Calculation of electron affinities of polycyclic aromatic hydrocarbons and solvation energies of their radical anion

Electron affinities (EAs) and free energies for electron attachment (DeltaGo(a,298K)) have been directly calculated for 45 polynuclear aromatic hydrocarbons (PAHs) and related molecules by a variety of theoretical methods, with standard regression errors of about 0.07 eV (mean unsigned error = 0.05 eV) at the B3LYP/6-31 + G(d,p) level and larger errors with HF or MP2 methods or using Koopmans' Theorem. Comparison of gas-phase free energies with solution-phase reduction potentials provides a measure of solvation energy differences between the radical anion and neutral PAH. A simple Born-charging model approximates the solvation effects on the radical anions, leading to a good correlation with experimental solvation energy differences. This is used to estimate unknown or questionable EAs from reduction potentials. Two independent methods are used to predict DeltaGo(a,298K) values: (1) based upon DFT methods, or (2) based upon reduction potentials and the Born model. They suggest reassignments or a resolution of conflicting experimental EAs for nearly one-half (17 of 38) of the PAH molecules for which experimental EAs have been reported. For the antiaromatic molecules, 1,3,5-tri-tert-butylpentalene and the dithia-substituted cyclobutadiene 1, the reduction potentials lead to estimated EAs close to those expected from DFT calculations and provide a basis for the prediction of the EAs and reduction potentials of pentalene and cyclobutadiene. The Born model has been used to relate the electrostatic solvation energies of PAH and hydrocarbon radical anions, and spherical halide anions, alkali metal cations, and ammonium ions to effective ionic radii from DFT electron-density envelopes. The Born model used for PAHs has been successfully extended here to quantitatively explain the solvation energy of the C60 radical anion.     

Atomic ionization potentials and electron affinities with relativistic and mass corrections

Relativistic corrections to ionization potentials (IPs) and electron affinities (EAs) of atoms with an atomic number Z≤54 are examined based on the first-order perturbation theory with an approximate Schr?dinger form of the Dirac-Coulomb-Breit Hamiltonian. Using a Hartree-Fock (HF) wave function from the numerical HF method as the unperturbed function, both the LS-non-splitting and fine-structure corrections are evaluated together with the normal and specific mass corrections. The LS-non-splitting corrections are found to be important for IPs and EAs of transition metal atoms. The fine-structure corrections are generally larger in magnitude than the LS-non-splitting corrections for the atoms of groups 13–18 with Z≥31, and can never be neglected. Comparison of the IPs and EAs presented here and experimental IPs and EAs gives an estimation of the electron correlation correction for these properties. For some light atoms, the estimated values agree with the results directly obtained from correlated calculations. Received: 28 January 1997 / Accepted: 4 March 1997     

Photoelectron imaging and theoretical studies of silver monohalides AgX- (X = Cl, Br, I) and AuCl-

Photodetachment of AgX(-) (X = Cl, Br, I) and AuCl(-) is studied by a photoelectron velocity map imaging technique and theoretical calculations. Photoelectron spectra (PES) and photoelectron angular distributions (PADs) were obtained. The vibrationally resolved spectra provided approximately equal electron affinities (EAs) for AgX: 1.593(22) eV for AgCl, 1.623(21) eV for AgBr, and 1.603(22) eV for AgI, respectively. Franck-Condon simulations of these spectra gave the equilibrium bond lengths and vibrational frequencies of the title anions. Relativistic density functional theory (DFT) calculations using BLYP, PW91, PBE, and BP86 functionals have been performed to predict the EAs of the AgX (X = Cl, Br, I) molecules. The computed EAs at the BP86 level of theory are in good agreement with the experimental values. Energy partitioning analyses (EPA) at the BP86(ZORA)/QZ4P level of theory of both anions and their neutrals were reported.     

