1
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Miyazaki M, Ono M, Otsuka R, Dopfer O, Fujii M. Electronic and vibrational spectroscopies of aromatic clusters with He in a supersonic jet: The case of neutral and cationic phenol-Hen (n = 1 and 2). J Chem Phys 2023; 159:134303. [PMID: 37787127 DOI: 10.1063/5.0169716] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Accepted: 09/15/2023] [Indexed: 10/04/2023] Open
Abstract
Van der Waals clusters composed of He and aromatic molecules provide fundamental information about intermolecular interactions in weakly bound systems. In this study, phenol-helium clusters (PhOH-Hen with n ≤ 2) are characterized for the first time by UV and IR spectroscopies. The S1 ← S0 origin and ionization energy both show small but additive shifts, suggesting π-bound structures of these clusters, a conclusion supported by rotational contour analyses of the S1 origin bands. The OH stretching vibrations of the PhOH moiety in the clusters match with those of bare PhOH in both the S0 and D0 states, illustrating the negligible perturbation of the He atoms on the molecular vibration. Matrix shifts induced by He attachment are discussed based on the observed band positions with the help of complementary quantum chemical calculations. For comparison, the UV and ionization spectra of PhOH-Ne are reported as well.
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Affiliation(s)
- Mitsuhiko Miyazaki
- Natural Science Division, Faculty of Core Research, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo 112-8610, Japan
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503, Japan
| | - Megumi Ono
- School of Life Science and Technology, Tokyo Institute of Technology, 4259, Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan
| | - Remina Otsuka
- School of Life Science and Technology, Tokyo Institute of Technology, 4259, Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan
| | - Otto Dopfer
- Institut für Optik und Atomare Physik, Technische Universität Berlin, 10623 Berlin, Germany
- International Research Frontiers Initiative (IRFI), Institute of Innovation Research, Tokyo Institute of Technology, 4259, Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan
| | - Masaaki Fujii
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503, Japan
- School of Life Science and Technology, Tokyo Institute of Technology, 4259, Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan
- International Research Frontiers Initiative (IRFI), Institute of Innovation Research, Tokyo Institute of Technology, 4259, Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan
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2
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Iguchi A, Singh A, Bergmeister S, Azhagesan AA, Mizuse K, Fujii A, Tanuma H, Azuma T, Scheier P, Kuma S, Vilesov AF. Isolation and Infrared Spectroscopic Characterization of Hemibonded Water Dimer Cation in Superfluid Helium Nanodroplets. J Phys Chem Lett 2023; 14:8199-8204. [PMID: 37672355 PMCID: PMC10510431 DOI: 10.1021/acs.jpclett.3c02150] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Accepted: 08/30/2023] [Indexed: 09/08/2023]
Abstract
The structure of the minimum unit of the radical cationic water clusters, the (H2O)2+ dimer, has attracted much attention because of its importance for the radiation chemistry of water. Previous spectroscopic studies indicated that the dimers have a proton-transferred structure (H3O+·OH), though the alternate metastable hemibonded structure (H2O·OH2)+ was also predicted based on theoretical calculations. Here, we produce (H2O)2+ dimers in superfluid helium nanodroplets and study their infrared spectra in the range of OH stretching vibrations. The observed spectra indicate the coexistence of the two structures in the droplets, supported by density functional theory calculations. This is the first spectroscopic identification of the hemibonded isomer of water radical cation dimers. The observation of the higher-energy isomer reveals efficient kinetic trapping for metastable ionic clusters due to the rapid cooling in helium droplets.
