Ab initio study of the electronic states of BS including spin–orbit coupling

The entire 30 Ω states generated from the 12 valence and two Rydberg Λ–S states of the BS radical have been studied at the MR-CISD + Q level of theory for the first time. The effects of spin–orbit coupling and the avoided crossing rule between electronic states of the same symmetry were analyzed. Spectroscopic constants of several excited states that have never been observed in experiment were obtained. The transition properties of several low-lying bound excited states to ground state transitions, including the transition dipole moments and the Franck–Condon factors, were also calculated, from which the corresponding single-channel radiative lifetimes were derived.     

Franck–Condon factors for diatomic molecules with anharmonic corrections

Some of the band systems of several astrophysically important molecules are calculated and compared with the results obtained by calculations based on realistic Klein–Dunham and Rydberg–Klein–Rees potential functions. The Morse potential is approximated by means of a fourth-order anharmonic oscillator model. In the second-quantized formalism, the anharmonic Hamiltonian is diagonalized by using the Bogoliubov–Tyablikov transformation. The diagonalization process gives a shift in the frequency associated with each normal mode of harmonic vibration of the molecules presented here. The Franck–Condon factors are estimated using this new frequency within the framework of a harmonic oscillator.     

A time-dependent density functional study of vibrationally resolved excitation, emission, and ionization spectra of the S1 state of phenol

Franck–Condon simulations of excitation, dispersed emission and ionization spectra, using geometries and force fields obtained with Time Dependent Density Functional Theory, are reported for the lowest excited singlet state of phenol. The quality of the simulations is much higher than that previously obtained with ab initio complete active space self-consistent field (CAS-SCF) calculations, demonstrating the large predictive power of these calculations and their usefulness for the interpretation of experimental, vibrationally resolved spectra. Specifically, the shortening of the C–O bond length in the excited state and the activity of the 6a mode, both missing in the CAS-SCF results, are modeled accurately.     

A density functional derived vibrational force field for β-ionone Use of the ultraviolet resonance Raman intensities to check the vibrational analysis accuracy

In the present article we aim to determine an accurate and transferable molecular force field for β-ionone in order to perform molecular dynamics calculations on the retinal isomers. For β-ionone, a force field is derived from calculations using the Density Functional Theory (DFT). The force constants expressed in the internal coordinate space were scaled fitting theoretical to experimental vibrational wavenumbers. The validity of the force field was checked using a comparison between calculated and observed resonance Raman intensities obtained from the A-term part (Franck–Condon) of the scattering tensor.     

CO internal excitation in the photodissociation of Cr(CO)6 at 278 nm

Time-resolved infrared diode laser spectroscopy has been used to probe CO internal excitation in the photodissociation of Cr(CO)₆ at 278 nm. At the high fluence level of these experiments, CO state distributions are not consistent with a statistical model of single-photon absorption. A simple Franck—Condon treatment, assuming multiphoton absorption into a dissociative continuum, qualitatively describes the observed CO vibrational distribution.     

Zero-field splitting in molecules with closely spaced triplet states : A theoretical investigation of three isomeric dimethylbenzaldehydes

It is shown by quantum-chemical calculations that the unusually large zero-field splitting observed in ³ππ^* states of 2,4-, 2,5- and 3,4-dimethylbenzaldehyde are mainly due to second-order spin—orbit coupling with ³nπ^* states modulated by Franck—Condon factors.     

Gas phase photoisomerization of urocanic acid – a theoretical study

The photochemistry of urocanic acid is investigated theoretically by means of time-dependent density functional theory. The topology of the potential energy surface along the isomerization pathway and close to the Franck–Condon region is investigated and consequences for the photoisomerization reactions are outlined. A recently published supersonic jet spectroscopy study is reinterpreted in the light of these and earlier theoretical results to give a clear picture of the gas phase photochemistry. It is found that the photochemistry of the two isomers is fundamentally different, in contrast to the situation in solution.     

Threshold photoelectron spectroscopy of iodine monobromide

A high-resolution (1–7 meV) threshold photoelectron spectroscopic study of IBr was performed using synchrotron radiation and a penetrating-field electron spectrometer over the valence ionization region of the molecule. Extensive vibrational structure was found in all three electronic-state band systems (X²Π_i, A²Π_i and B²Σ⁺) of IBr⁺. In the (X²Π_i) band system both spin–orbit components exhibited extended vibrational structure in the Franck–Condon gap regions that is attributed to resonance autoionization of neutral Rydberg states lying in these energy regions. Analysis of this vibrational structure yielded accurate spectroscopic constants.     