Carbon-13 NMR spectra of polybromoalkanes and polychlorobromoalkanes. Structural increments of halogens in polyhalogenated groups

The ¹³C NMR spectra of 48 polychlorobromoalkanes have been studied. Unlike the ¹³C signals of chlorine-containing groups (38–105 ppm), those of bromine-containing fragments, with the exception of CBr₂ (60–70 ppm), appear in a rather narrow range (25–50 ppm) and are shifted to higher field in relation to similar chlorine-containing groups. The spin–spin coupling constants in similar bromine- and chlorine-containing groups practically coinciEN. Calculation of the chemical shifts for the polyhaloalkanes under study according to the additivity scheme, as previously observed for polychloroalkanes, renders values which are in considerable discord with experimental values (up to –32 ppm for CBr₃). These discrepancies may be compensated for by corrections for the binary interaction of halogen atoms by grouping the halogen-containing fragments according to the geminal, vicinal, 1,3-, 1,3,5- and 1,2,3-arrangement of halogen atoms, and by introducing an increment for the position of the halogen at the secondary atom. It is established that as compared to 1-monohaloalkanes: (a) in the case of the geminal arrangement of halogen atoms the α- and γ-effects diminish (Δ α from –3.2 to –8 ppm; Δγ = 2.6 ppm), while the β-effect increases slightly (from 0 to 1.2 ppm); (b) in the case of a vicinal arrangement both the α- and β-effects diminish (by about –3.5 ppm) and the γ-effect remains constant, as if the vicinal system of the halogens was topologically insulated; (c) for the 1,3- and 1,3,5-arrangement of halogens their mutual influence is weak (about –0.5 ppm for each halogen atom in the α- and γ-positions); (d) the 1,2,3 system (serial arrangement of halogen atoms) is the sum of two vicinal fragments and hardly deviates from the additivity scheme; (e) the arrangement of a halogen at the secondary C atom enhances the α-effect (Δα = 2.8 and 1.0 for methyl and methylene, respectively, in the case of Cl, and 3.5 and 3.7 ppm in the case of Br); the variation of the β-effect has a different sign in relation to CH₃ and CH₂ groups (+1.2 and –1.7 for Cl, and +2.5 and –1.0 for Br). More distant effects of halogens (δ and ?) were not considered. The determined increments (Δα, Δβ and Δγ) for the α-, β- and γ-effects of chlorine and bromine atoms allow the prediction of the 13^C chemical shifts in polyhaloalkanes with an accuracy up to ±1.5 ppm. Some deviations of up to ±5 ppm may be connected with the influence of a three particle interaction of halogen atoms, which was taken into account only in the case of a geminal arrangement of halogen atoms.     

DFT calculations of the ionization potentials and electron affinities of serinamide

Adiabatic and vertical ionization potentials (IPs) and valence electron affinities (EAs) of serinamide in the gas phase have been determined using density functional theory (DFT) B3LYP, B3P86, and B3PW91 methods with the 6‐311++G** and 6‐311G** basis sets, respectively. IPs and EAs of serinamide in solution have been calculated with the B3LYP method using the 6‐311++G** and 6‐311G** basis sets. Eight possible conformers of serinamide and its charged states in the gas phase have been optimized employing the DFT B3LYP method with 6‐311++G** and 6‐311G** basis sets, respectively. All the adiabatic and vertical ionization potentials (AIPs and VIPs) of eight serinamide conformers in our work are positive values, whether in the gas phase or in solutions; the IPs in solutions are smaller than the results in the gas phase and decrease with increased dielectric constants in solutions. This finding indicates that the cationic states in solutions are more stable than those in the gas phase. All EAs of eight serinamide conformers are negative values in the gas phase, indicating that the anionic states are unstable with respect to electron autodetachment, both adiabatically and vertically. In contrast, all other adiabatic electron affinities (AEAs) are negative values in solutions except for 6S in water; 7S in chloroform, acetone, and water; and 8S in acetone and water, and increase with increasing of dielectric constants in solutions. All vertical electron affinities (VEAs) are negative values in solutions; however, no good rule has been found for these values in solutions. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Adsorption of 1-tetradecene/dodecane mixtures on different types of zeolites

The influence of heterogeneity parameters on the shape of excess adsorption isotherms has been discussed. These isotherms have been calculated according to the equations corresponding to different energy distributions. Next, the isotherm equations have been applied to examine the experimental excess isotherms for 1-tetradecene/dodecane mixture adsorption on different types ofX-zeolites at 293 K, 313 K and 333 K. The zeolite samples have been prepared from NaX-zeolite by exchanging the sodium ions for ions of alkalines and calcium group. Analysis of the above adsorption data by means of different isotherm equations showed that the parameters of aDubinin-Radushkevich-type equation change correctly with temperature and the contents of alkalines in the zeolite samples.     

