Potential energy curves for ground and excited states of NaLi from ab initio calculations with effective core polarization potentials

Sixteen low-lying electronic states of NaLi are investigated by SCF/valence Cl calculations including core polarization effects by means of an effective potential. Spectroscopic constants are obtained with estimated uncertainties of ΔR_e ? 0.01 Å, Δω_e ? 0.6 cm^?1 and ΔD_e ? 80 cm^?1. From a comparison of experimental and theoretical G(υ) values, we suggest a ground-state dissociation energy of 7093 ± 5 cm^?1. Using our rovibrational energies and recently measured excitation lines, we are able to improve the T_e values and dissociation energies of five excited states to an accuracv of ±8 cm^?1.     

Local many-electron states in transition metal oxides and their surface complexes with atomic and molecular oxygen

The local many-electron states in transition metal oxides (TMOs) are considered in the framework of the effective Hamiltonian of the crystal field (EHCF) method. The calculations are performed with use of the 5×5×5 clusters modeling TMOs with the rock salt crystal structure. The d-d excitation spectra are calculated and discussed with the aim of interpreting the experimental data on optical adsorption and electron energy loss spectra. The EHCF method is extended to account for the electron correlation in the d-shell and some electronic variables of ligands simultaneously. This approach is used to calculate the states of atomic and molecular oxygen on the surfaces of the TMOs. The possible role of geometric parameters of the adsorption complex is evaluated. The metal-oxygen distance and the exit of the metal ion from the surface plane are varied in a wide range. In the case of molecular oxygen different coordination forms are considered and for all adsorption systems the weights of different oxygen states (triplet, singlet, and charge transfer) are estimated.     

A Raman spectroscopic study of the low-frequency vibrations in anisole and anisole-d3

Low-frequency Raman spectra of solid anisole and of solid anisole-d₃ have been recorded at 130 K. The phenyl torsion observed at 148 cm^?1 is shifted to 133 cm^?1 upon deuteration of the methyl group. The twofold torsional barriers calculated from these frequencies are 4033 ± 110 cm^?1 and 4094 ± 123 cm^?1 indicating that coupling to other low-frequency modes in both cases is of the same order of magnitude. The methyl torsional mode was observed at 285 cm^?1 in the spectrum of solid anisole and at 183 cm^?1 in the spectrum of anisole-d₃. The threefold barriers calculated using these frequencies are 1847 ± 20 cm^?1 and 1465 ± 18 cm^?1 respectively. These barrier values indicate that the methyl torsion is coupled to another low-frequency mode. A doublet centered at 230 cm^?1 in anisole is shifted to 245 cm^?1 in anisole-d₃; it is proposed that this is due to a ring mode coupled to the methyl torsion. The splitting is interpreted as an example of Davydov splitting.     

Transition metal complexes with open d-shell in semiempirical context. Application to analysis of Mössbauer data on spin–active iron(II) compounds

With use of cumulants of two-electron density matrices semiempirical methods are analyzed from a point of view of their suitability to describe qualitative features of electronic correlation important for calculation of electronic structure of the transition metal complexes (TMC). It is shown that traditional semiempirical methods relying upon the Hartree–Fock–Roothaan form of the trial wave function suffer from a structural deficiency not allowing them to distinguish the energies of the atomic multiplets of the TMCs' d-shells. On the other hand, the effective Hamiltonian of the crystal field (EHCF) previously proposed by the authors is shown to be suitable for further parameterization and has been successfully applied for calculations on polyatomic TMCs. Here we describe in details its recent modifications performed in relation to the SINDO/1 parameterization scheme and present the results of the calculations on spin-active Fe(II) complexes with nitrogen-containing polydentate ligands in relation with interpretation of the Mössbauer measurements performed on these complexes.     

Line-profile analysis of excitation spectroscopy in the even 4p5(2P1/2)nl′ [K′]J（l′=1,3） autoionizing resonances of Kr

The even-parity autoionizing resonance series 4p5np′[3/2]1,2,[1/2]1,and 4p5nf′[5/2]3of krytpon have been investigated by laser excitation from the two metastable states 4p55s[3/2]2and 4p55s′[1/2]0in the photon energy region of 29000–40000 cm 1at experimental bandwidth of~0.1 cm 1.The excitation spectra of the even-parity autoionizing resonance series,most of which are experimentally studied for the first time in this work,show typical asymmetric line shapes.Complementary information on level energies,quantum defects,line profile indices and resonance widths,resonance lifetimes and reduced widths of the autoionizing resonances are derived by Fano-type line-shape analyses of the experimental results.Results from this work indicate that the line profile index(q)and the resonance width()are approximately proportional to the effective principal quantum number(n*);the line separation of the 4p5np′autoionizing resonances is also in good agreement with theoretical model.     

