Abstract:Electronenergyloss spectroscopy of the lowlying triplet states of styrene Electronenergyloss spectroscopy of condensed butadiene and cyclopentadiene: Vibrationally resolved excitation of the lowlying triplet states J. Chem. Phys. 98, 8397 (1993); 10.1063/1.464498Observation of the lowest triplet state in silane by electron energy loss spectroscopy
“…6,7 Furthermore, no study has been published on the electron impact cross sections for vibrational and electronic excitation of this molecule and their energy dependence. Owing to the low incident energy at which the EEL intensities are measured, 8 the present results should complement previous optical studies of pyrimidine in providing a sensitivity to symmetry and spin forbidden transitions. Owing to the low incident energy at which the EEL intensities are measured, 8 the present results should complement previous optical studies of pyrimidine in providing a sensitivity to symmetry and spin forbidden transitions.…”
Section: Introductionsupporting
confidence: 62%
“…9,10 A requirement of that analysis is to follow the variation of the elastic reflectivity over a relatively large film thickness. 8 Moreover, for sufficiently low molecular coverages, the EEL spectra can be obtained under the single collision regime. 11,12 In practice, charging disappears if only a few layers of these molecules are deposited on a rare gas solid substrate.…”
Low-energy vibrational and electronic electron-energy-loss (EEL) spectra of pyrimidine condensed on a thin film of solid argon held at 18 K are reported for the incident-energy range of 2-12 eV. Sensitivity to symmetry and spin forbidden transitions as well as correlations to the triplet states of benzene make it possible to ascribe the main features, below 7 eV in the electronic part of the EEL spectrum, to triplet transitions. The lowest EEL feature with an energy onset at 3.5 eV is attributed to a transition to the (3)B(1)(n-->pi(*)) valence electronic state and the next triplet n-->pi(*) transition to a (3)A(2) state located around 4.5 eV. The remaining EEL features at 4.3, 5.2, 5.8, and 6.5 eV are all assigned to pi-->pi(*) transitions to states of symmetry (3)B(2), (3)A(1), (3)B(2), and (3)B(2)+(3)A(1), respectively. The most intense maximum at 7.6 eV is found to correspond to both (1)B(2) and (1)A(1) transitions, as in the vacuum ultraviolet spectra. Absolute inelastic cross sections per scatterer are derived from a single collision treatment described herein. Their values are found to lie within the 10(-17) cm(2) range for both the electronic and the vibrational excitations. Features in the energy dependence of the cross sections are discussed, whenever possible, by comparison with data and mechanisms found in the gas phase. A maximum over the 4-5 eV range is attributed to a B (2)B(1) shape resonance and another one observed in the 6-7 eV range is ascribed to either or both sigma(*) shape resonances of (2)A(1) and (2)B(2) symmetries.
“…6,7 Furthermore, no study has been published on the electron impact cross sections for vibrational and electronic excitation of this molecule and their energy dependence. Owing to the low incident energy at which the EEL intensities are measured, 8 the present results should complement previous optical studies of pyrimidine in providing a sensitivity to symmetry and spin forbidden transitions. Owing to the low incident energy at which the EEL intensities are measured, 8 the present results should complement previous optical studies of pyrimidine in providing a sensitivity to symmetry and spin forbidden transitions.…”
Section: Introductionsupporting
confidence: 62%
“…9,10 A requirement of that analysis is to follow the variation of the elastic reflectivity over a relatively large film thickness. 8 Moreover, for sufficiently low molecular coverages, the EEL spectra can be obtained under the single collision regime. 11,12 In practice, charging disappears if only a few layers of these molecules are deposited on a rare gas solid substrate.…”
Low-energy vibrational and electronic electron-energy-loss (EEL) spectra of pyrimidine condensed on a thin film of solid argon held at 18 K are reported for the incident-energy range of 2-12 eV. Sensitivity to symmetry and spin forbidden transitions as well as correlations to the triplet states of benzene make it possible to ascribe the main features, below 7 eV in the electronic part of the EEL spectrum, to triplet transitions. The lowest EEL feature with an energy onset at 3.5 eV is attributed to a transition to the (3)B(1)(n-->pi(*)) valence electronic state and the next triplet n-->pi(*) transition to a (3)A(2) state located around 4.5 eV. The remaining EEL features at 4.3, 5.2, 5.8, and 6.5 eV are all assigned to pi-->pi(*) transitions to states of symmetry (3)B(2), (3)A(1), (3)B(2), and (3)B(2)+(3)A(1), respectively. The most intense maximum at 7.6 eV is found to correspond to both (1)B(2) and (1)A(1) transitions, as in the vacuum ultraviolet spectra. Absolute inelastic cross sections per scatterer are derived from a single collision treatment described herein. Their values are found to lie within the 10(-17) cm(2) range for both the electronic and the vibrational excitations. Features in the energy dependence of the cross sections are discussed, whenever possible, by comparison with data and mechanisms found in the gas phase. A maximum over the 4-5 eV range is attributed to a B (2)B(1) shape resonance and another one observed in the 6-7 eV range is ascribed to either or both sigma(*) shape resonances of (2)A(1) and (2)B(2) symmetries.
