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Michael H. Palmer - One of the best experts on this subject based on the ideXlab platform.
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The electronic states of pyridine-N-oxide studied by VUV photoabsorption and ab initio configuration interaction computations.
The Journal of chemical physics, 2013Co-Authors: Michael H. Palmer, Nykola C Jones, S V Hoffmann, Elliott R. Smith, Dennis L. LichtenbergerAbstract:The first vacuum-ultraviolet absorption Spectrum of pyridine-N-oxide has been obtained, and has led to the identification of nearly 30 Rydberg states. These states were identified by use of the vibrational envelope (“footprint”) of the UV-Photoelectron Spectrum, and are based on the first to the third ionization energies (IE). The adiabatic IE order, central to the Rydberg state symmetry identification, is confirmed by multi-configuration SCF calculations as: 12B1 < 12B2 < 12A2 < 22B1. Several excited valence state equilibrium structures were determined by multi-configuration SCF and coupled cluster procedures. Multi-reference multi-root CI was used to calculate both Rydberg and valence state vertical excitation energies and oscillator strengths, which were correlated with the experimental measurements.
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the electronic states of 1 2 3 triazole studied by vacuum ultraviolet photoabsorption and ultraviolet Photoelectron spectroscopy and a comparison with ab initio configuration interaction methods
Journal of Chemical Physics, 2011Co-Authors: Michael H. Palmer, Ashley R Head, Nykola C Jones, S V Hoffmann, Dennis L. LichtenbergerAbstract:The Rydberg states in the vacuum ultraviolet photoabsorption Spectrum of 1,2,3-triazole have been measured and analyzed with the aid of comparison to the UV valence Photoelectron ionizations and the results of ab initio configuration interaction (CI) calculations. Calculated electronic ionization and excitation energies for singlet, triplet valence, and Rydberg states were obtained using multireference multiroot CI procedures with an aug-cc-pVTZ [5s3p3d1f] basis set and a set of Rydberg [4s3p3d3f] functions. Adiabatic excitation energies obtained for several electronic states using coupled-cluster (singles, doubles, and triples) and complete active space self-consistent field procedures agree well with experimental values. Variations in bond lengths with the electronic state are discussed. The lowest energy UV band (∼5.5–6.5 eV) is assigned to three electronically excited states and demonstrates the occurrence of a nonplanar upper state on the low energy side. A UV Photoelectron Spectrum with an improved ...
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The electronic states of 1,2,5-oxadiazole studied by VUV absorption spectroscopy and CI, CCSD(T) and DFT methods
Chemical Physics, 2009Co-Authors: Michael H. PalmerAbstract:Abstract The 1,2,5-oxadiazole VUV absorption Spectrum in the range 5–11.5 eV, shows broad bands centred near 6.2, 7.1, 8.3, 8.8, 10.6 and 11.3 eV. Rydberg states associated with three ionisation energies ( IE ) were identified in the complex fine structure above 8.7 eV. Electronic vertical excitation energies for singlet and triplet valence, and Rydberg states were computed using ab initio multi-reference multi-root CI methods. There is generally a good correlation between the envelope of the theoretical intensities and the experimental Spectrum. The nature of the more intense calculated Rydberg states, and positions of the main valence and Rydberg bands are discussed. The lowest triplet, singlet and Rydberg 3s excited states have equilibrium structures that are non-planar with C S symmetry, in a chair-like orientation where the O and H atoms lie out of the NCCN plane. This finding is consistent with the doubling of the low energy UV spectral lines [B.J. Forrest, A.W. Richardson, Can. J. Chem., 50 (1972) 2088]. The nearly degenerate IE of the UV-Photoelectron Spectrum (UV–PES, Palmer et al. 1977) makes analysis of the VUV Spectrum difficult, leading to the necessity for reinvestigation. Vertical studies ( IE V ) using CI, Tamm–Dancoff (TDA) and Green’s Function (GF) methods all gave similar results, with near degeneracy of the first 3 IE V confirming the earlier study. Studies of the adiabatic IE ( IE A ) using CCSD(T) and B3LYP methods, showed the energy sequence 2 A 2 2 B 1 2 B 2 , but these states are all saddle points, in contrast to the 4th state ( 2 A 1 ) which is a minimum. In contrast, MP2 study of the 2 B 2 state showed a minimum, with only two saddle points. Complete minima were found after minor twisting of the structures. The lowest energy cationic state is 2 A ″ (C S ), which closely resembles the 2 B 2 state. The O–N–C–C skeleton is twisted by 8°. The corresponding 2 A ′ state (C S ) is effectively identical to the 2 B 1 state. Attempts to find minima for other symmetry states were unsuccessful.
