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Title: Experimental and Theoretical Studies of the F + H–F Transition-State Region by Photodetachment of [F–H–F] -

Abstract

The transition-state (TS) region of the simplest heavy-light-heavy type of reaction, F• + H-F F-H + F•, is investigated in this work by a joint experimental and theoretical approach. Photodetaching the bifluride anion, [F…H…F]–, generates a negative ion photoelectron (NIPE) spectrum with three partially resolved bands in the electron binding energy (eBE) range of 5.4 – 7.0 eV. These bands correspond to the transition from the ground state of the anion to the electronic ground state of [F-H-F]• neutral, with associated vibrational excitations. The significant increase of eBE of the bifluride anion, relative to that of F-, reflects a hydrogen bond energy between F- and HF of 46 kcal/mol. Theoretical modeling reveals that the antisymmetric motion of H between the two F atoms, near the TS on the neutral [F-H-F]• surface, dominates the observed three bands, while the F-H-F bending, F—F symmetric stretching modes, and the couplings between them is calculated to account for the breadth of the observed spectrum. From the NIPE spectrum, a lower limit on the activation enthalpy for F• + H-F F-H + F can be estimated to be H‡ = 12 ± 2 kcal/mol, a value below that of H‡ = 14.9 kcal/mol, given bymore » our G4 calculations.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]
  1. Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, MS K8-88, Richland, Washington 99352, United States
  2. Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
  3. Department of Chemistry and the Center for Advanced Scientific Computing and Modeling, University of North Texas, 1155 Union Circle, #305070, Denton, Texas 76203-5017, United States
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1411900
Report Number(s):
PNNL-SA-128287
Journal ID: ISSN 1089-5639; KC0301050
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory; Journal Volume: 121; Journal Issue: 41
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Hou, Gao-Lei, Wang, Xue-Bin, McCoy, Anne B., and Borden, Weston Thatcher. Experimental and Theoretical Studies of the F • + H–F Transition-State Region by Photodetachment of [F–H–F] -. United States: N. p., 2017. Web. doi:10.1021/acs.jpca.7b07682.
Hou, Gao-Lei, Wang, Xue-Bin, McCoy, Anne B., & Borden, Weston Thatcher. Experimental and Theoretical Studies of the F • + H–F Transition-State Region by Photodetachment of [F–H–F] -. United States. doi:10.1021/acs.jpca.7b07682.
Hou, Gao-Lei, Wang, Xue-Bin, McCoy, Anne B., and Borden, Weston Thatcher. Thu . "Experimental and Theoretical Studies of the F • + H–F Transition-State Region by Photodetachment of [F–H–F] -". United States. doi:10.1021/acs.jpca.7b07682.
@article{osti_1411900,
title = {Experimental and Theoretical Studies of the F • + H–F Transition-State Region by Photodetachment of [F–H–F] -},
author = {Hou, Gao-Lei and Wang, Xue-Bin and McCoy, Anne B. and Borden, Weston Thatcher},
abstractNote = {The transition-state (TS) region of the simplest heavy-light-heavy type of reaction, F• + H-F F-H + F•, is investigated in this work by a joint experimental and theoretical approach. Photodetaching the bifluride anion, [F…H…F]–, generates a negative ion photoelectron (NIPE) spectrum with three partially resolved bands in the electron binding energy (eBE) range of 5.4 – 7.0 eV. These bands correspond to the transition from the ground state of the anion to the electronic ground state of [F-H-F]• neutral, with associated vibrational excitations. The significant increase of eBE of the bifluride anion, relative to that of F-, reflects a hydrogen bond energy between F- and HF of 46 kcal/mol. Theoretical modeling reveals that the antisymmetric motion of H between the two F atoms, near the TS on the neutral [F-H-F]• surface, dominates the observed three bands, while the F-H-F bending, F—F symmetric stretching modes, and the couplings between them is calculated to account for the breadth of the observed spectrum. From the NIPE spectrum, a lower limit on the activation enthalpy for F• + H-F F-H + F can be estimated to be H‡ = 12 ± 2 kcal/mol, a value below that of H‡ = 14.9 kcal/mol, given by our G4 calculations.},
doi = {10.1021/acs.jpca.7b07682},
journal = {Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory},
number = 41,
volume = 121,
place = {United States},
year = {Thu Oct 05 00:00:00 EDT 2017},
month = {Thu Oct 05 00:00:00 EDT 2017}
}
  • The transition state region of the F+H[sub 2] reaction is studied by photoelectron spectroscopy of FH[sub 2][sup [minus]]. The photoelectron spectra consist of overlapping electronic bands with different angular distributions. The ground state band shows partially resolved features which differ depending on whether the anion is made from [ital normal] or [ital para] hydrogen. This dependence on the anion nuclear spin statistics implies that these features are due to progressions in bending levels of the neutral FH[sub 2] complex. In order to confirm this, and to determine the sensitivity of the photoelectron spectrum to the bend potential near the F+H[submore » 2] transition state, three-dimensional simulations of the FH[sub 2][sup [minus]] photoelectron spectrum were performed assuming various potential energy surfaces for the F+H[sub 2] reaction. We found that the London--Eyring--Polanyi--Sato surface proposed by Takayanagi and Sato gave better agreement than either the T5a or 5SEC surfaces. From the higher energy band, we can extract information on the F+H[sub 2] excited electronic states, and several approximate simulations on model surfaces for these states are presented.« less
