Fully quantum state-resolved inelastic scattering between He and NO(X (2)Pi)

Quantum mechanical close-coupling calculations have been used to obtain fully quantum state-resolved differential cross sections and opacity functions for the rotationally inelastic collisions of NO(X (2)Pi) with He at collision energies of 63 and 147 meV using the most recent ab initio potential energy surfaces of K?os et al. [J. Chem. Phys. 112, 2195 (2000)]. Double peaks observed in the Lambda-doublet resolved differential cross sections are shown to be related to the presence of analogous peaks in the corresponding opacity functions. These structures can be linked directly to a specific expansion term in the potential, and reflect the fact that NO is not quite homonuclear.     

Steric asymmetry and lambda-doublet propensities in state-to-state rotationally inelastic scattering of NO(2Pi(1/2)) with He

Relative integrated cross sections are measured for rotationally inelastic scattering of NO(2Pi(1/2)),hexapole selected in the upper lambda-doublet level of the ground rotational state (j = 0.5), in collisions with He at a nominal energy of 514 cm(-1). Application of a static electric field E in the scattering region, directed parallel or antiparallel to the relative velocity vector v, allows the state-selected NO molecule to be oriented with either the N end or the O end towards the incoming He atom. Laser-induced fluorescence detection of the final state of the NO molecule is used to determine the experimental steric asymmetry, [formula: see text], which is equal to within a factor of (- 1) to the molecular steric effect, S(i-->f) is identical with (sigma(He-->NO) - (sigma(He-->ON))/(sigma(He-->NO) + sigma(He-->ON)). The dependence of the integral inelastic cross section on the incoming lambda-doublet component is also observed as a function of the final rotational (j'), spin-orbit (omega'), and lambda-doublet (epsilon') state. The measured steric asymmetries are significantly larger than previously observed for NO-Ar scattering, supporting earlier proposals that the repulsive part of the interaction potential is responsible for the steric asymmetry. In contrast to the case of scattering with Ar, the steric asymmetry of NO-He collisions is not very sensitive to the value of omega'. However, the lambda-doublet propensities are very different for [omega=0.5(F1)-->omega'= 1.5(F2)] and [omega=0.5(F1)-->omega'=0.5(F1)] transitions. Spin-orbit manifold conserving collisions exhibit a propensity for parity conservation at low deltaj, but spin-orbit manifold changing collisions do not show this propensity. In conjunction with the experiments, state-to-state cross sections for scattering of oriented NO(2Pi) molecules with He atoms are predicted from close-coupling calculations on restricted coupled-cluster methods including single, double, and noniterated triple excitations [J. Klos, G. Chalasinski, M. T. Berry, R.Bukowski, and S. M. Cybulski, J. Chem. Phys. 112, 2195 (2000)] and correlated electron-pair approximation [M. Yang and M. H. Alexander, J. Chem. Phys. 103, 6973 (1995)] potential energy surfaces. The calculated steric asymmetry S(i-->f) of the inelastic cross sections at Etr= 514 cm(-1) is in reasonable agreement with that derived from the present experimental measurements for both spin-manifold conserving (F1-->Fl) and spin-manifold changing (F1 --F2) collisions, except that the overall sign of the effect is opposite. Additionally, calculated field-free integral cross sections for collisions at Etr = 508 cm(-1) are compared to the experimental data of Joswig et al. [J. Chem. Phys.85, 1904 (1986)]. Finally, the calculated differential cross section for collision energy Etr= 491 cm(-1) is compared to experimental data of Westley et al. [J. Chem. Phys. 114, 2669 (2001)] for the spin-orbit conserving transition F1 (j = 0.5) -F1f (j' = 3.5).     

第26届国际化学奥林匹克竞赛实验试题

在开始做实验前请把试题从头至尾读一遍！警告：你只要在实验室就要自始至终戴上防护眼镜（除非你是戴眼镜的）,而且必须使用吸液橡皮球移取液体。不管你出自什么原因摘下防护镜或者用嘴吸液,都将受到警告。     

Rotationally inelastic scattering from surfaces HF(g) + LiF(001)

Rotationally inelastic scattering has been measured for a supersonic beam of HF off a clean LiF(001) surface, as a function of surface temperature and incident and final scattering angles. Rotational accomodation was found to be incomplete. Angular distributions were broad (substantially broader than cos θ_f) and independent of the rotational inelasticity.     

