1
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Moonkaen P, Finney JM, McCoy AB. Isotope Effects on Ground and Excited States of Ethyl Cation, H +(C 2H 4). J Phys Chem A 2023; 127:1196-1205. [PMID: 36705480 DOI: 10.1021/acs.jpca.2c07334] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The structure and spectra of ethyl cation, H+(C2H4), and its deuterated analogues are investigated using diffusion Monte Carlo (DMC). These calculations all show that the ground state wave function for H+(C2H4) is localized near the minimum energy configuration in which the excess proton is in a bridging configuration, although the amplitude of the vibrational motions of the bridging proton is large. Deuteration of the bridging proton reduces the amplitude of this motion, while deuteration of only the ethylenic hydrogen atoms in H+(C2D4) has little effect on the amplitude of the motion of the bridging proton. Excited states that are accessed by spectroscopically observed transitions in H+(C2H4) are calculated using fixed-node DMC. The calculated and measured frequencies for the states with one quantum of excitation in the ethylenic CH stretching vibrations show good agreement. We also explore the excited state with one quantum of excitation in the proton transfer vibration of the bridging proton and obtain a frequency of 616 cm-1 for H+(C2H4). This frequency increases to 629 cm-1 in H+(C2D4). Deuteration decreases this frequency to 491 and 495 cm-1 in D+(C2H4) and D+(C2D4), respectively. The effects of partial deuteration on the frequencies of the CH stretching vibrations, and the corresponding probability amplitudes are also explored. Finally, we report the vibrationally averaged rotational constants for the four isotopologues of ethyl cation considered in this study.
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Affiliation(s)
- Pattarapon Moonkaen
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Jacob M Finney
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Anne B McCoy
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
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2
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DiRisio RJ, Finney JM, McCoy AB. Diffusion Monte Carlo approaches for studying nuclear quantum effects in fluxional molecules. WIRES COMPUTATIONAL MOLECULAR SCIENCE 2022. [DOI: 10.1002/wcms.1615] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Ryan J. DiRisio
- Department of Chemistry University of Washington Seattle Washington USA
| | - Jacob M. Finney
- Department of Chemistry University of Washington Seattle Washington USA
| | - Anne B. McCoy
- Department of Chemistry University of Washington Seattle Washington USA
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3
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DiRisio RJ, Finney JM, Dzugan LC, Madison LR, McCoy AB. Using Diffusion Monte Carlo Wave Functions to Analyze the Vibrational Spectra of H 7O 3+ and H 9O 4. J Phys Chem A 2021; 125:7185-7197. [PMID: 34433268 DOI: 10.1021/acs.jpca.1c05025] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
An approach for evaluating spectra from ground state probability amplitudes (GSPA) obtained from diffusion Monte Carlo (DMC) simulations is extended to improve the description of excited state energies and allow for coupling among vibrational excited states. This approach is applied to studies of the protonated water trimer and tetramer, and their deuterated analogs. These ions provide models for solvated hydronium, and analysis of these spectra provides insights into spectral signatures of proton transfer in aqueous environments. In this approach, we obtain a separable set of internal coordinates from the DMC ground state probability amplitude. A basis is then developed from products of the DMC ground state wave function and low-order polynomials in these internal coordinates. This approach provides a compact basis in which the Hamiltonian and dipole moment matrix are evaluated and used to obtain the spectrum. The resulting spectra are in good agreement with experiment and in many cases provide comparable agreement to the results obtained using much larger basis sets. In addition, the compact basis allows for interpretation of the spectral features and how they evolve with cluster size and deuteration.
