Photoinduced multi-mode quantum dynamics of pyrrole at the – conical intersections

The photoinduced dynamics of pyrrole at the – S₀ and – S₀ conical intersections has been investigated by multi-mode time-dependent quantum wave-packet calculations. Diabatic potential-energy surfaces have been constructed for both conical intersection using accurate multi-reference ab initio electronic-structure calculations. In addition to the NH stretching coordinate, the three (four) symmetry-allowed coupling modes of A₂ (B₁) symmetry have been considered for the – S₀ (– S₀) conical intersections. Wave-packet dynamics calculations have been performed for three-dimensional models, taking account of the two dominant coupling modes of each conical intersection. The electronic population-transfer processes at the conical intersections, the branching ratio for the dissociation to the ground and excited states of the pyrrolyl radical, and their dependence on the initial preparation of the system have been investigated. It is shown that the excitation of the NH stretching mode strongly enhances the photodissociation rate, while the excitation of the strongest coupling mode has a pronounced effect on the branching ratio of the photodissociation process. Although the inclusion of the second (weaker) coupling mode has little effect on the electronic population dynamics, it leads to interesting changes of the nodal pattern of the wave packet at the conical intersections. The calculations provide insight into the effect of the multiple coupling modes on the process of direct photodissociation through a conical intersection.     

Ab initio electronic and rovibrational structure of

The electronic structure of the ground state of has been investigated using relativistically-corrected CCSD(T) in conjunction with ANO-RCC (Mg) and aug-cc-pVQZ (H) basis sets. The molecular potential energy surface possessed minima corresponding to both ¹A₁ and equilibrium structures (with a ¹Σ⁺ transition state). The ¹A₁ structure possessed R_e and θ_e values of 2.0297 Å and of 22.09°, respectively. The higher-energy structure exhibited an R_e value of 2.1658 Å. Property surfaces were constructed to calculate rovibrational energies and spectral line intensities for the ground states of , (¹A′) MgHD²⁺ and . For the vibration ground state of , the vibration-averaged R_e and θ_e values were calculated to be 2.0209 Å and 22.53°, respectively. The A, B and C rotational constants were calculated to be 58.0, 2.21 and 2.11 cm⁻¹, respectively.     

Structures and properties of the tin-doped carbon clusters

A systemic density functional theory study of the tin-doped carbon clusters has been carried out using B3LYP method with TZP+ basis set. For each species, the electronic states, relative energies and geometries of various isomers are reported. Except for smaller SnC₂ and the largest , the Sn-terminated linear or quasi-linear isomer is the most stable structure for clusters. The electronic ground state is alternate between ³Σ (for n-odd member) and ¹Σ (for the n-even member) for linear SnC_n and invariably ²Π for linear and , except for SnC/SnC⁺/SnC⁻,, and . The incremental binding energy diagrams show that strong even–odd alternations in the cluster stability exist for both neutral SnC_n and anionic , with their n-even members being much more stable than the corresponding odd n − 1 and n + 1 ones, while for cationic , the alternation effect is less pronounced. These parity effects also reflect in the ionization potential and electron affinity curves. By comparing with the fragmentation energies accompanying various channels, the most favorable dissociation channel for each kind of the clusters are given. All these results are very similar to those obtained previously for the clusters.     

DFT study and IR spectra of hexaphenoxycyclotriphosphazene generation phosphorus dendrimer

The infrared (150–3500 cm⁻¹) spectra have been recorded for hexaphenoxycyclotriphosphazene [NP(OPh)₂]₃ and all-D isotope specie. These compounds include a cyclotriphosphazene core and terminal phenoxy groups of elementoorganic dendrimers. The structural optimization and normal mode analysis are performed for elementoorganic dendrimer on the basis of the ab initio density functional theory. It is found that the dendrimer exists in a single stable conformation with slightly non-planar cyclotriphosphazene core. Relying on DFT calculations a complete vibrational assignment is proposed for different parts of the studied dendrimers. The softness of sulphur atom in the thiophosphoryl core to nucleophilic attack is higher than the softness of the atoms of the cyclotriphosphazene core. The reactivity of the core is less than that of terminal groups.     

