The Electronic Structure of Azuleno[1,2,3-cd]phenalene and Azuleno[5,6,7-cd]phenalene,a Comparison

The photoelectron (PE.) spectra of azuleno[l, 2, 3-cd]phenalene ( 1 ) and azuleno- [5,6,7-cd]phenalene( 2 ) have been recorded. The first five bands of both compounds could be assigned to transitions corresponding to removal of electrons from 4a₂, 6b₁, 5b₁, 3a₂ and 4b_l orbitals. This assignment is based mainly on a comparison between the observed ionization potentials and orbital energies calculated in a HMO and a PPP model. The UV./VIS. polarized absorption spectrum of 1 in the region 10000–45000 cm^?1 has been measured by means of the stretched film technique. The measurements were performed in polyethylene sheets at 77°K. Several bands could be assigned to π* ← π transitions calculated by a PPP-CI method. A comparison between the electronic structures of 1 and 2 is made by means of a simple HMO diagram.     

线性BC2nB (n＝1～12)的结构特征和电子光谱的理论研究

应用密度泛函理论, 在B3LYP/6-31G^*水平上优化得到了线性簇合物BC_2nB (n＝1～12, D_(h)的平衡几何构型, 并计算了它们的谐振动频率. 在优化平衡几何构型下, 通过TD-B3LYP/cc-pvDZ和TD-B3LYP/cc-pvTZ计算, 分别得到了n＝1～12和n＝1～7的电子跃迁的垂直激发能和对应的振子强度. 在B3LYP/6-311＋G^*水平上计算得到了簇合物BC_2nB (n＝1～12, D_(h)的电离能. 基于计算结果, 导出了BC_2nB体系电子跃迁能以及第一电离能与体系大小n的解析表达式.     

Structures and Dynamic Solution Behavior of Cationic,Two‐Coordinate Gold(I)–π‐Allene Complexes

A family of seven cationic gold complexes that contain both an alkyl substituted π‐allene ligand and an electron‐rich, sterically hindered supporting ligand was isolated in >90 % yield and characterized by spectroscopy and, in three cases, by X‐ray crystallography. Solution‐phase and solid‐state analysis of these complexes established preferential binding of gold to the less substituted C?C bond of the allene and to the allene π face trans to the substituent on the uncomplexed allenyl C?C bond. Kinetic analysis of intermolecular allene exchange established two‐term rate laws of the form rate=k₁[complex]+k₂[complex][allene] consistent with allene‐independent and allene‐dependent exchange pathways with energy barriers of ΔG^≠₁=17.4–18.8 and ΔG^≠₂=15.2–17.6 kcal mol^?1, respectively. Variable temperature (VT) NMR analysis revealed fluxional behavior consistent with facile (ΔG^≠=8.9–11.4 kcal mol^?1) intramolecular exchange of the allene π faces through η¹‐allene transition states and/or intermediates that retain a staggered arrangement of the allene substituents. VT NMR/spin saturation transfer analysis of [{P(tBu)₂o‐binaphthyl}Au(η²‐4,5‐nonadiene) ]⁺SbF₆^? ( 5 ), which contains elements of chirality in both the phosphine and allene ligands, revealed no epimerization of the allene ligand below the threshold for intermolecular allene exchange (ΔG^≠_298K=17.4 kcal mol^?1), which ruled out the participation of a η¹‐allylic cation species in the low‐energy π‐face exchange process for this complex.     

Die Photoelektron-Spektren der Monohalogenacetylene

The photoelectron spectra of the four monohaloacetylenes X? C?C? H with X ? F, Cl, Br, I have been recorded. The first four bands of these spectra are assigned (in order of increasing ionization potentials) to the following states: band 1: ²Π_3/2(1), ²Π_1/2(1); band 2: ²Π_3/2(2), ²Π_1/2(2); band 3: ²Σ⁺(3); band 4: ²Σ⁺(4). A correlation diagram based on a simple ZDO-MO model shows that the observed band positions and the size of the splits due to spin-orbit coupling can be satisfactorily explained in terms of such a model. It is found that the orbital energies A_X of the postulated halogen n p λ(X)-basis orbitals are a linear function of the ionization potentials I(X) of the free atoms X. The validity of the ZDO-MO-model is confirmed by the excellent qualitative agreement between the observed and predicted spacings of the vibrational fine structure of the π-bands.     

