Predictive Abilities of Scaled Quantum Mechanical Molecular Force Fields: Application to 1,3-Butadiene

The positions of some IR bands of the s-trans-1,3-butadiene-h ₆ and -1,1,2-d ₃ isotopomers in the gas phase have been measured using a Brucker IFS 120 HR spectrometer with a resolution of 2 cm^–1. The structural parameters of the s-trans- and s-gauche-1,3-butadiene conformers were optimized completely at the MP2/6-31G* theoretical level and their MP2/6-31G*//MP2/6-31G* quantum mechanical force fields (QMFFs) were calculated. Using only the experimental vibrational frequencies of s-trans-1,3-butadiene-h ₆ the QMFF of the s-trans conformer was corrected by Pulay's scaling method (eight scale factors were involved). The scaled QMFF was used to calculate the mean vibrational amplitudes and the Coriolis coupling constants of s-trans-1,3-butadiene-h ₆ and the vibrational frequencies of 12 of its deuterated isotopomers. The set of scale factors obtained for correction of the s-trans QMFF was transferred to the QMFF of the s-gauche conformer. Its theoretical vibrational spectrum and those of some deuterated and C¹³ isotopomers were calculated. The ability of this scaling approach (transferring of scale factors) to predict the vibrational frequencies of rotational conformers and their isotopomers, as well as other molecular characteristics, and to permit detection of perturbations of the experimental bands are discussed.     

Infrared and Raman spectra, conformational stability, ab initio calculations and vibrational assignment for 1,2-pentadiene (ethyl allene)

The infrared (3500-50 cm⁻¹) and Raman (3500-20 cm⁻¹) spectra of 1,2-pentadiene, H₂C=C=C(H)CH₂CH₃ (ethyl allene), have been recorded for both the gaseous and solid states. Additionally, the Raman spectrum of the liquid has been obtained with qualitative depolarization values. In the fluid phases both the cis and gauche conformers have been identified, with the gauche rotamer being the predominant form although it may not be the conformer of lowest energy. In the solid state only the cis conformer remains after repeated annealing of the crystal. The asymmetric torsion of the cis conformer is observed as a series of Q-branch transitions beginning at 103.4 cm⁻¹ and falling to lower frequency. An estimate of the potential function governing conformer interconversion is provided. A complete assignment of the normal modes for the cis conformer is given and several of the fundamentals are assigned for the gauche rotamer. Ab initio electronic structure calculations of energies, conformational geometries, vibrational frequencies, and potential energy functions have been made to complement and assist the interpretation of the infrared and Raman spectra. In particular, the transitions among torsional energy levels for both the symmetric (methyl) and asymmetric (ethyl) motions have been calculated. The results are compared to the corresponding quantities for some similar molecules.     

Far infrared spectrum,conformational stability,barriers to internal rotation,vibrational assignment,and ab initio calculations of 2-chloro-3-fluoropropene

The far infrared spectrum (375 to 30 cm^–1) of gaseous 2-chloro-3-fluoropropene, CH₂=C(CH₂F)CI, has been recorded at a resolution of 0.10 cm^–1. The fundamental asymmetric torsional mode is observed at 117.5 cm^–1 with ten excited states falling to low frequency for thes-cis (fluorine atom eclipsing the double bond) conformer. For the higher energy gauche conformer, the asymmetric torsion is estimated to be at 94 cm^–1. From these data the asymmetric torsional potential function has been calculated. The potential function coefficients are calculated to be in cm^–1):V ₁=803±21,V ₂=–94±21,V ₃= 1025±10,V ₄=95±10, andV ₆=2±1, with an enthalpy difference between the more stables-cis and gauche conformera of 550±100 cm^–1 (1.57±0.29 kcal/mol). This function gives values of 1227±50cm^–1(3.51±0.14kcal/mol), 1266±200 cm^–1 (3.62±0.57 kcal/mol), and 665±100 cm^–1 (1.90±0.29 kcal/mol), for thes-cis to gauche, gauche to gauche, and gauche tos-cis barriers, respectively. From the relative intensities of the Raman lines of the gas at 652 cm^–1 (gauche) and 731 cm^–1 (s-cis) as a function temperature, the enthalpy difference is found to be 565±96 cm^–1 (1.62±0.27 kcal/mol). However, the more polar gauche conformer remains in the crystalline solid. The Raman spectrum of the gas has been recorded from 3500 to 70 cm^–1 and, utilizing these data and the previously reported infrared data, a complete vibrational analysis is proposed for both conformers. The conformational stability, barriers to internal rotation, fundamental vibrational frequencies, and structural parameters that have been determined experimentally are compared to those obtained from ab initio Hartree-Fock gradient calculations employing both the 3–21 G^* and 6–31G^* basis sets and to the corresponding quantities for some similar molecules.     

