Calculation of interaction of the stretching and bending vibrations of HF in the hydrogen-bonded complex [F(HF)2]?

Vibrations of the [F(HF)₂]^? complex are calculated with allowance for the anharmonic interactions of the stretching vibrations of HF monomers and their rotations about the centers of gravity of HF in the plane of the complex. A four-dimensional vibrational Schr?dinger equation is solved using a potential energy surface calculated in the MP2/6-311++G(3df,3pd) approximation with the superposition of atomic functions of the monomers taken into account. The equilibrium and vibrationally averaged structures of the complex are determined. The frequencies and intensities for spectral transitions from the ground state to a number of excited vibrational states are calculated. It is shown that, due to resonances between the excited states of the stretching modes and doubly excited states of the bending modes, the overtone transitions associated with the bending modes borrow a significant part of the intensity of fundamental stretching transitions.     

Ab initio Calculation of Normal Vibrations of Chlorobenzene in the First Singlet Electron-Excitebd State 1 B 2

An analysis of experimental assignments of the frequencies of normal vibrations of chlorobenzene in the first singlet electron-excited state ¹ B ₂ has been performed with the use of two quantum-mechanical prediction methods — the method of frequency shifts and the method of transfer of scaling factors. Based on the data of this analysis, a new assignment of a number of vibration frequencies has been made. Normal vibrations of the chlorobenzene molecule in the excited state have been calculated by the CIS method with a 6-311 + G ^** basic set. An algorithm of autoscaling in dependent natural coordinates has been proposed. The force field of chlorobenzene has been scaled in dependent natural coordinates. It is shown that the scaling factors of benzene in the electron state ¹ B _2u can be used for calculating the frequencies of normal vibrations of chlorobenzene in the first singlet excited state ¹ B ₂.     

Monte Carlo calculations of reaction rates and energy distributions among reaction products. Reactions of HF and DF with H and D-atoms

Rate coefficients are calculated for the reactions of H and D-atoms with vibrationally excited HF and DF molecules. Three-dimensional classical trajectories of the collision dynamics of these reactions have been calculated by means of the London-Eyring-Polanyi-Sato (LEPS) potential energy surface. The Monte Carlo procedure is used to start each collision trajectory. Results of this study indicate that (a) chemical exchange provides an efficient mechanism for relaxing vibrationally excited HF and DF molecules by H and D-atoms; (b) multiple-quantum transitions are important in the deactivation processes; and (c) both vibration-translation and vibration-rotation energy transfers contribute to vibrational relaxation of vibrationally excited HF and DF molecules by H and D-atoms. The vibrational relaxation of HF (v = 1) by H-atoms is faster than the vibrational relaxation of DF (v = 1) by H-atoms. A similar effect is indicated for D-atoms; i.e. the vibrational relaxation of DF (v = 1) by D-atoms is faster than the vibrational relaxation of HF (v = 1) by D-atoms. Room temperature vibration to translation-rotation (V → T, R) relaxation rates in units of (μsec Torr)^-1 are as follows: 13·8 × 10^-2 for HF (v = 1) by H, 3·1 × 10^-2 for DF (v = 1) by D, 5·5 × 10^-3 for HF (v = 1) by D, and 1·9 × 10^-2 for DF (v = 1) by H. Rates of deactivation of vibrationally excited HF and DF molecules by H and D-atoms are very fast. Rate coefficients are provided for many reactions that have not been measured experimentally.     

Influence of isotopic substitution on spectral and structural parameters of an isolated [F(HF)<Subscript>2</Subscript>]— complex. Substitution of a proton by a kaon and a triton

This paper continues the theoretical study (see V. P. Bulychev and M. V. Buturlimova, J. Mol. Struct. 928, 32 (2009)) of the isotopic effects in the H-bonded anionic complex [F(HF)₂]-. Isotopomers of the complex with significant differences between the masses of the light atoms are considered. The four-dimensional anharmonic vibrational problem are solved by the variational method for the symmetric complex [F(KaF)₂]-, in which both protons are substituted by a positive kaon (positive K-meson), and for the asymmetric complex [FKaFTF]-. Variables related to the changes in the lengths of molecular fragments LF (L = Ka and T) and the distances between the F^- anion and the centers of mass of LF are used as the vibra-tional coordinates. The potential energy surfaces are calculated in the MP2/6-311++G(3df,3pd) approximation taking into account the basis set superposition error. The vibrational energy levels, frequencies, and absolute intensities for spectral transitions are determined. To study the isotope effect on the geometrical parameters of the complex, the values of internuclear separations and the asymmetry parameter of the F^-…L-F bridge averaged over the ground state and several excited vibrational states are calculated, as well as their standard deviations. The calculated results are compared to the data obtained previously for the symmetric complexes [F(HF)₂]^-, [F(DF)₂]^-, and [F(TF)₂]^-.     

