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Ajit J Thakkar - One of the best experts on this subject based on the ideXlab platform.
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dipole Oscillator Strength distributions sum rules mean excitation energies and isotropic van der waals coefficients for benzene pyridazine pyrimidine pyrazine s triazine toluene hexafluorobenzene and nitrobenzene
Journal of Chemical Physics, 2020Co-Authors: Ajit J ThakkarAbstract:Experimental, theoretical, and additive-model photoabsorption cross sections combined with constraints provided by the Kuhn-Reiche-Thomas sum rule and the high-energy behavior of the dipole Oscillator Strength density are used to construct dipole Oscillator Strength distributions for benzene, pyridazine (1,2-diazine), pyrimidine (1,3-diazine), pyrazine (1,4-diazine), s-triazine (1,3,5-triazine), toluene (methylbenzene), hexafluorobenzene, and nitrobenzene. The distributions are used to predict dipole sum rules S(k) for -6 ≤ k ≤ 2, mean excitation energies I(k) for -2 ≤ k ≤ 2, and isotropic van der Waals C6 coefficients. A popular combination rule for estimating C6 coefficients for unlike interactions from the C6 coefficients of the like interactions is found to be accurate to better than 1% for 606 of 628 cases (96.4%) in the test set.
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dipole Oscillator Strength distributions with improved high energy behavior dipole sum rules and dispersion coefficients for ne ar kr and xe revisited
Journal of Chemical Physics, 2010Co-Authors: Ashok Kumar, Ajit J ThakkarAbstract:The construction of the dipole Oscillator Strength distribution (DOSD) from theoretical and experimental photoabsorption cross sections combined with constraints provided by the Kuhn-Reiche-Thomas sum rule and molar refractivity data is a well-established technique that has been successfully applied to more than 50 species. Such DOSDs are insufficiently accurate at large photon energies. A novel iterative procedure is developed that rectifies this deficiency by using the high-energy asymptotic behavior of the dipole Oscillator Strength density as an additional constraint. Pilot applications are made for the neon, argon, krypton, and xenon atoms. The resulting DOSDs improve the agreement of the predicted S(2) and S(1) sum rules with ab initio calculations while preserving the accuracy of the remainder of the moments. Our DOSDs exploit new and more accurate experimental data. Improved estimates of dipole properties for these four atoms and of dipole-dipole C(6) and triple-dipole C(9) dispersion coefficients for the interactions among them are reported.
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reliable anisotropic dipole properties and dispersion energy coefficients for o2 evaluated using constrained dipole Oscillator Strength techniques
Journal of Chemical Physics, 1996Co-Authors: Ashok Kumar, William J Meath, Peter Bundgen, Ajit J ThakkarAbstract:Constrained anisotropic dipole Oscillator Strength techniques are used to obtain reliable values for a wide range of anisotropic and isotropic dipole properties of O2, including the dipole–dipole dispersion energy coefficients for the interaction of O2 with O2, H2, N2, CO, He, Ne, Ar, Kr, and Xe. Some of the anisotropic constraints required for our calculations are obtained via dipole sum rules from ab initio, multireference configuration interaction (CI) wave functions for the ground state of O2. The individual dipole properties of O2 considered include the dipole Oscillator Strength sums S k , k=2,1,0(−1/2)−2,−3,−4,..., the logarithmic dipole sums L k and mean excitation energiesI k , k=2(−1)−2, and, as a function of wavelength, the dynamic polarizability and its anisotropy, the total depolarization ratio, the Rayleigh scattering cross section, and the Verdet constant. Our constrained dipole Oscillator Strength results are often the only reliable, and sometimes the only available, ones for many of the properties and dispersion energies considered.
P Limaovieira - One of the best experts on this subject based on the ideXlab platform.
