g)+) have been determined in a mixture of 7 vol % benzene in carbon tetrachloride, in chloroform, and in perdeuterated acetonitrile. They amount to 1.86, 1.40, and 0.58 ns, respectively. Furthermore, rate constants of O2(1sigma(g)+), O2(1delta(g)), and O2(3sigma(g)-) formation have been measured in these three solvents for five pi pi* triplet sensitizers with negligible CT interactions. The rate constants are independent of solvent polarity. After normalization for the multiplicity of the respective O2 product state, the rate constants follow a common dependence on the excess energies of the respective product channels. This empirical energy gap relation describes also quantitatively the rate constants of quenching of O2(1delta(g)) by 28 carotenoids. Therefore, it represents in the absence of CT interactions a generally valid energy gap law for the rate constants of electronic energy transfer to and from O2.     

Ab initio study of the mechanism for photoinduced Yl-oxygen exchange in uranyl(VI) in acidic aqueous solution

The mechanism for the photochemically induced isotope-exchange reaction U(17/18)O2(2+)(aq) + H2(16)O <==> U(16)O2(2+)(aq) + H2(17/18)O has been studied using quantum-chemical methods. There is a dense manifold of states between 22,000 and 54,000 cm(-1) that results from excitations from the sigma(u) and pi(u) bonding orbitals in the (1)Sigma(g)(+) ground state to the nonbonding f(delta) and f(phi) orbitals localized on uranium. On the basis of investigations of the reaction profile in the (1)Sigma(g)(+) ground state and the excited states (3)Delta(g) (the lowest triplet state) and (3)Gamma(g) (one of the several higher triplet states), the latter two of which have the electron configurations sigma(u)f(delta) and pi(u)f(phi), respectively, we suggest that the isotope exchange takes place in one of the higher triplet states, of which the (3)Gamma(g) state was used as a representative. The geometries of the luminescent (3)Delta(g) state, the lowest in the sigma(u)f(delta,phi) manifold (the "sigma" states), and the (1)Sigma(g)(+) ground state are very similar, except that the bond distances are slightly longer in the former. This is presumably a result of transfer of a bonding electron to a nonbonding f orbital, which makes the excited state in some respects similar to uranyl(V). As is the case for all of the states of the pi(u)f(delta,phi) manifold (the "pi" states), the geometry of the (3)Gamma(g) state is very different from that of the (3)Delta(g) "sigma" state and has nonequivalent U-O(yl) distances of 1.982 and 1.763 A; in the (3)Gamma(g) state, the yl-exchange takes place by transfer of a proton or hydrogen from water to the more distant yl-oxygen. The activation barriers for proton/hydrogen transfer in the ground state and the (3)Delta(g) and (3)Gamma(g) states are 186, 219, and 84 kJ/mol, respectively. The relaxation energy for the (3)Gamma(g) state in the solvent after photoexcitation is -86 kJ/mol, indicating that the energy barrier can be overcome; the "pi" states are therefore the most probable route for proton/hydrogen transfer. They can be populated after UV irradiation but are too high in energy (approximately 36,000-40,000 cm(-1)) to be reached by a single-photon absorption at 436 nm (22,900 cm(-1)), where experimental data have demonstrated that exchange can take place. Okuyama et al. [Bull. Res. Lab. Nucl. React. (Tokyo Inst. Technol.) 1978, 3, 39-50] have demonstrated that an intermediate is formed when an acidic solution of UO2(2+)(aq) is flash-photolyzed in the UV range. The absorption spectrum of this short-lived intermediate (which has a maximum at 560 nm) indicates that this species arises from 436 nm excitation of the luminescent (3)Delta(g) state (which has a lifetime of approximately 2 x 10(-6) s); this is sufficient to reach the reactive "pi" states. It has been speculated that the primary reaction in acidic solutions of UO2(2+)(aq) is the formation of a uranyl(V) species; our results indicate that the structure in the luminescent state has some similarity to that of UO2(+) but that the reactive species in the "pi" states is a cation radical with a distinctly different structure.     