A theoretical study of the photoelectron spectra of dichloroketene with accurate computation of ionization energies via complete basis set limit extrapolation

We calculated the equilibrium geometries and harmonic vibrational frequencies of the ground state and five cationic states of dichloroketene using (TD-)B3LYP, PBE0, and M06/M06-2X approaches. The photoelectron spectra of dichloroketene were simulated by computing Franck-Condon factors. The ionization energies were computed using the CCSD(T) approach with extrapolation to the complete basis set (CBS) limit. We propose two new CBS energy formulas (E = E_CBS + Aexp(-x) + B/(x−1) ⁿ, n = 2 or 3) and compare the performance of different CBS approaches. A new ionic state of dichloroketene belonging to the C_s point group is reported. This state is identified as the first excited state of Cl₂CCO⁺ having a double-well potential-energy curve along the CCO bending mode with a barrier height of 1.335 eV. The simulated photoelectron spectra are in agreement with the experiment. The vertical ionization energies calculated via spectral simulation are more accurate compared with those obtained at the ground-state structure. Among the CBS formulas used, the proposed ansatz with n = 2 performs best, with a mean absolute error of 0.021 and 0.012 eV for the adiabatic and vertical ionization energies, respectively.     

The Ionization Energies of Di-n-Alkyl Diacetylenes

The He(Iα) photoelectron spectra and the ionization energies of symmetrically substituted di-n-alkyl-diacetylenes R-(C?C)₂-R (with R ? CH₃, C₂H₅, n-C₃H₇, n-C₄H₉) are presented. The effect of the alkyl substitutents is that the two acetylenic ionization energies, I_v,1 and I_v,2, shift by the same amount, i.e. their difference I_v,2 – I_v,1 remains constant (2.45 ± 0.05 eV). Between 12.5 eV and 17 eV the band system in the photoelectron spectrum of R-(C?C)₂-R is superimposable with that in the spectrum of the corresponding alkane, RH, with the exception of a uniformly small shift of all the bands to higher ionization energy.     

Electronic structure and photoelectron spectrum Assignment of allene

In this paper a series of ab initio SCF and configuration calculations were reported forthe ground state and excited states X~2E, A~2E,~2B_2 and ~2A_1 of allene.For ground state X~2E Jahn-Teller distorsion was discussed and a twisted angle of 50° and a torsional barriers of 0.21—0.51 eVwere derived.Based on calculated results,the experimental photoelectron spectrum of allene has beenassigned.     

UVPES of some aliphatic azides. Part I

Ab-initio calculations for ethyl azide-CH₃CH₂N₃- and azidoacetone-N₃CH₂COCH₃-were performed with the aim of interpreting their ultraviolet photoelectron spectra. Some preliminary results are presented. The first bands of the photoelectron spectra of the azides under study are intense and sharp indicating ionization from a non-bonding orbital. This is in accordance with the performed calculations, which also predict a non-bonding character to the molecular orbitals corresponding to the first ionization energies. Good agreement was also found when comparing the second ionization energies given by the calculations with the second bands of the photoelectron spectra of the molecules.     

Strong vibronic coupling effects in ionization spectra: The “mystery band” of butatriene

A theory of vibronic coupling in molecules is presented and applied to butatriene. The energies and coupling constants which enter the calculation are computed using ab initio Hartree—Fock and many-body methods. The influence of the energy splitting and the coupling constants on the calculated spectrum is discussed. It is definitely shown that the “mystery band” in the photoelectron spectrum of butatriene arises from the vibronic coupling between the electronic states ²B_3g and ²B_3u. To reproduce the experimental observations it is essential to include in the calculation both totally and non-totally symmetric vibrational modes.     

