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2. The HITRAN2020 molecular spectroscopic database

Author

Gordon, I. E., Rothman, L. S., Hargreaves, R. J., Hashemi, R., Karlovets, E., V, Skinner, F. M., Conway, E. K., Hill, C., Kochanov, R., V, Tan, Y., Wcislo, P., Finenko, A. A., Nelson, K., Bernath, P. F., Birk, M., Boudon, V, Campargue, A., Chance, K., V, Coustenis, A., Drouin, B. J., Flaud, J-M, Gamache, R. R., Hodges, J. T., Jacquemart, D., Mlawer, E. J., Nikitin, A., V, Perevalov, V., I, Rotger, M., Tennyson, J., Toon, G. C., Tran, H., Tyuterev, V. G., Adkins, E. M., Baker, A., Barbe, A., Cane, E., Csaszar, A. G., Dudaryonok, A., Egorov, O., Fleisher, A. J., Fleurbaey, H., Foltynowicz, A., Furtenbacher, T., Harrison, J. J., Hartmann, J-M, Horneman, V-M, Huang, X., Karman, T., Karns, J., Kassi, S., Kleiner, I, Kofman, V, Kwabia-Tchana, F., Lavrentieva, N. N., Lee, T. J., Long, D. A., Lukashevskaya, A. A., Lyulin, O. M., Makhnev, V. Yu, Matt, W., Massie, S. T., Melosso, M., Mikhailenko, S. N., Mondelain, D., Mueller, H. S. P., Naumenko, O., V, Perrin, A., Polyansky, O. L., Raddaoui, E., Raston, P. L., Reed, Z. D., Rey, M., Richard, C., Tobias, R., Sadiek, I, Schwenke, D. W., Starikova, E., Sung, K., Tamassia, F., Tashkun, S. A., Vander Auwera, J., Vasilenko, I. A., Vigasin, A. A., Villanueva, G. L., Vispoel, B., Wagner, G., Yachmenev, A., Yurchenko, S. N., Gordon, I. E., Rothman, L. S., Hargreaves, R. J., Hashemi, R., Karlovets, E., V, Skinner, F. M., Conway, E. K., Hill, C., Kochanov, R., V, Tan, Y., Wcislo, P., Finenko, A. A., Nelson, K., Bernath, P. F., Birk, M., Boudon, V, Campargue, A., Chance, K., V, Coustenis, A., Drouin, B. J., Flaud, J-M, Gamache, R. R., Hodges, J. T., Jacquemart, D., Mlawer, E. J., Nikitin, A., V, Perevalov, V., I, Rotger, M., Tennyson, J., Toon, G. C., Tran, H., Tyuterev, V. G., Adkins, E. M., Baker, A., Barbe, A., Cane, E., Csaszar, A. G., Dudaryonok, A., Egorov, O., Fleisher, A. J., Fleurbaey, H., Foltynowicz, A., Furtenbacher, T., Harrison, J. J., Hartmann, J-M, Horneman, V-M, Huang, X., Karman, T., Karns, J., Kassi, S., Kleiner, I, Kofman, V, Kwabia-Tchana, F., Lavrentieva, N. N., Lee, T. J., Long, D. A., Lukashevskaya, A. A., Lyulin, O. M., Makhnev, V. Yu, Matt, W., Massie, S. T., Melosso, M., Mikhailenko, S. N., Mondelain, D., Mueller, H. S. P., Naumenko, O., V, Perrin, A., Polyansky, O. L., Raddaoui, E., Raston, P. L., Reed, Z. D., Rey, M., Richard, C., Tobias, R., Sadiek, I, Schwenke, D. W., Starikova, E., Sung, K., Tamassia, F., Tashkun, S. A., Vander Auwera, J., Vasilenko, I. A., Vigasin, A. A., Villanueva, G. L., Vispoel, B., Wagner, G., Yachmenev, A., and Yurchenko, S. N.