Far-infrared spectrum,conformational stability,barriers to internal rotation,normal coordinate calculations,and vibrational assignment for chloroacetaldehyde

The far infrared spectrum [350 to 25 cm^–1] of gaseous chloroacetaldehyde, ClCH₂CHO, has been recorded at a resolution of 0.10 cm^–1. The first excited-state transition of the asymmetric torsion of the more stable near s-cis [chlorine atom s-cis to the aldehyde hydrogen atom] conformer has been observed at 26.9 cm^–1, with seven additional upper state transitions falling to higher frequency. Additionally, the fundamental torsional transition of the s-trans conformer has been observed at 58.9 cm^–1 with two excited states also falling to higher frequency. From these data, the asymmetric torsional potential coefficients have been determined to be:V ₁=414±11;V ₂ = 191±3;V ₃=–203±5;V ₄=44±1 andV ₆=–26±1 cm^–1. The s-cis to s-trans barrier is 500±5 cm^–1 (1.43±0.01 kcal mol^–1) with the s-cis conformer being more stable by 267±19 cm^–1 (0.76±0.05 kcal mol^–1) than the s-trans form. The Raman [4000 to 100 cm^–1] and infrared (4000 to 400 cm^–1] spectra of the gas have been recorded. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values obtained. Complete vibrational assignments are proposed for both conformers based on band contours, depolarization values, and group frequencies. The assignments are supported by ab initio Hartree-Fock gradient calculations employing the 3–21G^* basis set to obtain the frequencies and the potential energy distributions for the normal vibrations for both rotamers. Additional ab initio calculations at the MP4/6-31G^* level have been carried out to determine the structural parameters for both conformers. The results are discussed and compared with the corresponding quantities obtained for some similar molecules.This contribution taken in part from the thesis of C. L. Tolley which will be submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree.     

Theoretical investigations on structure, electrostatics potentials and vibrational frequencies of Li+ - CH3- O- (CH2- CH2- O)n- CH3 (n=3-7) conformers

Electronic structure, charge distributions and vibrational characteristics of CH₃ O(CH₂ CH₂ O) _n CH₃ (n=3-7) have been derived using the ab initio Hartree Fock and density functional calculations. For tri- to hexaglymes the lowest energy conformers have trans- conformation around the C-C and C-O bonds of the backbone. For heptaglyme (n=7 in the series), however, gauche-conformation around the C-C bonds renders more stability to the conformer and turns out to be 10.1 kJ mol ⁻¹ lower in energy relative to the conformer having trans-orientation around the C-C and C-O bonds. The molecular electrostatic potential topographical investigations reveal deeper minima for the ether oxygen in conformers having the gauche conformation around the C-C bonds over those for the trans- conformers. A change from trans- to gauche-conformation around the C-C bonds of the lowest energy conformer of heptaglyme engenders a triplet of intense bands ∼1,150 cm ⁻¹ in the vibrational spectra. Theoretical calculations predict that Li ⁺ binds strongly to the heptaglyme conformer in the above series. The frequency shifts in the vibrational spectra of CH₃O(CH₂CH₂O) _n CH₃- Li⁺ (n=3-7) conformers have been discussed     

