Calculation of the Combination Scattering Spectrum of the H2O Molecule Based on the Effective Polarizability Operator

This paper presents a procedure for calculation of the combination scattering spectrum of a nonlinear molecule of the X₂Y type which is based on a transformed polarizability operator taking into account the vibration-rotation interaction in the molecule to within the second order of the perturbation theory. The matrix elements of the operator are determined and classified by molecule symmetry type. The combination scattering spectrum of the H₂O molecule is calculated in the region of the 2v ₂ band. The second derivative of the average polarizability of the H₂O molecule with respect to the normal coordinate q ₂, associated with deformation vibrations, and the vibrational dependence of the average polarizability of the H₂O molecule on the deformation quantum number v ₂ are estimated.     

SiF$lt;sub$gt;2$lt;/sub$gt;基态分子的结构与势能函数

运用Gaussian03软件包,采用密度泛函理论中的B3P86 方法,结合6-311++G^**（3df,3pd） 基组对基态SiF₂分子的平衡电子结构和谐振频率进行了优化计算,得到了其稳定结构为C_2v构型.SiF₂基态电子态为X¹A₁,平衡核间距R_Si—F=0.1061　nm,键角α_F—Si—F=100.6762°,离解能D_e=13.8　eV.应用多体项展式理论推导了基态SiF₂分子的解析势能函数,其等值势能图准确地再现了SiF₂分子的平衡构型特征和能量变化. 关键词： 2')" href="#">SiF₂ Murrell-Sorbie函数 多体项展式理论     

Rotational structure of the 000, 010, 100, 020, and 001 vibrational states of the D216O molecule: Spectroscopic assignment of rotational levels up to J, Ka = 30 and analysis of published data

The complete spectroscopic assignment of calculated Partridge-Schwenke rotational energy levels up to J, K _a = 30 is presented for the 000, 010, 100, 020, and 001 vibrational states of the D₂ ¹⁶O molecule. The nonpolynomial model of an effective rotational Hamiltonian is used to perform the assignment and to analyze the experimental energy levels available in the literature for these states. The results obtained are compared with the data calculated by other authors. The results of this study can be useful in searching for and identifying new, highly excited rotational levels of D₂ ¹⁶O, as well as in creating the databases of parameters of rovibrational transitions of the water molecule.     

Intensity dependence of multiphoton dissociation in formaldehyde

A new intensity-dependent measurement of multiple-photon dissociation (MPD) in H₂CO, HDCO, and D₂CO gases by the use of an intense pulsed CO₂TEA laser is reported. In this measurement the energy and duration of the laser pulses are kept constant, and the intensity is varied by irradiating the sample using concave mirrors of different focal lengths. A model calculation is used to analyze and fit the present and previous experimental MPD data of HDCO and D₂CO. In this model it is assumed that dissociation is obtained by a repeated mechanism in which coherent multiphoton excitation (CME) of the molecule to high vibration-rotation states |v, J〉 is followed by intramolecular transfer of the excitation energy (ITEE) to the other modes of the molecule. In the calculations the CME is described in the framework of the density matrix formalism with relaxations, and is used to calculate absorption from the ground state as well as absorption from excited states reached by the energy redistribution in the molecule. The ITEE process is assumed to be intensity independent and to cause a random energy distribution in each transferring process. It is found that the experimental results are consistent with the absorption of 14±4 and 17±5 photons per molecule for HDCO and D₂CO, respectively, and this is sufficient to cause their dissociation.     

Theoretical study of chemi- and physisorption processes of H2 molecules on a (1 0 0) surface of silver

A model system consisting of a cluster of 13 Ag atoms and n (n = 1, 2, 3) H₂ molecules has been used to study, by ab initio methods, the structural and energetic characteristics of the chemi- and physisorption processes of H₂ on a (1 0 0) surface of silver. The dissociative chemisorption of a first H₂ molecule is analyzed in terms of hydrides formation and it is shown that several electronic states are interacting in the vicinity of the activation barrier leading to complex electronic processes. The energy of the physisorption interaction of the first H₂ molecule for different orientations and that of further H₂ molecules coming directly on top of the first chemisorbed one are determined with highly correlated wavefunctions. As for the (H₂)_nCu₁₃ system, already studied with similar approaches, it is found for the (H₂)_nAg₁₃ system that the physisorption energy of the second layer is enhanced by a factor close to two compared to that of the first layer due to dipolar interactions with the polarized surface. The physisorption energy of the third and further layers tends to the van der Waals H₂/H₂ interaction energy.     