Abstract

The HITRAN database is a compilation of molecular spectroscopic parameters. It was established in the early 1970s and is used by various computer codes to predict and simulate the transmission and emission of light in gaseous media (with an emphasis on terrestrial and planetary atmospheres). The HITRAN compilation is composed of five major components: the line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, experimental infrared absorption cross-sections (for molecules where it is not yet feasible for representation in a line-by-line form), collision-induced absorption data, aerosol indices of refraction, and general tables (including partition sums) that apply globally to the data. This paper describes the contents of the 2020 quadrennial edition of HITRAN. The HITRAN2020 edition takes advantage of recent experimental and theoretical data that were meticulously validated, in particular, against laboratory and atmospheric spectra. The new edition replaces the previous HITRAN edition of 2016 (including its updates during the intervening years). All five components of HITRAN have undergone major updates. In particular, the extent of the updates in the HITRAN2020 edition range from updating a few lines of specific molecules to complete replacements of the lists, and also the introduction of additional isotopologues and new (to HITRAN) molecules: SO, CH3F, GeH4, CS2, CH3I and NF3. Many new vibrational bands were added, extending the spectral coverage and completeness of the line lists. Also, the accuracy of the parameters for major atmospheric absorbers has been increased substantially, often featuring sub-percent uncertainties. Broadening parameters associated with the ambient pressure of water vapor were introduced to HITRAN for the first time and are now available for several molecules. The HITRAN2020 edition continues to take advantage of the relational structure and efficient interface available at www.hitran.org and the HITR