A new method of determination of radii of ions with arbitrary effective charges

An equation for calculation of the radii of ions with an arbitrary effective charge has been derived. The ionic radii of halogens, chalcogens, and other atoms with different charges have been calculated. Under the assumption of pure ionic bond character, these values have been used for calculating the R ₁₂ distances for a large group of different molecules—halogens, interhalides, oxygen, chalcogens, and nitrogen and their compounds—by the previously derived equation for the a priori determination of internuclear distances. The error of calculation of the internuclear distance for halogens and interhalides is no more than 0.07 Å (3–4%). The internuclear distance in dihalogen cations Hal ₂ ⁺ and binary ionic molecules of p elements and their oxides and sulfides have been calculated. It has been demonstrated that the coordination (environment) of atoms should be taken into account and that there is a possibility of estimating the bond multiplicity and the character of bonding electron pairs in a molecule.     

Electron,hydride, and fluoride affinities of silicon-containing species: computational studies

The distance dependence of silicon substitution on the electron affinity (EA) of carbon radicals has been studied using computational methods in SiH3(CH2)nCH2 (A) and SiH2F(CH2)nCH2 (B). Large EAs result when n = 0 for both A and B. The result for A is compared with the experimental EA value of (CH3)3SiCH2. Similar comparisons with known EAs (CH3 and SiH3) establish the validity of the computational approach. Fluorine substitution in SiH2FCH2 is consistent with other fluorine substitution effects. When n > 1, the anions of both A and B cyclize to pentacoordinate structures in which silicon has trigonal bipyramidal geometry. The corresponding EA values raise important questions about computed EAs that result from profound geometry changes between radicals and anions. Anions that have not cyclized give rise to EA values more easily interpreted. Such results, combined with computations of vertical attachment energies, indicate that the EA values of A and B attenuate rapidly for n > 1, quickly approaching that of CH3. Pentacoordination effects of silicon anions were also studied for SiH4, (CH3)2SiH2, 1-silacyclopropane, 1-silacyclobutane, and 1-silacyclopentane.     

DFT study of ionization potentials and electron affinities of formamide and its methylation derivatives

The ionization potentials (IPs) and electron affinities (EAs) of formamide in the gas phase have been calculated using density functional theory (DFT), ab initio HF and Møller-Plesset perturbational theory (MP) at 6-311++G** basis set. The results indicate that the IPs of formamide obtained with DFT and MP are in agreement with the results obtained from experiment. And B3LYP has been confirmed to be the most accurate method in calculating the AIPs and VIPs of formamide through our work. IPs and EAs of formamide in solution are not known experimentally, therefore IPs and EAs of formamide in chloroform, acetone, and dimethylsulfoxide have been calculated using polarized continuum model (PCM) with B3LYP/6-311++G** level and have been compared with the values in the gas phase. The AIPs and VIPs of formamide have been compared with those of its methylation derivatives. All EAs of methylation derivatives of formamide are bigger than those of formamide conformers in the gas phase with BLYP, B3LYP, and B3P86 methods at 6-311++G** basis set. All these indicate that all anions of methylation derivatives of formamide are more stable than anions of formamide with respect to electron detachment adiabatically and vertically in the gas phase.     