Charge transfer versus molecular conductance: molecular orbital symmetry turns quantum interference rules upside down

Destructive quantum interference has been shown to strongly reduce charge tunneling rates across molecular bridges. The current consensus is that destructive quantum interference occurs in cross-conjugated molecules, while linearly conjugated molecules exhibit constructive interference. Our experimental results on photoinduced charge transfer in donor-bridge-acceptor systems, however, show that hole transfer is ten times faster through a cross-conjugated biphenyl bridge than through a linearly conjugated biphenyl bridge. Electronic structure calculations reveal that the surprisingly low hole transfer rate across the linearly conjugated biphenyl bridge is caused by the presence of destructive instead of constructive interference. We find that the specific molecular orbital symmetry of the involved donor and acceptor states leads to interference conditions that are different from those valid in single molecule conduction experiments. Furthermore, the results indicate that by utilizing molecular orbital symmetry in a smart way new opportunities of engineering charge transfer emerge.     

The effect of parity conservation on the spin-orbit conserving and spin-orbit changing differential cross sections for the inelastic scattering of NO(X) by Ar

The fully Λ-doublet resolved state-to-state differential cross sections (DCSs) for the collisions of NO(X, (2)Π, v = 0, j = 0.5) with Ar have been shown to depend sensitively on the conservation of the total parity of the NO molecular wavefunction. Parity changing collisions exhibit a single maximum only in the DCS, while parity conserving transitions exhibit multiple rainbow peaks. This behaviour is shown to arise directly from the constructive or destructive interference of collisions impacting on the two pointed ends and on the flatter middle of the NO molecule. A simple hard shell, four path model has been employed to determine the relative phase shifts of the paths contributing to the scattering amplitude. The model calculations using the V(sum) potential, together with the results of a quasi-quantum treatment, provide good qualitative agreement with the experimental spin-orbit conserving (Δ? = 0) DCSs, suggesting that the dynamics for all but the lowest Δj transitions are determined largely by the repulsive part of the potential. The collisions leading to spin-orbit changing transitions (Δ? = 1) have been also found to be dominated by repulsive forces, even for the lowest Δj values. However, they are less well reproduced by hard shell calculations, because of the crucial participation of the V(diff) potential in determining the outcome of these collisions.     

Rotationally inelastic scattering from surfaces CO(g) + LiF(OO1)

The rotationally inelastic scattering of a supersonic, rotanonally cold (T_rot^I = 4–30 k) CO molecular beam from a clean LiF(001) surface has been investigated by VUV laser-induced fluorescence. Rotational accommodation was incomplete for surface temperatures 350 <T_s < 900 K. The degree of accommodation decreased with T_s and was independent of collision energy.     

Reduced dimensionality quantum scattering calculations on the F + CH(4) --> FH + CH(3) reaction

The existence of recently observed scattering resonances in the hydrogen abstraction reaction F + CH4 --> FH + CH3 was investigated using the reduced dimensionality rotating line umbrella (RLU) quantum scattering model and employing an analytical potential energy surface, PES-2006, recently developed by our group. The calculations were performed in hyperspherical coordinates. The wells found in the hyperspherical adiabats, the oscillatory pattern in the cumulative and state-to-state reaction probabilities, the forward/backward predominance in the differential cross section at a collision energy of 1.8 kcal mol(-1), and the dramatic change of the scattering angle with energy are related to scattering resonances, and they are assigned to a quasi-bound complex on the vibrationally adiabatic ground-state potential.     

Addition of aluminium,zinc and magnesium hydrides to rhodium(iii)

We report the addition of M–H bonds (M = Al, Zn, Mg) to a Rh(iii) intermediate generated from the reductive elimination of triethylsilane from [Cp*Rh(H)₂(SiEt₃)₂]. A series of new heterobimetallic complexes possessing Rh–M bonds have been isolated and characterised by a number of spectroscopic (¹H, ²⁹Si, ¹³C, ¹⁰³Rh NMR, infrared, and X-ray diffraction) and computational techniques (NBO and QTAIM analysis). Experimental and computational data are consistent with cleavage of the M–H bond upon addition to rhodium with formation of new Rh–M and Rh–H bonds. Upon photolysis the Al analogue of this series undergoes a further elimination reaction producing triethylsilane and a highly unusual Rh₂Al₂H₄ containing cluster proposed to contain an Al(i) bridging ligand.     