Absorption and magnetic circular dichroism (MCD) studies of 1,4,5,8-naphthalenetetracarboxy diimides in terms of CASSCF method and FC theory

The electronic and geometrical structures of the low-energy states of 1,4,5,8-naphthalenetetracarboxylic dianhydride parent diimide (1) are studied in terms of the complete active space self-consistent field (CASSCF) method employed at different level with respect to the size and the quality of the active space. In the framework of the vibronic model based on the Franck–Condon (FC) effect the absorption and magnetic circular dichroism (MCD) spectra are studied in the excitation region corresponding to two low-energy 1¹A_g → 1¹B_2u and 1¹A_g → 1¹B_3u electronic transitions in diimides. In that (visible) excitation region the CASSCF computations with the 5π[4n]5π active space (i.e., the naphthalene-like π orbitals enriched by the four lone pair orbitals of the oxygen atoms) were found to reproduce very well the empirical absorption and the MCD spectra measured for the dicyclohexyl-N,N^′-substituted diimide (2). At the same CASSCF/5π[4n]5π level, the electronic absorption of diimides in the near UV excitation region were attributed to the 1¹A_g → 2¹B_1u, 1¹A_g → 2¹B_3u and 1¹A_g → 2¹B_2u electronic transitions; the latter two are mostly localized on the “diimide chromophore”. For these transitions the calculated magneto-optical characteristics, such as sign pattern and intensity distribution in the MCD spectrum, were found to be consistent with that experimentally observed for the diimide 2 compound.     

Microscopic modelling of the reduction of a Zn(II) aqua-complex on metal electrodes

The mechanism of the Zn(II) reduction from acid aqueous solution at a metal electrode surface has been elucidated at a microscopic level. The Anderson–Newns model was employed in order to construct the adiabatic potential energy surfaces along the solvent coordinate for several reactions as a function of the electrode–reactant distance and the overpotential. A quantum chemical approach was employed to treat the coupling of the reactant to the metal electrode within a cluster model. The reduction of a [Zn(H₂O)₆]²⁺ complex was found to proceed in the adiabatic regime, the transfer of the first electron being rate-determining. Main attention is focused on effects of a qualitative nature, which are discussed in the light of available experimental data. The electrode charge excess and distance of maximal approach were found to affect significantly the Frank–Condon barriers of the reaction. An experimentally observed dependence of the rate constant of Zn(II) reduction upon the electrode material has been interpreted.     

Sorption of lead(II) on transition metal hexacyanoferrates(II) and on nickel(II)-potassium hexacyanoferrate(II) resin composite in hydrochloric acid medium

Sorption of lead(II) on very poorly soluble hexacyanoferrates(II) of transition metals: Cu^II, Ni^II, Zn^II, Co^II and on the ion-exchange composite obtained by mixing of nickel(II)-potassium hexacyanoferrate(II) with sulfonated phenolic resin serving as matrix was studied. Sorption was performed from solutions of hydrochloric acid at concentrations ranging from 10^–4 to 10^–1 mol·dm^–3. Analytical distribution coefficients for lead(II) sorption on these adsorbents were determined. Lead(II) sorption on Dowex 50 and the composite resin was studied as well.     

Adsorption of Cu(II), Zn(II), Cd(II), Hg(II) and Pb(II) from aqueous solutions on a 2-mercaptobenzimidazole-modified silica gel

The chemically modified silica, obtained by reacting 2-mercaptobenz-imidazole with 3-chloropropyl silica gel, was used to adsorb Cu(II), Zn(II), Cd(II) and Pb(II) from aqueous solutions at various pH. Between pH 3–5, the order of selectivity was Hg(II) > Cd(II) Cu(II) Zn(II) Pb(II). Under batch conditions retentions of 100% were achieved for all metals except for Pb(II) where 93% was attained. Under column conditions recoveries of 100% were obtained for all metals.     

Spin transition in iron(III) and iron(II) complexes

The main stages of the studies on the spin transitions in iron(III) and iron(II) complexes are considered. The types of the spin transitions and the factors responsible for the latter are reported. The problems arising during experiments in this field are discussed.     

Time resolved spectroscopy on Pigment Yellow 101 in solid state

The photochemistry of the fluorescent Pigment Yellow 101 (P.Y.101) in the crystalline phase is investigated combining time resolved vibrational and electronic spectroscopy. The experiments reveal a complex reaction dynamics spanning several orders of magnitude in time and including excited state intramolecular proton transfer (ESIPT) from the initial trans-diol conformer. Following photoexcitation and the subsequent wavepacket motion out of the Franck–Condon region two tautomers, an excited trans-diol and trans-keto state are formed. The cis–trans isomerization of the keto form, which was experimentally observed and theoretically confirmed in DFT calculations in studies on P.Y.101 in solution is obstructed in the solid state, consequently the formation of the cis conformer is not directly observed. In addition, a long lived photoproduct with red shifted vibrational frequencies is identified. The life time of this intermediate is determined to be 50 μs, although an unambiguous assignment to a specific molecular configuration cannot be given at present.     