Published
2022

3. The HITRAN2020 molecular spectroscopic database

Author

Gordon, I. E. (I. E.), Rothman, L. S. (L. S.), Hargreaves, R. J. (R. J.), Hashemi, R. (R.), Karlovets, E. V. (E., V), Skinner, F. M. (F. M.), Conway, E. K. (E. K.), Hill, C. (C.), Kochanov, R. V. (R., V), Tan, Y. (Y.), Wcislo, P. (P.), Finenko, A. A. (A. A.), Nelson, K. (K.), Bernath, P. F. (P. F.), Birk, M. (M.), Boudon, V. (V), Campargue, A. (A.), Chance, K. V. (K., V), Coustenis, A. (A.), Drouin, B. J. (B. J.), Flaud, J.-M. (J-M), Gamache, R. R. (R. R.), Hodges, J. T. (J. T.), Jacquemart, D. (D.), Mlawer, E. J. (E. J.), Nikitin, A. V. (A., V), Perevalov, V. I. (V., I), Rotger, M. (M.), Tennyson, J. (J.), Toon, G. C. (G. C.), Tran, H. (H.), Tyuterev, V. G. (V. G.), Adkins, E. M. (E. M.), Baker, A. (A.), Barbe, A. (A.), Cane, E. (E.), Csaszar, A. G. (A. G.), Dudaryonok, A. (A.), Egorov, O. (O.), Fleisher, A. J. (A. J.), Fleurbaey, H. (H.), Foltynowicz, A. (A.), Furtenbacher, T. (T.), Harrison, J. J. (J. J.), Hartmann, J.-M. (J-M), Horneman, V.-M. (V-M), Huang, X. (X.), Karman, T. (T.), Karns, J. (J.), Kassi, S. (S.), Kleiner, I. (I), Kofman, V. (V), Kwabia-Tchana, F. (F.), Lavrentieva, N. N. (N. N.), Lee, T. J. (T. J.), Long, D. A. (D. A.), Lukashevskaya, A. A. (A. A.), Lyulin, O. M. (O. M.), Makhnev, V. Y. (V. Yu), Matt, W. (W.), Massie, S. T. (S. T.), Melosso, M. (M.), Mikhailenko, S. N. (S. N.), Mondelain, D. (D.), Mueller, H. S. (H. S. P.), Naumenko, O. V. (O., V), Perrin, A. (A.), Polyansky, O. L. (O. L.), Raddaoui, E. (E.), Raston, P. L. (P. L.), Reed, Z. D. (Z. D.), Rey, M. (M.), Richard, C. (C.), Tobias, R. (R.), Sadiek, I. (I), Schwenke, D. W. (D. W.), Starikova, E. (E.), Sung, K. (K.), Tamassia, F. (F.), Tashkun, S. A. (S. A.), Vander Auwera, J. (J.), Vasilenko, I. A. (I. A.), Vigasin, A. A. (A. A.), Villanueva, G. L. (G. L.), Vispoel, B. (B.), Wagner, G. (G.), Yachmenev, A. (A.), Yurchenko, S. N. (S. N.), Gordon, I. E. (I. E.), Rothman, L. S. (L. S.), Hargreaves, R. J. (R. J.), Hashemi, R. (R.), Karlovets, E. V. (E., V), Skinner, F. M. (F. M.), Conway, E. K. (E. K.), Hill, C. (C.), Kochanov, R. V. (R., V), Tan, Y. (Y.), Wcislo, P. (P.), Finenko, A. A. (A. A.), Nelson, K. (K.), Bernath, P. F. (P. F.), Birk, M. (M.), Boudon, V. (V), Campargue, A. (A.), Chance, K. V. (K., V), Coustenis, A. (A.), Drouin, B. J. (B. J.), Flaud, J.-M. (J-M), Gamache, R. R. (R. R.), Hodges, J. T. (J. T.), Jacquemart, D. (D.), Mlawer, E. J. (E. J.), Nikitin, A. V. (A., V), Perevalov, V. I. (V., I), Rotger, M. (M.), Tennyson, J. (J.), Toon, G. C. (G. C.), Tran, H. (H.), Tyuterev, V. G. (V. G.), Adkins, E. M. (E. M.), Baker, A. (A.), Barbe, A. (A.), Cane, E. (E.), Csaszar, A. G. (A. G.), Dudaryonok, A. (A.), Egorov, O. (O.), Fleisher, A. J. (A. J.), Fleurbaey, H. (H.), Foltynowicz, A. (A.), Furtenbacher, T. (T.), Harrison, J. J. (J. J.), Hartmann, J.-M. (J-M), Horneman, V.-M. (V-M), Huang, X. (X.), Karman, T. (T.), Karns, J. (J.), Kassi, S. (S.), Kleiner, I. (I), Kofman, V. (V), Kwabia-Tchana, F. (F.), Lavrentieva, N. N. (N. N.), Lee, T. J. (T. J.), Long, D. A. (D. A.), Lukashevskaya, A. A. (A. A.), Lyulin, O. M. (O. M.), Makhnev, V. Y. (V. Yu), Matt, W. (W.), Massie, S. T. (S. T.), Melosso, M. (M.), Mikhailenko, S. N. (S. N.), Mondelain, D. (D.), Mueller, H. S. (H. S. P.), Naumenko, O. V. (O., V), Perrin, A. (A.), Polyansky, O. L. (O. L.), Raddaoui, E. (E.), Raston, P. L. (P. L.), Reed, Z. D. (Z. D.), Rey, M. (M.), Richard, C. (C.), Tobias, R. (R.), Sadiek, I. (I), Schwenke, D. W. (D. W.), Starikova, E. (E.), Sung, K. (K.), Tamassia, F. (F.), Tashkun, S. A. (S. A.), Vander Auwera, J. (J.), Vasilenko, I. A. (I. A.), Vigasin, A. A. (A. A.), Villanueva, G. L. (G. L.), Vispoel, B. (B.), Wagner, G. (G.), Yachmenev, A. (A.), and Yurchenko, S. N. (S. N.)

Abstract

The HITRAN database is a compilation of molecular spectroscopic parameters. It was established in the early 1970s and is used by various computer codes to predict and simulate the transmission and emission of light in gaseous media (with an emphasis on terrestrial and planetary atmospheres). The HITRAN compilation is composed of five major components: the line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, experimental infrared absorption cross-sections (for molecules where it is not yet feasible for representation in a line-by-line form), collision-induced absorption data, aerosol indices of refraction, and general tables (including partition sums) that apply globally to the data. This paper describes the contents of the 2020 quadrennial edition of HITRAN. The HITRAN2020 edition takes advantage of recent experimental and theoretical data that were meticulously validated, in particular, against laboratory and atmospheric spectra. The new edition replaces the previous HITRAN edition of 2016 (including its updates during the intervening years). All five components of HITRAN have undergone major updates. In particular, the extent of the updates in the HITRAN2020 edition range from updating a few lines of specific molecules to complete replacements of the lists, and also the introduction of additional isotopologues and new (to HITRAN) molecules: SO, CH₃F, GeH₄, CS₂, CH₃I and NF₃. Many new vibrational bands were added, extending the spectral coverage and completeness of the line lists. Also, the accuracy of the parameters for major atmospheric absorbers has been increased substantially, often featuring sub-percent uncertainties. Broadening parameters associated with the ambient pressure of water vapor were introduced to HITRAN for the first time and are now available for several molecules. The HITRAN2020 edition continues to take advantage of the relational structure and efficient interface available at www.hitran.org and