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Affiliation(s)
- Arisa Iguchi
- Department
of Physics, Tokyo Metropolitan University, Tokyo 192-0397, Japan
- Atomic,
Molecular, and Optical Physics Laboratory, RIKEN, Saitama 351-0198, Japan
| | - Amandeep Singh
- Department
of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Stefan Bergmeister
- Institut
für Ionenphysik und Angewandte Physik, Universität Innsbruck, A-6020 Innsbruck, Austria
| | - Andrew A. Azhagesan
- Department
of Computer Science, University of Southern
California, Los Angeles, California 90089, United States
| | - Kenta Mizuse
- Department
of Chemistry, School of Science, Kitasato
University, Sagamihara, Kanagawa 252-0373, Japan
| | - Asuka Fujii
- Department
of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
| | - Hajime Tanuma
- Department
of Physics, Tokyo Metropolitan University, Tokyo 192-0397, Japan
| | - Toshiyuki Azuma
- Atomic,
Molecular, and Optical Physics Laboratory, RIKEN, Saitama 351-0198, Japan
| | - Paul Scheier
- Institut
für Ionenphysik und Angewandte Physik, Universität Innsbruck, A-6020 Innsbruck, Austria
| | - Susumu Kuma
- Atomic,
Molecular, and Optical Physics Laboratory, RIKEN, Saitama 351-0198, Japan
| | - Andrey F. Vilesov
- Department
of Chemistry, University of Southern California, Los Angeles, California 90089, United States
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3
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Singh A, Bergmeister S, Azhagesan A, Scheier P, Vilesov AF. Infrared spectroscopy of cations in helium nanodroplets. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2023; 94:093002. [PMID: 37695112 DOI: 10.1063/5.0163390] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Accepted: 08/21/2023] [Indexed: 09/12/2023]
Abstract
Here, we describe our pulsed helium droplet apparatus for spectroscopy of molecular ions. Our approach involves the doping of the droplets of about 10 nm in diameter with precursor molecules, such as ethylene, followed by electron impact ionization. Droplets containing ions are irradiated by the pulsed infrared laser beam. Vibrational excitation of the embedded cations leads to the evaporation of the helium atoms in the droplets and the release of the free ions, which are detected by the quadrupole mass spectrometer. In this work, we upgraded the experimental setup by introducing an octupole RF collision cell downstream from the electron impact ionizer. The implementation of the RF ion guide increases the transmission efficiency of the ions. Filling the collision cell with additional He gas leads to a decrease in the droplet size, enhancing sensitivity to the laser excitation. We show that the spectroscopic signal depends linearly on the laser pulse energy, and the number of ions generated per laser pulse is about 100 times greater than in our previous experiments. These improvements facilitate faster and more reproducible measurements of the spectra, yielding a handy laboratory technique for the spectroscopic study of diverse molecular ions and ionic clusters at low temperature (0.4 K) in He droplets.
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Affiliation(s)
- Amandeep Singh
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
| | - Stefan Bergmeister
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, A-6020 Innsbruck, Austria
| | - Andrew Azhagesan
- Department of Computer Science, University of Southern California, Los Angeles, California 90089, USA
| | - Paul Scheier
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, A-6020 Innsbruck, Austria
| | - Andrey F Vilesov
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
- Department of Physics, University of Southern California, Los Angeles, California 90089, USA
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4
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Beckmann R, Topolnicki R, Marx D. Deciphering the Impact of Helium Tagging on Flexible Molecules: Probing Microsolvation Effects of Protonated Acetylene by Quantum Configurational Entropy. J Phys Chem A 2023; 127:2460-2471. [PMID: 36917575 DOI: 10.1021/acs.jpca.2c08967] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/16/2023]
Abstract
Helium, the lightest and most weakly interacting noble gas, is well-known for its unsurpassed chemical inertness. In many applications of helium in experimental techniques, such as tagging, messenger, or nanodroplet isolation action spectroscopy of molecules or complexes, it is assumed that the interaction of helium with the respective species, and thus the resulting interaction-induced perturbation, is small enough not to affect their structure and dynamics. Here, we probe the impact of one up to many attached helium atoms on protonated acetylene─an important nonclassical carbocation subject to three-center two-electron bonding in its ground state structure─using highly accurate interaction potentials in conjunction with entropy-based higher-order nonlinear correlation analysis. In particular, using neural network potentials at CCSD(T) accuracy, we disclose the specific structural perturbations due to the tagging of C2H3+ with up to 20 He atoms at a temperature of 1 K. Analysis reveals that microsolvation by helium influences the structure of C2H3+ noticeably, while our investigation of the quantum configurational information entropy additionally shows that correlations between individual orientational degrees of freedom are affected as a function of cluster size. In particular, it is found that the most probable bridge-like structure of the ro-vibrational quantum ground state of C2H3+, which is nonplanar and trans-bent in contrast to the perfectly planar equilibrium structure, becomes increasingly more localized upon adding helium atoms. The remarkably nonlinear behavior of the angular correlations as a function of cluster size is traced back to the buildup of the quantum microsolvation shell that enhances anisotropy up to NHe = 6 while more and more isotropic solvation takes over beyond six. Our approach is general and thus sets the stage to investigate the salient effects on the structure of flexible molecules due to tagging beyond the specific case.
