| 1. |
- Wakelam, V., et al.
(författare)
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A KINETIC DATABASE FOR ASTROCHEMISTRY (KIDA)
- 2012
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Ingår i: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 199:1, s. 21-
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel chemical database for gas-phase astrochemistry. Named the KInetic Database for Astrochemistry (KIDA), this database consists of gas-phase reactions with rate coefficients and uncertainties that will be vetted to the greatest extent possible. Submissions of measured and calculated rate coefficients are welcome, and will be studied by experts before inclusion into the database. Besides providing kinetic information for the interstellar medium, KIDA is planned to contain such data for planetary atmospheres and for circumstellar envelopes. Each year, a subset of the reactions in the database (kida.uva) will be provided as a network for the simulation of the chemistry of dense interstellar clouds with temperatures between 10 K and 300 K. We also provide a code, named Nahoon, to study the time-dependent gas-phase chemistry of zero-dimensional and one-dimensional interstellar sources.
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| 2. |
- Abrahamsson, Erik, 1974, et al.
(författare)
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A new reaction path for the C + NO reaction: dynamics on the 4A'' potential-energy surface.
- 2008
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Ingår i: Physical chemistry chemical physics : PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 10:30, s. 4400-9
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Tidskriftsartikel (refereegranskat)abstract
- We present a new reaction path without significant barriers for the C + NO reaction, forming ground state N((4)S) and CO. Electronic structure (CASPT2) calculations have been performed for the two lowest (4)A'' states of the CNO system. The lowest of these states shows no significant barriers against reaction in the C + NO or O + CN channels. This surface has been fitted to an analytical function using a many-body expansion. Using this surface, and the previously published (2)A' and (2)A'' surfaces [Andersson et al., Phys. Chem. Chem. Phys., 2000, 2, 613; Andersson et al., Chem. Phys., 2000, 259, 99], we have performed quasiclassical trajectory (QCT) calculations, obtaining rate coefficients for the C((3)P) + NO(X(2)Pi) --> CO(X(1)Sigma(+)) + N((4)S,(2)D) and C((3)P) + NO(X(2)Pi) --> O((3)P) + CN(X(2)Sigma(+)) reactions. We have also simulated the crossed molecular beam experiments of Naulin et al. [Chem. Phys., 1991, 153, 519] The inclusion of the (4)A'' surface in the QCT calculations gives excellent agreement with experiments. This is the first time an adiabatic pathway from C((3)P) + NO(X(2)Pi) to CO(X(1)Sigma(+))+N((4)S) has been reported.
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| 3. |
- Abrahamsson, Erik, 1974, et al.
(författare)
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Classical and quantum dynamics of the O+CN reaction
- 2006
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 324:2-3, s. 507-514
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Tidskriftsartikel (refereegranskat)abstract
- Electronic structure (CASPT2) calculations have been performed for the (2)Pi and (4)Sigma(-) states of the NCO system. To create the potential energy surfaces, the generalized discrete variable representation (GDVR) method has been used. Wave packet calculations have been performed for the collinear O + CN reaction on both surfaces. These are the first reported quantum dynamics calculations on this reaction. State-to-state reaction probabilities are presented. On the (2)Pi surface, which has an almost 6 eV deep well, we obtain structure in the reaction probabilities at low kinetic energies but at higher energies they are smooth. The (4)Sigma(-) surface is highly exoergic and vibrationally non-adiabatic dynamics is observed. The (4)Sigma(-) surface has an early barrier and as a result we find that translational energy more efficiently promotes the reaction than vibrational energy does. The wave packet results are compared with QCT results. Generally the agreement is good as would be expected but some notable differences are found, particularly for reaction out of the vibrational ground state. (c) 2005 Elsevier B.V. All rights reserved.
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| 4. |
- Abrahamsson, Erik, 1974, et al.
(författare)
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Dynamics of the O + CN Reaction and N + CO Scattering on Two Coupled Surfaces
- 2009
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Ingår i: J. Phys. Chem. A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 113:52, s. 14824-14830
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Tidskriftsartikel (refereegranskat)abstract
- Spin−orbit coupling between the two collinear 2Π and 4Σ− potential energy surfaces for the NCO system are calculated using the RASSI method with CASSCF wave functions as basis set. The GDVR method has been used to interpolate a spin−orbit coupling surface. Wave packet and quasi-classical trajectory surface hopping calculations have been performed and compared for both the O(3P) + CN(X2Σ+) → N(4S) + CO(X1Σ+) reaction and for electronically inelastic scattering in the N + CO channels. The O + CN nonadiabatic reaction probabilities are small. The wavepacket study gives a resonance structure. Also for the N + CO electronically inelastic scattering the wave packet calculations give a distinct resonance structure with peak transition probabilities up to around 10%, which is somewhat lower than the trajectory surface hopping results.