Published
2022

4. On the Development of a New Nonequilibrium Chemistry Model for Mars Entry

Author

Jaffe, R. L, Schwenke, D. W, Chaban, G. M, Prabhu, D. K, Johnston, C. O, and Panesi, M

Subjects
Atomic And Molecular Physics, Inorganic, Organic And Physical Chemistry, Astronautics (General)
Abstract

This paper represents an on-going effort at NASA Ames Research Center to develop a physics-based nonequilibrium model for hypersonic entry into the Martian atmosphere.

Published
2017

5. Die photochemische Bildung des Chlorwasserstoffs Dynamics of Cl + H2 ⇌ HC1 + H on a New Potential Energy Surface: The Photosynthesis of Hydrogen Chloride Revisited 100 Years after Max Bodenstein

Author

Allison, T. C., Mielke, S. L., Schwenke, D. W., Lynch, G. C., Gordon, M. S., Truhlar, D. G., Goidanskii, Vitalii I., editor, Schäfer, Fritz Peter, editor, Toennies, J. Peter, editor, Lotsch, Helmut K. V., editor, Wolfrum, J., editor, Volpp, H.-R., editor, Rannacher, R., editor, and Warnatz, J., editor

Published
1996
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7. Vibrational energy levels for CH4 from an ab initio potential

Author

Schwenke, D. W and Partridge, H

Subjects
Life Sciences (General)
Abstract

Many areas of astronomy and astrophysics require an accurate high temperature spectrum of methane (CH4). The goal of the present research is to determine an accurate ab initio potential energy surface (PES) for CH4. As a first step towards this goal, we have determined a PES including up to octic terms. We compare our results with experiment and to a PES based on a quartic expansion. Our octic PES gives good agreement with experiment for all levels, while the quartic PES only for the lower levels.

Published
2001
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8. Anomalous Symmetries Of The Rovibrational Levels of HO2: Consequences Of A Conical Intersection

Author

Barclay, V. J, Dateo, C. E, Hamilton, I. P, Kendrick, B, Pack, R. T, Schwenke, D. W, and Langhoff, Stephen R

Subjects
Atomic And Molecular Physics
Abstract

We show that the geometric phase arising from a conical intersection of the lowest potential energy surfaces of HO2 causes its bending vibrational wavefunctions to be double valued, which allows them to be locally symmetric on one side of the intersection and locally antisymmetric on the other. The material of the proposed publication was reviewed and the technical content will not reveal any information not already in the public domain and will not give any foreign industry or government a competitive advantage.

Published
1995

10. High-accuracy ab initio rotation-vibration transitions for water

Author

Polyansky, O. L., Császár, A. G., Shirin, S. V., Zobov, N. F., Barletta, P., Tennyson, J., Schwenke, D. W., and Knowles, P. J.

Abstract

The spectrum of water vapor is of fundamental importance for a variety of processes, including the absorption and retention of sunlight in Earth's atmosphere. Therefore, there has long been an urgent need for a robust and accurate predictive model for this spectrum. In our work on the high-resolution spectrum of water, we report first-principles calculations that approach experimental accuracy. To achieve this, we performed exceptionally large electronic structure calculations and considered a variety of effects, including quantum electrodynamics, which have routinely been neglected in studies of small many-electron molecules. The high accuracy of the resulting ab initio procedure is demonstrated for the main isotopomers of water.

Published
2003

12. Construction of a coarse-grain quasi-classical trajectory method. I. Theory and application to N2–N2 system.

Author

Macdonald, R. L., Jaffe, R. L., Schwenke, D. W., and Panesi, M.