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Affiliation(s)
- Ryan J DiRisio
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Jacob M Finney
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Laura C Dzugan
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Lindsey R Madison
- Department of Chemistry, Colby College, Waterville, Maine 04901, United States
| | - Anne B McCoy
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
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4
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DiRisio RJ, Jones CM, Ma H, Rousseau BJG. Viewpoints on the 2020 Virtual Conference on Theoretical Chemistry. J Phys Chem A 2020; 124:8875-8883. [PMID: 33054223 DOI: 10.1021/acs.jpca.0c08955] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Ryan J DiRisio
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Chey M Jones
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - He Ma
- Institute for Molecular engineering, University of Chicago, 5640 S. Ellis Avenue, Chicago, Illinois 60637, United States
| | - Benjamin J G Rousseau
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
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5
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McDonald DC, Rittgers BM, Theis RA, Fortenberry RC, Marks JH, Leicht D, Duncan MA. Infrared spectroscopy and anharmonic theory of H 3 +Ar 2,3 complexes: The role of symmetry in solvation. J Chem Phys 2020; 153:134305. [PMID: 33032436 DOI: 10.1063/5.0023205] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The vibrational spectra of H3 +Ar2,3 and D3 +Ar2,3 are investigated in the 2000 cm-1 to 4500 cm-1 region through a combination of mass-selected infrared laser photodissociation spectroscopy and computational work including the effects of anharmonicity. In the reduced symmetry of the di-argon complex, vibrational activity is detected in the regions of both the symmetric and antisymmetric hydrogen stretching modes of H3 +. The tri-argon complex restores the D3h symmetry of the H3 + ion, with a concomitant reduction in the vibrational activity that is limited to the region of the antisymmetric stretch. Throughout these spectra, additional bands are detected beyond those predicted with harmonic vibrational theory. Anharmonic theory is able to reproduce some of the additional bands, with varying degrees of success.
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Affiliation(s)
- D C McDonald
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA
| | - B M Rittgers
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA
| | - R A Theis
- Department of Chemistry and Biochemistry, Georgia Southern University, Statesboro, Georgia 30460, USA
| | - R C Fortenberry
- Department of Chemistry and Biochemistry, University of Mississippi, University, Mississippi 38677, USA
| | - J H Marks
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA
| | - D Leicht
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA
| | - M A Duncan
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA
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6
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Boyer MA, Chiu CS, McDonald DC, Wagner JP, Colley JE, Orr DS, Duncan MA, McCoy AB. The Role of Tunneling in the Spectra of H 5+ and D 5+ up to 7300 cm -1. J Phys Chem A 2020; 124:4427-4439. [PMID: 32392420 DOI: 10.1021/acs.jpca.0c02299] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The spectra for H5+ and D5+ are extended to cover the region between 4830 and 7300 cm-1. These spectra are obtained using mass-selected photodissociation spectroscopy. To understand the nature of the states that are accessed by the transitions in this and prior studies, we develop a four-dimensional model Hamiltonian. This Hamiltonian is expressed in terms of the two outer H2 stretches, the displacement of the shared proton from the center of mass of these two H2 groups, and the distance between the H2 groups. This choice is motivated by the large oscillator strength associated with the shared proton stretch and the fact that the spectral regions that have been probed correspond to zero, one, and two quanta of excitation in the H2 stretches. This model is analyzed using an adiabatic separation of the H2 stretches from the other two vibrations and includes the non-adiabatic couplings between H2 stretch states with the same total number of quanta of excitation in the H2 stretches. Based on the analysis of the energies and wave functions obtained from this model, we find that when there are one or more quanta of excitation in the H2 stretches the states come in pairs that reflect tunneling doublets. The states accessed by the transitions in the spectrum with the largest intensity are assigned to the members of the doublets with requisite symmetry that are localized on the lowest-energy adiabat for a given level of H2 excitation.
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Affiliation(s)
- Mark A Boyer
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Chloe S Chiu
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - David C McDonald
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
| | - J Philipp Wagner
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
| | - Jason E Colley
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
| | - Dylan S Orr
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
| | - Michael A Duncan
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
| | - Anne B McCoy
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
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7
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Prosmiti R, Valdés Á. The smallest proton-bound dimer H 5+: theoretical progress. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2019; 377:20180396. [PMID: 31378176 PMCID: PMC6710890 DOI: 10.1098/rsta.2018.0396] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 03/19/2019] [Indexed: 06/10/2023]
Abstract
The protonated hydrogen dimer, H5+, is the smallest system including proton transfer, and has been of long-standing interest since its first laboratory observation in 1962. H5+ and its isotopologues are the intermediate complexes in deuterium fractionation reactions, and are of central importance in molecular astrophysics. The recently recorded infrared spectra of both H5+ and D5+ reveal a rich vibrational dynamics of the cations, which presents a challenge for standard theoretical approaches. Although H5+ is a four-electron ion, which makes highly accurate electronic structure calculations tractable, the construction of ab initio-based potential energy and dipole moment surfaces has proved a hard task. In the same vein, the difficulties in treating the nuclear motion could also become cumbersome due to their high dimensionality, floppiness and/or symmetry. These systems are prototypical examples for studying large-amplitude motions, as they are highly delocalized, interconverting between equivalent minima through internal rotation and proton transfer motions requiring state-of-the-art treatments. Recent advances in the computational vibrational spectroscopy of the H5+ cation and its isotopologues are reported from full quantum spectral simulations, providing important information in a rigorous manner, and open perspectives for further future investigations. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H3+, H5+ and beyond'.