Electro-catalysis by immobilised human flavin-containing monooxygenase isoform 3 (hFMO3)

Human flavin-containing monooxygenases are the second most important class of drug-metabolizing enzymes after cytochromes P450. Here we report a simple but functional and stable enzyme-electrode system based on a glassy carbon (GC) electrode with human flavin-containing monooxygenase isoform 3 (hFMO3) entrapped in a gel cross-linked with bovine serum albumin (BSA) by glutaraldehyde. The enzymatic electrochemical responsiveness is characterised by using well-known substrates: trimethylamine (TMA), ammonia (NH₃), triethylamine (TEA), and benzydamine (BZD). The apparent Michaelis–Menten constant (K′_M) and apparent maximum current (I′_max) are calculated by fitting the current signal to the Michaelis–Menten equation for each substrate. The enzyme-electrode has good characteristics: the calculated sensitivity was 40.9 ± 0.5 mA mol⁻¹ L cm⁻² for TMA, 43.3 ± 0.1 mA mol⁻¹ L cm⁻² for NH₃, 45.2 ± 2.2 mA mol⁻¹ L cm⁻² for TEA, and 39.3 ± 0.6 mA mol⁻¹ L cm⁻² for BZD. The stability was constant for 3 days and the inter-electrode reproducibility was 12.5%. This is a novel electrochemical tool that can be used to investigate new potential drugs against the catalytic activity of hFMO3.     

<Emphasis Type="Italic">Ab initio</Emphasis> Study of Structural and Conformational Properties of Five- to Nine-Membered Cyclic 1,2,3-Trienes

Summary.  The structures and relative energies of fundamental conformations of cyclopenta-1,2,3-triene, cyclohexa-1,2,3-triene, cylohepta-1,2,3-triene, cycloocta-1,2,3-triene, and cyclonona-1,2,3-triene were calculated by the HF/6-31G^* and MP2/6-31G^*//HF/6-31G^* methods. Only a C _2v symmetric planar conformation is available to cyclopenta-1,2,3-triene and cyclohexa-1,2,3-triene. The calculated energy barrier for ring inversion of the C _S symmetric puckerd conformation of cyclohepta-1,2,3-triene via the planar geometry is 62.2 kJ·mol⁻¹. The C ₂ symmetric twist conformation of cycloocta-1,2,3-triene was calculated to be the most stable one. Conformational racemization of the twist form takes place via the C _S symmetric half-chair geometry, which is by 60.8 kJ·mol⁻¹ less stable than the twist conformer. The C _S symmetric chair and unsymmetrical twist-boat conformations of cyclonona-1,2,3-triene were calculated to have similar energies; their interconversion takes place via an unsymmetrical low-energy (18.4 kJ·mol⁻¹) transition state. The twist (C ₂) and boat (C _S) geometries of cyclonona-1,2,3-triene are higher in energy by 13.2 and 33.9 kJ·mol⁻¹, respectively. Ring inversion in chair and twist-boat conformations takes place via a twist form as intermediate and requires 33.6 kJ·mol⁻¹. Corresponding author. E-mail: isayavar@yahoo.com Received March 25, 2002; accepted April 4, 2002     

The Potential Energies of Cohesion of a Crystalline Organic Enantiomer and the Racemate; on the Energy for the Liquid Racemate [1]

Summary. The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, −47.7 ± 0.1 kJ mol⁻¹ (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol⁻¹, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose the vibrational energy using the Debye energy function (E _vib 835.0 kJ mol⁻¹ (78.6°C), E ⁰ included). E _kin for the crystal (771.1 kJ mol⁻¹ (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy. The cohesion energy of the racemic crystal, −44.2 kJ mol⁻¹, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol⁻¹, 83.3°C) and E _kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E _{vib + rot} for the liquid in the way as to E _vib for the gas, the Debye entropy function being increasedly suited for the liquid (E _{vib + rot} 763.4 kJ mol⁻¹ (115.4°C)). Positive ΔE _pot, 13.0 kJ mol⁻¹, arised from the increase in electronic energy (Δ _l ν_mean − 154.3 cm⁻¹, by the dielectric nature of the liquid), added to the cohesion energy.     