UV spectroscopy of monosubstituted derivatives of 1,2-dihydro-C60-fullerenes

UV spectroscopy is used to determine the molar absorption coefficients of C₆₀ fullerene and monosubstituted 1,2-dihydro-C₆₀-fullerenes in different solvents. It is found that the extinction coefficient of C₆₀ at 330 nm (the main absorption band most frequently used for qualitative and quantitative determination of the C₆₀ content) is independent of the nature of the solvent and is ～54400 M^?1·cm^?1. The molar absorption coefficients of a series of monosubstituted 1,2-dihydro-C₆₀-fullerenes are practically independent of the chemical structure and the length of the substituent and are 35700 M^?1·cm^?1 (λ ～ 328 nm) and 115250 M^?1·cm^?1 (λ ～ 257 nm). It is shown that the substitution in fullerene proceeds via the double 6,6 bond, as evidenced by the absorption band at 424 nm in the spectra of these compounds, which is characteristic of monosubstituted methanofullerenes.     

Triplet-triplet energy transfer from aromatic to saturated compounds

Energy transfer from the upper triplet states of aromatic compounds to saturated compounds at 77 K has been investigated. Positions of triplet states of saturated molecules have been estimated in the ranges: 47800–48450 cm^?1 for methylcyclohexane, ethylcyclohexane, ethanol and ether, 47320–47800 cm^?1 for isopropylcyclohexane and transdecalin, and 48450–50000 cm^?1 for isoctane. The radius of the energy transfer sphere for biphenyl-d₁₀ and trans-decalin is found to be 5.1 Å. It is assumed that energy transfer occurs faster than vibrational relaxation.     

A precise determination of the first ionization potential of benzene

The first ionization potentials of benzene and benzene-d₆ have been precisely determined by the extrapolation of three-photon resonant Rydberg states in the four-photon ionization spectrum of the jet-cooled molecule. The convergence of resolved transitions in two Rydberg series for principal quantum numbers as high as 14 (-h₆) and 15 (-d₆) establish adiabatic thtesholds of 74573.0 ± 2.0 cm^?1, and 74592.5 = ± 1.2 cm^?1, respectively. These results are crucial for the understanding of the many excited states of benzene in terms of quantum defect theory. Precise quantum defects have been obtained for several Rydberg series and their variation with principal quantum number is reported. The results strongly suggest that the R? series of Wilkinson is derived from aπ(e_1g)→ nf±1 Rydberg excitation.     

Gas/gas and gas/wall average energy transfer from very low-pressure pyrolysis

It is shown that data obtained using very low-pressure pyrolysis (VLPP) on the pressure and temperature dependence of unimolecular rate coefficients of reactants with several reaction channels yield average energies transferred in gas/gas and gas/wall collisions (the wall being seasoned quartz at 800–1200 K). The downward average energy transferred, «ΔEå, for chlorocyclobutane/ethylene collisions is found to be 1600 cm^?1 at 970 K; «ΔEå for chlorocyclobutane/wall collisions varies from 5000 cm^?1 (wall efficiency β_w = 0.8) at 930 K to 3500 cm^?1 (β_w = 0.4) at 1150 K; similar values are found from published data on cycloheptatriene and cyclopropane-d₂. This indicates that the assumption of unit wall efficiency usually used in fitting VLPP experiments to RRKM theory needs revision.     

Energies of optical transitions in metal and semiconductor nanotubes

The energies of low-energy optical transitions were calculated, using the linearized attached cylindrical waves (LACW) method, as a function of inverse diameter d ^?1 for (n, n) metal nanotubes with n ranging from 3 to 12 and for (n, 0) semiconductor nanotubes with n ranging from 10 to 25. The calculations show that E ₁₁ in the metal nanotubes is higher than in the semiconductor nanotubes. Significant violations of the E ₁₁ ～ d ^?1 relationship are observed. For metal nanotubes, the situation is more complex because of the close energies of the π-π*-and σ-π* vertical transitions and because of the intersection of these characteristics in the range of 0.7 nm^?1 < d ^?1 < 1.0 nm^?1 (n = 8, 9, 10). For the semiconductor nanotubes, the E ₁₁ versus d ^?1 relationship is not linear, rather, it is oscillating; the E ₁₁(d ^?1) function alternates between two curves that refer to the (n, 0) nanotubes for which division of n by 3 gives 1 or 2 in the residue. On one hand, these features hamper the use of optical measurements in structure determination for the nanotubes; on the other, new criteria for nanotube classification appear.     