FT-IR and FT-Raman spectral investigation, computed IR intensity and Raman activity analysis and frequency estimation analysis on 4-chloro-2-bromoacetophenone using HF and DFT calculations

In this work, the experimental and theoretical spectra of 4-chloro-2-bromoacetophenone (4C2BAP) are studied. FT-IR and FT-Raman spectra of title molecule have been recorded in the region 4000-100 cm(-1). The structural and spectroscopic data of the molecule in the ground state have been calculated by using Hartree-Fock and density functional method (B3LYP) with the 6-31G (d, p) and 6-311G (d, p) basis sets. The vibrational frequencies are calculated and scaled values are compared with the experimental FT-IR and FT-Raman spectra. The DFT (B3LYP/6-311G (d, p)) calculations are more reliable than the ab initio HF/6-311G (d, p) calculations for the vibrational study of 4C2BAP. The optimized geometric parameters (bond lengths and bond angles) are compared with experimental values of the molecule. The alteration of vibrational bands of the carbonyl and acetyl groups due to the presence of halogens (Cl and Br) in the base molecule is also investigated from their characteristic region of linked spectrum.     

Degradation and epimerization of ergot alkaloids after baking and in vitro digestion

The degradation and epimerization of ergot alkaloids (EAs) in rye flour were investigated after baking cookies and subsequently subjecting them to an in vitro digestion model. Different steps of digestion were analyzed using salivary, gastric, and duodenal juices. The degradation and bidirectional conversion of the toxicologically relevant (R)-epimers and the biologically inactive (S)-epimers for seven pairs of EAs were determined by a HPLC method coupled with fluorescence detection. Baking cookies resulted in degradation of EAs (2–30?%) and a shift in the epimeric ratio toward the (S)-epimer for all EAs. The applied digestion model led to a selective toxification of ergotamine and ergosine, two ergotamine-type EAs. The initial percentage of the toxic (R)-epimer in relation to the total toxin content was considerably increased after digestion of cookies. Ergotamine and ergosine increased from 32 to 51?% and 35 to 55?%, respectively. In contrast, EAs of the ergotoxine type (ergocornine, α- and β-ergocryptine, and ergocristine) showed an epimeric shift toward their biologically inactive (S)-epimers. Further experiments indicated that the selective epimerization of ergotamine EAs occurs in the duodenal juice only. These results demonstrate that toxification of EAs in the intestinal tract should be taken into consideration.     

Determination of net atomic charges using a modified partial equalization of orbital electronegativity method. III. Application to halogenated and aromatic molecules

The net atomic charge parameters for halogen atoms and the atoms in aromatic molecules have been determined by the modified partial equalization of orbital electronegativity method. The same parameters are used for the halogen atoms both in aromatic and nonaromatic systems. The calculated dipole moments of haloalkanes agree well with experiment, but those of the halogenated aromatic molecules do not reproduce the experimental values as well as those of the haloalkanes; in particular, the computed dipole moments for monohalogenated benzenes are all lower than the experimental values because of the influence of the lonepair electrons on the halogens. Within the limitations of an atom-centered point-charge approximation, our calculated dipole moments, both for haloalkanes and halogented aromatic molecules, agree well with experimental values. © John Wiley & Sons, Inc.     

Studies in some new initiator systems for vinyl polymerization. III. Amine–halogen systems as redox initiators

Amine–halogen redox systems are very efficient initiators of polymerization of a number of vinyl monomers in benzene media and are rather inefficient initiators in aqueous media. A large number of aliphatic amines and a few aromatic amines have been used. Among the halogens, chlorine and bromine are very effective. Iodine initiates with a few amines only. Endgroups incorporated are halogen and amine totalling an average of nearly one per chain in the case of polymerization in benzene media and 0.5–0.7 per chain in polymerization in aqueous media. In the light of endgroup results, a mechanism of initiation through halogen and amine radicals has been suggested.     