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Assignment of the electronic states of pyrazole by ab initio multi-reference configuration interaction calculations
Chemical Physics, 2003Co-Authors: Michael H. Palmer, Martyn F. GuestAbstract:Abstract The gas-phase VUV absorption Spectrum of pyrazole, which we reported recently, has been further assigned in the light of multi-reference multi-root CI calculations, using basis sets of varying size up to quadruple zeta quality, and containing both valence and Rydberg type functions. A very intense VUV band centred near 7.8 eV appears to arise from the summation of three calculated bands of ππ * character, of which the first and third are the most intense. The window resonance near the band maximum is ascribed to mutual annihilation of a Rydberg state and valence state, and a probable assignment is discussed. The electron energy loss (EEL) Spectrum also obtained previously, showed low-lying triplet states at about 3.9 and 5.1 eV, respectively; the present computations suggest that two triplet ( 3 ππ * ) states lie within the 3.9 eV band, and identifies the species involved. The assignment of the UV-Photoelectron Spectrum has been reconsidered, but the identity of the first three IPs as π 3 2 N (lone pair) is confirmed; as a consequence most of the excited singlet and triplet states below 10 eV are likely to be of ππ * and πσ * character with both valence and Rydberg types. However, a number of σσ * and σπ * states including those derived from the lone pair electrons were obtained from the CI study, which give predictive values for the onset of such excitations. The highest pair of occupied orbitals (π 3 and π 2 ) both interact strongly with the lowest pair of valence VMOs (π 4 * and π 5 * ) leading to a wide variety of valence states, and as such the molecule behaves much more like a system with degenerate pairs of π-MOs. Evidence is presented that (short lived) anions formed by electron impact are in fact 2 Σ ( 2 A ′ ) rather than 2 Π ( 2 A ″) , and that this is likely to be true for the related anions of pyrrole, furan and isoxazole. The calculated vibration frequencies and a number of 1-electron properties of the ground state have been compared with experimental data.
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The electronic states of thiophene studied by optical (VUV) absorption, near-threshold electron energy-loss (EEL) spectroscopy and ab initio multi-reference configuration interaction calculations
1998Co-Authors: Michael H. Palmer, Isobel C. Walker, Martyn F. GuestAbstract:Abstract A reinvestigation and extension of the observed VUV and EEL Spectrum of pyrrole has been carried out, and the spectra assigned by means of high level multi-reference multi-root CI studies. A similar reasssessment of the UV-Photoelectron Spectrum leads to the conclusion that our previous assignment of IP3 to ionisation of the inner π-level (1b1) is correct and that most other assignments to ionisation of a σ-electron are incorrect. This is supported by the calculation of a wide range of Rydberg states derived from the five least bound orbitals, in the IP order: 1a2−1 1 ππ ∗ states of symmetry 1A1 and 1B2. The range of calculated valence states of ππ ∗ -type has been extended to include those from 1b1.
Dennis L. Lichtenberger - One of the best experts on this subject based on the ideXlab platform.
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The electronic states of pyridine-N-oxide studied by VUV photoabsorption and ab initio configuration interaction computations.
The Journal of chemical physics, 2013Co-Authors: Michael H. Palmer, Nykola C Jones, S V Hoffmann, Elliott R. Smith, Dennis L. LichtenbergerAbstract:The first vacuum-ultraviolet absorption Spectrum of pyridine-N-oxide has been obtained, and has led to the identification of nearly 30 Rydberg states. These states were identified by use of the vibrational envelope (“footprint”) of the UV-Photoelectron Spectrum, and are based on the first to the third ionization energies (IE). The adiabatic IE order, central to the Rydberg state symmetry identification, is confirmed by multi-configuration SCF calculations as: 12B1 < 12B2 < 12A2 < 22B1. Several excited valence state equilibrium structures were determined by multi-configuration SCF and coupled cluster procedures. Multi-reference multi-root CI was used to calculate both Rydberg and valence state vertical excitation energies and oscillator strengths, which were correlated with the experimental measurements.
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the electronic states of 1 2 3 triazole studied by vacuum ultraviolet photoabsorption and ultraviolet Photoelectron spectroscopy and a comparison with ab initio configuration interaction methods
Journal of Chemical Physics, 2011Co-Authors: Michael H. Palmer, Ashley R Head, Nykola C Jones, S V Hoffmann, Dennis L. LichtenbergerAbstract:The Rydberg states in the vacuum ultraviolet photoabsorption Spectrum of 1,2,3-triazole have been measured and analyzed with the aid of comparison to the UV valence Photoelectron ionizations and the results of ab initio configuration interaction (CI) calculations. Calculated electronic ionization and excitation energies for singlet, triplet valence, and Rydberg states were obtained using multireference multiroot CI procedures with an aug-cc-pVTZ [5s3p3d1f] basis set and a set of Rydberg [4s3p3d3f] functions. Adiabatic excitation energies obtained for several electronic states using coupled-cluster (singles, doubles, and triples) and complete active space self-consistent field procedures agree well with experimental values. Variations in bond lengths with the electronic state are discussed. The lowest energy UV band (∼5.5–6.5 eV) is assigned to three electronically excited states and demonstrates the occurrence of a nonplanar upper state on the low energy side. A UV Photoelectron Spectrum with an improved ...
