Article records
https://feeds.library.caltech.edu/people/Bowman-J-M/article.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 13:23:50 +0000Large quantum effects in the collinear F+H2-->FH+H reaction
https://resolver.caltech.edu/CaltechAUTHORS:SCHAjcp73a
Authors: {'items': [{'id': 'Schatz-G-C', 'name': {'family': 'Schatz', 'given': 'George C.'}}, {'id': 'Bowman-J-M', 'name': {'family': 'Bowman', 'given': 'Joel M.'}}, {'id': 'Kuppermann-A', 'name': {'family': 'Kuppermann', 'given': 'Aron'}}]}
Year: 1973
DOI: 10.1063/1.1679760
We have performed accurate quantum mechanical calculations of reaction probabilities for the collinear F+H2-->FH+H reaction as well as corresponding quasiclassical trajectory calculations. A comparison of these results shows that very significant quantum mechanical effects are present in this reaction.https://authors.library.caltech.edu/records/ft1mn-drw28Comparison of semiclassical, quasiclassical, and exact quantum transition probabilities for the collinear H + H2 exchange reaction
https://resolver.caltech.edu/CaltechAUTHORS:BOWjcp73
Authors: {'items': [{'id': 'Bowman-J-M', 'name': {'family': 'Bowman', 'given': 'Joel M.'}}, {'id': 'Kuppermann-A', 'name': {'family': 'Kuppermann', 'given': 'Aron'}}]}
Year: 1973
DOI: 10.1063/1.1680032
Using the classical (CSC), primitive (PSC), and uniform (USC) semiclassical expressions for transition probabilities given by Miller and co-workers, we have calculated the reactive and nonreactive 0 --> 0 and 0 --> 1 transition probabilities for the collinear H + H2 exchange reaction. Comparison with previously calculated exact quantum and quasiclassical results for the reactive and nonreactive 0 --> 0 transitions reveals that the semiclassical approximations are not very good, especially the CSC and PSC ones. All three semiclassical probabilities for the reactive 0 --> 0 transition exceed unity in the collision energy range from 0.0 to 0.2 eV above the quasiclassical reaction threshold. This feature coupled with the failure of any of the semiclassical approximations to produce the marked quantum effects present in this transition causes these results to be less accurate than the corresponding quasiclassical ones. For the reactive and nonreactive 0 --> 1 transitions the USC results are in qualitative agreement with the exact quantum ones and are better than the standard quasiclassical results. However, the reverse quasiclassical results are almost as good as the USC ones for these transitions. A probable reason for the inability of the USC expression to produce the strong oscillations observed in the exact quantum results is that the latter are due to interference between direct and resonant (i.e., compound state) processes whereas the present formulation of the semiclassical method does not encompass such phenomena. A comparison of the total reaction probabilities obtained by the USC and quasiclassical methods with the exact quantum one indicates that the USC result is more accurate than the quasiclassical one, except at collision energies less than 0.50 eV. This improved accuracy is due to a partial cancellation of errors in the contributing 0 --> 0 and 0 --> 1 USC reactive transition probabilities.https://authors.library.caltech.edu/records/1xr21-gm670Exact quantum, quasiclassical, and semiclassical reaction probabilities for the collinear F+H2 --> FH+H reaction
https://resolver.caltech.edu/CaltechAUTHORS:SCHAjcp75a
Authors: {'items': [{'id': 'Schatz-G-C', 'name': {'family': 'Schatz', 'given': 'George C.'}}, {'id': 'Bowman-J-M', 'name': {'family': 'Bowman', 'given': 'Joel M.'}}, {'id': 'Kuppermann-A', 'name': {'family': 'Kuppermann', 'given': 'Aron'}}]}
Year: 1975
DOI: 10.1063/1.431390
Exact quantum, quasiclassical, and semiclassical reaction probabilities and rate constants for the collinear reaction F+H2 --> FH+H are presented and compared. The exact quantum results indicate a large degree of population inversion of the FH product with P<sup>R</sup><sub>02</sub> and P<sup>R</sup><sub>03</sub> being the dominant reaction probabilities. The energy dependence of these two probabilities at low translational energies are quite different. P<sup>R</sup><sub>02</sub> shows an effective threshold of 0.005 eV which can largely be interpreted as resulting from tunneling through a vibrationally adiabatic barrier. P<sup>R</sup><sub>03</sub> has a much larger effective threshold (0.045 eV) apparently resulting from dynamical effects. Quasiclassical probabilities for the collinear F+H2 reaction were calculated by both the forward (initial conditions chosen for reagent F+H2) and reverse (initial conditions for product H+FH) trajectory methods. The results of both calculations correctly indicate that P<sup>R</sup><sub>03</sub> and P<sup>R</sup><sub>02</sub> should be the dominant reaction probabilities. However, the threshold behavior of the quasiclassical forward P<sup>R</sup><sub>03</sub> disagrees strongly with the corresponding exact quantum threshold energy dependence. By contrast, there is good agreement between the reversed trajectory results and the exact