Tetrakis-acridinyl peptide: distance dependence of photoinduced electron transfer in deoxyribonucleic acid assemblies

A simple determination method for halogens (Cl, Br, and I) in plant samples using inductively coupled plasma-mass spectrometry (ICP-MS) was developed. In order to extract these halogens into aqueous solution, a leaching step with tetramethyl ammonium hydroxide (TMAH) under mild conditions was carried out, i.e. a 0.1-g dried sample was left overnight (ca. 12 h) in contact with 1 mL of 25% TMAH in a small PFA vial at 60 °C. Then the sample was transferred to a 50-mL centrifuge tube and diluted to 50 mL with deionised water. After centrifugation, halogens in the supernatant were determined by ICP-MS. When standard reference materials were measured by the method, the data were within the 95% confidence range of the certified values. The results also agreed well with the values obtained by neutron activation analysis with correlation factor r > 0.99.     

Nonrelativistic molecular quantum mechanics without approximations: electron affinities of LiH and LiD

We took the complete nonrelativistic Hamiltonians for the LiH and LiH- systems, as well as their deuterated isotopomers, we separated the kinetic energy of the center of mass motion from the Hamiltonians, and with the use of the variational method we optimized the ground-state nonadiabatic wave functions for the systems expanding them in terms of n-particle explicitly correlated Gaussian functions. With 3600 functions in the expansions we obtained the lowest ever ground-state energies of LiH, LiD, LiH-, and LiD- and these values were used to determine LiH and LiD electrons affinities (EAs) yielding 0.330 30 and 0.327 13 eV, respectively. The present are the first high-accuracy ab initio quantum mechanical calculations of the LiH and LiD EAs that do not assume the Born-Oppenheimer approximation. The obtained EAs fall within the uncertainty brackets of the experimental results.     

Corresponding-states correlation for the saturated liquid density of metals and metal mixtures

A corresponding-states correlation for the prediction of the orthobaric liquid density of molten metals has been developed. The correlation is the extension of the recently developed correlation by Iglesias-Silva and Hall, which needs the values of the critical and triple point constants as well as an adjustable parameter. The critical constants are scarce for almost all metals. Our corresponding-states correlation uses the normal boiling and melting point constants plus an adjustable parameter. While the present correlation is simpler in form than the correlation by Iglesias-Silva and Hall, all of its input data are more readily available for almost all metals. In this work, we have applied the present correlation to molten alkali metals, mercury, bismuth, tin, and lead. From about 150 data points for pure liquid metals the average absolute deviation and the maximum deviation are 0.29 and 1.06%, respectively. Also, we have extended the correlation to mixtures of any number of components. The predicted results for the liquid densities of K–Cs and K–Na mixtures over the whole range of concentrations and that of a ternary molten eutectic of K–Na–Cs at temperatures ranging from melting point up to several hundred degrees above the normal boiling point are in excellent agreement with experimental data. From 247 data points examined for molten alloys, the average absolute deviation and the maximum deviation are 0.59 and 1.91%, respectively.     

The evaluation of molecular electron affinities

The performance of a variety of levels of theory in evaluating molecular electron affinities (EAs) has been systematically examined. Calculations have been carried out for six different basis sets and for nine theoretical procedures including unrestricted (UHF) and restricted (RHF) Hartree-Fock theory, Møler-Plesset perturbation theory (UMP2, UMP3, UMP4), configuration interaction (UCISD, RCISD, RCISD(Q)) and equations-of-motion (EOM) approaches. Electron affinities were evaluated for CH₃, NH₂, OH, F, C₂H, CN, BO, N₃, OCN, and NO₂. Very poor results are generally obtained unless diffuse functions are included in the basis set and electron correlation is incorporated. Even with the largest basis set used in the present study (6-311 + + G(2d, 2p)), there are still residual errors greater than 0.2 eV (UMP4) or 0.6 eV (CISD) in the absolute EAs. However, better results are obtained under certain circumstances for relative EAs. The results appear to be significantly affected by spin contamination in the UHF wave-functions. For those systems for which spin contamination is small, best absolute values of the EAs generally come from the EOM and UMP2 calculations, whereas the most constant errors (thereby allowing systematic correction) are found at the UMP4, CISD, and RCISD(Q) levels. For the systems for which spin contamination is larger, best results are obtained with the CI-based procedures (CISD and RCISD(Q)). The errors in calculated EAs for the molecules with differing electronic characteristics can vary quite widely. Caution must therefore be exercised before applying schemes which rely on a constancy of errors to estimate electron affinities. The UMP procedures appear particularly suspect in this regard if spin contamination is significant. The RCISD(Q) approach is recommended under such circumstances.     