“…Sache and co-workers reported the first observation of a triplet state in a compound with a pentafulvene π-electron system. Lowenergy electron-energy-loss spectra of 6,6′-dimethylfulvene placed on a thin film of solid argon were measured at 16 K. 405 Extensive efforts were later made to determine whether or not fulvenes are "aromatic chameleons". 406 The prior behavior was rationalized by application of Huckel's rule for the S 0 state and Baird's rule for the T 1 state (Figure 10a).…”
Section: Aromaticity and Substitution Effectsmentioning
Pentafulvenes are a unique class of compounds that originally attracted attention due to their propensity to display nonbenzenoid aromaticity. Subsequently, they were recognized as valuable synthons for the construction of a wide range of compounds by virtue of their ability to display multiple cycloaddition profiles. Naturally, this area of organic chemistry has experienced rapid growth over the last five decades, fueled by elegant work showcasing the unique reactivity of pentafulvenes in a plethora of cycloaddition reactions. In this Review, we have attempted to provide a systematic account of the methods for the generation of pentafulvenes, their rich and varied cycloaddition chemistry, organometallic reactions, and theoretical studies that support their versatility. Further, we have highlighted their applications in the synthesis of a variety of complex structural frameworks. It is our conviction that this Review will be useful to a wide range of chemists, and will spur further research in this promising area.
“…The ground state geometries of fulvene and dimethylfulvene were optimized using the density functional theory (DFT) B3LYP , method in combination with a triple-ζ plus double polarization (TZ2P) basis set. During optimization, the molecules were forced to preserve C 2 v symmetry, this assumption being justified by earlier experimental , and theoretical ,, studies. 1 Atom numbering in fulvene (R = H) and dimethylfulvene (R = CH 3 ).…”
Section: Methodsmentioning
confidence: 99%
“…Less information is available on the triplet states. The lowest excited triplet state of 6,6‘-dimethylfulvene (a more stable derivate of fulvene, hereafter referred to as dimethylfulvene) was recently observed in the electron-energy-loss (EEL) spectrum in the condensed phase, with the sample deposited at low temperature on a thin film of argon . Preliminary gas phase EEL spectra of dimethylfulvene were recorded in our laboratory but remained unpublished…”
Triplet and singlet excited states of fulvene and
6,6‘-dimethylfulvene were studied in the gas phase by
electron-energy-loss spectroscopy. Two valence triplet states were observed
for each compound, with vertical transition
energies of 2.35 and 3.10 eV for fulvene and 2.35 and 3.00 eV for
6,6‘-dimethylfulvene. The states are
assigned as 3B2 and
3A1. The 1B2 and
1A1 valence singlet states and two Rydberg
bands, known from
photoabsorption spectroscopy, were also observed. To support the
assignments multiconfigurational second-order perturbation calculations (CASSCF/CASPT2) were performed. The
calculated energies of the first
two valence triplet and singlet transitions are within 0.19 eV of the
experiment.
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