Cyclooct-1-en-5-yne. Preparation,spectroscopic characteristics and chemical reactivity

Cyclooct-1-en-5-yne (3) has been obtained as an isolable, but highly reactive hydrocarbon by oxidation of cyclooct-5-ene-1, 2-dihydrazone with lead tetraacetate (Scheme 2). Information regarding the structure and conformational mobility of 3 has been gained from the analysis of its ¹H- and ¹³C-NMR. spectra and was found to agree with the results of force field calculations. Photolysis (206 nm) of 3 in solution has induced cleavage to butatriene and butadiene. The first band in the photoelectron spectrum of 3 ( I _v 9.10 eV) is attributed to ionization from a rather delocalized orbital with predominant weight of the double bond p-AO's. Nevertheless, the high reactivity of 3 stems from the strained triple bond as evidenced by the reaction products obtained by pyrolysis, oxidation, Diels-Alder addition, and 1, 3-dipolar addition (Scheme 4).     

On the structure and valence ionization energies of o-benzyne

The valence ionization energies of o-benzyne, computed using a Green function method and by CI calculations at a molecular geometry optimized with the 6-31G^* basis using a two-term GVB wavefunction, suggest an assignment of the photoelectron spectrum of this molecule which differs from that given by a previous MNDO calculation. The first three ionization energies are found to be nearly degenerate.     

Photoelectron spectroscopic study of simple hydrogen-bonded dimers. II. The methanol dimer

HeI photoelectron spectra of a supersonic jet of methanol vapor have been obtained by using the temperature-controlled supersonic nozzle beam photoelectron spectrometer recently constructed in our laboratory. A HeI spectrum attributable to the methanol dimer (CH₃OH)₂ has been deduced by spectrum stripping. The first ten vertical ionization energies and the first adiabatic ionization energy of (CH₃OH)₂ have been determined from the stripped spectrum. Ab initio SCF MO calculations of ionization energies have also been carried out for (CH₃OH)₂ on the basis of Koopmans' theorem. The lower bound of the dissociation energy of (CH₃OH)₂⁺ has been estimated to be 1.2 ± 0.2 eV from the adiabatic ionization energies of the monomer and dimer. The equilibrium structure of (CH₃OH)₂ is also discussed.     

Gas phase high temperature photoelectron spectroscopy: The tin monoxide molecule

The HeI photoelectron spectrum of SnO (X¹Σ⁺) has been recorded. Two bands have been observed corresponding to ionization from the 6π and 13 ionization energies of 9.98 and 10.12 eV respectively. Vibrational structure associated with the first band has been analysed to give

and D_e = 3.23 ± 0.10 eV in the SnO⁺ (X²Π) state. An assessment has been made of the ability of Hartree-Fock-Slater calculations, multiple-scattering SCF-Xα calculations and ab ini energies for the group IV diatomic monoxide molecules.     

Reactions retrodieniques—v: Acces aux cumulenes par thermolyse eclair d'ethano-9,10 dihydro-9,10 anthracenes. Synthese du pentatetraene.

Allene, methylallene, 1,1-dimethylallene and butatriene have been obtained in excellent yield by flash thermolysis (involving retro-Diels-Alder decomposition) of various 9,10-ethano-9,10-dihydroanthracenes. Flash thermolysis of vinylallene 11 leads in 85% yield to a mixture of pentatetraene (1, 70%) and pentadiyne (17, 30%); pentatetraene is stable enough to be purified by GLC at 25° and its ¹H and ¹³C NMR, MS, IR and UV spectra have been recorded.     

Difluorocarbene Studied with Threshold Photoelectron Spectroscopy (TPES): Measurement of the First Adiabatic Ionization Energy (AIE) of CF2

The first photoelectron band of difluorocarbene CF₂, has been studied by threshold photoelectron (TPE) spectroscopy. CF₂ was prepared by microwave discharge of a flowing mixture of hexafluoropropene, C₃F₆, and argon. A vibrationally resolved band was observed in which at least twenty‐two components were observed. In the first PE band of CF₂, the adiabatic ionization energy differs significantly from the vertical ionization energy because, for the ionization CF₂⁺ (X?²A₁)+e^? ← CF₂ (X?¹A₁), there is an increase in the FCF bond angle (by ≈20°) and a decrease in the C? F bond length (by ≈0.7 Å). The adiabatic component was not observed in the experimental TPE spectrum. However, on comparing this spectrum with an ab initio/Franck–Condon simulation of this band, using results from high‐level ab initio calculations, the structure associated with the vibrational components could be assigned. This led to alignment of the experimental TPE spectrum and the computed Franck–Condon envelope, and a determination of the first adiabatic ionization energy of CF₂ as (11.362±0.005) eV. From the assignment of the vibrational structure, values were obtained for the harmonic and fundamental frequencies of the symmetric stretching mode (ν₁′) and symmetric bending mode (ν₂′) in CF₂⁺ (X?²A₁).     