Synthesis and characterization of piperazine-substituted dihydrofuran derivatives viaMn(OAc) 3 mediated radical cyclizations

The aim of this study is to synthesize novel piperazine-containing dihydrofuran compounds (3a-n)from radical additions and cyclizations of diacyl and alkyl-acyl piperazine derivatives (1a-h) with 1,3-dicarbonyl compounds (2a-c) mediated by Mn(OAc) ₃ for the first time. From the reactions of 1a-c with dimedone (2a);1a, 1c, and 1d with acetylacetone (2b); and 1a with ethylacetoacetate(2c) ,the dihydrofuran-piperazine compounds 3a-c, 3d-f, and 3g were obtained in medium to high yields (31%–81%), respectively. In addition, dihydrofuran-piperazine compounds 3h-j and 3k-n were prepared at low to medium yields (20%–40%) from the reactions of 1e-g with 2a and 1e-h with 2c , respectively.     

Quantum dynamics of inelastic excitations and charge transfer processes in the H+ +NO collisions

State-resolved differential cross section, integral cross section, average vibrational energy transfer, and the relative transition probability are computed for the H(+)+NO system using our newly obtained ab initio potential energy surfaces (PES) at the multireference configuration interaction level of accuracy employing the correlation consistent polarized valence triple zeta basis set. The quantum dynamics is treated within the vibrational close-coupling rotational infinite-order sudden approximation using the coupled ground state and first excited state ab initio quasidiabatic PES. The computed collision attributes for the inelastic vibrational excitation are compared with the state-to-state scattering data available at E(c.m.)=9.5 eV and E(c.m.)=29.03 eV and are found to be in overall good agreement with those of the experiments. The results for the vibrational charge transfer processes at these collision energies are also presented.     

Steric effects in RNA interference: probing the influence of nucleobase size and shape

Nonpolar nucleosides with varying size and shape have been used to study the hydrogen-bonding stabilization and steric effects on RNA interference. The uracil and adenine residues of siRNA guide strands have been replaced by nonpolar isosteres of uracil and adenine and by steric variants. RNAi experiments targeting Renilla luciferase mRNA have shown close correlation between siRNA thermal stability and gene suppression. Interestingly, siRNA modified at position 7 on the guide strand does not follow this correlation, having substantial RNAi activity despite low thermal stability. Sequence-selectivity studies were carried out at this position with mutated target mRNAs and nucleobase analogues with varied size (2,4-difluoro- and 2,4-dichlorobenzene) and different shape (2,3-dichlorobenzene, 4-methylbenzimidazole). The results point out the importance of nucleobase shape and steric effects in RNA interference.     

Experimental and theoretical investigations of the inelastic and reactive scattering dynamics of O(3p) + D2

This paper presents a combined experimental and theoretical study of the dynamics of O((3)P) + D(2) collisions, with emphasis on a center-of-mass (c.m.) collision energy of 25 kcal mol(-1). The experiments were conducted with a crossed-molecular-beams apparatus, employing a laser detonation source to produce hyperthermal atomic oxygen and mass spectrometric detection to measure the product angular and time-of-flight distributions. The novel beam source, which enabled these experiments to be conducted, contributed unique challenges to the experiments and to the analysis, so the experimental methods and approach to the analysis are discussed in detail. Three different levels of theory were used: (1) quasiclassical trajectories (QCT), (2) time-independent quantum scattering calculations based on high-quality potential surfaces for the two lower-energy triplet states, and (3) trajectory-surface-hopping (TSH) studies that couple the triplet surfaces with the lowest singlet surface using a spin-orbit Hamiltonian derived from ab-initio calculations. The latter calculations explore the importance of intersystem crossing in the dynamics. Both experiment and theory show that inelastically scattered O atoms scatter almost exclusively in the forward direction, with little or no loss of translational energy. For the reaction, O((3)P) + D(2) --> OD + D, the experiment shows that, on average, approximately 50% of the available energy goes into product translation and that the OD product angular distributions are largely backward-peaked. These results may be interpreted in light of the QCT and TSH calculations, leading to the conclusion that the reaction occurs mainly on triplet potential energy surfaces with, at most, minor intersystem crossing to a singlet surface. Reaction on either of the two low-lying reactive triplet surfaces proceeds through a rebound mechanism in which the angular distributions are backward-peaked and the product OD is both vibrationally and rotationally excited. The quantum scattering results are in good agreement with QCT calculations, indicating that quantum effects are relatively small for this reaction at a collision energy of 25 kcal mol(-1).     

