Etude par spectrometrie de photoelectrons de la structure electronique des enynes conjugues

We have measured by UV excited photoelectron spectroscopy the ionization potentials of 22 conjugated alkynes, in particular, those associated with three π orbitals (π_, π_, π₊. The corresponding bands appear in this order in the spectrum. We have also calculated the orbital energies of these compounds by two semi-empirical quantum mechanical methods (INDO and SPINDO).Discussion of the ionization potential variations in terms of polar effects confirms the spatial distribution of the orbitals predicted by calculation.The vibrational structure of the photoelectron bands confirms their attribution and the role predicted for the orbitals associated with the chemical bonds of these compounds.     

Interpretation of the photoelectron spectrum of norbornadiene: A green's function approach

The ionization potentials of norbornadiene are calculated by an ab initio many-body Green's function method. The photoelectron spectrum as recorded by Heilbronner and co-workers can thus be interpreted. The first two ionization potentials are 5b₂ (π) and 7a₁ (π) (with increasing binding energy) in agreement with previous investigations.     

The electronic structure of molecules by a many-body approach III. Ionization potentials and one-electron properties of furan and thiophene

The valence ionization potentials (IP's) of furan and thiophene are studied by an ab initio many-body approach which includes the effects of electron correlation and reorganization beyond the Hartree—Fock approximation. For both molecules it is found that the ordering of the IP's as obtained in the Hartree—Fock approximation is correct. The assignment made for furan agrees with the ab initio calculation of Siegbahn, but it does not agree with the ordering proposed by Derrick et al. from their experimental investigations. For thiophene both the ordering of Derrick et al. and the one of Gelius et al. is shown to be incorrect concerning the position of the 1b₁(π) IP. For both molecules the first two IP's are due to the 1a₂(π) and the 2b₁(π) molecular orbitals. For furan four orbitals of σ-type symmetry are placed between the 2b₁ and the 1b₁ π-orbitals, for thiophene there is only one. Several one-electron properties are calculated in the one-particle approximation and compared with experimental and other theoretical data. The localized molecular orbitals are also discussed.     

Etude par spectrometrie de photoelectrons de la structure electronique des ynals et des ynones conjugues

This study proposes an interpretation of the UV photoelectron spectrum of propynal mainly with semi-empirical calculations. The electronic structure of 16 other conjugated ynals and ynones has been studied by the same techniques, and the variations of the first ionization potential, associated with the exceptionally deep oxygen lone pair, may be interpreted in terms of polar effect and intramolecular interactions. The discussion about the set π_-, π_≡ that cannot be separated yields only some qualitative results.     

Electronic structure of amino acids and ureas

The outer electronic levels of glycine, alanine, glycine ethyl ester, urea, and thiourea have been investigated by means of photoelectron spectroscopy using He I (584 Å) and He II (304 Å) radiation and CNDO/2 molecular orbital calculations. In the amino acids the molecular orbital (MO) ordering ha been found to be [σ core and carbonyl π > a″(O) a′(O) > a″(N)] with a first ionization potential of ～8.8 eV. Glycine and alanine are foun to exist as the undissociated amino carboxylic acids rather than zwitterions in the high temperature vapor. In urea the three lowest energy molecular o are near-degenerate [σ(4b₁) ～ π(1a₂) ～ π(2b₂)] while in thiourea only the two lowest energy MO's are near-degenerate [π(1a₂ σ(4b₁) ～ π(2b₂)]. The first ionization potentials of urea and thiourea are 9.7 and 7.9 eV respectively.     

A green's function calculation of the lowest ionization potential of some radicals

By using the so-called two particle-hole extended Tamm-Dancoff Approximation (2ph ex-TDA) to the one-particle Green's function (GF), we calculated the lowest ionization potentials (IP) for the radicals NO, NS, PO, PS, CF, NH₂, HCO and FCO. Though these molecules have an open-shell electronic structure, for which the usual (closed shell) GF development cannot be applied, we circumvented this difficulty by reversing in the actual calculation the physical order of the ionization process. The underlying ab initio SCF calculations were performed by using basis sets of double- to triple-zeta quality plus polarization functions. A comparison of the 2ph ex-TDA results with experiment shows the satisfactory usual accuracy (⋍0.2ev) of this method. A short comparison with other ΔSCF results is also done. A theoretical prediction for the ionization potential of the PS radical, where no experimental values are available, is finally proposed.     