quantum ones. The uniform semiclassical results also agree well with the corresponding exact quantum ones indicating that the quasiclassical reverse and the semiclassical methods are preferable to the quasiclassical forward method for this reaction. The important differences between the threshold behavior of the exact quantum and quasiclassical forward reaction probabilities are manifested in the corresponding rate constants primarily as large differences in their activation energies. Additional exact quantum results at higher total energies indicate that threshold effects are no longer important for reactions with vibrationally excited H2. Resonances play an important role in certain reaction probabilities primarily at higher relative translational energies.https://authors.library.caltech.edu/records/c4x9k-c9f29Exact quantum quasiclassical, and semiclassical reaction
probabilities for the collinear F+D_2 → FD+D reaction
https://resolver.caltech.edu/CaltechAUTHORS:20120810-073044903
Authors: {'items': [{'id': 'Schatz-G-C', 'name': {'family': 'Schatz', 'given': 'George C.'}}, {'id': 'Bowman-J-M', 'name': {'family': 'Bowman', 'given': 'Joel M.'}}, {'id': 'Kuppermann-A', 'name': {'family': 'Kuppermann', 'given': 'Aron'}}]}
Year: 1975
DOI: 10.1063/1.431391
Exact quantum, quasiclassical, and semiclassical reaction probabilities and rate constants for the collinear reaction F+D_2 → FD+D are presented. In all calculations, a high degree of population inversion is predicted with P^R_(03) and P^R(04) being the dominant reaction probabilities. In analogy with the F+H_2 reaction (preceding paper), the exact quantum 0→3 and 0→4 probabilities show markedly different energy dependence with PR03 having a much smaller effective threshold energy (E_T=0.014 eV) than P^R_(04) (0.055 eV). The corresponding quasiclassical forward probabilities P^R_(03) and P^R_(04) are in poor agreement with the exact quantum ones, while their quasiclassical reverse and semiclassical counterparts provide much better approximations to the exact results. Similar comparisons are also made in the analysis of the corresponding EQ, QCF, QCR, and USC rate constants. An information theoretic analysis of the EQ and QCF reaction probabilities indicates nonlinear surprisal behavior as well as a significant isotope dependence. Additional quantum results at higher energies are presented and discussed in terms of threshold behavior and resonances. Exact quantum reaction probabilities for the related F+HD → FH+D and F+DH → FD+H reactions are given and an attempt to explain the observed isotope effects is made.https://authors.library.caltech.edu/records/31vew-5k535Equilibrium Clumped-Isotope Effects in Doubly Substituted Isotopologues of Ethane
https://resolver.caltech.edu/CaltechAUTHORS:20161024-085559620
Authors: {'items': [{'id': 'Webb-M-A', 'name': {'family': 'Webb', 'given': 'Michael A.'}, 'orcid': '0000-0002-7420-4474'}, {'id': 'Wang-Yimin', 'name': {'family': 'Wang', 'given': 'Yimin'}}, {'id': 'Braams-B-J', 'name': {'family': 'Braams', 'given': 'Bastiaan J.'}}, {'id': 'Bowman-J-M', 'name': {'family': 'Bowman', 'given': 'Joel M.'}}, {'id': 'Miller-T-F-III', 'name': {'family': 'Miller', 'given': 'Thomas F., III'}, 'orcid': '0000-0002-1882-5380'}]}
Year: 2017
DOI: 10.1016/j.gca.2016.10.001
We combine path-integral Monte Carlo methods with a new intramolecular potential energy surface to quantify the equilibrium enrichment of doubly substituted ethane isotopologues due to clumped-isotope effects. Ethane represents the simplest molecule to simultaneously exhibit ^(13)C–^(13)C, ^(13)C–D, and D–D clumped-isotope effects, and the analysis of corresponding signatures may provide useful geochemical and biogeochemical proxies of formation temperatures or reaction pathways. Utilizing path-integral statistical mechanics, we predict equilibrium fractionation factors that fully incorporate nuclear quantum effects, such as anharmonicity and rotational-vibrational coupling which are typically neglected by the widely used Urey model. The magnitude of the calculated fractionation factors for the doubly substituted ethane isotopologues indicates that isotopic clumping can be observed if rare-isotope substitutions are separated by up to three chemical bonds, but the diminishing strength of these effects suggests that enrichment at further separations will be negligible. The Urey model systematically underestimates enrichment due to ^(13)C–D and D–D clumped-isotope effects in ethane, leading to small relative errors in the apparent equilibrium temperature, ranging from 5 K at 273.15 K to 30 K at 873.15 K. We additionally note that the rotameric dependence of isotopologue enrichment must be carefully considered when using the Urey model, whereas the path-integral calculations automatically account for such effects due to configurational sampling. These findings are of direct relevance to future clumped-isotope studies of ethane, as well as studies of ^(13)C–^(13)C, ^(13)C–D, and D–D clumped-isotope effects in other hydrocarbons.https://authors.library.caltech.edu/records/c2jh2-v6q37