Theoretical electronic structure including spin–orbit effects of the alkali dimer cation

A theoretical study of the electronic structure of has been performed, including or not spin–orbit coupling. Potential energy curves for all the molecular states dissociating up to the limit Cs⁺ + Cs (8s ²S_1/2), i.e 26 states in the representation and 38 states in the representation Ω_g,u, are displayed. Equilibrium distances, transition energies and depths for the wells predicted at short and large range of internuclear separation R are reported. The existence of some of the long-range wells are confirmed by a long range model. Extensive tables of energy values versus internuclear distances are available at the following address: http://lasim.univ-lyon1.fr/allouche/cs2plus.htm.     

Vibrational relaxation on the mixed vibronic levels of the and states in all-trans-neurosporene as revealed by subpicosecond time-resolved, stimulated emission and transient absorption spectroscopy

In all-trans-neurosporene, whose level is lower than the level by one vibrational quantum, the following two steps of vibrational relaxation from the mixed vibronic states were identified, in the order, stimulated emission stimulated emission transient absorption. The stimulated emission patterns were simulated by the use of Franck–Condon factors in the transitions from the pair of mixed vibronic levels down to the ground vibronic levels. The vibronic levels of the mixed and state were characterized theoretically based on the diabatic approximation.     

Theoretical study on the structures and properties of LiCn, , and (n = 1–10) clusters

The lithium-doped carbon clusters LiC_n, , and (n = 1–10) have been investigated systemically with density functional theory (DFT) method at the B3LYP/6-311+G* level. According to the total energies of different kinds of isomers, the LiC_n, , and (n = 1–10) clusters have Li-terminated linear ground states structures, except for LiC₂, LiC₃, , and (n = 4–6). The incremental binding energies are evaluated to elucidate the stabilities of the clusters with different numbers of carbon atoms for neutral molecules, cations, and anions, respectively. Clear even–odd alternation effects are observed for the stability of the cationic clusters and anionic clusters, while for neutral LiC_n clusters the alternation effect is less pronounced. Similarly, the ionization potentials and electron affinities of LiC_n also express an obvious parity alternation. In addition, the most favorable dissociation channels are acquired according to the fragmentation energies accompanying various pathways.     

DFT study of the structure of hydroxybenzoic acids and their reactions with OH and radicals

B3LYP/6-31++G(d) method was used for the structural study of 3,4,5-trihydroxybenzoic acid (3,4,5-THBA), 3,4-dihydroxybenzoic acid (3,4-DHBA), and 4-hydroxybenzoic acid (4-HBA). Calculated structures agree with available X-ray experimental data within 2%. The phenolic OH bond dissociation enthalpy (BDE) of all sites in each benzoic acid were determined and compared with those of phenol (for 4-HBA) and catechol (for 3,4-DHBA). The consistency between the calculated values and experimental ones are within 5.4% and 9.2%, respectively, for 4-HBA and 3,4-DHBA. The reactions of benzoic acids with and OH radicals were studied and it turns out that benzoic acids react differently with both radicals. We have shown that the reaction of hydroxybenzoic acids with the hydroxyl radical was governed by a phenolic hydrogen (H⁺ + e⁻) transfer from the acid to the radical, while for the superoxide radical, the reaction is governed by a proton (H⁺) transfer from the acid to the radical. The first reaction is evidenced by the delocalization of the radical on the entire quinone moiety, and the second reaction is evidenced by the negative NBO charge on the phenoxide moiety as well as the localization of the radical on the hydroperoxy (O₂H) moiety.     

A DFT study of the hydration of monophosphate complexes of iron (III),

A systematic theoretical DFT study of the bonding between the cation Fe³⁺ and the anion was carried out. The role of water ligands is presented. Several isomers with tetrahedral, bipyramidal and octahedral environments around the iron ion were investigated. 5-fold coordination of the Fe³⁺ cation is found when 5 and 6 water molecules are included. Calculated infrared spectra are also presented.     

