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Coupled-cluster electronic spectra for the Ca+–acetylene π complex and comparisons to its alkaline earth analogs (2000)

Wesolowski, Steven S. ; King, Rollin A. ; Schaefer, Henry F. ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 113 (2000), S. 701-706

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Equation of motion coupled-cluster (EOM-CCSD) predictions of structures and electronic excitation energies for the recently detected Ca+–acetylene π-complex confirm three experimental state assignments, but suggest reinterpretation of the signals associated with the (2) 2B1 and (2) 2B2 states that correlate to the 2P←2S Ca+ atomic transition. The originally assigned 000 band for the (2) 2B1 state corresponds to the computed excitation energy to the (2) 2B2 state and simple reassignment is proposed. The true (2) 2B1 state was not assigned in the original spectrum. However, the computed oscillator strength is large and its optimized geometry is similar to that of the ground state. Furthermore, the experimental band tentatively attributed to the onset of the symmetric C–H stretching progression of the assigned state has a relative energy conspicuously close to the computed electronic energy for the unassigned (2) 2B1 state. Based on the computed energy separations of the optimized EOM-CCSD structures, reassignment of this vibronic band to the 000 line of the (2) 2B1 state is proposed. The newly assigned bands are also compared to the analogous transitions in the beryllium–and magnesium–acetylene π complexes. © 2000 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.481845

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On apparent quantized transition-state thresholds in the photofragmentation of acetaldehyde (2000)

King, Rollin A. ; Allen, Wesley D. ; Schaefer, Henry F.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 112 (2000), S. 5585-5592

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Recent photofragmentation experiments have observed stepwise increases in the dissociation rate for CH3CHO (T1)→CH3 (X˜ 2A2″)+HCO (X˜ 2A′) as a function of excitation energy. In accord with the Rice–Ramsperger–Kassel–Marcus (RRKM) form of transition-state theory, these steps were interpreted as corresponding to vibrational levels of the fragmentation transition state on the triplet surface. We have investigated this acetaldehyde dissociation using coupled cluster (CC) and density functional (DFT) methods with [C,O/H] atomic-orbital basis sets ranging in quality from [4s2p1d/2s1p] to [6s5p4d3f2g1h/5s4p3d2 f1g]. A high-level focal point analysis, along with harmonic force field computations, results in predictions of the dissociation energy, D0=1583 cm−1, and the association barrier height, V0*=3149 cm−1. With a basis set of triple-ζ plus double-polarization plus f(TZ2Pf ) quality, the DFT method UB3LYP and the CC method RCCSD predict barrier frequencies of 355i cm−1 and 516i cm−1, respectively, while the empirical value inferred from RRKM models is only 60i cm−1. The RRKM-derived frequencies for the degrees of freedom orthogonal to the reaction path are more reasonable but still not in convincing agreement with electronic structure theory. Thus, while the experimental steps in the dissociation rate of acetaldehyde (as well as ketene) have yet to be satisfactorily explained, proven ab initio methods provide strong evidence that simple RRKM fits to the k(E) profile provide misleading vibrational frequencies of the transition state on the corresponding triplet potential energy surface. © 2000 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.481598

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Analyses of the ScO− and ScO2− photoelectron spectra (2000)

Gonzales, Jason M. ; King, Rollin A. ; Schaefer, Henry F.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 113 (2000), S. 567-572

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: We have optimized geometries for various electronic states of both neutral and anionic ScO and ScO2 using density functional theory (DFT) and coupled cluster theory. Adiabatic and vertical separation energies have been computed using both DFT and coupled cluster theory. For the ScO− anion the 1Σ+ state is predicted to lie lower than the 3Δ state by 1.48 eV. In fact, the anion 3Δ state is higher in energy than the 2Σ+ neutral ground state. This contradicts the assignment of the ScO− ground state made by Wu and Wang, in their recent report of photoelectron spectroscopy experiments. The CCSD(T) adiabatic electron affinity for the ground state of ScO is 1.30 eV, while the vertical detachment energy is 1.33 eV. This compares favorably with the experimental value of 1.35 eV. For ScO2 the 2B2 ground state with a CCSD(T) bond angle of 140.5° is lower in energy than the 2A1 state with a bond angle of 48.4° by 1.13 eV. The anion minima include two 1A1 states, with the CCSD(T) global minimum corresponding to 140.9° and the 2.00 eV higher energy state having a bond angle of 47.4°. For ScO2 the adiabatic electron affinity was computed with CCSD(T) to be 2.22 eV with a corresponding vertical detachment energy of 2.30 eV. This compares with an experimental vertical detachment of 2.32 eV. © 2000 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.481832