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Affiliation(s)
- Rita Prosmiti
- Departamento PAMS, Instituto de Física Fundamental (IFF-CSIC), CSIC, Serrano 123, 28006 Madrid, Spain
| | - Álvaro Valdés
- Departamento de Física, Universidad Nacional de Colombia, Calle 26, Cra 39, Edificio 404, Bogotá, Colombia
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8
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Lee VGM, McCoy AB. An Efficient Approach for Studies of Water Clusters Using Diffusion Monte Carlo. J Phys Chem A 2019; 123:8063-8070. [DOI: 10.1021/acs.jpca.9b06444] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- Victor G. M. Lee
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Anne B. McCoy
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
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9
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Teplukhin A, Kendrick BK, Babikov D. Calculation of Molecular Vibrational Spectra on a Quantum Annealer. J Chem Theory Comput 2019; 15:4555-4563. [PMID: 31314517 DOI: 10.1021/acs.jctc.9b00402] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Until recently molecular energy calculations using quantum computing hardware have been limited to gate-based quantum computers. In this paper, a new methodology is presented to calculate the vibrational spectrum of a molecule on a quantum annealer. The key idea of the method is a mapping of the ground state variational problem onto an Ising or quadratic unconstrained binary optimization (QUBO) problem by expressing the expansion coefficients using spins or qubits. The algorithm is general and represents a new revolutionary approach for solving the real symmetric eigenvalue problem on a quantum annealer. The method is applied to two chemically important molecules: O2 (oxygen) and O3 (ozone). The lowest two vibrational states of these molecules are computed using both a hardware quantum annealer and a software based classical annealer. Extension of the algorithm to higher dimensions is explicitly demonstrated for an N-dimensional harmonic oscillator (N ≤ 5). The algorithm scales exponentially with dimensionality if a direct product basis is used but will exhibit polynomial scaling for a nondirect product basis.
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Affiliation(s)
- Alexander Teplukhin
- Theoretical Division (T-1, MS B221) , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | - Brian K Kendrick
- Theoretical Division (T-1, MS B221) , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | - Dmitri Babikov
- Department of Chemistry , Marquette University , Milwaukee , Wisconsin 53021 , United States
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10
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Császár AG, Fábri C, Sarka J. Quasistructural molecules. WILEY INTERDISCIPLINARY REVIEWS-COMPUTATIONAL MOLECULAR SCIENCE 2019. [DOI: 10.1002/wcms.1432] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Attila G. Császár
- Laboratory of Molecular Structure and Dynamics, Institute of Chemistry ELTE Eötvös Loránd University Budapest Hungary
- MTA‐ELTE Complex Chemical Systems Research Group Budapest Hungary
| | - Csaba Fábri
- Laboratory of Molecular Structure and Dynamics, Institute of Chemistry ELTE Eötvös Loránd University Budapest Hungary
- MTA‐ELTE Complex Chemical Systems Research Group Budapest Hungary
| | - János Sarka
- Department of Chemistry and Biochemistry Texas Tech University Lubbock Texas USA
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11
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McDonald DC, Wagner JP, Duncan MA. Communication: Infrared photodissociation spectroscopy of the H 6+ cation in the gas phase. J Chem Phys 2018; 149:031105. [PMID: 30037249 DOI: 10.1063/1.5043425] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The H6+ cation was generated in a pulsed-discharge supersonic expansion of hydrogen and mass-selected in a time-of-flight spectrometer. Its vibrational spectrum was measured in the region of 2050-4550 cm-1 using infrared photodissociation with a tunable OPO/OPA laser system. The H6+ photodissociates, producing H5+, H4+, and H3+ fragments; each of these fragment channels has a different spectrum. Computational studies identify two low-lying isomers described in previous work, whose energies were evaluated at the CCSD(T)/cc-pVTZ//MP2/cc-pVTZ level of theory. A D2d species having an H2+ cation bridging between two perpendicular H2 molecules is the global minimum structure. A Cs structure with an H3+ core ion bound to both H2 and an H atom lies 4.0 kcal mol-1 higher in energy. Anharmonic vibrational spectra were computed for each of these isomers with second-order vibrational perturbation theory (VPT2) in combination with density functional theory at the B2PLYP/cc-pVTZ level. The comparison between experimental and predicted spectra confirms the presence of both the D2d and Cs structures and explains the spectra in different fragmentation channels. Although we find reasonable agreement between the experiment and the spectra predicted by VPT2 computations, a more sophisticated computational approach is needed to better understand this complex system.