Aggregation-induced emission and aggregation-promoted photochromism of bis(diphenylmethylene)dihydroacenes

Reported herein is a new class of pure polycyclic hydrocarbon molecules, designed through a novel aggregation-induced emission (AIE) strategy, with unexpected photochromic properties. The restriction of intramolecular motion was found as a comprehensive mechanism for the AIE effect. The photochromism mechanism study revealed that the photocyclization reaction of cis-stilbene, the molecular conformation in the single crystal and the tetracene backbone should contribute to the unique photo behavior. In particular, the fast responsive, photo-reversible and thermo-irreversible photochromic effect facilitated in the solid state opens a new field of aggregation-promoted photochromism.     

Transition-metal-free controlled polymerization for poly(p-aryleneethynylene)s

A transition-metal-free controlled polymerization for the attainment of poly(p-aryleneethynylene)s is developed. The polymerization of 1-pentafluorophenyl-4-[(trimethylsilyl)ethynyl]benzene with a catalytic amount of fluoride anions proceeds in a chain-growth-like manner to afford polymers with controlled molecular weights and low polydispersity indexes. The mechanism involves a pentacoordinated fluorosilicate as a key intermediate. The anionic “living” nature of this process is applied to block copolymerization and also surface-terminated polymerization.     

Vibrational distribution in NO(X2Pi) formed by self quenching of NO A 2Sigma+ (v=0)

Time-resolved FTIR has been used to study the emission from the NO X 2Pi (v) products formed both by fluorescence and by collisional self quenching of the NO A 2Sigma+ (v=0) state. Vibrational excitation has been observed in ground state NO with populations up to at least v=20. Under conditions where fluorescence is the dominant removal process the nascent distribution in ground state NO(v) was found to be determined by the relative magnitude of the emission coefficients. Collisional quenching by ground state NO populates higher vibrational levels in NO(v) than fluorescence. By comparing distributions acquired at different pressures and by using a surprisal analysis, a nascent distribution of NO(v=0-20) is estimated for collisional relaxation of NO A 2Sigma+ (v=0) by NO. This distribution was found to be slightly hotter than statistical (prior) and showed evidence of oscillations at specific vibrational levels. This work is one of the first to be published concerning the vibrational ground state products of the quenching of electronically excited molecules and the first to report emission over such a large number of vibrational levels.     

Structure observation of graphene quantum dots by single-layered formation in layered confinement space

Graphene quantum dots (GQDs) have received much research attention due to their unique optical/electrical/magnetic features. However, the intrinsic relationship between the structure and properties of GQDs remains not fully understood, because the controlled synthesis and the accurate structure determination of GQDs are still a great challenge. Here, single-layered GQDs are successfully obtained by the hydrothermal treatment of intercalated citrate in the confined space of 2D interlayer galleries of layered double hydroxides (LDHs). The distinct molecular structures of the single-layered GQDs reveal that the blue photoluminescence of the GQDs derives from a rigid π-conjugate plane structure, which is in accordance with theoretical calculations. This work will open the door towards a quantitative understanding of the structure-property effects of GQDs.     

Rotationally inelastic scattering of HD from Cu(100) and Pd(111)

Rotational excitation of HD scattered from Cu(100), Pd(111), and Pd(111):H(D) was measured using molecular beam and quantum-state-specific laser spectroscopy techniques. Greater than 91% of the incident HD population was in the v = 0, J = 0 state. The final rotational distributions from Cu(100), Pd(111), and Pd(111):H(D) were compared for a HD beam at an incident energy of 74 meV. For all the three surfaces studied, rotationally inelastic scattering probabilities were large. We find that the final HD rotational distributions are remarkably similar for the three surfaces even though Pd(111) is very reactive to dissociative adsorption of HD whereas Cu(100) and Pd(111):H(D) are chemically inert.