Vibrational spectra of the tetramethylpnikogenonium ions

The tetramethylpnikogenonium ions (CH₃)₄X⁺ (X = N, P, As, Sb) have been studied by infrared and Raman spectroscopy. Additionally, their structures and vibrational frequencies were ab initio calculated at the HF/6-31+G* and for (CH₃)₄Sb⁺ at the HF/6-31+G*/LANL2DZ level of theory. For the tetrahedral cations an assignment of the vibrational frequencies is discussed on the basis of a comparison of calculated and measured frequencies.     

Excited high spin states of novel π conjugated verdazyl radicals: photoinduced spin alignment utilizing the excited molecular field

This paper reports the excited quartet (S = 3/2) and quintet (S = 2) states arising from the intramolecular radical-triplet pair in the purely organic π conjugated spin systems. A previous paper reported the excited quartet and quintet states of 9-anthracene-(4-phenyliminonitroxide) and 9,10-anthracene-bis(4-phenyliminonitroxide), respectively, in which iminonitroxide radicals are linked to the phenyl- or diphenylanthracene moiety (a spin-coupler) through the π conjugation. The similar excited quartet and quintet states were observed for the 9-anthra-cene-(4-phenylverdazyl) radical (1) and 9,10-anthracene-bis(4-phenylverdazyl) diradical (2) by time resolved electron spin resonance (TRESR). The TRESR spectrum was analysed by the ordinary spin Hamiltonian with the Zeeman and fine structure terms. For the quartet state of 1, the g value, fine structure splitting, and relative population of the Ms sublevels have been determined to be g = 2.0035, D = 0.0230 cm^?1, E = 0.0, P _1/2′ = P _?1/2′ = 0.5 and P _3/2′ = P _?3/2′ = 0.0, respectively, by spectral simulation. The spin Hamiltonian parameters of the quintet state of 2 were determined to be g = 2.0035, D = 0.0128 cm^?1, E = 0.0, P _2′ = P _?2′ = 0.0, P _1′ = P _?1′ = 0.37 and P _0′ = 0.26, respectively. Direct observation of the excited high spin state showed that photoinduced intramolecular spin alignment is realized between the excited triplet state (S = 1) of the phenyl- or diphenylanthracene moiety and the doublet spin (S = 1/2) of the dangling verdazyl radicals. Ab initio MO calculations (DFT) were carried out in order to clarify the mechanism of the photoinduced spin alignment.     

The LIF Excitation Spectrum of Jet-Cooled 2,6-Dicyano-3, 5-Dimethylaniline

The laser-induced fluorescence (LIF) excitation spectrum of jet-cooled 2, 6-dicyano-3,5-dimethylaniline (DCDMA) has been measured in the spectral range of 29,750–32,250cm^–1. The band origin at 29,860.8 cm^–1 and as many as 250 vibrational bands have been identified in the excitation spectrum. The analysis of the excitation spectrum of DCDMA gives more than 28 vibrational modes involving aromatic ring oscillations and oscillations related to the substituent groups. DCDMA is nonplanar in the ground state, with the NH₂ plane at about 9° with respect to the molecular plane (RHF/6-31G*). The singlet excited molecule is planar (CIS/6-31G*). Both CIS/6-31G* and CASPT2 calculations predict that the lowest excited state of DCDMA involves a dominant HOMO-LUMO excited configuration. The characteristic feature of the excitation spectrum of DCDMA is the presence of progressions in the low-frequency mode, 112 cm^–1. The calculations suggest that this mode and some other active modes involve motions of the amino group and strongly interacting adjacent cyano substituents.     