  • We present measured and calculated photodetachment spectra of OHCl[sup [minus]], and we interpret the results in terms of the vibrational structure of the transition state of the O+HCl[r arrow]OH+Cl reaction. The measured spectra exhibit two distinct features---an intense broad peak at high electron kinetic energies and a less intense shoulder at lower energies. Superimposed on these broad features are several sharper structures, but they are barely discernible from noise in the spectrum. To interpret these spectra, we have used a recently developed global [sup 3][ital A][double prime] potential surface for the O+HCl reaction to calculate Franck--Condon factors, using an [italmore » L][sup 2] method (i.e., expansion in terms of square integrable basis functions) to approximate the scattering wave functions on the reactive surface. Assignment of the spectrum has been assisted using the results of quantum coupled channel calculations for the same surface. The resulting calculated spectrum shows the same broad features as the measured spectrum. There is also fine structure with spacings and energies that are similar to the experiment, but specific features do not match. To interpret both the broad and fine features in the theoretical spectrum, a hierarchical analysis is applied wherein this spectrum is decomposed by a tree construction into components of increasingly higher resolution. The physical meaning of each of these components is then determined by plotting smoothed states'' that are obtained from the tree coefficients. This leads to the conclusion that the two broad features in the spectrum are made up of progressions in hindered rotor states of the Cl--OH complex, with the most intense feature corresponding to OH([ital v]=0) and the weaker shoulder corresponding to OH([ital v]=1). There is evidence for Feshbach resonance features in the [ital v]=1 feature, but it appears that most of the fine structure is due to hindered rotor states.« less
  • The transition state region of the reaction OH + H{sub 2} {yields} H{sub 2}O + H is investigated by photoelectron spectroscopy of the H{sub 3}O{sup -} and D{sub 3}O{sup -} anions. The peaks observed in the spectra are from a combination of vibrational progressions and overlapping anion {yields} neutral electronic transitions. The photoelectron angular distributions indicate that two processes contribute to the spectra; these are assigned to photodetachment from the H{sup -}(H{sub 2}O) and OH (H{sub 2}) forms of the anion. A comparison of experiments performed in two different laboratories shows that the two forms of the ion readily interconvertmore » and that the relative populations are determined solely by the temperature of the ions. To interpret the spectra, a two-dimensional ab initio potential energy surface for the anion was constructed, wave functions for the first few vibrational levels were determined, and the photoelectron spectra were simulated using the Walch-Dunning-Schatz-Elgersma surface for the OH + H{sub 2} reaction. A comparison of the experimental and simulated spectra showed that photodetachment from the {nu} = 0 level of the anion, which is localized in the H{sup -}(H{sub 2}O) well, primarily probes the H + H{sub 2}O exit valley of the neutral surface. The {nu} = 2 level of the anion is the first with significant amplitude in the OH{sup -}(H{sub 2}) well, and photodetachment from this level probes the OH + H{sub 2} transition state region. 36 refs., 13 figs., 2 tabs.« less
  • Total state-selected and state-to-state absolute cross sections for the reactions Ar{sup +}({sup 2}{ital P}{sub 3/2,1/2})+H{sub 2}({ital X},{ital v}=0){r arrow}Ar ({sup 1}{ital S}{sub 0})+H{sup +}{sub 2}({ital {tilde X}},{ital v}{prime}) (reaction (1)), ArH{sup +}+H (reaction (2)), and H{sup +}+H+Ar (reaction (3)) have been measured in the center-of-mass collision energy {ital E}{sub c.m.} range of 0.24--19.1 eV. Absolute spin--orbit state transition total cross sections ({sigma}{sub 3/2{r arrow}1/2},{sigma}{sub 1/2{r arrow}3/2}) for the collisions of Ar{sup +}({sup 2}{ital P}{sub 3/2,1/2}) with H{sub 2} at {ital E}{sub c.m.}=1.2--19.1 eV have been obtained.
  • Accurate cumulative reaction probabilities and densities of reactive states have been obtained for the reactions F+H{sub 2}{r arrow}H+HF and F+D{sub 2}{r arrow}D+DF using the hyperspherical (APH) coordinate scattering method developed by Pack and Parker. Results for scattering energies ranging from threshold to 0.7 eV above threshold have been obtained using two different potential energy surfaces that have been proposed for this system. The predicted peaks in the densities of reactive states are due to the presence of scattering resonances. The characteristic steps in the cumulative reaction probabilities are used to identify the resonance peaks due to quantized dynamical bottlenecks. Themore » trapped-state or Feshbach-type resonances are identified by narrow oscillations in the density of reactive states. The positions of these resonance peaks in the density of reactive states are in good agreement with the peaks in the Franck--Condon factors for the photodetachment of H{sub 2}F{sup {minus}} and D{sub 2}F{sup {minus}}. Significant changes in resonance types are found for the T5a and 5SEC potential energy surfaces for H{sub 2}F. While the assignment of resonance peaks presented is in reasonable agreement with the assignments suggested by Hahn and Taylor based on their classical mechanical analysis, there are some differences that will require further study.« less