Radiative lifetimes for the A2Σ+ (v′ = 0–7) and D2Σ+ (v′ = 0–5) Rydberg states of NO

Intensities for the γ(A²Σ⁺?→?X²Π), ε(D²Σ⁺?→?X²Π) and (D²Σ⁺?→?A²Σ⁺) bands for NO have been calculated using the Molecular Quantum Defect Orbital (MQDO) methodology. Radiative lifetimes for the A²Σ⁺ and D²Σ⁺ vibrational Rydberg states have also been determined. The present results are in excellent accord with measurements available in the literature. Additionally, predictions for a number of unknown intensities and radiative lifetimes are made, given their potential usefulness.     

The S21 lines of the A2Σ+ (v′ = 1)←X2Π (v″ = 0) transitions of OH and OD

The S₂₁ lines of the OH radical for the A²Σ⁺ (v′ = 1)←X²Π (v″ = 0) transition have been observed in the 278–280 nm region from the laser-excitation spectrum. The OH radical was generated from either the H + NO₂ or the H + O₃ reaction in a flow system and the fluorescence passing through a 309.6 nm interference filter was detected with a photomultiplier-boxcar integrator arrangement. The weak S₂₁ lines were observed at laser energies above 0.2 mJ. The observed peak wavenumbers are in excellent agreement with those predicted for the S₂₁ bands of the A (v>′ = 1)←X (v″ = 0) transition from the known spectroscopic parameters. Observation of the corresponding S₂₁ system for OD in the 286.0–286.9 nm region further confirms this assignment. The relative absorption cross-sections of about one-tenth those of the P₁ lines are in good agreement with theoretical considerations.     

Pressure broadening parameters of the hydroxyl radical A 2 Σ+ (υ’=0) ← X 2 Π3/2 (υ=0) transitions at ca. 308 nm

Pressure broadening widths and pressure-induced frequency shifts for the hydroxyl radical Q11([see full textsee full text]), Q21([see full textsee full text]), Q11(2), Q21(2) absorption lines in the A band at ca. 308 nm have been determined in the presence of a variety of gases (N2, Ar, Ne and He). Hydroxyl radicals were formed using either a microwave discharge or a vacuum ultra-violet photolysis of water vapour and were detected using direct absorption spectroscopy with a bandwidth normalised noise equivalent absorption sensitivity of 5 ×10-5 Hz-1/2. A tunable external cavity diode laser at 835 nm and a single-frequency continuous-wave intracavity frequency-doubled diode laser at 488 nm were used to produce tunable continuous-wave light at 308 nm by sum-frequency generation in a -BaB2O4 crystal.     

SiH4+H→H2+SiH3反应的约化维数计算

对SiH4+ H→H2+SiH3反应体系应用SVRT模型进行了4维的量子动力学计算.将得到的速率常数与实验数据以及其他理论方法进行比较,得出了一些有意义的结论,并与CH4+H→H2+CH3反应在同种理论模型下做了对比,较好的与实验相吻合.最后验证了理论方法以及势能面的正确性.     

碰撞能对S(1D) +H2(v=0, j=0)→SH+H反应立体动力学性质的影响

利用1A′态的势能面[ Ho et al., J. Chem. Phys. 116, 4124 (2002)],采用准经典轨线方法研究了在不同碰撞能条件下,S(1D) +H2(v=0, j=0)→SH+H反应的立体动力学性质. 通过计算得到了描述反应物速度矢量k与产物的转动角动量矢量j′这两个矢量相关的分布函数P(r)、描述反应物速度矢量k、产物速度矢量k′与产物的转动角动量矢量j′这三个矢量相关的二面角分布函数P(r)以及描述反应产物角动量极化的分布函数P(r,r).计算结果表明产物的转动角动量矢量j′在空间具有明显的定向和取向效应,并且产物的转动角动量具有强烈的极化. 另外,计算结果还表明这些立体动力学性质对碰撞能非常敏感.     

碰撞能对S(1D) +H2(v=0, j=0)→SH+H反应立体动力学性质的影响

利用1A′态的势能面[ Ho et al., J. Chem. Phys. 116, 4124 (2002)]，采用准经典轨线方法研究了在不同碰撞能条件下，S(1D) +H2(v=0, j=0)→SH+H反应的立体动力学性质. 通过计算得到了描述反应物速度矢量k与产物的转动角动量矢量j′这两个矢量相关的分布函数P(r)、描述反应物速度矢量k、产物速度矢量k′与产物的转动角动量矢量j′这三个矢量相关的二面角分布函数P(r)以及描述反应产物角动量极化的分布函数P(r,r).计算结果表明产物的转动角动量矢量j′在空间具有明显的定向和取向效应，并且产物的转动角动量具有强烈的极化. 另外，计算结果还表明这些立体动力学性质对碰撞能非常敏感.     