The Potential Energies of Cohesion of a Crystalline Organic Enantiomer and the Racemate; on the Energy for the Liquid Racemate [1]

The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, −47.7 ± 0.1 kJ mol⁻¹ (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol⁻¹, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose the vibrational energy using the Debye energy function (E _vib 835.0 kJ mol⁻¹ (78.6°C), E ⁰ included). E _kin for the crystal (771.1 kJ mol⁻¹ (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy. The cohesion energy of the racemic crystal, −44.2 kJ mol⁻¹, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol⁻¹, 83.3°C) and E _kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E _{vib + rot} for the liquid in the way as to E _vib for the gas, the Debye entropy function being increasedly suited for the liquid (E _{vib + rot} 763.4 kJ mol⁻¹ (115.4°C)). Positive ΔE _pot, 13.0 kJ mol⁻¹, arised from the increase in electronic energy (Δ _l ν_mean − 154.3 cm⁻¹, by the dielectric nature of the liquid), added to the cohesion energy.     

A theoretical study of the acetylide anion, HCC−

The results of various ab initio calculations are reported for the electronic ground state of the acetylide anion. An “Eyring's lake” in the T-shaped configuration is identified with six different methods (SCF, MP2, CCSD, CCSD-T, CCSD(T), and CEPA–1). The equilibrium bond lengths of HCC⁻ are estimated to be r _e (CH)=1.0689(3) ? and R _e (CC)=1.2464(2) ?, and the ground-state rotational constant is predicted to be B ₀=41636(20)MHz. The large permanent dipole moment of μ₀=−3.093D should facilitate detection of the anion by microwave spectroscopy. The band centers are predicted to be 3211.3cm⁻¹(ν₁), 511.1cm⁻¹(ν₂), and 1805.0cm⁻¹(ν₃). A large transition dipole moment of 0.477 D is calculated for the ν₂ band. Rovibrational levels of HCC⁻ up to approximately 20 000 cm⁻¹ above equilibrium are calculated with DVR-DGB and FBR methods on the basis of a previous CEPA–1 potential energy surface. Different energy patterns are found and discussed, for which anharmonic and Coriolis resonances are shown to play an important role. Received: 27 July 1998 Accepted: 12 August 1998 / Published online: 19 October 1998     

Spectra and structure of silicon containing compounds

The Raman (50 to 3200 cm^–1) and infrared (50 to 3500 cm^–1) spectra of chlorodimethylmethoxysilane, Cl(CH₃)₂SiOCH₃, in the vapor and solid phases have been recorded. Raman spectra of the liquid including depolarization ratios have also been recorded. Optimized geometries and conformational stabilities have been obtained from ab initio calculations utilizing the RHF/3–21G* and RHF/6–31G* basis sets. The calculations from both of these basis sets indicated the gauche conformer to be significantly more stable than the trans conformer. Since the gauche has twice the multiplicity of the trans form it is unlikely that the trans conformer will be detected in the fluid phases at room temperature. This is supported by the fact that no infrared or Raman bands were found to vanish in the spectra of the crystalline solid. The vibrational frequencies have been calculated using appropriate scaling factors, and the vibrational spectra are interpreted in detail. The results have been compared with those obtained for some related molecules.Dedicated to Professor Dr. H. Kriegsmann on the occasion of his 70th birthdayFor part XX, see J Raman Spectrosc 26:in press (1995)Analytical R/D Department, Organic Products Division, Miles Inc., Bushy Park Plant. Charleston, SC 9411, USAChemistry Department, Mu'tah University, P.O.Box 7, Mu'tah-Karak, JordanDepartment of Chemistry, Moscow State University, Moscow, B-234, RussiaDepartment of Ceramic Engineering, Inha University, Nam-Ku, Incheon 160, KoreaDepartment of Chemistry, University of Oslo, P.O.Box 1033, 0315 Oslo, Norway     