Design of low band gap polymers employing density functional theory—hybrid functionals ameliorate band gap problem

Band gaps in solids and excitation energies in finite systems are underestimated significantly if estimated from differences between eigenvalues obtained within the local spin density approximation (LSDA). In this article we present results on 20 small- and medium-sized π-systems which show that HOMO–LUMO energy differences obtained with the B3LYP, B3P86, and B3PW91 functionals are in good agreement with vertical excitation energies from UV-absorption spectra. The improvement is a result of the use of the exact Hartree–Fock exchange with hybrid methods. Negative HOMO energies and negative LUMO energies do not provide good estimates for IPs and EAs. In contrast to Hartree–Fock theory, where IPs are approximated well and EAs are given poorly, DFT hybrid methods underestimate IPs and EAs by about the same amount. LSDA yields reasonable EAs but poor IPs. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1943–1953, 1997     

The correlation consistent composite approach (ccCA): an alternative to the Gaussian-n methods

An alternative to the Gaussian-n (G1, G2, and G3) composite methods of computing molecular energies is proposed and is named the "correlation consistent composite approach" (ccCA, ccCA-CBS-1, ccCA-CBS-2). This approach uses the correlation consistent polarized valence (cc-pVXZ) basis sets. The G2-1 test set of 48 enthalpies of formation (DeltaHf), 38 adiabatic ionization potentials (IPs), 25 adiabatic electron affinities (EAs), and 8 adiabatic proton affinities (PAs) are computed using this approach, as well as the DeltaHf values of 30 more systems. Equilibrium molecular geometries and vibrational frequencies are obtained using B3LYP density functional theory. When applying the ccCA-CBS method with the cc-pVXZ series of basis sets augmented with diffuse functions, mean absolute deviations within the G2-1 test set compared to experiment are 1.33 kcal mol(-1) for DeltaHf,0.81 kcal mol(-1) for IPs, 1.02 kcal mol(-1) for EAs, and 1.51 kcal mol(-1) for PAs, without including the "high-level correction" (HLC) contained in the original Gn methods. Whereas the HLC originated in the Gaussian-1 method as an isogyric correction, it evolved into a fitted parameter that minimized the error of the composite methods, eliminating its physical meaning. Recomputing the G1 and G3 enthalpies of formation without the HLC reveals a systematic trend where most DeltaHf values are significantly higher than experimental values. By extrapolating electronic energies to the complete basis set (CBS) limit and adding G3-like corrections for the core-valence and infinite-order electron correlation effects, ccCA-CBS-2 often underestimates the experimental DeltaHf, especially for larger systems. This is desired as inclusion of relativistic and atomic spin-orbit effects subsequently improves theoretical DeltaHf values to give a 0.81 kcal mol(-1) mean absolute deviation with ccCA-CBS-2. The ccCA-CBS method is a viable "black box" method that can be used on systems with at least 10-15 heavy atoms.     

Experimental (FT-IR and FT-Raman) and theoretical (HF and DFT) investigation, IR intensity, Raman activity and frequency estimation analyses on 1-bromo-4-chlorobenzene

The FT-IR and FT-Raman spectra of 1-bromo-4-chlorobenzene (1-Br-4-CB) have been recorded using Bruker IFS 66V spectrometer in the region of 4000-100 cm(-1). Ab-initio-HF (HF/6-311+G (d, p)) and DFT (B3LYP/6-31++G (d, p)/6-311++G (d, p)) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, depolarization ratios, IR intensities, Raman activities. The vibrational frequencies are calculated and scaled values are compared with FT-IR and FT-Raman experimental values. Comparison of simulated spectra with the experimental spectra provides important information, the computational method have the ability to describe the vibrational methods. The frequency estimation analysis on HF and DFT is made. The impact of di-substituted halogens on the benzene molecule has also been discussed.