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experimental scaling of plane born cross sections and ab initio assignments for electron impact excitation and dissociation of xf4 x c si and ge molecules
Journal of Chemical Physics, 2017Co-Authors: M Hoshino, P Limaovieira, Denis Duflot, S Ohtomi, H TanakaAbstract:Electron energy loss spectra of carbon tetrafluoride, silicon tetrafluoride, and germanium tetrafluoride molecules (CF4, SiF4, and GeF4) have been measured for incident electron energies of 50–360 eV at 1.5°–15.5° and for 30 eV and 30° scattering angle, while sweeping the energy loss over the range 9.0–20.0 eV. Low-lying valence excited triplet and singlet states are investigated by quantum chemical ab initio calculations. The Rydberg series converging to the (lowest) ionisation energy limits of XF4 (X = C, Si, Ge) are also identified and classified using the systematic behaviour according to the magnitude of the quantum defects. A generalized Oscillator Strength analysis is employed to derive Oscillator Strength f0 value and the apparent Born integral cross sections from the corresponding differential cross sections by using the Vriens formula for the optically allowed transitions. The f0 value is compared with the optical Oscillator Strength of the photoabsorption, pseudo-photon measurements, and theore...
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electronic excitation of carbonyl sulphide cos by high resolution vacuum ultraviolet photoabsorption and electron impact spectroscopy in the energy region from 4 to 11 ev
Journal of Chemical Physics, 2015Co-Authors: P Limaovieira, Ferreira F Da Silva, Diogo Almeida, Masamitsu Hoshino, D Mogi, Tetsuya Tanioka, Hideaki Tanaka, N. J. MasonAbstract:The electronic state spectroscopy of carbonyl sulphide, COS, has been investigated using high resolution vacuum ultraviolet photoabsorption spectroscopy and electron energy loss spectroscopy in the energy range of 4.0–10.8 eV. The spectrum reveals several new features not previously reported in the literature. Vibronic structure has been observed, notably in the low energy absorption dipole forbidden band assigned to the (4π←3π) (1Δ←1Σ+) transition, with a new weak transition assigned to (1Σ−←1Σ+) reported here for the first time. The absolute optical Oscillator Strengths are determined for ground state to 1Σ+ and 1Π transitions. Based on our recent measurements of differential cross sections for the optically allowed (1Σ+ and 1Π) transitions of COS by electron impact, the optical Oscillator Strength f0 value and integral cross sections (ICSs) are derived by applying a generalized Oscillator Strength analysis. Subsequently, ICSs predicted by the scaling are confirmed down to 60 eV in the intermediate energy region. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of carbonyl sulphide in the upper stratosphere (20–50 km).
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electronic excitation of carbonyl sulphide cos by high resolution vacuum ultraviolet photoabsorption and electron impact spectroscopy in the energy region from 4 to 11 ev
Journal of Chemical Physics, 2015Co-Authors: P Limaovieira, Ferreira F Da Silva, Diogo Almeida, Masamitsu Hoshino, D Mogi, Tetsuya Tanioka, Hideaki Tanaka, N. J. MasonAbstract:The electronic state spectroscopy of carbonyl sulphide, COS, has been investigated using high resolution vacuum ultraviolet photoabsorption spectroscopy and electron energy loss spectroscopy in the energy range of 4.0–10.8 eV. The spectrum reveals several new features not previously reported in the literature. Vibronic structure has been observed, notably in the low energy absorption dipole forbidden band assigned to the (4π←3π) (1Δ←1Σ+) transition, with a new weak transition assigned to (1Σ−←1Σ+) reported here for the first time. The absolute optical Oscillator Strengths are determined for ground state to 1Σ+ and 1Π transitions. Based on our recent measurements of differential cross sections for the optically allowed (1Σ+ and 1Π) transitions of COS by electron impact, the optical Oscillator Strength f0 value and integral cross sections (ICSs) are derived by applying a generalized Oscillator Strength analysis. Subsequently, ICSs predicted by the scaling are confirmed down to 60 eV in the intermediate ener...
Ashok Kumar - One of the best experts on this subject based on the ideXlab platform.
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dipole Oscillator Strength distributions with improved high energy behavior dipole sum rules and dispersion coefficients for ne ar kr and xe revisited
Journal of Chemical Physics, 2010Co-Authors: Ashok Kumar, Ajit J ThakkarAbstract:The construction of the dipole Oscillator Strength distribution (DOSD) from theoretical and experimental photoabsorption cross sections combined with constraints provided by the Kuhn-Reiche-Thomas sum rule and molar refractivity data is a well-established technique that has been successfully applied to more than 50 species. Such DOSDs are insufficiently accurate at large photon energies. A novel iterative procedure is developed that rectifies this deficiency by using the high-energy asymptotic behavior of the dipole Oscillator Strength density as an additional constraint. Pilot applications are made for the neon, argon, krypton, and xenon atoms. The resulting DOSDs improve the agreement of the predicted S(2) and S(1) sum rules with ab initio calculations while preserving the accuracy of the remainder of the moments. Our DOSDs exploit new and more accurate experimental data. Improved estimates of dipole properties for these four atoms and of dipole-dipole C(6) and triple-dipole C(9) dispersion coefficients for the interactions among them are reported.
