Vibrational Structure of the Absorption Spectra and a Model of the HNO and DNO Molecules in the Excited State

The vibrational structure of the absorption spectra of the first n–^*–electron transitions of the HNO and DNO molecules is calculated in the Franck–Condon approximation. A structural model of the molecules in the excited electronic state is constructed on the basis of correlations and with the aid of a method of hybrid atomic orbitals. Evaluation of the influence of deuterium substitution on the intensities of the vibrational components upon electronic excitation is made. A comparison of the experimental and theoretical absorption spectra calculated for different models of the molecules is carried out.     

Application of Symbolic Computations in Calculation of Electronic–Vibrational Spectra of Molecules

An algorithm of calculation of multidimensional integrals of overlapping harmonic vibrational wave functions that employs symbolic computations has been developed. The algorithm is implemented in a Matlab 5.x system and allows one to perform calculations many orders of magnitude more rapidly than those described heretofore. The speed of computation by this algorithm depends weakly on the dimensionality of the overlap integral, and this makes it possible to use this integral to calculate the intensities of lines in the electronic–vibrational spectra of multiatomic molecules.     

Calculation of the Spectroscopic Constants and Strength of the Electron Transition <Emphasis Type="Italic">A</Emphasis>0<Superscript>+</Superscript>-<Emphasis Type="Italic">X</Emphasis><Superscript>1</Superscript>Σ<Superscript>+</Superscript> of the AgAu Molecule

The vibrational, rotational, and centrifugal constants for the electronic states A and X ¹Σ⁺ of the AgAu molecule have been calculated. The calculation is based on the Morse potential functions that were used to approximate the real potential curves of the ground and excited states of AgAu. Using the experimental data on the lifetime of the vibrational levels of the excited electronic state, the strength of the A-X transition was calculated.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 2, pp. 176–180, March–April, 2005     

Vibrational excitation dynamics in photodesorption

Quantum state specific detection of photodesorbed molecules enables measuring their final state distributions in the translational and internal degrees of freedom, which contain a wealth of information about the desorption mechanism and dynamics. Vibrational state populations are of particular interest because of the information they contain about the lifetime and nature of the electronic excited states responsible for desorption. The measured vibrational distributions for nondissociative photodesorption of diatomic molecules tend to resemble Boltzmann distributions with temperatures of 600–1200 K for desorption from metal surfaces, and 1700–2000 K for semiconductors and oxides. Two-dimensional quantum dynamics calculations of the desorption process show that these vibrational distributions can be reproduced only if the intramolecular equilibrium bondlength in the electronic excited state is remarkably similar to that of the ground state. In particular, the results are inconsistent with a desorption mechanism in which the intramolecular bondlength change upon excitation is similar to that of electron capture in the gas phase.     

Anharmonic resonances in the vibrational spectra of pyrazine

The quartic force field of pyrazine has been calculated in the B3LYP/6-31G(d) hybrid density-functional approximation. Based on the results of this calculation, the total IR (250–3800 cm^–1) and Raman (400–3200 cm^–1) spectra of pyrazine have been interpreted with consideration for the Fermi and Darling-Dennison resonances and their spectral manifestations. A precision method is proposed for anharmonic analysis of the vibrational states of polyatomic molecules on the basis of consideration of their theoretical anharmonicity constants in combination with the corresponding experimental frequencies. The method of linear scaling of frequencies has been theoretically substantiated.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 13–22, January–February, 2005.     

Theory of non-adiabatic vibrational relaxation in atom-molecular collisions

The transition complex method is used for calculating the rate constant of non-adiabatic vibrational deactivation of diatomic molecules in the ²II electronic state upon collisions with inert gas atoms. The main contribution to the rate constant comes from vibronic transition caused by spin-orbital and orbital-rotational couplings. The two-dimensional Landau-Zener approximation is considered in connection with calculation of the nonadiabatic transition near the crossing line of two potential surfaces, and the limitations of ideas concerning the activated complex are discussed. The general expression for the rate constant derived from the diatomic molecule-atom collision is correlated with that for the atomic collision.     