Normal coordinate analysis for the IR spectra of thiirene and deuterated thiirenes

Previous band assignments for thiirene-d_O, -d₁ and -d₂ are re-evaluated in the light of new spectroscopic data on cyclopropene. Evidence is presented for the assignment of the 657 cm^?1 absorption to the symmetric ring deformation mode of thürene supporting the assignment of the 910 cm^?1 band to the H-CC bending in-plane mode. Normal coordinate analysis reproduced the observed frequencies.     

Low frequency raman spectra of isotopic mixed benzophenone crystals

In this paper, we present an experimental study of vibrational lattice modes in isotopic mixed crystals of benzophenone-h₁₀ and -d₁₀. Our results are discussed using theoretical and experimental data concerning other molecular isotopic mixed crystals. The spectra show two regions; in the first (ν < 100 cm^?1) we did not observe an interaction between the various vibrational lattice bands; in the second region (ν > 100 cm^?1), the interaction appears clearly. The 111.5 cm^?1 and 73 cm^?1 torsional modes of benzophenone-h₁₀ have the same behaviour as the external modes throughout the whole concentration range (0–100% of benzophenone-d₁₀).     

Quasiresonance charge exchange of hydrogen isotopes mesic atoms in excited states

Processes of charge exchange of hydrogen isotopes mesic atoms in excited states at low collision energies 10^?2?E?1 eV are studied. The cross sections calculated depend on energy like ～E ^?1 and are of an order of the atomic cross sections (～10^?16 cm²). It is shown that the high rates (～10¹² s^?1) of charge exchange and thermalization of mesic atoms in excited states at the liquid hydrogen density are comparable with the rates of cascade transitions in mesic atoms.     

Spectra and structure of small ring compounds: Part XXXV. Vibrational spectra and ring-puckering and torsional potential functions of cyclobutylamine

The IR spectra (50–4000 cm^?1) of gaseous and solid cyclobutylamine and cyclobutylamine-N-d₂ and the Raman spectra (25–4000 cm^?1) of gaseous, liquid and solid cyclobutylamine and cyclobutylamine-N-d₂ have been recorded. Depolarization values were measured for both the gaseous and liquid states. Most of the thirty-six fundamental vibrations have been assigned and support for more than one molecular configuration is presented. In the low frequency region for the “light” compound, a series of four Q-branches have been assigned to transitions between energy levels of the ring-puckering vibration for the equatorial isomer. The transitional frequencies were fitted to an asymmetric single-minimum potential function of the form: V(X) = 0.474 × 10⁶X⁴ - 0.204 × 10⁵X² + 0.993 × 10⁵X³ with a reduced mass of 160 amu. The following torsional potential constants were determined for the “light” molecule- V¹ = 77.8 ± 17.0 cm^?1, V₃ = 784.0 ± 3.3 cm^?1. The trans conformation was found to be more stable than the gauche form by approximately 58 cm^?1 (0.17 kcal mol^?1). The barriers to trans-gauche, gauche-trans, and gauche-gauche interconversion are 803, 745 and 803 cm^?1, respectively.     

Analysis of methods for calculating the transition frequencies of the torsional vibration of acrolein isomers in the ground (S 0) electronic state

B3LYP, MP2, CCSD(T), and MP4/MP2 in the 6-311G(d, p), 6-311++G(d, p), cc-pVTZ, aug-cc-pVTZ bases used to calculate the transition frequencies of torsional vibration of trans- and cis-isomers of acrolein in the ground electronic state (S ₀) are analyzed. It is found that for trans-isomers, all methods of calculation except for B3LYP in the cc-pVTZ basis yield good agreement between the calculated and experimental values. It is noted that for the cis-isomer of acrolein, no method of calculation confirms the experimental value of the frequency of torsional vibration (138 cm^?1). It is shown that the calculated and experimental values for obertones at 273.0 cm^?1 and other transitions of torsional vibration are different for this isomer in particular. However, it is established that in some calculation methods (B3LYP, MP2), the frequency of the torsional vibration of the cis-isomer coincides with another experimental value of this frequency (166.5 cm^?1). It is concluded that in analyzing the vibrational structure of the UV spectrum, the calculated and experimental values of its obertone (331.3 cm^?1) coincide, along with its frequency. It is also noted that the frequency of torsional vibration for the cis-isomer (166.5 cm^?1) can also be found in other experimental works if we change the allocation of torsional transition 18 ₁ ¹ .     