DFT and TD-DFT approach for the analysis of NLO and OLED applications of 9-anthraldehyde

The geometric parameters characterization and ground state energies for 9-anthraldehyde have been calculated using density functional theory (DFT). NBO analysis has been done on the same level to investigate the hyper conjugative interaction. HF/6-31G (d) method is adopted to calculate the first order hyperpolarizability (β). Frontier molecular orbital analysis has also been done in support of β. The excited state energies, as well as absorption wavelengths, are computed using time dependent-density functional theory (TD-DFT). For the emission wavelength the excited state geometry optimization has been carried out using configuration interaction singlets (CIS). The emission wavelength has been calculated in TD-DFT approach. The theoretical data so obtained is analyzed for the applications of NLO and OLED. One of the important conclusions from our study is that this material is suitable for both the applications. The macroscopic second harmonic generation (SHG) efficiency has also been identified through Kurtz–Perry powder technique.     

CASPT2 and CCSD(T) calculations of dipole moments and polarizabilities of acetone in excited states

The acetone molecule is investigated in its ground state and valence ^1,3n-π*, ^1,3π-π*, and ^1,3σ-π* excited states and Rydberg ^1,3n-3s, ^1,3π-3?, ^1,3n-3p_y and ^1,3π-3p_y states using the CASSCF, CASPT2, and CCSD(T) methods. Equilibrium geometries of excited states are obtained and their changes with respect to the ground state are discussed. For most excited states the C_2v symmetry of the ground state is lowered to the C_s symmetry. A series of valence vertical and adiabatic excitation energies is presented along with excitation energies for Rydberg states. The main body of the paper contains Finite-Field Perturbation Theory (FFPT) calculations of electric properties of the vertically as well as geometry relaxed excited states. Dipole moments of valence excited states decrease significantly upon excitation, being about one half of the ground state dipole moment. Polarizabilities usually change upon excitation much less (increase by about 30%) but hyperpolarizabilities are enhanced up to one or two orders of magnitude. The orientation of the dipole moment is reversed in some vertically excited Rydberg states. Properties of the ground and excited states are discussed considering alterations of the electronic structure and shifts in the geometry.     

Comparative electronic structure of a lanthanide and actinide diatomic oxide: Nd versus U

Using a modified version of the Alchemy electronic structure code and relativistic pseudopotentials, the electronic structure of the ground and low lying excited states of UO, NdO, and NdO⁺ have been calculated at the Hartree—Fock (HF) and multiconfiguration self-consistent field (MCSCF) levels of theory. Including results from an earlier study of UO⁺ this provides the information for a comparative analysis of a lanthanide and an actinide diatomic oxide. UO and NdO are both described formally as M⁺²O^?2 and the cations as M⁺³O^?2, but the HF and MCSCF calculations show that these systems are considerably less ionic due to large charge back-transfer in the π orbitals. The electronic states putatively arise from the ligand field (oxygen anion) perturbed f⁴, sf³, df³, sdf², or s²f² states of M⁺² and f³, sf² or df² states of M⁺³. Molecular orbital results show a substantial stabilization of the sf³ or s²f² configurations relative to the f⁴ or df³ configurations that are the even or odd parity ground states in the M⁺² free ion. The compact f and d orbitals are more destabilized by the anion field than the diffuse s orbital. The ground states of the neutral species are dominated by orbitals arising from the M⁺²sf³ term, and all the potential energy curves arising from this configuration are similar, which allows an estimate of the vibrational frequencies for UO and NdO of 862 cm^?1 and 836 cm^?1, respectively. For NdO⁺ and UO⁺ the excitation energies for the Ω states were calculated with a valence configuration interaction method using ab initio effective spin—orbit operators to couple the molecular orbital configurations. The results for NdO⁺ are very comparable with the results for UO⁺, and show the vibrational and electronic states to be interleaved.     

