Valence Ionization Energies of Hydrocarbons
TL;DR: In this paper, the experimental valence ionisation energies of 143 hydrocarbons, CnHm, have been determined from their He (IIα) (40.80 eV) and He (Iα)(21.22 eV)-excited photoelectron spectra.
Abstract: Experimental valence ionisation energies of 143 hydrocarbons, CnHm, have been determined from their He (IIα) (40.80 eV) and He (Iα) (21.22 eV) excited photoelectron spectra. Ionization energies, usually up to 26 eV are given in tabular form for 108 hydrocarbons with n≤6, together with their (tentative) assignment. The ionization energies up to approximately 25 eV, of 35 selected hydrocarbons with 7≤n≤10, are presented by means of their He (IIα) photoelectron spectra.
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TL;DR: The use of transition metal catalysts allows an effective control of their transformations enabling highly selecitive syntheses ranging from three-to seven-membered carbocycles as mentioned in this paper.
Abstract: The tremendous potential of cyclopropenes and methylene-cyclopropanes as multifunctional reagents in organic syntheses has only been recognized in the last decade. The use of transition metal catalysts allows an effective control of their transformations enabling highly selecitive syntheses ranging from three- to sevenmembered carbocycles. The activities in this field are summarized in this review for the first time with an emphasis on the preparative aspects of this work.
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TL;DR: Experimental investigations of electron exchange between redox partners separated by molecular bridges have elucidated many fundamental properties of these reactions, particularly the variation of rate constants with distance, and theoretical work has provided critical insights into the superexchange mechanism of electronic coupling between distant redox centers.
Abstract: Electrons have so little mass that in less than a second they can tunnel through potential energy barriers that are several electron-volts high and several nanometers wide. Electron tunneling is a critical functional element in a broad spectrum of applications, ranging from semiconductor diodes to the photosynthetic and respiratory charge transport chains. Prior to the 1970s, chemists generally believed that reactants had to collide in order to effect a transformation. Experimental demonstrations that electrons can transfer between reactants separated by several nanometers led to a revision of the chemical reaction paradigm. Experimental investigations of electron exchange between redox partners separated by molecular bridges have elucidated many fundamental properties of these reactions, particularly the variation of rate constants with distance. Theoretical work has provided critical insights into the superexchange mechanism of electronic coupling between distant redox centers. Kinetics measurements have shown that electrons can tunnel about 2.5 nm through proteins on biologically relevant time scales. Longer-distance biological charge flow requires multiple electron tunneling steps through chains of redox cofactors. The range of phenomena that depends on long-range electron tunneling continues to expand, providing new challenges for both theory and experiment.
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TL;DR: In this paper, the spectral intensity for ionization as a function of binding energy for the valence electrons of ethylene, allene, butatriene, trans-butadiene, acetylene, benzene, methane, ethane, and cyclopropane is computed by a manybody Green's function method.
Abstract: The spectral intensity for ionization as a function of binding energy for the valence electrons of ethylene, allene, butatriene, trans‐butadiene, acetylene, benzene, methane, ethane, and cyclopropane is computed by a many‐body Green’s function method. The results are used to interpret unidentified structures in experimental ionization spectra. For the ionization out of the inner valence orbitals of the unsaturated molecules the spectral intensity is found to be distributed over several lines, in sharp contrast to the ionization out of the inner valence orbitals of the saturated molecules where the greater part of the intensity appears in one main line. The reasons for this behavior are discussed. It is also found that there is a correspondence between the behavior of the spectral intensity in the inner valence region and the satellite structure in the outer valence region. For C6H6, C4H4, and C4H6 interesting satellite lines of considerable intensity are predicted to be situated in the outer valence regio...
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TL;DR: In this article, the concerted photochemical ring opening of 1,3-cyclohexadiene was investigated in the gas phase by low-intensity pumping at 267 nm and subsequent probing by high-intensity photoionization at 800 nm and mass-selective detection of the ion yields.