Conformational stability,barriers to internal rotation,normal coordinate analysis,and vibrational assignment of chloroacetyl bromide

The infrared spectra (3200 to 30 cm^–1) of gaseous and solid chloroacetyl bromide, CH₂ClC(O)Br, and the Raman spectra (3200 to 10 cm^–1) of the gas, liquid (with depolarization data), and solid have been recorded. From the observed asymmetric torsional transitions, the potential function governing internal rotation of the CH₂Cl moiety has been determined with the following coefficients:V ₁=336±11,V ₂=73±10,V ₃=757+7,V ₄=103±3, andV ₆=5±2 cm^–1. This potential function is consistent with s-trans to gauche and gauche to gauche barriers of 963±11 and 709±12cm^–1, respectively, and enthalpy difference of 373 ± 24 cm^–1 with the dihedral angle of the gauche rotamer being 115°. The enthalpy difference has been determined experimentally from the studies of the Raman spectra at different temperatures to be 359±68 cm^–1 (1.03±0.19 kcal mol^–1) and 507±24 cm^–1 (1.45±0.07 kcal mol^–1) for the gas and liquid, respectively, with the s-trans conformer being the more stable conformer in the gas and liquid and the only one present in the annealed solid. A complete assignment of the vibrational fundamentals is proposed from spectral data obtained for the gas, liquid, and solid. The assignment is supported by a normal coordinate calculation utilizing a modified valence force field to obtain the frequencies for the normal vibrations and the potential energy distribution. The results are discussed and compared to the corresponding quantities for some similar molecules.Taken in part from the thesis of H. V. Phan, which will be submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree.     

Ab initio study of molecular structure and internal rotation in methyldicyanophosphine and methyldiisocyanophosphine. The Raman spectrum of methyldicyanophosphine and its interpretation with the use of scaling ofab initio force fields

The equilibrium geometric parameters and structures of transition states of internal rotation for the molecules of methyldicyanophospine MeP(CN)₂ and its isocyano analog MeP(NC)₂ were calculated by the RHF and MP2 methods with the 6–31G^* and 6–31G^** basis sets. At the MP2 level, the total energy of cyanide is −35 kcal mol⁻¹ lower than that of isocyanide and the barriers to internal rotation of methyl group for MeP(CN)₂ and MeP(NC)₂ are 2.2 and 2.7 kcal mol⁻¹, respectively. For both molecules, the one-dimensionalab initio potential functions of internal rotation approximated by a truncated Fourier series were used to determine the frequencies of torsional transitions by solving direct vibrational problems for a non-rigid model. The Raman spectrum of crystalline MeP(CN)₂ was recorded in the range 3500–50 cm⁻¹. The vibrational spectra of this compound were interpreted by scalingab initio force fields calculated by the RHF and MP2 method. The vibrational spectrum of methyldiisocyanophosphine was predicted with the use of the obtained scale factors. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1703–1714, September, 1998.     

Solid state voltammetric characterization of iron hexacyanoferrate encapsulated in silica

We describe a sol-gel approach by which iron hexacyanoferrate is immobilized in silica in a manner suited to investigation by electrochemistry in the absence of a contacting liquid phase. Such physicochemical parameters as concentration of redox sites (C _o) and apparent (effective) diffusion coefficient (D _app) are estimated by performing cyclic voltammetric and potential step experiments in two time regimes, which are characterized by linear and spherical diffusional patterns, respectively. Values of D _app and C _o thereby obtained are 2.0 × 10⁻⁶ cm² s⁻¹ and 1.4 × 10⁻² mol dm⁻³. The D _app value is larger than expected for a typical solid redox-conducting material. Analogous measurements done in iron(III) hexacyanoferrate(III) solutions of comparable concentrations, 1.0 × 10⁻² and 5.0 × 10⁻³ mol dm⁻³, yield D _app on the level of 5–6 × 10⁻⁶ cm² s⁻¹. Thus, the dynamics of charge propagation in this sol-gel material is almost as high as in the liquid phase. The residual water in the silica, along with the pore structure, are important to the overall mechanism of charge transport, which apparently is limited by physical diffusion rather than electron self-exchange. Under conditions of a solid state voltammetric experiment which utilizes an ultramicroelectrode, encapsulated iron hexacyanoferrate redox centers seem to be in the dispersed colloidal state rather than in a form of the rigid polymeric film. Received: 8 April 1999 / Accepted: 13 August 1999     