The prediction of core-level binding-energy shifts from CNDO molecular orbitals

A theory is described for calculating core-level binding-energy shifts with potential models that employ “intermediate-level” molecular-orbital wave functions. The relaxation-energy term in atomic core-level binding energies is considered first. The ground-state potential model (GPM) and relaxation-potential model (RPM) are developed for calculating core-level binding energy shifts in molecules from CNDO wavefunctions. It is shown that neglect of certain two- and three-center integrals in these models limits their accuracy when unlike molecules are compared. The models are modified by calculating r^?1 integrals, to be sensitive to bond directions of p orbitals. The pp′ modification, in which a subset of the neglected integrals is retained to recover invariance to coordinate transformations, is thereby necessitated. The GPM approach yields shifts in very good agreement with experiment when comparisons are restricted to similar molecules. The RPM version gives better agreement especially over wider classes of molecules. It also provides relaxation energies V_R that can be combined with ab initio orbital energies to give binding energies. Several applications of these potential models are discussed.     

Low-rank canonical-tensor decomposition of potential energy surfaces: application to grid-based diagrammatic vibrational Green's function theory

ABSTRACT

A new method is proposed for a fast evaluation of high-dimensional integrals of potential energy surfaces (PES) that arise in many areas of quantum dynamics. It decomposes a PES into a canonical low-rank tensor format, reducing its integral into a relatively short sum of products of low-dimensional integrals. The decomposition is achieved by the alternating least squares (ALS) algorithm, requiring only a small number of single-point energy evaluations. Therefore, it eradicates a force-constant evaluation as the hotspot of many quantum dynamics simulations and also possibly lifts the curse of dimensionality. This general method is applied to the anharmonic vibrational zero-point and transition energy calculations of molecules using the second-order diagrammatic vibrational many-body Green's function (XVH2) theory with a harmonic-approximation reference. In this application, high dimensional PES and Green's functions are both subjected to a low-rank decomposition. Evaluating the molecular integrals over a low-rank PES and Green's functions as sums of low-dimensional integrals using the Gauss–Hermite quadrature, this canonical-tensor-decomposition-based XVH2 (CT-XVH2) achieves an accuracy of 0.1 cm^?1 or higher and nearly an order of magnitude speedup as compared with the original algorithm using force constants for water and formaldehyde.     

Geometry Relaxation of Photoexcited States in Conjugated Molecules

The random phase approximation combined with semiempirical Hamiltonians is applied to compute and analyze electronic structure and excited state adiabatic potentials of several conjugated molecules. Calculated excited state energies and parameters of molecular adiabatic surfaces characterize the coupled dynamics of vibrational and electronic degrees of freedom. The analysis identifies the specific torsional and bond-stretching nuclear motions that dominate the excited state relaxation and lead to self-localized excitations. This approach is an inexpensive and numerically efficient method of computing molecular excited state adiabatic surfaces and modeling femto-to-pico second time-dependent photoexcitation processes along chosen trajectories.     

Temperature Dependence of the Efficiency of Collisional Transfer of Vibrational Energy in Mixtures of Vibrationally Excited Triplet Molecules with Foreign Gases

By the pressure dependences of the decay rates of delayed fluorescence activated by vibrational excitation of triplet molecules of benzophenone and anthraquinone, the efficiencies of collisional transfer of vibrational energy (V–V-transfer) in the vibrational quasi-continuum of the triplet state have been estimated. It is shown that the efficiencies of the process in mixtures with foreign gases increase with increasing dipole moment and polarizability of colliding molecules. In the temperature range 433–513 K, we obtained an inverse temperature dependence of the V–V-transfer efficiency, which is satisfactorily described by empirical relations taking into account long-range attractive forces. The results obtained point to the determining role of long-range attractive forces in quasi-resonance V–V-transfer of vibrational energy by molecules excited in vibrational quasi-continuum.     