Subjects
NONEQUILIBRIUM thermodynamics, CHEMICAL systems, CHEMICAL reduction, VIBRATIONAL spectra, MAXWELL-Boltzmann distribution law
Abstract

This work aims to construct a reduced order model for energy transfer and dissociation in non-equilibrium nitrogen mixtures. The objective is twofold: to present the Coarse-Grain Quasi-Classical Trajectory (CG-QCT) method, a novel framework for constructing a reduced order model for diatom-diatom systems; and to analyze the physics of non-equilibrium relaxation of the nitrogen molecules undergoing dissociation in an ideal chemical reactor. The CG-QCT method couples the construction of the reduced order model under the coarse-grain model framework with the quasi-classical trajectory calculations to directly construct the reduced model without the need for computing the individual rovibrational specific kinetic data. In the coarse-grain model, the energy states are lumped together into groups containing states with similar properties, and the distribution of states within each of these groups is prescribed by a Boltzmann distribution at the local translational temperature. The required grouped kinetic properties are obtained directly by the QCT calculations. Two grouping strategies are considered: energy-based grouping, in which states of similar internal energy are lumped together, and vibrational grouping, in which states with the same vibrational quantum number are grouped together. A zero-dimensional chemical reactor simulation, in which the molecules are instantaneously heated, forcing the system into strong non-equilibrium, is used to study the differences between the two grouping strategies. The comparison of the numerical results against available experimental data demonstrates that the energy-based grouping is more suitable to capture dissociation, while the energy transfer process is better described with a vibrational grouping scheme. The dissociation process is found to be strongly dependent on the behavior of the high energy states, which contribute up to 50% of the dissociating molecules. Furthermore, up to 40% of the energy required to dissociate the molecules comes from the rotational mode, underscoring the importance of accounting for this mode when constructing non-equilibrium kinetic models. In contrast, the relaxation process is governed primarily by low energy states, which exhibit significantly slower transitions in the vibrational binning model due to the prevalence of mode separation in these states. [ABSTRACT FROM AUTHOR]

Published
2018
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13. Quantum mechanical calculations of vibrational population inversion in chemical reactions - Numerically exact L-squared-amplitude-density study of the H2Br reactive system

Author

Zhang, Y. C, Zhang, J. Z. H, Kouri, D. J, Haug, K, and Schwenke, D. W

Subjects
Lasers And Masers
Abstract

Numerically exact, fully three-dimensional quantum mechanicl reactive scattering calculations are reported for the H2Br system. Both the exchange (H + H-prime Br to H-prime + HBr) and abstraction (H + HBR to H2 + Br) reaction channels are included in the calculations. The present results are the first completely converged three-dimensional quantum calculations for a system involving a highly exoergic reaction channel (the abstraction process). It is found that the production of vibrationally hot H2 in the abstraction reaction, and hence the extent of population inversion in the products, is a sensitive function of initial HBr rotational state and collision energy.

Published
1988
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14. On the Enthalpy of Formation of Hydroxyl Radical and Gas-Phase Bond Dissociation Energies of Water and Hydroxyl

Author

Ruscic, B., Wagner, A. F., Harding, L. B., Asher, R. L., Feller, D., Dixon, D. A., Peterson, K. A., Song, Y., Qian, X., Ng, C.-Y., Liu, J., Chen, W., and Schwenke, D. W.