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dipole Oscillator Strength distributions properties and dispersion energies for the dimethyl diethyl and methyl propyl ethers
Molecular Physics, 2008Co-Authors: Ashok Kumar, William J MeathAbstract:Isotropic dipole Oscillator Strength distributions (DOSDs) have been constructed for the dimethyl, diethyl and methyl–propyl ether molecules through the use of quantum mechanical constraint techniques and experimental dipole Oscillator Strength data. The constraints are furnished by molar refractivity data and the Thomas–Reiche–Kuhn sum rule. The DOSDs are used to obtain recommended values for a variety of isotropic dipole Oscillator Strength sums, logarithmic dipole Oscillator Strength sums, and mean excitation energies for the molecules. Pseudo-DOSDs for the ethers are also constructed and used to obtain reliable results for the isotropic dipole–dipole dispersion energy coefficients for all two-body interactions of the ethers with each other and with fifty other species. In addition reliable results are also obtained for the triple–dipole dispersion energy coefficients for all three-body interactions involving the ethers. 1Dedicated to Anthony Stone, an excellent scientist and friend, on the occasion of...
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Dipole Oscillator Strength properties and dispersion energies for CI2
Molecular Physics, 2002Co-Authors: Mukesh Kumar, Ashok Kumar, William J MeathAbstract:A recommended isotropic dipole Oscillator Strength distribution (DOSD) has been constructed for the chlorine molecule through the use of quantum mechanical constraint techniques and experimental dipole Oscillator Strength and molar refractivity data. It has been used to evaluate a variety of dipole Oscillator Strength sums, logarithmic dipole Oscillator Strength sums, and mean excitation energies for the molecule. A pseudo-DOSD for C12 is also presented which is used to obtain reliable results for the isotropic dipole-dipole dispersion energy coefficients C6, for the interaction of Cl2 with itself and forty-two other species, and the triple-dipole dispersion energy coefficient C9 for (Cl2)3.
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reliable anisotropic dipole properties and dispersion energy coefficients for o2 evaluated using constrained dipole Oscillator Strength techniques
Journal of Chemical Physics, 1996Co-Authors: Ashok Kumar, William J Meath, Peter Bundgen, Ajit J ThakkarAbstract:Constrained anisotropic dipole Oscillator Strength techniques are used to obtain reliable values for a wide range of anisotropic and isotropic dipole properties of O2, including the dipole–dipole dispersion energy coefficients for the interaction of O2 with O2, H2, N2, CO, He, Ne, Ar, Kr, and Xe. Some of the anisotropic constraints required for our calculations are obtained via dipole sum rules from ab initio, multireference configuration interaction (CI) wave functions for the ground state of O2. The individual dipole properties of O2 considered include the dipole Oscillator Strength sums S k , k=2,1,0(−1/2)−2,−3,−4,..., the logarithmic dipole sums L k and mean excitation energiesI k , k=2(−1)−2, and, as a function of wavelength, the dynamic polarizability and its anisotropy, the total depolarization ratio, the Rayleigh scattering cross section, and the Verdet constant. Our constrained dipole Oscillator Strength results are often the only reliable, and sometimes the only available, ones for many of the properties and dispersion energies considered.
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reliable isotropic and anisotropic dipole properties and dipolar dispersion energy coefficients for co evaluated using constrained dipole Oscillator Strength techniques
Journal of Chemical Physics, 1994Co-Authors: Ashok Kumar, William J MeathAbstract:Abstract Constrained anisotropic dipole Oscillator Strength methods are applied to obtain reliable results for a wide selection of anisotropic and isotropic dipole properties of CO and for the dipole-dipole dispersion energy coefficients for the interaction of CO with CO, N 2 , H 2 , He, Ne, Ar, Kr and Xe. The properties of CO evaluated include the dipole Oscillator Strength sums S k , k = 2, 1, 0(− 1 2 ) −2, −3, −4, ⋯, the logarithmic dipole sums L k and mean excitation energies I k , k = 2(−1) −2, and, as a function of wavelength, the dynamic polarizability and its anisotropy, the total depolarization ratio, the Rayleigh scattering cross section, and the Verdet constant. Our constrained dipole Oscillator Strength results are often the only reliable, and sometimes the only, results available for many of the anisotropic dipole properties and dispersion energies considered in this paper.