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Affiliation(s)
- David C McDonald
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA
| | - J Philipp Wagner
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA
| | - Michael A Duncan
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA
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12
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Curotto E, Mella M. Diffusion Monte Carlo simulations of gas phase and adsorbed D 2-(H 2) n clusters. J Chem Phys 2018; 148:102315. [PMID: 29544319 DOI: 10.1063/1.5000372] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
We have computed ground state energies and analyzed radial distributions for several gas phase and adsorbed D2(H2)n and HD(H2)n clusters. An external model potential designed to mimic ionic adsorption sites inside porous materials is used [M. Mella and E. Curotto, J. Phys. Chem. A 121, 5005 (2017)]. The isotopic substitution lowers the ground state energies by the expected amount based on the mass differences when these are compared with the energies of the pure clusters in the gas phase. A similar impact is found for adsorbed aggregates. The dissociation energy of D2 from the adsorbed clusters is always much higher than that of H2 from both pure and doped aggregates. Radial distributions of D2 and H2 are compared for both the gas phase and adsorbed species. For the gas phase clusters, two types of hydrogen-hydrogen interactions are considered: one based on the assumption that rotations and translations are adiabatically decoupled and the other based on nonisotropic four-dimensional potential. In the gas phase clusters of sufficiently large size, we find the heavier isotopomer more likely to be near the center of mass. However, there is a considerable overlap among the radial distributions of the two species. For the adsorbed clusters, we invariably find the heavy isotope located closer to the attractive interaction source than H2, and at the periphery of the aggregate, H2 molecules being substantially excluded from the interaction with the source. This finding rationalizes the dissociation energy results. For D2-(H2)n clusters with n≥12, such preference leads to the desorption of D2 from the aggregate, a phenomenon driven by the minimization of the total energy that can be obtained by reducing the confinement of (H2)12. The same happens for (H2)13, indicating that such an effect may be quite general and impact on the absorption of quantum species inside porous materials.
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Affiliation(s)
- E Curotto
- Department of Chemistry and Physics, Arcadia University, Glenside, Pennsylvania 19038-3295, USA
| | - M Mella
- Dipartimento di Scienza ed Alta Tecnologia, Università degli Studi dell'Insubria, Via Valleggio 11, 22100 Como, Italy
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13
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Tennyson J. Perspective: Accurate ro-vibrational calculations on small molecules. J Chem Phys 2016; 145:120901. [DOI: 10.1063/1.4962907] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- Jonathan Tennyson
- Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London, United Kingdom
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14
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Sarka J, Császár AG. Interpretation of the vibrational energy level structure of the astructural molecular ion H5+ and all of its deuterated isotopomers. J Chem Phys 2016; 144:154309. [DOI: 10.1063/1.4946808] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- János Sarka
- Laboratory of Molecular Structure and Dynamics, Institute of Chemistry, Eötvös University, Pázmány Péter sétány 1/A, H-1117 Budapest, Hungary
- MTA-ELTE Complex Chemical Systems Research Group, P.O. Box 32, H-1518 Budapest 112, Hungary
| | - Attila G. Császár
- Laboratory of Molecular Structure and Dynamics, Institute of Chemistry, Eötvös University, Pázmány Péter sétány 1/A, H-1117 Budapest, Hungary
- MTA-ELTE Complex Chemical Systems Research Group, P.O. Box 32, H-1518 Budapest 112, Hungary
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15
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Calculating rovibrationally excited states of H2D+ and HD2+ by combination of fixed node and multi-state rotational diffusion Monte Carlo. Chem Phys Lett 2016. [DOI: 10.1016/j.cplett.2015.12.030] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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16