Electrostatic investigation into the bonding of poly(phenylene) thiols to gold

The advancement of nanotechnology relies on the understanding of electrical connection to individual molecules. Electrostatic surface potential measurements of self-assembled monolayers can provide insight into the structural and electronic properties of molecules attached to surfaces. In this paper we report on the electrostatic potential of poly(phenylene) thiol molecules bound to gold surfaces. Kelvin force microscopy is used to probe self-assembled monolayers of a series of phenyl, biphenyl, and triphenyl thiol molecules. The dipole moments of the isolated molecules have been determined and show similar electronic trends. A difference in polarity between the isolated molecules and the electrostatic surface potential of a monolayer attached to gold reflects the electron transfer on to the bound molecule.     

Modeling and Calculation of the Dynamics of Spectra with Allowance for Isomerization of Complex Molecules

A semiempirical parametric method for modeling of dynamic (time-resolved) electron-vibrational spectra of complex molecules with allowance for isomer-isomer transformations is proposed. It is based on the method developed earlier for construction of three-dimensional spectra of complex molecules without regard for isomer-isomer transformations. All the matrix elements necessary for calculation of spectra can be determined by the methods developed earlier. The time dependence of the population of a large number of vibronic levels has been determined using the iteration numerical method of integrating kinetic equations. Handy computational algorithms and a specialized software for a personal computer have been developed. The computer experiments conducted have shown that the method proposed can be used for modeling of dynamic spectra of complex molecules with allowance for their isomer-isomer transformations in the real-time scale.     

CO dynamics induced by tunneling electrons: differences on Cu(110) and Ag(110)

The electronic current originating in a scanning tunneling microscope (STM) can be used to induce motion and desorption of adsorbates on surfaces. The manipulation of CO molecules on noble metal surfaces is an academic case that has received little theoretical attention. Here, we do thorough density functional theory calculations that explore the chemisorption of CO on Cu(110) and Ag(110) surface and its vibrational properties. The STM induced dynamics are explored after excitation of the highest lying mode, the C–O stretch. In order to give a complete account of this dynamics, the lifetime of the different CO modes is evaluated (by only including the mode decay into electronic excitations of the host surface) as well as the intermode coupling. Hence, after excitation of the stretch mode, the lower-energy modes are populated via intermode coupling and depopulated by electron-hole excitations. This study reveals the intrinsic features of the STM induced motion of CO on Cu(110) and Ag(110).     

An analytical algorithm for the evaluation of two-electron integrals in diatomics: A test calculation with an elliptical basis set

A purely analytical method designed to compute the two-electron integrals that appear in anab-initio calculation of the electronic structures of diatomic molecules using elliptical basis set is presented. Test calculations are successfully carried out on LiH molecule.     

Analysis of electronic-vibrational spectra of uracil,thymine, and cytosine

A theoretical analysis of absorption spectra of uracil, thymine, and cytosine—nucleic acid bases— is carried out. Structural dynamic models of these molecules in their electronically excited states are constructed. On the basis of the calculated vibrational structure of the electronic spectra, different tautomeric forms of these molecules are determined. The possibility of modeling the influence of hydrogen bonds on the electronic-vibrational spectra is shown.     

Narrow-band model for nonequilibrium air plasma radiation

A band model is developed for the prediction of radiative transfer in air plasma applications under equilibrium and non-equilibrium conditions. For non-equilibrium applications, the medium is described by rotational–translational and vibrational temperatures but the populations of electronic states can be arbitrary. A specific formulation of the statistical narrow-band (SNB) model is developed for optically thick electronic systems of diatomic molecules when their populations are described by an electronic temperature. Model parameters, deduced from line by line calculations in the Voigt regime, are shown to be also convenient for arbitrary distribution of molecular electronic populations. This model is then complemented to include optically thin electronic systems and the continuum radiation through the simple box model, and line by line calculations for atomic lines. Several tests including equilibrium, non-equilibrium, uniform, and non-uniform conditions show the ability of this hybrid model to provide accurate and efficient solutions for radiative transfer problems in air plasmas.     