John M. Dyke - One of the best experts on this subject based on the ideXlab platform.
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Ab initio calculations on SF2 and its low-lying cationic states: Anharmonic Franck-Condon simulation of the UV Photoelectron Spectrum of SF2
The Journal of chemical physics, 2006Co-Authors: Edmond P. F. Lee, Daniel K. W. Mok, Foo-tim Chau, John M. DykeAbstract:Geometry optimization calculations were carried out on the X (1)A(1) state of SF2 and the X B-2(1), A (2)A(1), B B-2(2), C B-2(2), D (2)A(1), and E (2)A(2) states of SF2+ employing the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] method and basis sets of up to the augmented correlation-consistent polarized quintuple-zeta [aug-cc-pV(5+d)Z] quality. Effects of core electron (S 2s(2)2p(6) and F 1s(2) electrons) correlation and basis set extension to the complete basis set limit on the computed minimum-energy geometries and relative electronic energies (adiabatic and vertical ionization energies) were investigated. RCCSD(T) potential energy functions (PEFs) were calculated for the X (1)A(1) state of SF2 and the low-lying states of SF2+ listed above employing the aug-cc-pV(5+d)Z and aug-cc-pV5Z basis sets for S and F, respectively. Anharmonic vibrational wave functions of these neutral and cationic states of SF2, and Franck-Condon (FC) factors of the lowest four one-electron allowed neutral photoionizations were computed employing the RCCSD(T) PEFs. Calculated FC factors with allowance for Duschinsky rotation and anharmonicity were used to simulate the first four Photoelectron bands of SF2. The agreement between the simulated and observed first bands in the He I Photoelectron Spectrum reported by de Leeuw [Chem. Phys. 34, 287 (1978)] is excellent. Our calculations largely support assignments made by de Leeuw on the higher ionization energy bands of SF2.
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Ab initio calculations on SCl2 and low-lying cationic states of SCl2+: Franck-Condon simulation of the UV Photoelectron Spectrum of SCl2
The Journal of chemical physics, 2006Co-Authors: Daniel K. W. Mok, Edmond P. F. Lee, Foo-tim Chau, John M. DykeAbstract:Geometry optimization calculations were carried out on the XA11 state of SCl2 and the XB12, AB22, BA12, CA12, DA22, and EB22 states of SCl2+ at the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] level with basis sets of up to the augmented correlation-consistent polarized quintuple-zeta [aug-cc-pV(5+d)Z] quality. Effects of core electron correlation, basis set extension to the complete basis set limit, and relativistic contributions on computed minimum-energy geometrical parameters and/or relative electronic energies were also investigated. RCCSD(T) potential energy functions (PEFs) were calculated for the XA11 state of SCl2 and the low-lying states of SCl2+ listed above employing the aug-cc-pV(5+d)Z basis set. Anharmonic vibrational wave functions of these neutral and cationic states of SCl2, and Franck-Condon (FC) factors of the lowest four one-electron allowed neutral photoionizations were computed employing the RCCSD(T)∕aug-cc-pV(5+d)Z PEFs. Calcul...
Edmond P. F. Lee - One of the best experts on this subject based on the ideXlab platform.
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Ab initio calculations on SF2 and its low-lying cationic states: Anharmonic Franck-Condon simulation of the UV Photoelectron Spectrum of SF2
The Journal of chemical physics, 2006Co-Authors: Edmond P. F. Lee, Daniel K. W. Mok, Foo-tim Chau, John M. DykeAbstract:Geometry optimization calculations were carried out on the X (1)A(1) state of SF2 and the X B-2(1), A (2)A(1), B B-2(2), C B-2(2), D (2)A(1), and E (2)A(2) states of SF2+ employing the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] method and basis sets of up to the augmented correlation-consistent polarized quintuple-zeta [aug-cc-pV(5+d)Z] quality. Effects of core electron (S 2s(2)2p(6) and F 1s(2) electrons) correlation and basis set extension to the complete basis set limit on the computed minimum-energy geometries and relative electronic energies (adiabatic and vertical ionization energies) were investigated. RCCSD(T) potential energy functions (PEFs) were calculated for the X (1)A(1) state of SF2 and the low-lying states of SF2+ listed above employing the aug-cc-pV(5+d)Z and aug-cc-pV5Z basis sets for S and F, respectively. Anharmonic vibrational wave functions of these neutral and cationic states of SF2, and Franck-Condon (FC) factors of the lowest four one-electron allowed neutral photoionizations were computed employing the RCCSD(T) PEFs. Calculated FC factors with allowance for Duschinsky rotation and anharmonicity were used to simulate the first four Photoelectron bands of SF2. The agreement between the simulated and observed first bands in the He I Photoelectron Spectrum reported by de Leeuw [Chem. Phys. 34, 287 (1978)] is excellent. Our calculations largely support assignments made by de Leeuw on the higher ionization energy bands of SF2.