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The structures, electron affinities, and energetic stabilities of TiOn and TiOn− (n=1–3) (1999)

Walsh, Mary B. ; King, Rollin A. ; Schaefer, Henry F.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 110 (1999), S. 5224-5230

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: By use of density functional and coupled cluster methods, we report energetic and structural information concerning the ground states of TiOn and TiOn− (n=1–3), much of which has not previously been observed experimentally or predicted theoretically. This study establishes the following geometrical symmetries and electronic ground states: X˜ 1A′ TiO3 (Cs), X˜ 2A2′ or 2B2 TiO3− (D3h or C2v), and X˜ 2A1 TiO2− (C2v). In addition, the electronic ground state of TiO− is established as 2Δ, arising from the 9σ21δ configuration. This finding is contrary to the suggestion of Wu and Wang, contained in their report of recent photoelectron experiments, that ground state TiO− has a 9σ1δ2 electronic configuration and 4Σ− symmetry. The ground state minimum-energy structure for TiO3− contains no oxygen–oxygen bonds and has D3h or C2v symmetry. The first theoretical adiabatic electron affinities, as predicted by the CCSD(T)//B3LYP level of theory, for TiO, TiO2, and TiO3 are 1.25 eV, 1.60 eV, and 3.34 eV, while Wu and Wang's photoelectron measurements for these were 1.30 eV, 1.59 eV, and 4.2 eV, respectively. The results for the mon- and dioxide cases are in excellent accord with experiment; however, the experimental result for TiO3 is approached with similar accuracy only when compared with our CCSD(T)//B3LYP value for the vertical detachment energy for TiO3− of 4.02 eV. The latter prediction reflects the fact that the theoretical structures for TiO3 and TiO3− are qualitatively different. Finally, several of the lowest-lying minima on the potential energy surfaces of TiO3 and TiO3− are elucidated. © 1999 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.478418

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The electron affinities of the silicon fluorides SiFn (n=1–5) (1996)

King, Rollin A. ; Mastryukov, Vladimir S. ; Schaefer, Henry F.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 105 (1996), S. 6880-6886

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Several independent density functional methods have been employed to determine the molecular structures and total energies of SiFn and SiF−n (n=1–5). Three significant measures of neutral–anion separation are reported: the adiabatic electron affinity, the vertical electron affinity, and the vertical detachment energy of the anion. The first Si–F ligand dissociation energies D(Fn−1Si–F), D(Fn−1Si−–F), and D(Fn−1Si–F−) as well as the harmonic vibrational frequencies of SiFn and SiF−n are also reported. Trends in the predictions of the different DFT methods are discussed. Self-consistent Kohn–Sham orbitals were obtained using various exchange correlation functionals and a double-ζ plus polarization basis set augmented with diffuse s-type and p-type functions. The method (BHLYP) based upon the Becke half-and-half exchange functional and the Lee–Yang–Parr correlation functional predicts molecular geometries in best agreement with experiment, while the other methods tend to produce bond lengths that are slightly longer. The BHLYP vibrational frequencies are also superior to those obtained via the other three DFT methods utilized. In previous studies of AFn molecules, the density functional methods have predicted electron affinities a few tenths of an electron volt above experiment with the BHLYP value being the best. Although experimental information concerning the electron affinities of the SiFn series is scarce, the BHLYP method does continue to predict electron affinities that are lower than the other methods. The BHLYP adiabatic electron affinities are 0.83 eV (SiF), 0.42 eV (SiF2), 2.50 eV (SiF3), and −0.22 eV (SiF4). The (unknown) Si–F bond distances for the anions are 0.076–0.088 A(ring) longer than their respective neutral counterparts. The SiF−3 anion is more strongly pyramidal than SiF3. The SiF−4 species is predicted to lie energetically above SiF4, despite its experimental identification. No significantly bound minimum was found for the SiF5 molecule, although SiF−5 is predicted to exist and M+SiF−5 has been experimentally observed. The predicted vertical detachment energy of SiF−5 is 8.54 eV with the BHLYP method. © 1996 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.471846