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Affiliation(s)
- Richard Beckmann
- Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, 44780 Bochum, Germany
| | - Rafal Topolnicki
- Dioscuri Center in Topological Data Analysis, Institute of Mathematics, Polish Academy of Sciences, Śniadeckich 8, Warsaw 00-656, Poland
- Institute of Experimental Physics, University of Wrocław, 50-204 Wrocław, Poland
| | - Dominik Marx
- Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, 44780 Bochum, Germany
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5
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Davies JA, Schran C, Brieuc F, Marx D, Ellis AM. Onset of Rotational Decoupling for a Molecular Ion Solvated in Helium: From Tags to Rings and Shells. PHYSICAL REVIEW LETTERS 2023; 130:083001. [PMID: 36898117 DOI: 10.1103/physrevlett.130.083001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Revised: 12/05/2022] [Accepted: 01/18/2023] [Indexed: 06/18/2023]
Abstract
Little is known about how rotating molecular ions interact with multiple ^{4}He atoms and how this relates to microscopic superfluidity. Here, we use infrared spectroscopy to investigate ^{4}He_{N}⋯H_{3}O^{+} complexes and find that H_{3}O^{+} undergoes dramatic changes in rotational behavior as ^{4}He atoms are added. We present evidence of clear rotational decoupling of the ion core from the surrounding helium for N>3, with sudden changes in rotational constants at N=6 and 12. In sharp contrast to studies on small neutral molecules microsolvated in helium, accompanying path integral simulations show that an incipient superfluid effect is not needed to account for these findings.
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Affiliation(s)
- Julia A Davies
- School of Chemistry, University of Leicester, University Road, Leicester, LE1 7RH, United Kingdom
| | - Christoph Schran
- Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, 44780 Bochum, Germany
| | - Fabien Brieuc
- Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, 44780 Bochum, Germany
| | - Dominik Marx
- Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, 44780 Bochum, Germany
| | - Andrew M Ellis
- School of Chemistry, University of Leicester, University Road, Leicester, LE1 7RH, United Kingdom
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6
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Albertini S, Gruber E, Zappa F, Krasnokutski S, Laimer F, Scheier P. Chemistry and physics of dopants embedded in helium droplets. MASS SPECTROMETRY REVIEWS 2022; 41:529-567. [PMID: 33993543 DOI: 10.1002/mas.21699] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 04/20/2021] [Accepted: 04/20/2021] [Indexed: 05/18/2023]
Abstract
Helium droplets represent a cold inert matrix, free of walls with outstanding properties to grow complexes and clusters at conditions that are perfect to simulate cold and dense regions of the interstellar medium. At sub-Kelvin temperatures, barrierless reactions triggered by radicals or ions have been observed and studied by optical spectroscopy and mass spectrometry. The present review summarizes developments of experimental techniques and methods and recent results they enabled.