Product polarization and mechanism of Li + HF(v=0, j=0) → LiF(v', j') + H collision reaction

A state-to-state dynamics analysis for the Li+HF(v=0,j=0)→LiF(v',j')+H collision reaction has been performed through quasiclassical trajectory(QCT)calculations.It is found that the differential cross section(DCS)of the LiF products from the title reaction is preferentially backward scattering for v=0,yet forward scattering for v=1 and 2.For v=3,the DCS exhibits forward,backward,and sideways scatterings.The variation of the internuclear distances and angles along the propagation time reveals that more than 99.08%of reaction trajectories undergo the direct reaction mechanism.The values of the polarization parameters a{1}1and a{2}0demonstrate that the product rotational angular moment j' is not only aligned perpendicular to the reagent relative velocity vector,but also oriented along the negative y axis.These product polarization results agree well with the recent quantum mechanical studies.The mechanism of these results was proposed and discussed in detail.     

Theoretical study of stereodynamics for the D'+ DS(v=0,j=0) → D'D + S abstraction reaction

Quasiclassical trajectory (QCT) calculations have been performed for the abstraction reaction, D'+ DS(v = 0, j = 0) → D'D + S on a new LZHH potential energy surface (PES) of the adiabatic 3 A electronic state [Lü et al. 2012 J. Chem. Phys. 136 094308]. The collision energy effect on the integral cross section and product polarization are studied over a wide collision energy range from 0.1 to 2.0 eV. The cross sections calculated by the QCT procedure are in good accordance with previous quantum wave packet results. The three angular distribution functions, P(θr), P(φr), and P(θr,φr), together with the four commonly used polarization-dependent differential cross sections ((2π/σ)(dσ00/dωt), (2π/σ)(dσ20/dωt), (2π/σ)(dσ22+/dωt), (2π/σ)(dσ21/dωt)) are obtained to gain insight into the chemical stereodynamics of the title reaction. Influences of the collision energy on the product polarization are exhibited and discussed.     

Exact quantum dynamics study of the H(2S)+SiH+(X1Σ+) reaction on a new potential energy surface of SiH2+(X2A1)

Based on a new global potential energy surface of SiH₂⁺(X²A₁), the exact quantum dynamical calculation for the H(²S)+SiH⁺(X¹Σ⁺)→H₂+Si⁺ reaction has been carried out by using the Chebyshev wave packet method. The initial state specified (ν_i=0, j_i=0) probabilities, integral cross sections (ICS) and thermal rate constants of the title reaction are calculated. All partial wave contributions up to J=90 are calculated in exact quantum calculation including the full Coriolis coupling (CC) effect. The dynamical behaviors of probabilities, ICSs and rate constants are found to be in accord with an exothermic reaction without potential barrier. By comparing the probabilities of CC with the corresponding centrifugal sudden (CS) approximation ones, it can be concluded that neglecting CC effect will decrease the collision time, increase the amplitude of oscillation and lead to overestimation or underestimation of the reaction probability. For ICSs and rate constants, it is found that the deviation of CC and CS ICSs is small in the most of collision energy range except for the range of 0 eV-0.05 eV, while the deviation of both rate constants is considerable in the temperature range of 16 K-1000 K.     

Dynamics of the CH4+ O(~3 P) → CH_3(ν= 0) + OH(■= 0) reaction

The dynamics of the ground-state reaction of CH_4+ O(~3P) → CH_3(ν = 0) + OH( ν= 0) have attracted a great deal of attention both theoretically and experimentally. This rapid communication represents extensive quasi-classical trajectory calculations of the vibrational distributions on a unique full-dimensional ab initio potential energy surface for the title reaction, at the collision energy of relevance to previous crossed molecular beam experiments. The surface is constructed using the all electrons coupled-cluster singles and doubles approach plus quasi-perturbative triple excitations with optimized basis sets. A modified Shepard interpolation method is also employed for the construction. Good agreement between our calculations and the available experimental results has been achieved, opening the door for accurate dynamics on this surface.     