Spectroscopic and structural proprieties of LiAr and LiAr<Subscript>2</Subscript> molecules

We determined and tried to understand the spectroscopic and structural properties of small LiAr and LiAr₂ molecules within a simple model considering LiAr as a result of interaction between a valence electron and a LiAr⁺ molecular ion. Potential energy curves, spectroscopic constants, and vibrational levels corresponding to the Li(2s, 2p, 3s, and 3p)+Ar dissociation are reported for the LiAr molecule. The depth of the potential well for the X ²Σ⁺ ground state is found to be 50 cm⁻¹ (the corresponding experimental value is (42.5±1.2) cm⁻1 [1]). R _e is determined to be 9.36 a.u. (the experimental value is 9.24 a.u.). For the first excited state A, R _e = 4.97 a.u. and D _e = 993cm ⁻¹ (the corresponding experimental values are 4.68 a.u. and (925−40) cm⁻¹, respectively [1]). The spacing between the vibrational levels for the ground and first excited states is in very good agreement with the experiment. For the ground state, the difference between our results and the data of the most recent experiment is about 1 cm⁻¹. The model has been extended to study the LiAr₂ molecule in two forms (linear and triangular). We have determined the potential energy surfaces of the states dissociating to Li(2s, 2p)+Ar₂ and thus found the triangular form to be more stable as compared to the linear one. We have also calculated the transition energy between the ground state and first excited states of this molecule. The emission spectrum of the Li(2s)+Ar₂→Li(2p)+Ar₂ transition in both forms redshifts as compared to the Li(2s)→Li(2p) atomic transition.     

On the calculation of the orientational correlation parameter g 2

The g ₂ factor for a model of liquid carbon disulphide has been calculated by molecular dynamics simulation. The values of g ₂ for the model at three points along the orthobaric curve are: 1·17 ± 0·04 (298 K), 1·27 ± 0·03 (245 K), 1·39 ± 0·06 (193 K). These values are in good agreement with available experimental values. By calculating g ₂ in shells of cubic symmetry it is found that the value of g ₂ is determined by the orientational correlation of a molecule with neighbours within a few (two to three) molecular diameters. Spurious orientational correlations are introduced by the periodic boundary conditions and the calculation of collective correlation functions by averaging over the whole cube is shown to be unreliable. A theoretical calculation of g ₂ using RISM + SSA fails to reproduce the state dependence of the g ₂ values calculated from the simulation. This failure is not due to the small differences between the simulation and RISM g _αβ(r) for r < 4·5 Å but to inaccuracies in the SSA in the intermediate region r ～ 6 Å.     

Spin-one-Ising model for (CO)1−x (N2) x mixtures: A finite size scaling study of random-field-type critical phenomena

A qualitative model for solid mixtures of diatomic molecules, where one species (called CO, to be specific) carries both a dipole moment and a quadrupole moment, while the other species (calledN ₂) has only a quadrupole moment, is studied by Monte Carlo methods. We use spinsS _i =±1 to represent the orientations of the CO electric dipole moment, if the lattice sitei is taken by a CO molecule, whileS _i =0 if the site is taken by anN ₂ molecule. Assuming nearest-neighbor antiferroelectric interactions between CO molecules, and a bilinear dipole-quadrupole coupling between CO andN ₂, the randomly quenchedN ₂ molecules act like random fields do in the random field Ising model. In previous work it was already shown that this crude model is in very good agreement with experimental data in two dimensions (adsorbed layers), where the random fields induces a rounding of the transition. Here Monte Carlo simulations of the three-dimensional version of this model are presented and analyzed with finite size scaling concepts. As expected from the theory, a behaviour qualitatively different from the two-dimensional case is detected. The Monte Carlo data provide qualitative evidence that the random field induces crossover to an universality class with critical exponents distinct from the pure Ising model, but it is not feasible to us to study large enough systems that would allow a reliable estimation of these exponents. But the results show that dilution without dipole-quadrupole coupling has much less drastic effects on the critical behavior, and that in the presence of this coupling very small impurity concentrations do indeed change the critical behavior.This paper is dedicated to Professor Herbert Wagner on the occasion of his 60th birthday     

On the additivity of atomic and molecular dipole properties and dispersion energies using H,N, O,H2, N2, O2, NO,N2O,NH3 and H2O as models