异核双原子和三原子分子在红外强激光场中的电离抑制

Ionization is the fundamental process in interaction of atoms/molecules with femtosecond strong laser fields. Comparing to atoms, molecules exhibit peculiar behaviors in strong-field ionization because of their diverse geometric structures, molecular electronic orbitals as well as extra nuclear degrees of freedom. In this study, we investigate strong field single and double ionization of carbon monoxide (CO) and carbon dioxide (CO₂) in linearly polarized 50-fs, 800-nm laser fields with peak intensity in the range of 2×10¹³ W/cm² to 2×10¹⁴ W/cm² using time-of-flight mass spectrometer. By comparing the ionization yields with that of the companion atom krypton (Kr), which has similar ionization potential to the molecules, we investigate the effect of molecular electronic orbitals on the strong-field ionization. The results show that comparing to Kr, no significant suppression is observed in single ionization of both molecules and in non-sequential double ionization (NSDI) of CO, while the NSDI probability of CO₂ is strongly suppressed. Based on our results and previous studies on homonuclear diatomic molecules (N₂ and O₂), the mechanism of different suppression effect is discussed. It is indicated that the different structure of the highest occupied molecular orbitals of CO and CO₂ leads to distinct behaviors in two-center interference by the electronic wave-packet and angular distributions of the ionized electrons, resulting in different suppression effect in strong-field ionization.     

Photoelectron spectra of substituted benzenes: II. Seven valence electron substituents

The He I photoelectron spectra of the isoelectronic series of substituted benzenes toluene, aniline, phenol, and fluorobenzene have been measured and the ionization bands in the low binding energy region of the spectra have been identified and assigned. The spectrum of pentafluoroaniline has also been obtained in order to use the “perfluoro effect” to identify the lowest energy σ ionization band. The photoelectron bands were assigned by using a “composite molecule” approach in which the known levels of benzene and the various substituents are correlated with those of the molecule, by using information supplied by vibrational analysis of the bands, and by reference to CNDO/2 and INDO MO calculations. The spectra of these composite molecules are consistent with the … 1a_2u(π), 3e_2g(σ), 1e_1g(π) MO configuration of benzene. The e_1g(π) orbital is split into two components in all of these substituted benzenes. Vibrational progressions in the ring CC stretching and the X-sensitive modes have been identified in these π ionization bands. Excitation of these two modes is evidence for delocalization of the π electrons over the composite molecule. The n (nonbonding) orbital of the substituents is shown to occur in the penultimate region along with the 1a_2u(π) and 3e_2g(σ) orbitals. The shifts in the n and π orbitals between the composite molecules and their constituent molecules are discussed in terms of resonance and inductive effects.     

Photoelectron spectra of ethylene and of the six deuterated derivatives

The photoelectron spectra of C₂H₄ and of six deuterated molecules of ethylene — C₂D₄, C₂D₃H, C₂H₃D, cis-C₂H₂D₂, trans-C₂H₂D₂ and gem-C₂H₂D₂ — have been recorded with the 584-Å resonance line of He. The adiabatic ionization potentials of the X²B_3u and the ²B_3g states of the seven isotopic components have been determined with an accuracy of about 7 meV. The ionization potentials of the other excited electronic states have been measured with a lower accuracy owing to a less well defined onset. The measured ionization potentials of C₂H₄ are 10.514 eV, 12.431 eV, 14.4₃ eV, 15.7₄ eV and 18.7 eV. The vibrational structure of the first electronic band shows that the two normal modes ν₂ (symmetric CC stretching) and ν₃ (symmetric HCH bending) are excited simultaneously. The measured vibrational frequencies show no abnormal isotopic effect if the assignment given in the literature for the ν₂ and ν₃ modes in C₂H₄⁺ are reversed and if a stronger excitation of the ν₃ symmetric bending mode in the least deuterated compounds is assumed. The vibrational modes most strongly excited in the second and third electronic bands are ν₁ (symmetric CH stretching) and ν₃, and in the fourth band ν₃.     

Electronic structure of the octachlorodimolybdenum(II) anion using X-ray emission and X-ray photoelectron spectroscopies

X-ray emission (Mo Lβ_{2, 15} and Cl Kβ_{1, 3}) and X-ray photoelectron spectra from K₄ [Mo₂ Cl₈] have been combined to give a detailed picture of the electronic structure of the octachlorodimolybdenum(II) anion. Chlorine 3p orbitals form a relatively narrow band which has the same range of ionization energies as the more tightly bound orbitals with molybdenum 4d character. The molecular orbitals of the MoMo quadruple bond can be identified as well as those involved in MoCl bond formation and Cl non-bonding orbitals.     

The temperature dependence of penning ionization electron energy spectra: He(23S)—ar,N2, NO,O2, N2O,CO2

Using two intense thermal energy He(2³S) sources of different temperatures (≈400 and ≈ 1000 K, resp.) and a transmission-calibrated electron energy analyzer with about 30meV resolution, the dependence of He(2³S) Penning ionization electron spectra on collision energy for the target species Ar, N₂, NO, O₂, N₂O and CO₂ have been studied. The energy shifts of the Penning electron energy distributions and the branching ratios for the population of different electronic states in the molecular ions are determined quantitatively and compared for the two different collision temperatures. These results and the shapes of the observed Penning electron energy distributions are discussed in the light of current models for the Penning procen; the observed temperature dependences are correlated with the nature of the ionized orbitals in cases of only one entrance channel (closed shell targets) and, in addition, to the existence of qualitatively different entrance channels (open shell targets).     

