1,720,964 research outputs found
Anharmonic Franck-Condon factor analysis and simulation of the Cl20HeIphotoelectron spectrum
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Ab initio study of low-lying electronic states of SnCl2+
No full textComplete active space self-consistent field (CASSCF), multireference configuration interaction (MRCI), and restricted-spin coupled-cluster singles-doubles with perturbative triples [RCCSD(T)] calculations have been carried out on low-lying doublet and quartet states of SnCl2+, employing basis sets of up to aug-cc-pV5Z quality. Effects of core correlation and off-diagonal spin-orbit interaction on computed vertical ionization energies were investigated. The best theoretical estimate of the adiabatic ionization energy (including zero-point vibrational energy correction) to the 2A1 state of SnCl2+ is 10.093 ± 0.010 eV. The first photoelectron band of SnCl2 has also been simulated by employing RCCSD(T)/ aug-cc-pV5Z potential energy functions and including Duschinsky rotation and anharmonicity
DFT and ab initio calculations on two reactions between hydrogen atoms and the fire suppressants 2-H heptafluoropropane and CF3Br
No full textReaction enthalpies and barrier heights of the reactions CF3Br + H CF3 + HBr {reaction (1)} and CF3CHFCF3 + H CF3CFCF3 + H2 {reaction (2)} have been calculated at the near state-of-the-art ab initio level, and also by employing the B3LYP, BH&HLYP, BB1K, MPW1K, MPWB1K and TPSS1KCIS functionals. In addition, the integrated molecular orbital + molecular orbital (IMOMO) method has been used to study reaction (2). The ab initio benchmark values of the reaction enthalpy (298 K) and barrier height (0 K) of reaction (2) are reported for the first time {-(0.7 ± 0.7) and 13.3 ± 0.5 kcal/mole respectively}. When density functional theory (DFT) results are compared with ab initio benchmarks for both reactions (1) and (2), the MPWB1K functional is found to have the best performance of the six functionals used. The IMOMO method with the RCCSD/aug-cc-pVTZ and/or RCCSD(T)/aug-cc-pVTZ levels, as the high levels of calculation on the model system, gives reaction enthalpies and barrier heights of reaction (2), which agree with ab initio benchmark values to within 1 kcal/mole. Computed key geometrical parameters and imaginary vibrational frequencies of the transition state structures of reactions (1) and (2) obtained at different levels of calculation are compared. The magnitudes of the computed imaginary vibrational frequencies of the transition states of both reactions considered are found to be very sensitive to the levels of calculation used to obtain them. The heat of formation (298 K) of CF3CFCF3 calculated at the near state-of-the-art level has a value of -(318 ± 3) kcal/mole
The heat of formation of 2-H Heptafluoropropane by ab initio calculations
No full textThe heat of formation of the fire suppressant, 2-H Heptafluoropropane, which is a replacement for ozone depleting halons, AH(f.298) (K)(CF3CHFCF3) has been calculated at the B3LYP, MP2 and CCSD(T) levels with basis sets of up to cc-pVQZ quality, and with the model chemistry methods: G2(MP2), G2, G3 and CBS-Q, employing three reaction schemes. The CBS limit value of -370.6 +/- 2.3 kcal/mol obtained is believed to be the most reliable value currently available. This is recommended to be used in thermochemical/kinetic modelling of the inhibition chemistry of CF3CHFCF3 in flames
DFT and ab initio calculations on the reaction between fluorine atoms and the fire suppressant, 2-H heptafluoropropane
No full textBenchmark values for the reaction enthalpy (298 K) and the barrier height(0 K) of the reaction, CF3CHFCF3 + F -> CF3CFCF3 + HF, have been calculated at state-of-the-art ab initio level to be -34.7 +/- 1.0 and -0.9 +/- 0.9 kcal/mole, respectively. The B3LYP, BH&HLYP, BB1K, MPW1K, MPWB1K and TPSS1KCIS functionals and the model method, the integrated molecular orbital + molecular orbital (IMOMO) method, have also been used to study this reaction
Reaction enthalpies and activation energies of two important reactions in flame suppression by CF3BR
No full textReaction enthalpies and activation energies of the reactions: CF3Br ? CF3 + Br and CF3Br + H ? CF3 + HBr, were calculated at near state-of-the-art level, and compared with available experimental values and values employed in kinetic modelling of flame suppression. An ab initio strategy for evaluating reliable reaction enthalpies and activation energies for reactions considered in kinetic modelling of fire inhibition is recommended
Study of pentafluoroethane and its thermal decomposition using UV photoelectron spectroscopy and ab initio molecular orbital calculations
No full textThe UV photoelectron spectrum of CF3CHF2 has been recorded and assigned using EOM-CCSD calculations. For the first band, the adiabatic ionization energy (AIE) and vertical ionization energy (VIE) have been measured as (12.71 ± 0.05) and (13.76 ± 0.02) eV, respectively. The measured AIE is higher than the recommended value from state-of-the-art ab initio calculations of (12.26 ± 0.02) eV because of a large geometry change on ionization, mainly arising from a significant increase in the C-C bond length, which results in poor Franck-Condon factors in the adiabatic region. The experimental VIE also shows poor agreement with the computed value of 14.05 ± 0.06 eV because, in the higher energy region of the first photoelectron band, dissociation of CF3CHF2+ to CHF 2- + CF3 occurs. This has a calculated thermodynamic onset of (12.89 ± 0.20) eV. Recommendations are made for the heats of formation, ΔHØf,298, of CF 3CHF2 and CF3CHF2+, based on the results of the ab initio calculations. Pyrolysis of flowing CF 3CHF2 diluted in argon shows evidence of production of C2F4 and HF at lower temperatures and CF2 and CF3H at higher temperatures. The relative temperature dependence of the observed photoelectron bands associated with these molecules is interpreted in terms of two decomposition reactions of CF3CHF2 as well as the reaction C2F4 →2CF2.Department of Building Services Engineerin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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