Excess thermodynamic properties, and for the binary systems {1,2-dichloropropane + 2-alkoxyethanols} at T = 298.15 K

This article presents the experimental data of and , obtained at T = 298.15 K and atmospheric pressure, for four binary systems composed of 1,2-dichloropropane (1,2-DCP) and four 2-alkoxyethanols. The 2-alkoxyethanols are 2-methoxyethanol (2-ME), 2-ethoxyethanol (2-EE), 2-propoxyethanol (2-PE) and 2-butoxyethanol (2-BE). The of the mixture has been shown positive for 2-ME, ‘s-shaped’ for all remaining systems, being negative at low and positive at high mole fraction of 1,2-DCP. The values for all binary mixtures are also shown both positive at low and negative at high mole fraction of 1,2-DCP. The experimental results of and were fitted to Redlich–Kister equation to correlate the composition dependence of both excess properties. In this work, data were also used to test the suitability of thermodynamic models (Wilson, NRTL, and UNIQUAC equations) based on local-composition theory. The results have been qualitatively discussed in terms of the polarity, self-association, and hydrogen bond among molecules.     

Synthesis, crystal structures and magnetic properties of trinuclear oxo-centered homo- and mixed-valence manganese pivalate complexes with imidazole (Im) and 1-methylimidazole (1-MeIm): and

Two new μ₃-oxo-centered trinuclear manganese complexes, one of them a homo-valence (1) pivalate complex and the other a mixed-valence (2) pivalate complex (where Im = imidazole, 1-MeIm = 1-methylimidazole), have been synthesized and characterized by IR spectroscopy, thermogravimetric analysis, X-ray crystallography and magnetochemistry. Complexes 1 and 2 are μ₃-oxo-trinuclear compounds with the three manganese atoms bridged by six pivalate groups. At each axial position there is an Im (1) or 1-MeIm (2) molecule. In both compounds, the manganese coordination geometry is slightly distorted octahedral, consisting of the oxygen of the central triangle, four oxygen atoms from bridging pivalate ligands, and a terminal Im or 1-MeIm nitrogen atom. The crystal packing of 1 involves hydrogen bonding between complex cations [Mn₃O(Piv)₆(Im)₃]⁺ and outersphere pivalate ions, whereas in compound 2 interactions of the C–Hπ type, formed by both the aromatic and methyl C–H groups of 1-MeIm molecules, are present. Magnetic studies reveal that both compounds represent antiferromagnetically coupled, spin-frustrated triangular systems exhibiting weak to moderate exchange coupling constants.     

DFT study of electronic structure and geometry of anionic silver clusters (n = 11, 12, 17)

Based on both total energy calculations and comparison of experimental and calculated characteristics of photoelectron spectra (PHES), the structural assignment of clusters and has been made using DFT model with recently developed S2LYP functional. The calculated characteristics of PHES for the assigned structures are in excellent agreement with the experimental ones. The electronic structure, geometry and energetic characteristics of low-lying isomers have also been studied. The calculated geometrical parameters of and clusters as well as the geometries of earlier established clusters have been compared with the geometrical characteristics of anionic sodium clusters. The structures of anionic silver and sodium clusters have been found to be very similar. The difference has been observed only for . Based on similarity of the geometries of silver and sodium clusters as well as on the comparison of calculated and experimental characteristics of PHES, the geometry of cluster has been assigned.     