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Lin Z, McCoy AB. Probing the Relationship Between Large-Amplitude Motions in H5(+) and Proton Exchange Between H3(+) and H2. J Phys Chem A 2015; 119:12109-18. [PMID: 26244451 DOI: 10.1021/acs.jpca.5b05774] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Understanding the spectroscopy and dynamics of H5(+) is central in gaining insights into the H3(+) + H2 → H5(+) → H2 + H3(+) proton transfer reaction. This molecular ion exhibits large-amplitude vibrations, which allow for the transfer of a proton between H3(+) and H2 even in its ground vibrational state. With vibrational excitation, the number of open channels for permutations of protons increase. In this work, the minimized energy path variant of diffusion Monte Carlo is used to investigate how the energetically accessible proton permutations evolve as H5(+) is dissociated into H3(+) + H2. Two mechanisms for proton permutation are investigated. The first is the proton hop, which correlates to large-amplitude vibrations of the central proton in H5(+). The second is the exchange of a pair of hydrogen atoms between H3(+) and H2. This mechanism requires several proton hops along with a 120° rotation of H3(+) within the H5(+) molecular ion. This analysis shows that while there is a narrow region of configuration space over which both isomerization processes are energetically accessible, full permutation of the five protons in H5(+) more likely occurs through a stepwise mechanism. Such full permutation of the protons becomes accessible when the shared proton stretch is excited to the vpt = 2 or 3 excited state. The effects of deuteration and rotational excitation of the H2 and H3(+) products are also investigated. Deuteration inhibits permutation of protons, while rotational excitation has only a small impact on these processes.
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Affiliation(s)
- Zhou Lin
- Department of Chemistry and Biochemistry, The Ohio State University , Columbus, Ohio 43210, United States
| | - Anne B McCoy
- Department of Chemistry and Biochemistry, The Ohio State University , Columbus, Ohio 43210, United States
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17
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Marlett ML, Lin Z, McCoy AB. Rotation/Torsion Coupling in H5+, D5+, H4D+, and HD4+ Using Diffusion Monte Carlo. J Phys Chem A 2015. [DOI: 10.1021/acs.jpca.5b05773] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Melanie L. Marlett
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
| | - Zhou Lin
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
| | - Anne B. McCoy
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
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18
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Mallory JD, Brown SE, Mandelshtam VA. Assessing the Performance of the Diffusion Monte Carlo Method As Applied to the Water Monomer, Dimer, and Hexamer. J Phys Chem A 2015; 119:6504-15. [PMID: 26001418 DOI: 10.1021/acs.jpca.5b02511] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The diffusion Monte Carlo (DMC) method is applied to the water monomer, dimer, and hexamer using q-TIP4P/F, one of the most simple empirical water models with flexible monomers. The bias in the time step (Δτ) and population size (Nw) is investigated. For the binding energies, the bias in Δτ cancels nearly completely, whereas a noticeable bias in Nw remains. However, for the isotope shift (e.g, in the dimer binding energies between (H2O)2 and (D2O)2), the systematic errors in Nw do cancel. Consequently, very accurate results for the latter (within ∼0.01 kcal/mol) are obtained with moderate numerical effort (Nw ∼ 10(3)). For the water hexamer and its (D2O)6 isotopomer, the DMC results as a function of Nw are examined for the cage and prism isomers. For a given isomer, the issue of the walker population leaking out of the corresponding basin of attraction is addressed by using appropriate geometric constraints. The population size bias for the hexamer is more severe, and to maintain accuracy similar to that of the dimer, Nw must be increased by ∼2 orders of magnitude. Fortunately, when the energy difference between the cage and prism is taken, the biases cancel, thereby reducing the systematic errors to within ∼0.01 kcal/mol when using a population of Nw = 4.8 × 10(5) walkers. Consequently, a very accurate result for the isotope shift is also obtained. Notably, both the quantum and isotope effects for the prism-cage energy difference are small.