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| 5. |
- Andersson, Stefan, 1973, et al.
(författare)
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Comparison of quantum dynamics and quantum transition state theory estimates of the H + CH4 reaction rate.
- 2009
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Ingår i: The journal of physical chemistry. A. - : American Chemical Society (ACS). - 1520-5215 .- 1089-5639. ; 113:16, s. 4468-78
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Tidskriftsartikel (refereegranskat)abstract
- Thermal rate constants are calculated for the H + CH(4) --> CH(3) + H(2) reaction employing the potential energy surface of Espinosa-Garcia (Espinosa-Garcia, J. J. Chem. Phys. 2002, 116, 10664). Two theoretical approaches are used. First, we employ the multiconfigurational time-dependent Hartree method combined with flux correlation functions. In this way rate constants in the range 225-400 K are obtained and compared with previous results using the same theoretical method but the potential energy surface of Wu et al. (Wu, T.; Werner, H.-J.; Manthe, U. Science 2004, 306, 2227). It is found that the Espinosa-Garcia surface results in larger rate constants. Second, a harmonic quantum transition state theory (HQTST) implementation of instanton theory is used to obtain rate constants in a temperature interval from 20 K up to the crossover temperature at 296 K. The HQTST estimates are larger than MCTDH ones by a factor of about three in the common temperature range. Comparison is also made with various tunneling corrections to transition state theory and quantum instanton theory.
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| 6. |
- Andersson, Stefan, 1973, et al.
(författare)
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Rotational Transitions of CO+ Induced by Atomic Hydrogen
- 2008
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Ingår i: The Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 678, s. 1042-1048
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Tidskriftsartikel (refereegranskat)abstract
- The CO+ molecular ion has been observed in photon-dominated regions. Recent modeling has not been able to explain the abundances of CO+ in these regions. The most abundant collision partners are believed to be hydrogen atoms, hydrogen molecules, and electrons. The reactions of these species with CO+ have been studied previously and found to be fast. The only inelastic processes studied before were collisions of CO+ with electrons. Here we investigate the inelastic collisions of CO+ with hydrogen atoms. We argue that this can be done on the lowest triplet electronic state. This implies that CO+ ions, in a hydrogen atom dominated surrounding, experiences a few inelastic collisions before reacting. Rotationally inelastic state-to-state cross sections ( ) are presented together with state-resolved thermal rate coefficients. The results suggest that the rotationally inelastic collision cross sections can be of comparable magnitude to the reactive ones. Implications for the rotational temperature of CO+ in PDRs are discussed. To perform the calculations, a potential energy surface is fitted using the reproducing-kernel Hilbert space method based on multireference configuration-interaction calculations employing the aug-cc-pVQZ basis set.
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| 7. |
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| 8. |
- Antipov, Sergey V., 1986, et al.
(författare)
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Rate coefficient of CN formation through radiative association: A theoretical study of quantum effects
- 2009
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Ingår i: J. Chem. Phys.. - : AIP Publishing. ; 131
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Tidskriftsartikel (refereegranskat)abstract
- Radiative association of CN is simulated using a quantum dynamical as well as a semiclassical approach. A comparison of the resulting energy-resolved cross sections reveals striking quantum effects that are due to shape resonances. These, in turn, arise because of states that are quasibound by the centrifugal barrier. The quantal rate coefficient for temperatures from 40 to 1900 K has been computed using the Breit–Wigner theory to account for the resonances. Comparison with the results obtained by Singh and Andreazza [ Astrophys. J. 537, 261 (2000) ] shows that the semiclassical method, which completely omits the shape resonances, is accurate to within 25% above room temperature. At lower temperatures the contribution from the shape resonances to the radiative association rate is more significant.
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| 9. |
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| 10. |
- Antipov, Sergey V., 1986, et al.
(författare)
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Spin-orbit and rotational couplings in radiative association of C((3)P) and N((4)S) atoms.
- 2011
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Ingår i: The Journal of chemical physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 135:18
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Tidskriftsartikel (refereegranskat)abstract
- The role of spin-orbit and rotational couplings in radiative association of C((3)P) and N((4)S) atoms is investigated. Couplings among doublet electronic states of the CN radical are considered, giving rise to a 6-state model of the process. The solution of the dynamical problem is based on the L(2) method, where a complex absorbing potential is added to the Hamiltonian operator in order to treat continuum and bound levels in the same manner. Comparison of the energy-dependent rate coefficients calculated with and without spin-orbit and rotational couplings shows that the couplings have a strong effect on the resonance structure and low-energy baseline of the rate coefficient.
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