Sum-frequency generation at electrochemical interfaces: Cyanide vibrations on Pt(111) and Pt(110)

We use optical sum-frequency generation to investigate the stretching vibrations of cyanide (CN^–) molecules chemisorbed from aqueous electrolytes on single-crystalline Pt(111)- and Pt(110)-electrode surfaces. For clean and well-ordered Pt(111) electrodes, a single vibrational band between 2080 and 2150 cm^–1 with a nonlinear frequency dependence on the potential is observed and assigned to the CN stretching vibration of chemisorbed cyanide. A second band between 2145 and 2150 cm^–1 with very weak potential dependence appears on a surface which was subjected to oxidation-reduction cycles and is attributed to cyanide associated with a microscopically disordered surface. This assignment is supported by preliminary results for a Pt(110) single-crystal electrode. On a well-ordered (110) surface a single and potential-dependent cyanide vibration between 2070 and 2112 cm^–1 is observed. After oxidation of the cyanide and readsorption, this band is replaced by a higher frequency band at 2144 cm^–1 which is essentially not potential-dependent. Occasionally, additional vibrational bands at lower frequencies not reported in corresponding IR studies are observed on Pt(111).Paper presented at the 129th WE-Heraeus-Seminar on Surface Studies by Nonlinear Laser Spectroscopies, Kassel, Germany, May 30 to June 1, 1994     

C72O3的结构和光谱的理论研究

采用AM 1方法理论研究了C70 五元环酸酐衍生物C72 O3 的 8种可能异构体的结构和稳定性 ;以各异构体稳定构型为基础 ,分别用AM 1和ZINDO/CI方法计算了它们的振动光谱和电子光谱。结果表明 ,酸酐基团—C2 O3 主要加成在CⅠ CⅡ(异构体A)和CⅢ CⅢ(异构体B)键上形成闭环结构 ,异构体B的稳定性与实验已证实存在的异构体A十分相近 ;异构体A的振动光谱理论计算值与实验值符合较好 ,B的振动光谱理论计算值与A相似 ;对C72 O3 各异构体的电子跃迁进行了理论指认 ,讨论了其电子光谱的红移现象 ;其他异构体的振动和电子光谱属于理论预测。     

Visualization of rigorous sum rules for Franck–Condon factors: spectroscopic applications to Xe2

A fully quantum mechanical approach to the calculation and normalization of the Franck–Condon factors for diatomic species is described. The treatment is based on the fundamental demand of completeness of the energy eigenfunctions, which results in the rigorous sum rule for the Franck–Condon overlap integrals. The importance of this general rule has been discussed and thoroughly illustrated in the case of diatomic xenon molecules. Exactly solvable reference potentials for this system have been constructed and a complete basis of the actual energy eigenstates (including both bound and scattering states) has been created. Several direct spectroscopic applications to xenon excimers are presented, and their good agreement with relevant experimental data demonstrated. In particular, a kinetic model is proposed to explain the observed oscillatory structures in the fluorescence spectra of Xe₂^* [Chem. Phys. Lett. 117 (1985) 301] related to their classical left turning points. The same model gives a uniform explanation to the well-known first and second emission continua of rare gases.     

Point defects along metallic atomic wires on vicinal Si surfaces: Si(5 5 7)–Au and Si(5 5 3)–Au

Point defects on the metallic atomic wires induced by Au adsorbates on vicinal Si surfaces were investigated using scanning tunneling microscopy and spectroscopy (STM and STS). High-resolution STM images revealed that there exist several different types of defects on the Si(5 5 7)–Au surface, which are categorized by their apparent bias-dependent images and compared to the previous report on Si(5 5 3)–Au [Phys. Rev. B (2007) 205325]. The chemical characteristics of these defects were investigated by monitoring them upon the variation of the Au coverage and the adsorption of water molecules. The chemical origins and the tentative atomic structures of the defects are suggested as Si adatoms (and dimers) in different registries, the Au deficiency on terraces, and water molecules adsorbed dissociatively on step edges, respectively. STS measurements disclosed the electronic property of the majority kinds of defects on both Si(5 5 7)–Au and Si(5 5 3)–Au surfaces. In particular, the dominating water-induced defects on both surfaces induce a substantial band gap of about 0.5 eV in clear contrast to Si adatom-type defects. The conduction channels along the metallic step-edge chains thus must be very susceptible to the contamination through the electronic termination by the water adsorption.