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Affiliation(s)
- Joel D Mallory
- Department of Chemistry, University of California, Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| | - Sandra E Brown
- Department of Chemistry, University of California, Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| | - Vladimir A Mandelshtam
- Department of Chemistry, University of California, Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
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19
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Valdés Á, Prosmiti R. Theoretical predictions on the role of the internal H3(+) rotation in the IR spectra of the H5(+) and D5(+) cations. Phys Chem Chem Phys 2015; 16:6217-24. [PMID: 24562473 DOI: 10.1039/c3cp55301a] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The IR spectra of the H5(+) and D5(+) cations in the mid- and far-IR spectral regions have been recently reported by experimentalists. These spectra show very rich vibrational patterns representing a challenge for state-of-the-art theoretical methods to provide definitive interpretations of them. Using a full-dimensional quantum anharmonic treatment, within the MCTDH approach, together with ab initio potential and dipole moment surfaces, the predominant features in the spectra are assigned, completing an important part in previous theoretical and experimental comparisons. The internal rotation of the H3(+) unit by exciting the H3(+)-H2 stretching mode is found to correspond to the new calculated features at 1182, 1876, and 2139 cm(-1) of the H5(+) spectrum, leading to a consistent assignment with the experimental spectra. In the calculated spectra of both H5(+) and D5(+) clusters, the progressions in the H3(+)-H2 stretch of the shared proton and the in- and out-of- plane H3(+) rotation are demonstrated to be the main features. Such states are expected to play a central role in the low temperature hydrogen/deuterium proton hop/exchange H3(+) + H2 reactions.
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Affiliation(s)
- Álvaro Valdés
- Instituto de Física Fundamental (IFF-CSIC), CSIC, Serrano 123, 28006 Madrid, Spain.
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20
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Sarka J, Fábri C, Szidarovszky T, Császár AG, Lin Z, McCoy AB. Modelling rotations, vibrations, and rovibrational couplings in astructural molecules – a case study based on the H+5 molecular ion. Mol Phys 2015. [DOI: 10.1080/00268976.2015.1020074] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- János Sarka
- Laboratory of Molecular Structure and Dynamics, Institute of Chemistry, Eötvös University, Budapest, Hungary
- MTA-ELTE Complex Chemical Systems Research Group, Budapest, Hungary
| | - Csaba Fábri
- Laboratory of Physical Chemistry, ETH Zürich, Zürich, Switzerland
| | - Tamás Szidarovszky
- MTA-ELTE Complex Chemical Systems Research Group, Budapest, Hungary
- Department of Chemistry, School of Science, The University of Tokyo, Tokyo, Japan
| | - Attila G. Császár
- Laboratory of Molecular Structure and Dynamics, Institute of Chemistry, Eötvös University, Budapest, Hungary
- MTA-ELTE Complex Chemical Systems Research Group, Budapest, Hungary
| | - Zhou Lin
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, USA
| | - Anne B. McCoy
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, USA
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21
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Qu C, Bowman JM. Diffusion Monte Carlo Calculations of Zero-Point Structures of Partially Deuterated Isotopologues of H7+. J Phys Chem B 2014; 118:8221-6. [DOI: 10.1021/jp501371z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Chen Qu
- Department of Chemistry and
Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, United States
| | - Joel M. Bowman
- Department of Chemistry and
Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, United States
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22
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Lin Z, McCoy AB. The role of large-amplitude motions in the spectroscopy and dynamics of H5+. J Chem Phys 2014; 140:114305. [DOI: 10.1063/1.4868098] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
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23
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Fábri C, Sarka J, Császár AG. Communication: Rigidity of the molecular ion H5+. J Chem Phys 2014; 140:051101. [DOI: 10.1063/1.4864360] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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24
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Qu C, Prosmiti R, Bowman JM. MULTIMODE calculations of the infrared spectra of H 7 + and D 7 + using ab initio potential energy and dipole moment surfaces. Theor Chem Acc 2013. [DOI: 10.1007/s00214-013-1413-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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25
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Petit AS, Ford JE, McCoy AB. Simultaneous Evaluation of Multiple Rotationally Excited States of H3+, H3O+, and CH5+ Using Diffusion Monte Carlo. J Phys Chem A 2013; 118:7206-20. [DOI: 10.1021/jp408821a] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Andrew S. Petit
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
| | - Jason E. Ford
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
| | - Anne B. McCoy
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
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