Studies of oxygen transport mechanism in electrolytes based on doped lanthanum silicate with apatite structure using techniques of oxygen isotopic heteroexchange and impedance spectroscopy

The work presents the results of studying the mechanism of oxygen transport for a new promising class of oxygen-containing electrolytes based on lanthanum silicate with an apatite structure using impedance spectroscopy and isotopic oxygen heteroexchange. At 1000 K, in the case of samples with an optimum composition including codoped Fe and Al, σ ～ 3 × 10^?3 to 10^?2 S/cm and D* reaches ～10^?8 cm²/s, which is close to the values of YSZ and Ce_0.9Gd_0.1O_{2 ? δ} (GDC). Lower energies of conductivity activation and oxygen diffusion for doped apatites (～0.5–0.8 eV instead of ～1 eV for GDC) and also equivalence as regards exchange of all oxygen atoms within apatite agree with the model, in which oxygen mobility is determined by a nonlinear cooperative migration process of oxygen atoms with fast exchange between interstitial and regular sites.     

CN stretching and NO2 deformation vibrations and normal coordinate analysis of m-dinitrobenzene and m-dinitrobenzene-d4

Two bands appear for each CN stretching and nitro deformation vibration in the infrared and Raman spectra of m-dinitrobenzene and m-dinitrobenzene-d₄. The 907 cm^?1 bending mode in the vibrational spectra of m-dinitrobenzene undergo 30 cm^?1 upward shift upon d₄ substitution. A normal coordinate analysis pointed out that the 937 cm^?1 bending and 727 cm^?1 CN stretching vibrations as well as 18b CD in-plane deformation are mixed to a great extent. The other nitro bending mode undergo also an inverse isotopic effect (2 cm^?1 upward shift) due to coupling with the 18a CD in-plane deformation vibration.     

Blackbody infrared radiative dissociation of oligonucleotide anions

The dissociation kinetics of a series of doubly deprotonated oligonucleotide 7-mers [d(A) ₇ ^2? , d(AATTAAT)^2?, d(TTAATTA)^2?, and d(CCGGCCG)^2?] were measured using blackbody infrared radiative dissociation in a Fourier-transform mass spectrometer. The oligonucleotides dissociate first by cleavage at the glycosidic bond leading to the loss of a neutral nucleobase, followed by cleavage at the adjacent (5′) phosphodiester bond to produce structurally informative a-base and w type ions. From the temperature dependence of the unimolecular dissociation rate constants, Arrhenius activation parameters in the zero-pressure limit are obtained for the loss of base. The measured Arrhenius parameters are dependent on the identity of the nucleobase. The process involving the loss of an adenine base from the dianions, d(A) ₇ ^2? , d(AATTAAT)^2?, and d(TTAATTA)^2? has an average activation energy (E _a ) of ～1.0 eV and a preexponential factor (A) of 10¹⁰ s^?1. Both guanine and cytosine base loss occurs for d(CCGGCCG)^2?. The average Arrhenius parameters for the loss of cytosine and guanine are E _a =1.32 ± 0.03 eV and A=10^13.3±0.3 s^?1. No loss of thymine was observed for mixed adenine-thymine oligonucleotides. Neither base loss nor any other fragmentation reactions occur for d(T) ₇ ^2? over a 600 s reaction delay at 207 °C, a temperature close to the upper limit accessible with our instrument. The Arrhenius parameters indicate that the preferred cleavage sites for mixed oligonucleotides of similar mass-to-charge ratio will be strongly dependent on the internal energy of the precursor ions. At low internal energies (effective temperatures below 475 K), loss of adenine and subsequent cleavage of the adjacent phosphoester bonds will dominate, whereas at higher energies, preferential cleavage at C and G residues will occur. The magnitude of the A factors ≤10¹³ s^?1 measured for the loss of the three nucleobases (A, G, and C) is indicative of an entropically neutral or disfavored process as the rate limiting step for this reaction.     

The Raman spectra of ferrocene-b10 and -d10: librational modes and comments upon previous polarization data

The librational modes of ferrocene-h₁₀ and -d₁₀ have been observed near 62 cm^?1 (-h₁₀) and 40, 52 and 60 cm^?1 (-d₁₀). The polarization measurements at low temperatures can give no useful information concerning the vibrational assignment until the low temperature crystal structure is completely determined.