Abstract: The concerted photochemical ring opening of 1,3-cyclohexadiene was investigated in the gas phase by low-intensity pumping at 267 nm and subsequent probing by high-intensity photoionization at 800 nm and mass-selective detection of the ion yields. We found five different time constants which can be assigned to traveling times along consecutive parts of the potential energy surfaces. The molecule is first accelerated in the spectroscopic state 1B along Franck–Condon active coordinates, then alters direction before changing over to the dark state 2A. All constants including that for leaving the 2A surface are below 100 fs. These times are shorter than appropriate vibrational periods. Such a maximum speed is evidence that the pathway is continuous leading from surface to surface via real crossings (conical intersections) and that the molecule is accelerated right into the outlet of the 2A/1A funnel. On the ground state it arrives as a compact wave packet, indicating a certain degree of coherence. The experimental method promises a high potential for investigating dynamics, since many consecutive phases of the process can be detected. This is because the fragmentation pattern depends on the location on the potential energy surface, so that monitoring several different ions permits to conclude on the population flow through these locations. Ionization at the intensities used is normally considered to be an effect of the electric field of the radiation. But in our case it is enhanced by resonances in the neutral molecule and in particular in the singly positive ion, and it is not sensitive for the length of the molecule (different conformers of the product hexatriene). The ionic resonances explain why hexatriene has a much richer fragmentation pattern than cyclohexadiene. Coulomb explosion is observed from an excited state of a doubly positive ion. Its mechanism is discussed.
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TL;DR: In this paper, the authors used a monochromated VUV synchrotron light source with an energy resolution of 40meV (fwhm) comparable to that used for flame-sampling molecular beam PIMS studies of flame chemistry and reaction kinetics.
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References
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TL;DR: In this paper, Fock's Naherungsmethode zur Behandung des quantenmechanischen Mehrelektronenproblems aufgestellten Gleichungen werden auf etwas allgemeinerer Grundlage diskutiert.
5,844 citations
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17 Dec 1968TL;DR: In this paper, the spectra of the 584 A (21·22 eV) photoelectron were reported for the following linear unsaturated molecules: acetylene, dideutero-acetylene, hydrogen cyanide, deuterium cyanide and diacetylene.
Abstract: The 584 A (21·22 eV) photoelectron, spectra of the following linear unsaturated molecules are reported: acetylene, dideutero-acetylene, hydrogen cyanide, deuterium cyanide, diacetylene, dideutero-diacetylene, cyanoacetylene, cyanogen, dicyanoacetylene, methylacetylene and dimethyltriacetylene. The ionization potentials of the molecules, and the vibrational fine structure observed in many of the bands, are discussed.
156 citations
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TL;DR: In this paper, it was shown that in many molecules the summed binding energies of the molecular orbitals built from 2s atomic orbitals may be divided up into atomic contributions which agree in magnitude with those obtained for the same atoms in other molecules.
Abstract: Ionization energies have been obtained for all the valence orbitals of some simple hydrocarbons and also some of their isoelectronic analogues in which a nitrogen or an oxygen atom replaces CH or CH2 respectively. This required the use of a helium discharge run under conditions such that a high proportion of 30.4 nm radiation was emitted. In order to utilize the full range of the 41 eV photon it was further necessary to use filters, usually polystyrene films about 100 nm thick, selectively to absorb 58.4 nm radiation.Analysis of the results show that in many molecules the summed binding energies of the molecular orbitals built from 2s atomic orbitals may be divided up into atomic contributions which agree in magnitude with those obtained for the same atoms in other molecules, i.e., the atomic contributions are additive as is expected from the application of simple theory. A similar additive behaviour was also found for the orbitals built from 2p and 1s(H) atomic orbitals though theory does not directly indicate this for incompletely filled orbital systems of this type.Certain weak photoelectron bands have been found at high energies which arise from transitions to configurationally mixed ionized states. The experimental results are compared with theoretical predictions.
96 citations
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TL;DR: In this paper, a photo-electron spectrometer is described which uses focusing deflexion in a radial electrostatic field for energy analysis, and an over-all limit of about 0.002 eV is deduced as the smallest attainable line width in ordinary circumstances.
Abstract: The processes which set fundamental limits to the minimum line widths observable in photo-electron spectroscopy are outlined. An over-all limit of about 0.002 eV is deduced as the smallest attainable line width in ordinary circumstances. A photoelectron spectrometer is described which uses focusing deflexion in a radial electrostatic field for energy analysis. This instrument has energy resolution of 0.015 eV, smaller than the normal width of rotational envelopes in spectra of polyatomic molecules. The applications to the study of molecular hydrogen and oxygen is described.
92 citations