A density functional theory study on the reactions of Y atom and Y+ cation with carbonyl sulfide

The mechanism of the title reactions have been studied by using the DFT (B3LYP/ECP/6‐311+G*) level of theory. Both ground and excited state potential energy surfaces are discussed. It is found the reaction mechanism is insertion mechanism both along the C? S and C? O bond activation branches, but the C? S bond activation is much more favorable in energy than the C? O bond activation. The reaction of Y atom with SCO was shown to occur preferentially on the ground state (doublet) PES throughout the reaction process, and the experimentally observed species, have been explained according to the mechanism revealed in this work. Different from that of Y + SCO system, the reaction between Y⁺ cation and SCO involves potential energy curve‐crossing which dramatically affects reaction mechanism. Due to the intersystem crossing existing in the reaction process of Y⁺ with SCO, the intermediates SY⁺(η²CO) and OY⁺(η²CS) may not form. All our theoretical results not only support the existing conclusions inferred from early experiment, but also complement the pathway and mechanism for this reaction. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

气相中W+活化CO2分解的自旋禁阻反应机理

用密度泛函理论中的UB3LYP方法, 对W采用相对论校正赝势基组(SDD), 对C、O采用6-311+G(3d)基组, 研究了气相中不同自旋态W+活化CO2分解的反应机理. 计算结果表明, W+活化CO2分解反应以六重态进入反应通道, 经过六重态势能面到四重态势能面的系间窜越(ISC),最后产物WO+和CO以四重态离开反应通道. 运用Harvey方法优化出最低能量交叉点(MECP), 并计算了MECP处的自旋-轨道耦合(SOC)常数(494.95 cm-1), 势能面的交叉和在MECP处较强的自旋-轨道耦合作用降低了自旋禁阻反应能垒, 为反应提供了一条低能反应路径, 反应总放热量为122.33 kJ·mol-1.     

Base-induced decomposition of alkyl hydroperoxides in the gas phase. Part 3. Kinetics and dynamics in HO- + CH3OOH, C2H5OOH, and tert-C4H9OOH reactions

The E(CO)2 elimination reactions of alkyl hydroperoxides proceed via abstraction of an alpha-hydrogen by a base: X(-) + R(1)R(2)HCOOH --> HX + R(1)R(2)C=O + HO(-). Efficiencies and product distributions for the reactions of the hydroxide anion with methyl, ethyl, and tert-butyl hydroperoxides are studied in the gas phase. On the basis of experiments using three isotopic analogues, HO(-) + CH3OOH, HO(-) + CD3OOH, and H(18)O(-) + CH3OOH, the overall intrinsic reaction efficiency is determined to be 80% or greater. The E(CO)2 decomposition is facile for these methylperoxide reactions, and predominates over competing proton transfer at the hydroperoxide moiety. The CH3CH2OOH reaction displays a similar E(CO)2 reactivity, whereas proton transfer and the formation of HOO(-) are the exclusive pathways observed for (CH3)3COOH, which has no alpha-hydrogen. All results are consistent with the E(CO)2 mechanism, transition state structure, and reaction energy diagrams calculated using the hybrid density functional B3LYP approach. Isotope labeling for HO(-) + CH3OOH also reveals some interaction between H2O and HO(-) within the E(CO)2 product complex [H2O...CH2=O...HO(-)]. There is little evidence, however, for the formation of the most exothermic products H2O + CH2(OH)O(-), which would arise from nucleophilic condensation of CH2=O and HO(-). The results suggest that the product dynamics are not totally statistical but are rather direct after the E(CO)2 transition state. The larger HO(-) + CH3CH2OOH system displays more statistical behavior during complex dissociation.     

Variational analysis of the phenyl + O2 and phenoxy + O reactions

Variational transition state analysis was performed on the barrierless phenyl + O2 and phenoxy + O association reactions. In addition, we also calculated rate constants for the related vinyl radical (C2H3) + O2 and vinoxy radical (C2H3O) + O reactions and provided rate constant estimates for analogous reactions in substituted aromatic systems. Potential energy scans along the dissociating C-OO and CO-O bonds (with consideration of C-OO internal rotation) were obtained at the O3LYP/6-31G(d) density functional theory level. The CO-O and C-OO bond scission reactions were observed to be barrierless, in both phenyl and vinyl systems. Potential energy wells were scaled by G3B3 reaction enthalpies to obtain accurate activation enthalpies. Frequency calculations were performed for all reactants and products and at points along the potential energy surfaces, allowing us to evaluate thermochemical properties as a function of temperature according to the principles of statistical mechanics and the rigid rotor harmonic oscillator (RRHO) approximation. The low-frequency vibrational modes corresponding to R-OO internal rotation were omitted from the RRHO analysis and replaced with a hindered internal rotor analysis using O3LYP/6-31G(d) rotor potentials. Rate constants were calculated as a function of temperature (300-2000 K) and position from activation entropies and enthalpies, according to canonical transition state theory; these rate constants were minimized with respect to position to obtain variational rate constants as a function of temperature. For the phenyl + O2 reaction, we identified the transition state to be located at a C-OO bond length of between 2.56 and 2.16 A (300-2000 K), while for the phenoxy + O reaction, the transition state was located at a CO-O bond length of 2.00-1.90 A. Variational rate constants were fit to a three-parameter form of the Arrhenius equation, and for the phenyl + O2 association reaction, we found k(T) = 1.860 x 1013T-0.217 exp(0.358/T) (with k in cm3 mol-1 s-1 and T in K); this rate equation provides good agreement with low-temperature experimental measurements of the phenyl + O2 rate constant. Preliminary results were presented for a correlation between activation energy (or reaction enthalpy) and pre-exponential factor for heterolytic O-O bond scission reactions.     