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The electron affinities of the perfluorocarbons C2Fn, n=1–6 (1997)

King, Rollin A. ; Pettigrew, Nathan D. ; Schaefer, Henry F.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 107 (1997), S. 8536-8544

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Several independent density functional theory (DFT) methods have been employed to determine the molecular structures and total energies of C2Fn and C2Fn− (n=1–6). Three measures of neutral-anion separation are reported: the adiabatic electron affinity, the vertical electron affinity, and the vertical detachment energy of the anion. The first fluorine atom and fluoride ion dissociation energies as well as the harmonic vibrational frequencies of C2Fn and C2Fn− are also reported. Self-consistent Kohn–Sham orbitals were obtained using various exchange correlation functionals and a double-ζ plus polarization basis set augmented with diffuse s-type and p-type functions. Previously observed trends in the prediction of bond lengths by the DFT methods continue for the C2Fn/C2Fn− series. The BHLYP method, based upon the Becke half-and-half exchange functional and the Lee–Yang–Parr correlation functional, continues to predict the shortest and most accurate bond lengths of all of the DFT methods. More generally, the Hartree–Fock/DFT hybrid methods predict shorter and more accurate bond lengths than the pure DFT methods, as expected. As in previous studies, the BHLYP method predicts the lowest electron affinity values which are also those generally closest to available experiments. Agreement to within a few tenths of an electronvolt is typically achieved. The BHLYP adiabatic electron affinities are: C2F, 2.97 eV; C2F2, 1.26 eV; C2F3, 2.25 eV; C2F4, 0.21 eV; C2F5, 1.77 eV; and C2F6, 〈0.0 eV. Further, C2F6− is found to have a negative vertical detachment energy, while C2F2, C2F4, and C2F6 are predicted to have negative vertical electron affinities. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.475005

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Correction. Rearrangements of α-Hydroxy Ketals and Derivatives of α-Hydroxy Ketals. (1978)

Creary, X ; Rollin, A

s.l. : American Chemical Society

The @journal of organic chemistry 43 (1978), S. 5027-5027

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ISSN: 1520-6904

Source: ACS Legacy Archives

Topics: Chemistry and Pharmacology

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1021/jo00420a614

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8

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Etude de la copolymerisation dans un reacteur tubulaire (1985)

Bataille, P. ; Estaque, L. ; Patterson, I. ; [et al.]

New York : Wiley-Blackwell

Die Makromolekulare Chemie 10 (1985), S. 185-197

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ISSN: 0025-116X

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Physics

Notes: A study was conducted for the polymerization of styrene and α-methyl-styrene in a batch and in a tubular reactor. The results were compared with some earlier work done in a batch reactor; it confirmed the validity of the concept of using a continuous tubular reactor. It also showed that the maximum rate of copolymerization occurs at the laminar turbulent flow transition.

Additional Material: 8 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/macp.1985.020101985115

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9

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Value recovery from polymer wastes by pyrolysis (1978)

Roy, M. ; Rollin, A. L. ; Schreiber, H. P.

Stamford, Conn. [u.a.] : Wiley-Blackwell

Polymer Engineering and Science 18 (1978), S. 721-727

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ISSN: 0032-3888

Keywords: Chemistry ; Chemical Engineering

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics

Notes: Pyrolysis of polymer wastes appears to be a suitable means of dealing with an increasingly important environmental problem. To provide background on the pyrolytic behavior of wastes, model mixtures of polyethylene and polystyrene have been pyrolyzed in various gas phases including nitrogen and carbon monoxide, at atmospheric and at reduced pressures and at temperatures from about 300-900°C. When the pyrolyzing temperature is attained by gradual heating, and when pyrolysis occurs at pressures in excess of about 200 torr, the process occurs as if each component were present alone - that is, no evidence for component interaction was noted. In these cases, the known mechanisms for pyrolysis of the pure polymers can be applied to the behavior of mixtures. Complicating effects due to interactions between the starting polymers, or among the pyrolysis products, were observed in low pressure pyrolysis (≲20 torr); further, it was shown that the balance of pyrolysis products depends on rates of attaining the pyrolyzing temperature, more rapid rates favoring the production of carbon-rich solid residues of possible use as carbon blacks. More detailed understanding of pyrolytic processes in polymer mixtures is needed to permit selection of conditions producing the optimum balance of useful products.

Additional Material: 7 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/pen.760180907

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