Conformational Properties of (Z,Z)-, (E,Z)-, and (E,E)-Cycloocta-1,4-dienes

Summary.  Ab initio calculations at the HF/6-31G^* level of theory for geometry optimization and the MP2/6-31G^*//HF/6-31G^* level for a single point total energy calculation are reported for (Z,Z)-, (E,Z)-, and (E,E)-cycloocta-1,4-dienes. The C ₂-symmetric twist-boat conformation of (Z,Z)-cycloocta-1,4-diene was calculated to be by 3.6 kJ·mol⁻¹ more stable than the C _S-symmetric boat-chair form; the calculated energy barrier for ring inversion of the twist-boat conformation via the C _S-symmetric boat-boat geometry is 19.1 kJ·mol⁻¹. Interconversion between twist-boat and boat-chair conformations takes place via a half-chair (C ₁) transition state which is 43.5 kJ·mol⁻¹ above the twist-boat form. The unsymmetrical twist-boat-chair conformation of (E,Z)-cycloocta-1,4-diene was calculated to be by 18.7 kJ·mol⁻¹ more stable than the unsymmetrical boat-chair form. The calculated energy barrier for the interconversion of twist-boat-chair and boat-chair is 69.5 kJ·mol⁻¹, whereas the barrier for swiveling of the trans-double bond through the bridge is 172.6 kJ·mol⁻¹. The C _S symmetric crown conformation of the parallel family of (E,E)-cycloocta-1,4-diene was calculated to be by 16.5 kJ·mol⁻¹ more stable than the C _S-symmetric boat-chair form. Interconversion of crown and boat-chair takes place via a chair (C _S) transition state which is 37.2 kJ·mol⁻¹ above the crown conformation. The axial- symmetrical twist geometry of the crossed family of (E,E)-cycloocta-1,4-diene is 5.9 kJ·mol⁻¹ less stable than the crown conformation. Corresponding author. E-mail: isayavar@yahoo.com Received March 25, 2002; accepted April 3, 2002     

The parathiocyanogen electrode

Stable, yellow anodic films of parathiocyanogen (SCN) _x were formed on a platinum electrode from 2.8 M KSCN in methanol at 45 °C at a constant current of 20–40 mA cm⁻² for 15–30 min. Loosely bound orange crystals of a more amorphous character were removed by rinsing to leave an adherent yellow film with sharp Raman bands under 647.1 nm laser excitation at 627 cm⁻¹ (vCS), 1152 cm⁻¹ and 1236–1261 cm⁻¹ (vNN and vCN). The lack of electroactivity and short-lived photocurrents pointed to an insulating film at potentials up to 1.0 V (SHE). At more positive potentials, longer-lasting photocurrents were obtained, consistent with breakdown of the insulating film. XPS scans confirmed N:C:S ratios close to 1:1:1, with a deficiency of S of some 10% due to S lost as sulfate at the film surface. Oxidation of SeCN⁻ in neutral aqueous solution led to the formation of a less-stable orange paraselenocyanogen film with a Raman band at 1256–1267 cm⁻¹, which decomposed within a day to grey selenium. Received: 12 December 1997 / Accepted: 23 March 1998     

Synthesis of Aryl(hetero)methylene-1,3-indandione Based Molecular Glasses

Summary. Novel glass-forming 2-(1-phenyl-1,2,3,4-tetrahydroquinoline-6-ylmethylene)-1,3-indandione derivatives were synthesized and their thermal properties were studied. The results of a preliminary investigation of the photoelectric properties of amorphous films of the title compounds are briefly reported. The ionization potential of these molecular glasses is ca. 5.6 eV and the hole drift mobility exceeds 10⁻⁸ cm² V⁻¹ s⁻¹ at strong electric fields.     