Electronic structure of the photoactive yellow protein chromophore: Ab initio study of the low-lying excited singlet states

The excited electronic states of the p-coumaric acid thio-ester chromophore of the Photoactive Yellow Protein (PYP) are characterized in view of identifying the key factors determining the chromophore's isomerisation. These factors include the anionic nature of the chromophore, the presence of sulfur (rather than oxygen or nitrogen) in the ester moiety, and the presence of a hydrogen-bonding environment stabilizing the phenolate moiety. Two twisted stationary S₁ structures are identified, corresponding to a twist around the double bond conjugated with the aromatic ring, and the single bond adjacent to the ring, respectively. The latter structure is accessed directly by relaxation from the Franck–Condon (FC) geometry. These structures are shown to entail a substantial polarization effect (increasing charge separation when moving towards the twisted geometry). Further, an inversion of charge character is observed for the double-bond twisted minimum, which can be accounted for by the vicinity of an S₁–S₀ conical intersection. The S₁–S₀ gap at the minimum geometries depends in a sensitive fashion on the -carbonyl heteroatom. Based upon these observations for the intrinsic properties of the chromophore, we further address the effect of the Arg52 residue, which acts as a counter-ion in the native protein environment.     

Gas chromatography of ternary complexes of manganese(II), iron(II), cobalt(II) and nickel(II) with hexafluoroacetylacetone and DI-n-butylsulphoxide

The gas Chromatographic behaviour of the ternary complexes of selected bivalent first-row transition metal ions with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione H(HFA), and di-n-butylsulphoxide, DBSO, was studied. Calibration plots of peak area vs. amount of metal injected were linear over a range of 60–900 ng for manganese(II), iron(II), cobalt(II) and nickel(II). The average relative standard deviation was less than 3·0% for all the metals studied. Detection limits of 60, 109, 112 and 115ng for cobalt(II), nickel(II), iron(II) and manganese(II), respectively, were obtained with flame-ionization detection. Various liquid phases, including OV-1, SE-30, and Dexsil 300 were used. The best results were obtained on columns of 5% Dexsil 300. No appreciable thermal decomposition was observed on stainless-steel or glass columns, but the best formed peaks were obtained on all-glass columns. The elution of the metallic species was confirmed by venting the exit gases from the gas chromatograph directly into an atomic-absorption spectrophotometer.     

Comparative study on the photophysical properties between carbene-based Fe (II) and Ru (II) complexes

The comparative study on the photophysical properties between cheap metal Fe (II) complexes and noble metal Ru (II) complexes with identical ligand coordination is performed by the combination of density functional theory (DFT) and time-dependent density functional theory (TDDFT) to evaluate the potential alternative applications of Fe (II) complexes. RuBIP (BIP = 2,6-bis (imidazol-2- ylidene)pyridine) is theoretically established that the radiative lifetime of the second lowest triplet state is more consistence with experimental value. However, FeBIP retains nonluminous because of low-lying ³MC originated from weak d orbital splitting. FeBIPC (FeBIP with carboxylic acid groups) has twice longer lifetime than its parent complex FeBIP due to the great decrease of the energy gap between ³MLCT and ³MC. What's more, the lifetimes of Fe (II) complexes detected in the experiments are more accessible to nonradiative decay lifetimes of ³MC. The carboxylic acid groups are beneficial for the improvement of luminescent possibility and controllability of Fe (II) complexes, while there is still a huge challenge for effective material replacement comparing with Ru (II) complexes.     

Transition probabilities for the ionization of N2, O2, NO and CO molecules

Franck–Condon factors are presented for the normal and stable isotope-labelled N₂, O₂, NO and CO molecules for transitions to the observed ionized states by using the Rydberg–Klein–Rees (RKR ) potential energy curves of the various electronic states involved. It has been observed that for some transitions, the Franck–Condon factors based on the RKR potential energy curves differ appreciably from those based on the Morse potential function. The effect of isotopic substitution on the transition probabilities is also quite significant in a number of cases.     

Reaction of copper(II) and nickel(II) ammoniates with ethanol-amines

Thermogravimetry combined with thermal gas titrimetry were used to study the ligand substitution reactions by mono- and diethanolamine in nickel(II) hexaamminochloride and copper(II) tetraamminosulfate. It has been shown that the reactions proceed in stages and the temperature intervals of the individual stages have been determined. The kinetics of the described reactions have also been studied at isothermal conditions. The E_a values of the reactions have been calculated on the basis of the data obtained. A reaction mechanism has been proposed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 6, pp. 745–749, November–December, 1990.