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Ab initio calculations on SCl2 and low-lying cationic states of SCl2+: Franck-Condon simulation of the UV Photoelectron Spectrum of SCl2
The Journal of chemical physics, 2006Co-Authors: Daniel K. W. Mok, Edmond P. F. Lee, Foo-tim Chau, John M. DykeAbstract:Geometry optimization calculations were carried out on the XA11 state of SCl2 and the XB12, AB22, BA12, CA12, DA22, and EB22 states of SCl2+ at the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] level with basis sets of up to the augmented correlation-consistent polarized quintuple-zeta [aug-cc-pV(5+d)Z] quality. Effects of core electron correlation, basis set extension to the complete basis set limit, and relativistic contributions on computed minimum-energy geometrical parameters and/or relative electronic energies were also investigated. RCCSD(T) potential energy functions (PEFs) were calculated for the XA11 state of SCl2 and the low-lying states of SCl2+ listed above employing the aug-cc-pV(5+d)Z basis set. Anharmonic vibrational wave functions of these neutral and cationic states of SCl2, and Franck-Condon (FC) factors of the lowest four one-electron allowed neutral photoionizations were computed employing the RCCSD(T)∕aug-cc-pV(5+d)Z PEFs. Calcul...
Daniel K. W. Mok - One of the best experts on this subject based on the ideXlab platform.
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Ab initio calculations on SF2 and its low-lying cationic states: Anharmonic Franck-Condon simulation of the UV Photoelectron Spectrum of SF2
The Journal of chemical physics, 2006Co-Authors: Edmond P. F. Lee, Daniel K. W. Mok, Foo-tim Chau, John M. DykeAbstract:Geometry optimization calculations were carried out on the X (1)A(1) state of SF2 and the X B-2(1), A (2)A(1), B B-2(2), C B-2(2), D (2)A(1), and E (2)A(2) states of SF2+ employing the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] method and basis sets of up to the augmented correlation-consistent polarized quintuple-zeta [aug-cc-pV(5+d)Z] quality. Effects of core electron (S 2s(2)2p(6) and F 1s(2) electrons) correlation and basis set extension to the complete basis set limit on the computed minimum-energy geometries and relative electronic energies (adiabatic and vertical ionization energies) were investigated. RCCSD(T) potential energy functions (PEFs) were calculated for the X (1)A(1) state of SF2 and the low-lying states of SF2+ listed above employing the aug-cc-pV(5+d)Z and aug-cc-pV5Z basis sets for S and F, respectively. Anharmonic vibrational wave functions of these neutral and cationic states of SF2, and Franck-Condon (FC) factors of the lowest four one-electron allowed neutral photoionizations were computed employing the RCCSD(T) PEFs. Calculated FC factors with allowance for Duschinsky rotation and anharmonicity were used to simulate the first four Photoelectron bands of SF2. The agreement between the simulated and observed first bands in the He I Photoelectron Spectrum reported by de Leeuw [Chem. Phys. 34, 287 (1978)] is excellent. Our calculations largely support assignments made by de Leeuw on the higher ionization energy bands of SF2.
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Ab initio calculations on SCl2 and low-lying cationic states of SCl2+: Franck-Condon simulation of the UV Photoelectron Spectrum of SCl2
The Journal of chemical physics, 2006Co-Authors: Daniel K. W. Mok, Edmond P. F. Lee, Foo-tim Chau, John M. DykeAbstract:Geometry optimization calculations were carried out on the XA11 state of SCl2 and the XB12, AB22, BA12, CA12, DA22, and EB22 states of SCl2+ at the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] level with basis sets of up to the augmented correlation-consistent polarized quintuple-zeta [aug-cc-pV(5+d)Z] quality. Effects of core electron correlation, basis set extension to the complete basis set limit, and relativistic contributions on computed minimum-energy geometrical parameters and/or relative electronic energies were also investigated. RCCSD(T) potential energy functions (PEFs) were calculated for the XA11 state of SCl2 and the low-lying states of SCl2+ listed above employing the aug-cc-pV(5+d)Z basis set. Anharmonic vibrational wave functions of these neutral and cationic states of SCl2, and Franck-Condon (FC) factors of the lowest four one-electron allowed neutral photoionizations were computed employing the RCCSD(T)∕aug-cc-pV(5+d)Z PEFs. Calcul...