Intermolecular/interionic interactions in l-isoleucine-, l-proline-, and l-glutamine-aqueous electrolyte systems

Speed of sound and density values for ternary systems (amino acid + salt + water): l-isoleucine/l-proline/l-glutamine in aqueous solutions of 1.5 M KCl, 1 M KNO₃, and 0.5 M K₂SO₄ have been measured for several concentrations of amino acids at different temperatures (303.15, 308.15, 313.15, 318.15, and 323.15 K). Using speed of sound and density data, the thermodynamic parameters such as isentropic compressibility (κ_s), change in isentropic compressibility (Δκ_s) and relative change (Δκ_s/κ₀) in isentropic compressibility have been computed. The isentropic compressibility values decrease with increase in the amino acid concentration as well as with temperature. The decrease in κ_s values with increase in concentration of l-isoleucine/l-proline/l-glutamine in 1.5 M KCl, 1 M KNO₃, and 0.5 M K₂SO₄ has been ascribed to an increase in the number of incompressible zwitterions in solutions, and the formation of ‘zwitterions-ions’ and ‘zwitterions-water dipole’ entities in solutions. The decrease in κ_s values with increase in temperature has been attributed to the corresponding decrease of κ_relax (a relaxational part of compressibility), which is dominant over the corresponding increase of κ_∞ (an instantaneous part of compressibility). The trends of variation of Δκ_s and Δκ_s/κ₀ with variations in solute concentration and temperature have also been discussed in terms of solute-solute and solute-solvent intermolecular/interionic interactions operative in the systems.     

Selecting high stability water clusters by examining locations of free OH bonds: Application in the study of clusters

Computational studies on water clusters can be quite challenging, especially when an irregular cage with non-equivalent oxygen sites are considered which may yield a large number of starting geometries that differ in relative positions of non-H-bonding H (NHB H, free OH) atoms. A detailed study on water octamers suggests that the fewest number of NHB H atoms on neighboring oxygen sites yields the most stable neutral isomer followed by those with increasing number of NHB H atoms on adjacent sites. The least stable cluster has all the NHB H atoms around a ring. By considering a regular cage structure and minimum number of NHB H atoms on adjacent sites, one can readily identify a limited number of starting geometries that are optimized to highly stable isomers. This method has been verified in the identification of the most stable isomer of (H₂O)₈ cubic cage and (H₂O)₂₀ dodecahedral cage. The same method has been applied in the study of cluster isomers.     

Synthesis of homochiral 2-C-perfluoroalkyl substituted d- and l-riboses

Homochiral 2-C-perfluoroalkyl substituted d- and l-riboses were synthesized via Barbier, Grignard and Ruppert type reactions. The influence of the size of the perfluoroalkyl groups, attached to C-2, on the furanose/pyranose as well as on the α-furanose/β-furanose and α-pyranose/β-pyranose ratio in solution was studied.     

Proton and protonic entities in solid heteropoly compounds: An ab initio calculation of the environmental effect on the ion

Systematic experimental investigations of heteropoly compounds, particularly their structure and activity, led to the conclusion that most of their characteristics are governed by the presence of protons and protonic entities. Special attention has been paid to two forms of 12-tungstophosphoric acid: hexahydrate (WPA-6) and dehydrated phase (WPA-0). It was postulated that in WPA-6 dynamic equilibrium of protonic entities exists, and that dehydrated phase is stabilized by protons. To confirm the role of the “free protons” or “proton gas” derived on the basis of thermal, structural and spectroscopic experimental studies, we carried out also ab initio calculations on a number of systems containing ion. We were not able to perform direct calculations on the real systems investigated experimentally since the structure of heteropoly compounds is too complex. However, it has been found that ion in WPA-6 definitely is not planar and the results obtained indirectly support the postulated dynamic equilibrium, i.e. possibility of existing of free protons.     

Fluorinated stannanes : Part 1. The stereospecific synthesis of fluorinated stannanes via a novel transmetalation of fluorinated zinc and cadmium reagents

Fluorinated stannanes are versatile synthetic intermediates. Reaction of fluorinated vinyl, alkyl and aryl zinc or cadmium reagents with tri-n-butyltin chloride at room temperature yielded the corresponding tri-n-butyl stannanes in moderate to excellent yields. The zinc or cadmium reagents also reacted efficiently with other trialkyl and triaryl chlorostannanes. These zinc and cadmium reagents were prepared in excellent yields by stirring the fluorinated halides with activated zinc or cadmium metal.