UV angle resolved photoelectron spectra of fluoro and chloromethane using synchrotron radiation

Photoelectron asymmetry parameters (β) and partial photoionization cross-sections have been measured for ionization from the molecular orbitals of CH₃F and CH₃Cl using synchrotron radiation in the photon energy range 19 to 115 eV. Cooper minima are observed in the β spectra of CH₃C1 for ionization from orbitals with Cl 3p character. Several shake-up bands observed in the F 2s and Cl 38 ionization energy region indicate a breakdown of the one-electron picture of ionization. The position and relative intensities of the satellite bands are compared with the results of Green's function calculations.     

Alternate interpretation of final state relaxation for chemisorbed molecules

Ab initio Xα electronic spectra have been calculated for CO before and after chemisorption onto Ni(001) in the observed c(2 × 2) symmetry. The electronic spectra of a monolayer of C₂H₂ has also been calculated and referenced to E_F of Ni. The theoretical eigenvalue spectra of these two molecules agrees colosely with ionization potentials measured by UPS when these molecules are chemisorbed onto Ni. Charge density calculations for CO indicate that the molecular orbitais are delocalized by the COCO and CONi bonds. These results suggest that final state relaxation effects are small and possibly zero for the chemisorbed molecule and that the relaxation energy of chemisorbed molecules is approximately the correlation energy.     

用能量自洽法研究碱金属双原子分子的势能曲线

用能量自洽法(ECM)研究了碱金属双原子分子一些电子激发态的势能曲线：Na₂ 分子的2¹Π_g,4³Π_g和b³Π< sub>u电子激发态,K₂分子的a³Σ^＋_{u,2¹Πg,B¹Πu和A^{关键词： 能量自洽 双原子分子 势能 碱金属}}     

Influence of one CO molecule on structural and electronic properties of monatomic Cu chain

By using first-principles calculations, we have systematically investigated the structural and electronic properties of an infinite linear monatomic Cu chain with an adsorbed CO molecule. We find that the bridge geometry is energeticabsally favored not only when the Cu–Cu bond below the molecule is unstretched, but also for a wide range of d_Cu–Cu up to about 4.20 Å, while the substitutional geometry is favored only in the hyperstretched situation d_Cu–Cu>4.80 Å. Charge density differences point out the electron transfer is from the Cu atoms to the adsorbed CO molecule. The binding mechanism of CO to Cu chain can be described by the Blyholder’s model, in terms of σ-donation of electron density from the nonbonding CO-5σ orbital into empty metal orbitals and π-backdonation from the occupied metal d orbitals to empty CO-2π^⁎ orbital. The donation/backdonation process leads to the formation of bonding/antibonding pairs, 5σ_b/5σ_a and 2π_b^⁎/2π_a^⁎, with the 5σ_a lying above E_f and the 2π_b^⁎ below E_f.     

Relative partial photoionization cross-sections and photoelectron branching ratios of ethylene

Relative partial photoionization cross-sections and photoelectron branching ratios of the valence bands (~10–25 eV binding energy) of ethylene are reported over the photon energy ranges 18–100 eV and 21–100 eV, respectively. The four lowest ionization energy bands (1b⁻¹_1u, 1b⁻¹_1g, 3a⁻¹_g, and 1b⁻¹_2u) show monotonic cross-section decreases with photon energy from 33 eV, the 1b⁻¹_1u CC π band showing the least rapid decline. In contrast, the 2b⁻¹_3u and 2a⁻¹_g bands show almost constant cross-sections up to ~50 eV photon energy, followed by similar, although slower, monotonic decreases. This is attributed to the substantial carbon 2s character of the 2b_3u and 2a_g orbitais. The cross-section behaviour of all bands is interpreted with the aid of SCF-LCAO-MO calculations on the neutral molecule using the Gaussian-80 series of programs.     

Experimental and theoretical investigations into the electronic structure of CF2Br2 by electron momentum spectroscopy

The binding energy spectra and electron momentum density distributions for the valence orbitals of CF₂Br₂ have been obtained by using electron momentum spectroscopy (EMS) at an impact energy of 1200 eV plus binding energy. The measured electron momentum profiles are compared with Hartree–Fock (HF) and density functional theory (DFT) calculations with different-sized basis sets. In general, the DFT-B3LYP calculation using the large basis sets of 6-311++G** and aug-cc-pVTZ fairly describe the experimental results. Moreover, the controversial orderings of the outer valence orbitals have been reassigned. The pole strength of the main ionization transition from the inner valence orbital of 1b₂ is determined.