Abstract

In a recent letter (J. Phys. Chem. A, 2001, 105,1), we argued that, although all major thermochemical tables recommend a value of %@mt;sys@%Δ%@ital@%H%@rsf@%%@/xs;55;%lnwidth@%°%@/xs;63;(%lnwidth-x55)@%%@mh;-x63@%%@sb@%f0%@sbx@%%@mx@% (OH) based on a spectroscopic approach, the correct value is 0.5 kcal/mol lower as determined from an ion cycle. In this paper, we expand upon and augment both the experimental and theoretical arguments presented in the letter. In particular, three separate experiments (mass-selected photoionization measurements, pulsed-field-ionization photoelectron spectroscopy measurements, and photoelectron-photoion coincidence measurements) utilizing the positive ion cycle to derive the O−H bond energy are shown to converge to a consensus value of the appearance energy AE0(OH+/H2O) = 146117 ± 24 cm-1 (18.1162 ± 0.0030 eV). With the most accurate currently available zero kinetic energy photoionization value for the ionization energy IE(OH) = 104989 ± 2 cm-1, corroborated by a number of photoelectron measurements, this leads to D0(H−OH) = 41128 ± 24 cm-1 = 117.59 ± 0.07 kcal/mol. This corresponds to ΔHf0(OH) = 8.85 ± 0.07 kcal/mol and implies D0(OH) = 35593 ± 24 cm-1 = 101.76 ± 0.07 kcal/mol. These results are completely supported by the most sophisticated theoretical calculations ever performed on the HxO system, CCSD(T)/aug-cc-pVnZ, n = Q, 5, 6, and 7, extrapolated to the CBS limit and including corrections for core-valence effects, scalar relativistic effects, incomplete correlation recovery, and diagonal Born−Oppenheimer corrections. These calculations have an estimated theoretical error of ≤0.2 kcal/mol based on basis set convergence properties. They reproduce the experimental results for dissociation energies, atomization energies, and ionization energies for the HxO system to within 0.0−0.2 kcal/mol. In contrast, the previously accepted values of the two successive bond dissociation energies of water differ from the current values by 0.5 kcal/mol. These values were derived from the spectroscopic determinations of D0(OH) using a very short Birge−Sponer extrapolation on OH/OD A1Σ+. However, on the basis of a calculation of the A state potential energy curve (with a multireference single and double excitation wave function and an aug-cc-pV5Z basis set) and an exhaustive reanalyzis of the original measured data on both the A and B states of OH, the Birge−Sponer extrapolation can be demonstrated to significantly underestimate the bond dissociation energy, although only the last vibrational level was not observed experimentally. The recommended values of this paper affect a large number of other thermochemical quantities which directly or indirectly rely on or refer to D0(H−OH), D0(OH), or %@mt;sys@%Δ%@ital@%H%@rsf@%%@/xs;55;%lnwidth@%°%@/xs;63;(%lnwidth-x55)@%%@mh;-x63@%%@sb@%f%@sbx@%%@/hd@%%@fn;(;vis;full;auto@%OH%@fnx;);vis;full@%%@/hd@%%@mx@% . This is illustrated by an analysis of several reaction enthalpies, deprotonation enthalpies, and proton affinities.

Published
2002
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15. Beyond the Potential Energy Surface:  Ab initio Corrections to the Born−Oppenheimer Approximation for H<INF>2</INF>O

Author

Schwenke, D. W.

Abstract

It is customary when computing ro−vibrational transitions in molecules to invoke the Born−Oppenheimer separation between nuclear and electronic motion. However, it is known from accurate calculations on H2+ and H2 that the first-order (diagonal adiabatic) and second-order (nonadiabatic) corrections are not negligible and are both important. In the present work, we have made an ab initio implementation of the Bunker and Moss formalism for the nonadiabatic correction and applied it to H2 and H2O. From comparison to accurate calculations for H2, we find that we can obtain good results for the nonadiabatic correction using CI singles to treat the electronically excited states if we scale the results, but we must go beyond the SCF approximation to obtain an accurate diagonal adiabatic correction. For H2O, we find that the first-order correction is more important than the second-order correction for bending energy levels, but the second-order correction is more important than the first-order correction for stretching energy levels. The correction to rotational levels is also significant. Thus, first- and second-order corrections are vital for accurate ab initio predictions of transition frequencies.

Published
2001

18. Do Semiclassical Trajectory Theories Provide an Accurate Picture of Radiationless Decay for Systems with Accessible Surface Crossings?

Author

Hack, M. D., Jasper, A. W., Volobuev, Y. L., Schwenke, D. W., and Truhlar, D. G.