Theoretical studies on the electronic and optical properties of arene‐ versus fluoroarene‐thiophene co‐oligomer

A series of regiochemically varied and core size extension‐modulated arene‐ and fluoroarene‐thiophene co‐oligomers and the unsubstituted sexithiophene α6T were investigated theoretically to explore their electronic and optical properties. These phenylene‐thiophene oligomers show great potential for application in organic light‐emitting diodes (OLEDs), organic diode lasers, and organic thin‐film transistors (OTFTs) because of their feasible tuning of optical and electronic properties by the various structural tunings. Density functional theory (DFT) and the ab initio HF were employed to investigate the geometric and electronic structures of the oligomers in the ground state, and the singles configuration interaction (CIS) methods were used to study the lowest singlet excited state. The lowest excitation energies (E_gs), the radiative lifetime τ, and the maximal absorption/emission wavelength of the oligomers were studied within time‐dependent DFT (TDDFT). All calculations were performed using the 6‐31G(d) basis set. The results show that the HOMOs, LUMOs, energy gaps, ionization potentials (IPs), electron affinities (EAs), and reorganization energies are significantly affected by the various structural tunings in these co‐oligomers, which is important for the improvement of the hole and electron injection into OLEDs. Interestingly, the LUMO energy of 1b , 2b , and 3b is lower than that of α6T and 1a , 2a , 3a by about 0.12 ～ 0.47 eV, indicating that the fluorophenyl‐substitution has significantly improved the electron injection properties of the oligomers. Copyright © 2008 John Wiley & Sons, Ltd.     

Towards the assignment of the REMPI spectrum of Ph2O using CIS and TD-DFT methods

Tentative assignment of the low-lying vibrational features of the first electronic excited singlet-state S₁ of diphenyl ether (Ph₂O), obtained from resonance-enhanced multiphoton ionisation (REMPI) spectroscopy, is performed using CIS and time-dependent density functional theory (TD-DFT) methods. The potential energy surfaces, regarding the rotation of the phenyl rings relatively to the C–O–C plane, are obtained at the B3LYP/6-31G(d) level of theory, for the ground-state of neutral and cationic Ph₂O and for its first excited singlet state. The torsional barriers of the ground state of diphenyl ether were studied by means of quantum-chemical perturbations of increasing accuracy and an extrapolation to the complete basis set limit and full configuration interaction (FCI) was performed through the use of correlation consistent basis sets and the continued fraction method. The first adiabatic ionisation energy (AIE) of the twist conformer is computed at 8.60 eV in the FCI limit, much higher than the experimental results of Terlouw et al. (8.09±0.03 eV) and Paiva et al. (7.8±0.1 eV). The B3LYP result of 7.82 eV is, however, in reasonable agreement with the result of Paiva et al. The first singlet excitation energy for the twist conformation is found to be 5.5 eV at the CIS/6-311++G(d,p) level of theory. Some features of the experimental REMPI spectrum, previously obtained by one of the authors, are explained and a new insight on the ionisation energy of diphenyl ether is presented.     

Time-dependent Hartree-Fock theory

The lowest singlet and triplet excited states of the two paired electrons in a chemical bond are treated by the time-dependent Hartree-Fock (H.F.) method, with the π electrons of the double bond in ethylene as an example. The results depend on a dimensionless parameter g which describes the strength of the electron correlation effects, and they are compared with a simple configuration interaction calculation. When g is small the frequencies and amplitudes of the Hartree-Fock oscillations give an accurate estimate of the energies and intensities of the two lowest transitions, the correlation energy and the pair distribution function of the gound state. The correlation energy is related to the zero-point energy of the oscillations. As g increases the H.F. method overestimates the correlation corrections and breaks down completely if g = 1. At this point the triplet oscillation becomes unstable, because the molecular orbital wave-function with two paired electrons ceases to be the state of lowest energy. When g is large the H.F. results violate spin conservation and the exclusion principle.     

The rotational spectrum of acrylonitrile in excited states of the two low-frequency CCN bending vibrational modes

The strongest vibrational satellites in the rotational spectrum of acrylonitrile have been assigned and frequencies of μ_a- and μ_b-type transitions in the frequency range 27–184 GHz are reported for the first two excited states in the lowest frequency in-plane CCN bending vibrational mode and the first excited state in the out-of-plane CCN bending mode. The values of the rotational constants, the quartic and sextic centrifugal distortion constants, and one octic centrifugal distortion constant are determined for each of these states. Less extensive results are also presented for the third quantum of the in-plane bend. The data set for the ground state has been extended by a number of new measurements and the improved ground state constants are used in a discussion of changes in rotational and centrifugal distortion constants with vibrational state where all constants associated with P_zⁿ and P²P_z⁽ⁿ⁻²⁾ terms in the Hamiltonian are found to reflect the common origin of the two CCN bends.     