Anion-molecular interaction through CH3 groups: Model ab initio studies

3-21G, 6–31G and 6–31 +G calculations have been performed on Cr…H₃CCl and LiCl…H₃CCl complexes with two different configurations each. Optimized geometries, stabilization energies, CH force constants and harmonic vibrational frequencies for CH₃Cl and its complexes are reported. Comparison of the calculated frequency shifts of CH-stretching bands of CH₃C1, on complexation, with experimental results of related systems indicate that the interaction of Cl^- with CH₃ group takes place in a linear manner with the CH bond. A lower frequency shift for LiCl…H₃CX with reference to the C1^-…H₃CX complexes is explained on the basis of the reduction of the basicity of Cl^- ion in the presence of counter ion in the former complex considered.     

Assignment of the first photoelectron band of the CH<Subscript>3</Subscript>CHCl radical using ab initio quantum mechanical calculations

HeI photoelectron spectra have been recorded for the reaction of atomic fluorine with ethyl chloride at different reaction times. A structured band associated with a short-lived primary reaction product has been recorded with adiabatic and vertical ionization energies of (7.84±0.02) and (8.18±0.02) eV respectively. An average vibrational separation of (680±30) cm^–1was observed in this band. Comparison between the experimental vertical and adiabatic ionization energies and ionization energies computed for CH₃CHCl (X²A) and CH₂CH₂Cl (X²A) at different levels of theory led to the assignment of the observed first photoelectron band to the ionization of CH₃CHCl (X²A). The observed vibrational structure was assigned to excitation of the C–Cl stretching mode in CH₃CHCl⁺(X¹A).Proceedings of the 11th International Congress of Quantum Chemistry satellite meeting in honor of Jean-Louis Rivail     

Photoelectron Spectroscopy of peri-Amino Naphthalenes

The He I photoelectron spectra of peri-amino and dimethylamino naphthalenes are presented. The differences in the ionization energies of the π-bands are interpreted by separation of the perturbation of the amino substituent into an inductive destabilization and conjugative stabilization. This affords the assignment of the photoelectron bands of ionization energies below 11 eV and an estimation of the dihedral angle in the peri-dimethylamino derivatives. The data on the peri-amino naphthalenes indicate some angular distortion in contrast to 2-aminonaphthalene.     

Novel physically adapted STO##‐3G basis sets. Efficiency for prediction of second‐order electric and magnetic properties of aromatic hydrocarbons

Efficient scheme for construction of physically justified STO^##‐3G_el and STO^##‐3G_mag basis sets has been proposed. It is based upon the analysis of analytical form of the first‐order correction functions to unperturbed STO basis sets under the perturbation by electric or magnetic fields. The test calculations of polarizability, magnetic susceptibility and chemical shifts performed for a series of aromatic compounds within the developed basis set in the framework of Hartree‐Fock and Density Functional Theory (DFT) approaches show good agreement of the predicted properties with experiments. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Vacuum ultraviolet photoelectron spectroscopy of transient species. XVII. The SiH3(X 2A1) radical

The first band in the vacuum ultraviolet photoelectron spectrum of the silyl radical, corresponding to the process SiH₃ (X ¹A′₁) ← SiH₃(X ²A₁), has been observed with HeI radiation. Extensive vibrational fine structure associated with the SiH₃⁺ deformation vibration was observed in this band and analysis of the structure gave a value of ω = 820 = 40 cm^-1 for the out-of-plane deformation mode in the ion. The vertical and adiabatic ionization energies were measured as 8.74 = 0.01 eV and 8.14 ± 0.01 eV respectively and use of the latter value together with the established heat of formation of the silyl radical allows an improved heat of formation of SiH₃^-. ΔH₂₉₈⁰ (SiH₃^-) to be derived as 980 ± 7 kJ mol^?1.