Abstract

We present quantum mechanical and semiclassical calculations of Feshbach funnel resonances that correspond to long-lived exciplexes in the à 2B2 state of NaH2. These exciplexes decay to the ground state, &Xtilde; 2A1, by a surface crossing in C2v geometry. The quantum mechanical lifetimes and the branching probabilities for competing decay mechanisms are computed for two different NaH2 potential energy matrices, and we explain the results in terms of features of the potential energy matrices. We compare the quantum mechanical calculations of the lifetimes and the average vibrational and rotational quantum numbers of the decay product, H2, to two kinds of semiclassical trajectory calculations:  the trajectory surface hopping method and the Ehrenfest self-consistent potential method (also called the time-dependent self-consistent field method). The trajectory surface hopping calculations use Tully's fewest switches algorithm and two different prescriptions for adjusting the momentum during a hop. Both the adiabatic and the diabatic representations are used for the trajectory surface hopping calculations. We show that the diabatic surface hopping calculations agree better with the quantum mechanical calculations than the adiabatic surface hopping calculations or the Ehrenfest calculations do for one potential energy matrix, and the adiabatic surface hopping calculations agree best with the quantum mechanical calculations for the other potential energy matrix. We test three criteria for predicting which representation is most accurate for surface hopping calculations. We compare the ability of the semiclassical methods to accurately reproduce the quantum mechanical trends between the two potential matrices, and we review other recent comparisons of semiclassical and quantum mechanical calculations for a variety of potential matrices. On the basis of the evidence so far accumulated, we conclude that for general three-dimensional two-state systems, Tully's fewest switches method is the most accurate semiclassical method currently available if (i) one uses the nonadiabatic coupling vector as the hopping vector and (ii) one propagates the trajectories in the representation that minimizes the number of surface hops.

Published
2000

20. Quantum Mechanical and Quasiclassical Trajectory Surface Hopping Studies of the Electronically Nonadiabatic Predissociation of the à State of NaH<INF>2</INF>

Author

Hack, M. D., Jasper, A. W., Volobuev, Y. L., Schwenke, D. W., and Truhlar, D. G.

Abstract

Fully coupled quantum mechanical scattering calculations and adiabatic uncoupled bound-state calculations are used to identify Feshbach funnel resonances that correspond to long-lived exciplexes in the à state of NaH2, and the scattering calculations are used to determine their partial and total widths. The total widths determine the lifetimes, and the partial widths determine the branching probabilities for competing decay mechanisms. We compare the quantum mechanical calculations of the resonance lifetimes and the average final vibrational and rotational quantum numbers of the decay product, H2(ν‘, j‘), to trajectory surface hopping calculations carried out by various prescriptions for the hopping event. Tully's fewest switches algorithm is used for the trajectory surface hopping calculations, and we present a new strategy for adaptive stepsize control that dramatically improves the convergence of the numerical propagation of the solution of the coupled classical and quantum mechanical differential equations. We performed the trajectory surface hopping calculations with four prescriptions for the hopping vector that is used for adjusting the momentum at hopping events. These include changing the momentum along the nonadiabatic coupling vector (d), along the gradient of the difference in the adiabatic energies of the two states (g), and along two new vectors that we describe as the rotated-d and the rotated-g vectors. We show that the dynamics obtained from the d and g prescriptions are significantly different from each other, and we show that the d prescription agrees better with the quantum results. The results of the rotated methods show systematic deviations from the nonrotated results, and in general, the error of the nonrotated methods is smaller. The nonrotated TFS-d method is thus the most accurate method for this system, which was selected for detailed study precisely because it is more sensitive to the choice of hopping vector than previously studied systems.

Published
1999

21. Transition State Resonances in the Reaction Cl + H<INF>2</INF> → HCl + H

Author

Srinivasan, J., Allison, T. C., Schwenke, D. W., and Truhlar, D. G.

Abstract

This paper discusses converged quantum mechanical scattering calculations for the reaction Cl + H2 → HCl + H and its reverse and analyzes them for the properties of quantized dynamical bottlenecks controlling the total and state-specific microcanonical-ensemble rate constants. These rate constants show clear evidence for quantized transition states. We assign bend and stretch quantum numbers to the transition states for total angular momentum J = 0 with parity P = +1, for J = 1 with P = +1 and −1, and for J = 2 and 6 with P = +1. Then, state-specific densities of reactive states (transition state spectra) are examined to obtain a detailed picture of the reaction. A quantal estimate of the rotational constant, B, for several different transition states is obtained by comparing transition state energies at different values of the total angular momentum. These quantal estimates are in good agreement with the values calculated from the moments of inertia, and this enables us to interpret the results in terms of state-dependent geometries for the individual dynamical bottlenecks. By treating the transition states as poles in the scattering matrix, we also obtain estimates for the lifetimes of the states. The JP-specific rate coefficients, the reactant-state-specific rate coefficients, and the contribution from each transition state to the JP-specific and the reactant-state-specified rate coefficient are also calculated and the trends analyzed. These trends help explain the dependence of the rate coefficient on initial vibrational and rotational quantum numbers.