Andries Meijerink - One of the best experts on this subject based on the ideXlab platform.
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the different nature of band edge absorption and emission in colloidal pbse cdse core shell quantum dots
ACS Nano, 2011Co-Authors: Bram De Geyter, Yolanda Justo, Iwan Moreels, Karel Lambert, Philippe Smet, Dries Van Thourhout, Arjan J Houtepen, Dominika Grodzinska, Celso De Mello Donega, Andries MeijerinkAbstract:We present a quantitative analysis of the absorption and luminescence of colloidal PbSe/CdSe core/shell quantum dots (QDs). In absorption, both the energy and the Oscillator Strength of the first exciton transition coincide with that of plain PbSe QDs. In contrast, luminescence lifetime measurements indicate that the Oscillator Strength of the emitting transition is reduced by at least a factor of 4 compared to PbSe core QDs. Moreover, the addition of an electron scavenger quenches the PbSe/CdSe emission, while a hole scavenger does not. This implies that the electron wave function reaches the QD surface, while the hole is confined to the PbSe core. These observations are consistent with calculations based on the effective mass model, which show that PbSe/CdSe QDs are at the boundary between the type-I and quasi-type-II regime, where the electron spreads over the entire nanoparticle and the hole remains confined in the PbSe core. However, as this only leads to a minor reduction of the Oscillator Strength, it follows that the drastic reduction of the Oscillator Strength in emission cannot be explained in terms of electron delocalization. In combination with the increased Stokes shift for PbSe/CdSe QDs, this indicates that the emission results from lower energy states that are fundamentally different from the absorbing states.
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the different nature of band edge absorption and emission in colloidal pbse cdse core shell quantum dots
ACS Nano, 2011Co-Authors: Bram De Geyter, Iwan Moreels, Karel Lambert, Philippe Smet, Arjan J Houtepen, Dominika Grodzinska, Celso De Mello Donega, J Justo, D Van Thourhout, Andries MeijerinkAbstract:We present a quantitative analysis of the absorption and luminescence of colloidal PbSe/CdSe core/shell quantum dots (QDs). In absorption, both the energy and the Oscillator Strength of the first exciton transition coincide with that of plain PbSe QDs. In contrast, luminescence lifetime measurements indicate that the Oscillator Strength of the emitting transition is reduced by at least a factor of 4 compared to PbSe core QDs. Moreover, the addition of an electron scavenger quenches the PbSe/CdSe emission, while a hole scavenger does not. This implies that the electron wave function reaches the QD surface, while the hole is confined to the PbSe core. These observations are consistent with calculations based on the effective mass model, which show that PbSe/CdSe QDs are at the boundary between the type-I and quasi-type-II regime, where the electron spreads over the entire nanoparticle and the hole remains confined in the PbSe core. However, as this only leads to a minor reduction of the Oscillator Strength,...
William J Meath - One of the best experts on this subject based on the ideXlab platform.
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dipole Oscillator Strength distributions properties and dispersion energies for the dimethyl diethyl and methyl propyl ethers
Molecular Physics, 2008Co-Authors: Ashok Kumar, William J MeathAbstract:Isotropic dipole Oscillator Strength distributions (DOSDs) have been constructed for the dimethyl, diethyl and methyl–propyl ether molecules through the use of quantum mechanical constraint techniques and experimental dipole Oscillator Strength data. The constraints are furnished by molar refractivity data and the Thomas–Reiche–Kuhn sum rule. The DOSDs are used to obtain recommended values for a variety of isotropic dipole Oscillator Strength sums, logarithmic dipole Oscillator Strength sums, and mean excitation energies for the molecules. Pseudo-DOSDs for the ethers are also constructed and used to obtain reliable results for the isotropic dipole–dipole dispersion energy coefficients for all two-body interactions of the ethers with each other and with fifty other species. In addition reliable results are also obtained for the triple–dipole dispersion energy coefficients for all three-body interactions involving the ethers. 1Dedicated to Anthony Stone, an excellent scientist and friend, on the occasion of...