The zeroth-order theory of intermolecular forces is used to derive additivity relations for rotationally averaged molecular dipole properties and dispersion energy constants by assuming that a molecule is comprised of non-interacting atoms or molecules. Some of the additivity rules are new and others, for example the mixture rule for dipole oscillator strength distributions (DOSDs), Bragg's rule for stopping cross sections and Landolt's rule for molecular refractivities, are well known. The additivity rules are tested by using previously constructed DOSDs and reliable values for the dipole oscillator strength sums S_k , L_k and I_k , and dispersion energy constants C ₆, for H, N, O, H₂, N₂, O₂, NO, N₂O, NH₃ and H₂O as models. It is found that additivity is generally unreliable for estimating molecular properties corresponding to k < -2. Generally for k ≥ -2 and for C ₆, and if the hydrogen molecule is used to represent the hydrogen atom in the additivity rules, the additivity relations yield results that are reliable to within ?20 per cent and the estimates improve substantially as k increases. The effects of molecule formation on DOSDs is examined by comparing the various molecular DOSDs with the sum of the DOSDs for the atoms making up the molecules. Molecule formation results in a net decrease in the amount of dipole oscillator strength for low excitation energies and a compensating net increase for higher energies in a region extending from the absorption threshold to about 100 eV. This is shown to imply that estimates of the stopping average energy I ₀, obtained by using bona fide atomic I ₀ values, are lower bounds to the correct molecular I ₀ results.     

CARS study of the vibrational kinetics of nitrogen molecules in the burning and afterglow stages of a pulsed discharge

The vibrational kinetics of the nitrogen molecule in the ground state X ¹Σ _g ⁺ in the burning and afterglow stages of a pulsed discharge are investigated by coherent anti-Stokes Raman spectroscopy (CARS). The total cross section for vibrational excitation of the nitrogen molecule by electron impact to the first eight vibrational levels is determined. The rate constant for the associative ionization reaction involving nitrogen atoms in the metastable states ² P and ² D is estimated. It is found that the best agreement between the calculated and measured populations of the nitrogen molecules in the ground state X ¹Σ _g ⁺ in the afterglow stage of a pulsed discharge is obtained when the rate constant for VV exchange K ₀₁ ¹⁰ has the value predicted by the quantum-classical Billing-Fisher model. Zh. Tekh. Fiz. 67, 34–42 (May 1997)     

Role of structural elements of chloronaphthalene molecules in spin-orbit coupling: Phosphorescence

The dipole moments (P ^s ) of the T ₁ ^S → S ₀ transition from the triplet sublevels s = z, y, x, which are determined by the spin-orbit (SO) coupling, are studied for a series of mono- and dichloro derivatives of naphthalene. Based on the model calculations, the effects of different factors (SO coupling in individual chlorine atoms occupying the α and β positions in the molecule, SO coupling in the carbon backbone of the molecule, and the compensation effect caused by the interference of SO interactions in individual structural elements of the molecule) on P ^s are differentiated and discussed.     

Reactive scattering of oxygen atoms: O+I2, ICl,Br2

Angular and velocity distribution measurements of IO reactive scattering from crossed beams of O atoms and halogen molecules I₂, ICl are reported. Angular distribution measurements are reported for BrO from O + Br₂. The O atom beam was generated at ～350 K from a microwave discharge source and the halogen molecule beam from a supersonic nozzle source at ～380 K. The product time-of-flight distribution was recorded at each laboratory scattering angle by a mini-computer. The scattering data are found to be in excellent agreement with the RRKM-AM model of reactive scattering via a long-lived collision complex. The observation of IO product from O + ICl identifies the complex with a bound O-I-Cl triplet state, previously observed for O-Cl-Cl in matrix isolation studies, as proposed by Herschbach. The maximum centrifugal barrier B _m′ for dissociation of the long-lived complex can be accurately determined, particularly for O + I₂. The B _m′ values indicate that both the entrance and exit valleys of the potential energy surface are governed by centrifugal barriers in the region of long-range van der Waals potentials. The comparatively small reaction cross section (e.g. Q ～ 2 Ų for O + Br₂ from discharge flow measurements) is attributed primarily to an orientation requirement for reaction. The RRKM-AM model indicates a ‘tight linear’ transition state for dissociation of the O-I-I complex, corresponding to significant long-range IO orienting forces in the exit valley of the potential energy surface.     