Published
1999

22. Test of Trajectory Surface Hopping Against Accurate Quantum Dynamics for an Electronically Nonadiabatic Chemical Reaction

Author

Topaler, M. S., Allison, T. C., Schwenke, D. W., and Truhlar, D. G.

Abstract

This paper presents the first test of the popular trajectory surface-hopping (TSH) method against accurate three-dimensional quantum mechanics for a reactive system. The system considered is a model system in which an excited atom with an excitation energy of 0.76 eV reacts with or is quenched by the H2 molecule. The electronically nonadiabatic collisions occur primarily near a conical intersection of an exciplex with a repulsive ground state. The accurate quantal results are calculated using the outgoing wave variational principle in an electronically diabatic representation. Four variants of the TSH method are tested, differing in the criteria for hopping and the component of momentum that is adjusted in order to conserve energy when a hop occurs. Coupling between the ground and excited surface occurs primarily in the vicinity of a conical intersection and is mediated by an exciplex found on the upper surface. We find that the overall TSH quenching probabilities are in good agreement with quantum mechanical results, but the branching ratios between reactive and nonreactive trajectories and many of the state-selected results are poorly reproduced by trajectory calculations. The agreement between trajectory surface hopping and quantal results is on average worse for the relatively more “quantum mechanical” j = 0 initial state and M + H2 quenching process and better for the relatively more “classical” j = 2 initial state and MH + H‘ reactive process. We also perform a statistical calculation of overall quenching probability and unimolecular rate of the nonadiabatic decay of the exciplex. We find that only about 10 % of trajectories can be described as “statistical” and that statistical calculation overestimates the total quenching rate significantly.

Published
1998

34. Construction of a coarse-grain quasi-classical trajectory method. I. Theory and application to N 2 -N 2 system.

Author

Macdonald RL, Jaffe RL, Schwenke DW, and Panesi M

Abstract

This work aims to construct a reduced order model for energy transfer and dissociation in non-equilibrium nitrogen mixtures. The objective is twofold: to present the Coarse-Grain Quasi-Classical Trajectory (CG-QCT) method, a novel framework for constructing a reduced order model for diatom-diatom systems; and to analyze the physics of non-equilibrium relaxation of the nitrogen molecules undergoing dissociation in an ideal chemical reactor. The CG-QCT method couples the construction of the reduced order model under the coarse-grain model framework with the quasi-classical trajectory calculations to directly construct the reduced model without the need for computing the individual rovibrational specific kinetic data. In the coarse-grain model, the energy states are lumped together into groups containing states with similar properties, and the distribution of states within each of these groups is prescribed by a Boltzmann distribution at the local translational temperature. The required grouped kinetic properties are obtained directly by the QCT calculations. Two grouping strategies are considered: energy-based grouping, in which states of similar internal energy are lumped together, and vibrational grouping, in which states with the same vibrational quantum number are grouped together. A zero-dimensional chemical reactor simulation, in which the molecules are instantaneously heated, forcing the system into strong non-equilibrium, is used to study the differences between the two grouping strategies. The comparison of the numerical results against available experimental data demonstrates that the energy-based grouping is more suitable to capture dissociation, while the energy transfer process is better described with a vibrational grouping scheme. The dissociation process is found to be strongly dependent on the behavior of the high energy states, which contribute up to 50% of the dissociating molecules. Furthermore, up to 40% of the energy required to dissociate the molecules comes from the rotational mode, underscoring the importance of accounting for this mode when constructing non-equilibrium kinetic models. In contrast, the relaxation process is governed primarily by low energy states, which exhibit significantly slower transitions in the vibrational binning model due to the prevalence of mode separation in these states.

Published
2018
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