The effect of surface temperature on H2/D2(v = 0, j = 0)–Ni(100) scattering processes

We carry out both four-dimensional (4D×2D) and six-dimensional (6D) quantum dynamics on a parametrically time- and temperature-dependent effective Hamiltonian for H₂/D₂(v = 0,j = 0)–Ni(100) collision process. Such an effective potential was derived within a theoretical framework of mean-field approximation by considering weakly correlated interaction between molecular degrees of freedom, phonon modes and electron– hole pair (elhp) coupling through a Hartree-product-type wave function, where the initial state distribution of the surface modes and elhp coupling were introduced through Bose– Einstein and Fermi– Dirac probability factor, respectively. The temperature-dependent dissociation and state-to-state transition probabilities for H₂/D₂(v = 0,j = 0)–Ni(100) system are depicted as a function of initial kinetic energ of the incoming diatom. Though such effect appears negligibly small for H₂(v = 0,j = 0)–Ni(100) system, it is prominent in the case of D₂(v = 0,j = 0)–Ni(100) collision. It appears that the change of dissociation and transition probabilities of D₂ with the increase of surface temperature is exclusively dictated by the phonon modes directed along Z-axis, but the effect of elhp coupling particularly for transition probabilities is insignificant.     

A study of the ground states of CaC2H2+,CaC2D2+ and CaC2H4+

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用变分过渡态理论研究CH3SiH3+H→CH3SiH2+H2反应动力学

用变分过渡态理论对ＣＨ３ＳｉＨ３与Ｈ的抽提取应进行了理论研究;利用从头算计算了反应体系的构型、振动频率和能量等信息;计算了温度在２９８￣１７００Ｋ内反应的速率常数和穿透系数。结果表明,在室温下,变分对于此反应影响较大,隧道效应特别明显,计算得到的速率常数和实验值符合得很好。     

Theoretical study of stereodynamics for the D'+DS(ν = 0,j = 0)→D'D+S abstraction reaction

Quasiclassical trajectory (QCT) calculations have been performed for the abstraction reaction, D' +DS(v = 0, j = 0)→D'D+S on a new LZHH potential energy surface (PES) of the adiabatic 3A' electronic state [Lü et al. 2012 J. Chem. Phys. 136 094308]. The collision energy effect on the integral cross section and product polarization are studied over a wide collision energy range from 0.1 to 2.0 eV. The cross sections calculated by the QCT procedure are in good accordance with previous quantum wave packet results. The three angular distribution functions, P(θ_r), P(φ_r), and P(θ_r,φ_r), together with the four commonly used polarization-dependent differential cross sections ((2π/σ)(ds₀₀/dω_t), (2π/σ)(ds₂₀/dω_t), (2π/σ)(ds₂₂₊/dω_t), (2π/σ)(ds_21-/dω_t)) are obtained to gain insight into the chemical stereodynamics of the title reaction. Influences of the collision energy on the product polarization are exhibited and discussed.     

Complexation of hydrogen by lithium: structures,energies and vibrational spectra of Li+ (H2) n (n = 1–4), Li-H(H2) m and Li-H + (H2) m (m = 1–3)

The interaction of metals with hydrogen is of importance in several areas of technology. Lithium-hydrogen complexes are particularly amenable to theoretical study. Although no stable compound of the Li atom and H₂ has been found, a weak dative interaction forms between the σ bond of H₂ and the positively charged Li atom for Li⁺, Li-H⁺, and Li-H. At least four H₂ molecules can be complexed by Li⁺, and three by Li-H⁺ and Li-H. The presence of the Li ion does not substantially weaken the H₂ bond, nor is the energy of dissociation affected; however, the Li ion does form stable complexes with the dissociated H atoms.     

A measurement of the total cross section of the capture reaction2H(n,t)γ atE n=25 MeV

The total cross section of the capture reaction²H(n, t) has been measured atE _n=25 MeV using a deuterium gas target and a scintillation counter telescope. The resulting value =(7.6±0.8) b is compared with existing photodisintegration data and theoretical calculations.     

A study of π states of H2 + in the one centre approach

The statistical theory of the elastic constants of nematic liquid crystals is applied to detailed calculations based on well-defined approximations for the direct correlation function of Ornstein and Zernike and for the singlet orientational distribution. The model of hard spherocylinders with superimposed r ^-6 attraction modulated by a Maier-Saupe P ₂(cos ?_{1 2}) term, is used. The dependence on temperature, on the order parameter and on the length to breadth ratio, of the reduced elastic constants K* _i (i=1, 2, 3), is discussed in some detail and comparison with experiment is included.     

Local theory of solutions for the 0(2k+1) σ-model

We develop a theory of solutionsn for the Euclidean nonlinear 0(2k+1)-model for arbitraryk and for a regionG². We consider a subclass of solutions characterized by a condition which is fulfilled, forG=², by thosen that live on the Riemann sphere S²². We are able to characterize this class completely in terms ofk meromorphic functions, and we give an explicit inductive procedure which allows us to calculate all 0(2k+1) solutions from the trivial 0(1) solutions.