Theoretical study of the reaction of Cr+ with SCO in gas phase

To elucidate the mechanism of reaction M⁺ + SCO, the reaction of Cr⁺ + SCO has been investigated using density functional theory (DFT) with the popular hybrid functional, B3LYP, in conjunction with 6‐311+G* basis set on both the sextet and quartet potential energy surfaces (PESs). To obtain an accurate evaluation of the activation barrier and reaction energy, the coupled cluster single‐point calculations using the B3LYP structures is performed. The crossing points (CPs) of the different PESs have been localized with the approach suggested by Yoshizawa and colleagues. The involving potential energy curve‐crossing dramatically affects reaction mechanism. The present results show that the reaction mechanism is insertion‐elimination mechanism both along the C? S and C? O bond activation branches, but the C? S bond activation is much more favorable than the C? O bond activation in energy. All theoretical results not only support the existing conclusions inferred from early experiment study, but also complement the pathway and mechanism for this reaction. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Molecular vibrational energy flow and dilution factors in an anharmonic state space

A fourth-order resonance Hamiltonian is derived from the experimental normal-mode Hamiltonian of SCCl2. The anharmonic vibrational state space constructed from the effective Hamiltonian provides a realistic model for vibrational energy flow from bright states accessible by pulsed laser excitation. We study the experimentally derived distribution PE(sigma) of dilution factors sigma as a function of energy. This distribution characterizes the dynamics in the long-time limit. State space models predict that PE(sigma) should be bimodal, with some states undergoing facile intramolecular vibrational energy redistribution (small sigma), while others at the same total energy remain "protected" (sigma approximately 1). The bimodal distribution is in qualitative agreement with analytical and numerical local density of states models. However, there are fewer states protected from energy flow, and the protected states begin to fragment at higher energy, shifting from sigma approximately 1 to sigma approximately 0.5. We also examine how dilution factors are distributed in the vibrational state space of SCCl2 and how the power law specifying the survival probability of harmonic initial states correlates with the dilution factor distribution of anharmonic initial states.     

Electrical conducting bis(oxalato)platinate complex with direct connection of CuII ions

Reactions of K1.62[Pt(ox)2].2H2O and [Cu(bpy)(H2O)3](NO3)2 yielded partially oxidized one-dimensional (1D) bis(oxalato)platinates of [Cu(bpy)(H2O)n]6[Pt(ox)2]7.7H2O (n = 2, 3, or 4) (1) and [Cu(bpy)(H2O)n]8[Pt(ox)2]10.8H2O (n = 3 or 4) (2). The average oxidation numbers of the platinum ions in 1 and 2 are +2.29 and +2.40, respectively. Complexes 1 and 2 crystallize in the triclinic P and monoclinic C2/c space groups, respectively, and the [Pt(ox)2]n- anions are stacked along the crystallographic b axis with 7-fold periodicity for 1 and 10-fold periodicity for 2. In 1, an oxalato ligand in the platinum chain directly coordinates to a paramagnetic [Cu(bpy)(H2O)3]2+ ion, whereas no such direct coordination was observed for 2. The electrical conductivity of 2 at room temperature along the platinum chain is approximately 3 orders of magnitude smaller (sigma||= 1.3 x 10(-3) S cm(-1)) than that of 1 (sigma|| = 0.9-0.5 S cm(-1)), and the activation energies of 1 and 2 are 29 and 67 meV, respectively. The longest inter-platinum distances in 1 and 2 are 2.762 and 3.0082 A, respectively, and this is responsible for the lower electrical conductivity of 2. An X-ray oscillation photograph taken along the b axis of 1 reveals the 7-fold periodicity in the 1D chain, consistent with the period of the Peierls distortion estimated from the degree of partial oxidation. The semiconducting state of 1 can therefore be regarded as a commensurate Peierls state. The magnetoresistance of 1 at ambient pressure indicates no interaction between conduction electrons in the platinum chain and local spins of the paramagnetic CuII ions. Application of hydrostatic pressures of up to 3 GPa enhances electrical conduction, as is often seen as the usual pressure effect on the electrical conductivity, which is due to enhanced orbital (Pt-5dz2) overlap by pressure application.