Absolute integrated intensities of vapor-phase hydrogen peroxide (H2O2) in the mid-infrared at atmospheric pressure

We report quantitative infrared spectra of vapor-phase hydrogen peroxide (H₂O₂) with all spectra pressure-broadened to atmospheric pressure. The data were generated by injecting a concentrated solution (83%) of H₂O₂ into a gently heated disseminator and diluting it with pure N₂ carrier gas. The water vapor lines were quantitatively subtracted from the resulting spectra to yield the spectrum of pure H₂O₂. The results for the ν₆ band strength (including hot bands) compare favorably with the results of Klee et al. (J Mol. Spectrosc. 195:154, 1999) as well as with the HITRAN values. The present results are 433 and 467 cm^-2 atm⁻¹ (±8 and ±3% as measured at 298 and 323 K, respectively, and reduced to 296 K) for the band strength, matching well the value reported by Klee et al. (S = 467 cm⁻² atm⁻¹ at 296 K) for the integrated band. The ν₁ + ν₅ near-infrared band between 6,900 and 7,200 cm⁻¹ has an integrated intensity S = 26.3 cm⁻² atm⁻¹, larger than previously reported values. Other infrared and near-infrared bands and their potential for atmospheric monitoring are discussed.     

Pseudopotential study of lanthanum and lutetium dimers

Relativistic energy-consistent small-core lanthanide pseudopotentials of the Stuttgart–Bonn variety and extended valence basis sets have been used for the investigation of the dimers La₂ and Lu₂. It was found that the ground states for La₂ and Lu₂ are most likely ¹∑ _g ⁺ (σ _g ²π _u ⁴) and ³∑ _g ⁻ (4f ¹⁴4f ¹⁴σ _g ²σ _u ²π_u ²), respectively. The molecular constants including error bars were derived from multireference configuration interaction as well as coupled-cluster calculations, taking into account corrections for atomic spin–orbit splitting as well as possible basis set superposition errors. The theoretical values for La₂ (R _e=2.70±0.03 ?, D _e=2.31±0.13 eV, ω_e=186±13 cm⁻¹) show good agreement with the experimental binding energy (D _e=2.52±0.22 eV), but the experimental vibrational constant in an Ar matrix (ω_e=236±0.8 cm⁻¹) is significantly higher. For Lu₂ the theoretical values (R _e=3.07±0.03 ?, D _e=1.40±0.12 eV, ω_e=123±1 cm⁻¹) are in overall excellent agreement with experimental data (D _e=1.43±0.34 eV, ω_e=122± 1 cm⁻¹). The electronic structures of La₂ and Lu₂ are compared to those other lanthanide dimers and trends in the series are discussed. Received: 25 March 2002 / Accepted: 2 June 2002 / Published online: 21 August 2002     

Π delocalisation in 1,3-butadiene: a nonempirical molecular orbital study

A value of −0.33 eV or −7.6 kcal mol⁻¹ has been obtained for the vertical delocalisation energy of trans-1,3-butadiene from a nonempirical molecular orbital calculation on the π system. The result agrees well enough with ab initio calculations to suggest that a simplified approach need not be semiempirical. In a basis of orthogonalised atomic orbitals the central bond order is found to be 0.295 (Hückel value 0.447) for the delocalised structure and 0.125 for the localised (Hückel value zero). Core resonance integrals between neighbouring atoms, the analogues of Hückel's β, have theoretical values of −3.9 and −3.2 eV compared with −3.6 eV in benzene. Received: 11 May 1999 / Accepted: 22 July 1999 / Published online: 2 November 1999