Resonance-enhanced multiphoton ionization (REMPI) spectroscopy of the Cl and Cl isotopomers of p-chloroanisole

The geometric structures and vibrations of p-chloroanisole isotopomers in the first electronically excited state were studied by mass-analyzed resonance-enhanced two-photon ionization spectroscopy and by theoretical calculations. The band origins of the S₁ ← S₀ electronic transitions of ³⁵Cl and ³⁷Cl isotopomers were found to be equivalent at 34 859 ± 3 cm⁻¹. Assignments of the observed vibrational bands of the two isotopomers were made mainly based on the CIS/cc-PVDZ calculations and on conformity with the available data in the literature. Although the general spectral features of these two isotopomers are similar, the frequencies of some vibrational modes are different. This frequency shift partially depends on the degree of involvement of the chlorine atom in the molecular vibrations.     

Spectral and luminescent properties of ammonia cyclopalladated complexes

The synthesis of ammonia cyclometalated palladium(II) complexes [Pd(NH₃)₂C^N]ClO₄ (C^N is the deprotonated form of 2-phenylpyridine, 2-(para-tolyl)pyridine, 7,8-benzo(h)quinoline, 2,6-diphenylpyridine, and 4-phenylpyrimidine) is developed. The IR and electronic absorption and emission spectra of these complexes are studied. It is found that the ammine and analogous ethylenediamine cyclometalated Pd(II) complexes have similar spectral and luminescent properties and the same nature of the electronically excited ³(π-π*)-type state responsible for the long-lived luminescence, the π and π* orbitals being localized on the corresponding cyclometalating ligand. The efficient temperature quenching of the luminescence of Pd(II) complexes at room temperature is assigned to the thermally activated population of metal-centered electronically excited states with subsequent nonradiative deactivation.     

A theoretical analysis of the excited states in 2-benzoylthiophene

The lower excited states of 2-benzoylthiophene have been studied using ab initio quantum chemical methods based on multiconfigurational wave functions. Six singlet and six triplet excited states have been characterized. The geometry has been optimized for the two lowest triplet states, which are responsible for the photoreactivity of the chromophore in the photosensitizing drug tiaprofenic acid. The T¹(π → π?) and T₂(n → π?) states have been found to be close in energy with the π → π? state slightly lower. The excited states have been characterized using density difference and spin density plots. The different photochemical behaviour of the two triplet states can be rationalized from the theoretical data.     

Excess polarizabilities upon the first dipole‐allowed excitation of some conjugated oligomers

This paper presents theoretical predictions for the excess polarizabilities upon excitation from the ground state to the first dipole‐allowed excited state (1¹B_u) of some conjugated oligomers. The excess polarizability was obtained by simulating the Stark shift, which was predicted by the time‐dependent density functional theory (TDDFT) with the hybrid Becke‐3 Lee–Yang–Parr (B3LYP) potential. The Stark shift in solution was simulated by employing the non‐equilibrium integral equation formalism polarizable continuum model (IEFPCM). All the model molecules considered in this study were fully optimized by the Hartree–Fock (HF) method and the density functional theory (DFT) with the B3LYP potential, respectively. For diphenylpolyenes, the excess polarizabilities displayed by the DFT/B3LYP‐optimized geometries are more reasonable than those displayed by the HF‐optimized geometries when compared with the experimental results. However, this feature is not clearly demonstrated by our results in the cases of oligo(phenylenevinylene)s (OPVs). Copyright © 2008 John Wiley & Sons, Ltd.     

Calculation of the Normal Vibrations of Benzene in the First Singlet Electron-Excited State 1 B 2u

Using the CIS/6-311+G^** method, the normal vibrations of the benzene molecule in the first singlet electron-excited state ¹ B _2u have been calculated. The algorithm of calculation of the force field in dependent coordinates by the method of generalized inversion is described. A method of autoscaling in dependent natural coordinates is suggested. For six groups of natural coordinates scaling factors have been obtained, the use of which has led to agreement between the calculated and experimental frequencies of the vibrations of benzene. The frequencies of the B _1u -symmetry-type vibrations, for which there is no experimental assignment, have been calculated. The problem of selection of the force field in dependent coordinates is discussed.