On the local mode behaviour of the XH2/XD2 and XD/XH fragments with respect to the deuterated species of the near local mode XH3(C3v ) molecule

Effect of isotopic substitution in the near local mode, XH₃(C_3v ), molecules is considered. On that basis it is shown that the spectroscopic properties of deuterated and/or di-deuterated isotopic species of the XH₃(C_3v ) molecule with the value of interbond angle close to π/2 are analogous to the spectroscopic properties of its separate fragments: of a three-atomic local mode ‘molecule’ XH₂/XD₂ and of a diatomic XD/XH ‘molecule’. The phosphine molecule is considered as an illustration.     

LiO2(C2V，X2A2)分子的结构与势能函数

使用二次组态相互作用方法，在aug-cc-pvtz基组水平上对LiO₂(C_2V，X²A₂)基态分子进行了几何优化，得到了它的平衡几何构型和力常数.根据原子分子反应静力学原理得到可能的电子状态和离解极限.应用多体展式理论方法推导出了LiO₂(C_2V，X²A₂)基态分子的解析势能函数.     

Temperature dependence of Rb2 molecule formation rate constant in a magneto-optical trap

In this paper, we report the measurement of Rb₂ molecule formation rate constant due to a two body process in a magneto-optical trap as a function of the sample temperature. The ground state molecules are detected by two-photon ionization, through the intermediate a ³Σ _u ⁺ → 2³Π _g molecular band. Our results show that the Rb₂ molecules formed in the MOT could be due to a wave shape resonance, which enhances the molecule formation rate. This effect may be used to enhance the molecule production; and therefore it maybe important to future experiments involving production and trapping of cold ground state molecules.     

Absorption and resonance Raman spectroscopy of the 1Bu state of trans‐1,3,5‐hexatriene including vibronic coupling

The vibronic coupling between the first excited S₁ (2¹A_g) and the second excited S₂ (1¹B_u) singlet electronic states in spectroscopy of trans‐1,3,5‐hexatriene molecule is investigated on the basis of a model consisting of two electronic states coupled by two vibrational modes. Employing a perturbation theory that treats the intramolecular couplings in a perturbative manner, the absorption and resonance Raman cross sections and excitation profiles of this molecule are calculated using the time‐correlation function formalism. The non‐Condon corrections are included in evaluation of cross sections. The multidimensional time‐domain integrals that arise in these calculations have been evaluated for the case in which S₀ (1¹A_g) S₂ (1¹B_u) electronic transition takes place between displaced and distorted harmonic potential energy surfaces. The calculated spectra are in good agreement with the experimental ones. Copyright © 2011 John Wiley & Sons, Ltd.     

Perturbation of the angular correlation of γ-rays by molecular motion

The time dependent angular correlation of successive gamma rays emitted by a nucleus coupled by a quadrupolar field to a randomly reorienting molecule is calculated for a complete range of rates of molecular motion using a strong collision model. The results in the fast and slow motion limits are similar to those previously obtained using a diffusional model. Calculated curves of G ₂₂(t) are given in the intermediate range of rates of motion and the results compared with published experimental observations.     

Temperature Dependence of the Vibrational Relaxation Rate Constants of CO2 (0001) in Binary Mixtures

The rate constants of intramolecular intermode relaxation of the CO₂ molecule (00⁰1) in pure CO₂ and in binary mixtures with He, Ar, H₂, O₂, N₂, CO, NO, N₂O, and H₂O were measured in the temperature range 300–1000 K by means of a laser-induced luminescence method. It is shown that these relaxation rate constants K for all the gas mixtures investigated increase with increase in the gas temperature in this range; the most efficient in deactivation of the 00⁰1 level are the collisions of CO₂ molecules with H₂O molecules; the mechanisms of relaxation of the 00⁰1 level of CO₂ and their channels depend not only on the temperature but also on the parameters of colliding particles; for each of the colliding partners of the CO₂ molecules there is a certain temperature T _c above which the temperature dependence of K is coordinated with the Landau–Teller dependence, and, moreover, the simpler the structure of the colliding partner of the CO₂ molecule, the higher the temperature T _c. Deviations from these dependences at temperatures T < T _c are attributed to the influence of intermolecular forces of attraction, change of relaxation channels, and formation of molecular clusters. For all the colliding partners of the CO₂ molecules, the interaction radii are determined from the intermolecular potentials of interaction used in the theoretical model.