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Dipole Oscillator Strength properties and dispersion energies for CI2
Molecular Physics, 2002Co-Authors: Mukesh Kumar, Ashok Kumar, William J MeathAbstract:A recommended isotropic dipole Oscillator Strength distribution (DOSD) has been constructed for the chlorine molecule through the use of quantum mechanical constraint techniques and experimental dipole Oscillator Strength and molar refractivity data. It has been used to evaluate a variety of dipole Oscillator Strength sums, logarithmic dipole Oscillator Strength sums, and mean excitation energies for the molecule. A pseudo-DOSD for C12 is also presented which is used to obtain reliable results for the isotropic dipole-dipole dispersion energy coefficients C6, for the interaction of Cl2 with itself and forty-two other species, and the triple-dipole dispersion energy coefficient C9 for (Cl2)3.
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reliable anisotropic dipole properties and dispersion energy coefficients for o2 evaluated using constrained dipole Oscillator Strength techniques
Journal of Chemical Physics, 1996Co-Authors: Ashok Kumar, William J Meath, Peter Bundgen, Ajit J ThakkarAbstract:Constrained anisotropic dipole Oscillator Strength techniques are used to obtain reliable values for a wide range of anisotropic and isotropic dipole properties of O2, including the dipole–dipole dispersion energy coefficients for the interaction of O2 with O2, H2, N2, CO, He, Ne, Ar, Kr, and Xe. Some of the anisotropic constraints required for our calculations are obtained via dipole sum rules from ab initio, multireference configuration interaction (CI) wave functions for the ground state of O2. The individual dipole properties of O2 considered include the dipole Oscillator Strength sums S k , k=2,1,0(−1/2)−2,−3,−4,..., the logarithmic dipole sums L k and mean excitation energiesI k , k=2(−1)−2, and, as a function of wavelength, the dynamic polarizability and its anisotropy, the total depolarization ratio, the Rayleigh scattering cross section, and the Verdet constant. Our constrained dipole Oscillator Strength results are often the only reliable, and sometimes the only available, ones for many of the properties and dispersion energies considered.
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reliable isotropic and anisotropic dipole properties and dipolar dispersion energy coefficients for co evaluated using constrained dipole Oscillator Strength techniques
Journal of Chemical Physics, 1994Co-Authors: Ashok Kumar, William J MeathAbstract:Abstract Constrained anisotropic dipole Oscillator Strength methods are applied to obtain reliable results for a wide selection of anisotropic and isotropic dipole properties of CO and for the dipole-dipole dispersion energy coefficients for the interaction of CO with CO, N 2 , H 2 , He, Ne, Ar, Kr and Xe. The properties of CO evaluated include the dipole Oscillator Strength sums S k , k = 2, 1, 0(− 1 2 ) −2, −3, −4, ⋯, the logarithmic dipole sums L k and mean excitation energies I k , k = 2(−1) −2, and, as a function of wavelength, the dynamic polarizability and its anisotropy, the total depolarization ratio, the Rayleigh scattering cross section, and the Verdet constant. Our constrained dipole Oscillator Strength results are often the only reliable, and sometimes the only, results available for many of the anisotropic dipole properties and dispersion energies considered in this paper.
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dipole Oscillator Strength properties and dispersion energies for acetylene and benzene
Molecular Physics, 1992Co-Authors: Ashok Kumar, William J MeathAbstract:Dipole Oscillator Strength distributions (DOSDs), which are globally reliable, have been constructed for the acetylene and benzene molecules, through the use of quantum mechanical constraint techniques and experimental dipole Oscillator Strength and molar refractivity data. A recommended isotropic DOSD for each molecule is used to evaluate a wide variety of dipole Oscillator stength sums, logarithmic dipole sums, and mean excitation energies, for C2H2 and C6H6. Also obtained are reliable results for the isotropic dipole-dipole dispersion energy coefficients C 6, for the interaction of acetylene and benzene with themselves and with forty-one other species, and for the triple-dipole dispersion energy coefficients C 9, for (C2H2)3 and (C6H6)3. Psuedo-DOSDs for acetylene and benzene are presented which greatly facilitate the evaluation of C 6's and C 9's for a variety of interactions.