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Affiliation(s)
- Simon Albertini
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - Elisabeth Gruber
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - Fabio Zappa
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - Serge Krasnokutski
- Laboratory Astrophysics Group of the MPI for Astronomy, University of Jena, Jena, Germany
| | - Felix Laimer
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - Paul Scheier
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
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7
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Erukala S, Feinberg AJ, Moon CJ, Choi MY, Vilesov AF. Infrared spectroscopy of ions and ionic clusters upon ionization of ethane in helium droplets. J Chem Phys 2022; 156:204306. [DOI: 10.1063/5.0091819] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Helium droplets are unique hosts for isolating diverse molecular ions for infrared spectroscopic experiments. Recently, it was found that electron impact ionization of ethylene clusters embedded in helium droplets produces diverse carbocations containing three and four carbon atoms, indicating effective ion–molecule reactions. In this work, similar experiments are reported but with the saturated hydrocarbon precursor of ethane. In distinction to ethylene, no characteristic bands of larger covalently bound carbocations were found, indicating inefficient ion–molecule reactions. Instead, the ionization in helium droplets leads to formation of weaker bound dimers, such as (C2H6)(C2H4)+, (C2H6)(C2H5)+, and (C2H6)(C2H6)+, as well as larger clusters containing several ethane molecules attached to C2H4+, C2H5+, and C2H6+ ionic cores. The spectra of larger clusters resemble those for neutral, neat ethane clusters. This work shows the utility of the helium droplets to study small ionic clusters at ultra-low temperatures.
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Affiliation(s)
- Swetha Erukala
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
| | - Alexandra J. Feinberg
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
| | - Cheol Joo Moon
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
- Research Institute for Green Energy Convergence Technology, Gyeongsang National University, Jinju 52828, Republic of Korea
| | - Myong Yong Choi
- Core‐Facility Center for Photochemistry and Nanomaterials, Department of Chemistry (BK21 FOUR), Research Institute of Natural Sciences, Gyeongsang National University, Jinju, Republic of Korea
| | - Andrey F. Vilesov
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, USA
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8
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Müller D, Dopfer O. Microsolvation of H 2O +, H 3O +, and CH 3OH 2+ by He in a cryogenic ion trap: structure of solvation shells. Phys Chem Chem Phys 2022; 24:11222-11233. [PMID: 35481676 DOI: 10.1039/d2cp01192a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Due to the weak interactions of He atoms with neutral molecules and ions, the preparation of size-selected clusters for the spectroscopic characterization of their structures, energies, and large amplitude motions is a challenging task. Herein, we generate H2O+Hen (n ≤ 9) and H3O+Hen (n ≤ 5) clusters by stepwise addition of He atoms to mass-selected ions stored in a cryogenic 22-pole ion trap held at 5 K. The population of the clusters as a function of n provides insight into the structure of the first He solvation shell around these ions given by the anisotropy of the cation-He interaction potential. To rationalize the observed cluster size distributions, the structural, energetic, and vibrational properties of the clusters are characterized by ab initio calculations up to the CCSD(T)/aug-cc-pVTZ level. The cluster growth around both the open-shell H2O+ and closed-shell H3O+ ions begins by forming nearly linear and equivalent OH⋯He hydrogen bonds (H-bonds) leading to symmetric structures. The strength of these H-bonds decreases slightly with n due to noncooperative three-body induction forces and is weaker for H3O+ than for H2O+ due to both enhanced charge delocalization and reduced acidity of the OH protons. After filling all available H-bonded sites, addition of further He ligands around H2O+ (n = 3-4) occurs at the electrophilic singly occupied 2pz orbital of O leading to O⋯He p-bonds stabilized by induction and small charge transfer from H2O+ to He. As this orbital is filled for H3O+, He atoms occupy in the n = 4-6 clusters positions between the H-bonded He atoms, leading to a slightly distorted regular hexagon ring for n = 6. Comparison between H3O+Hen and CH3OH2+Hen illustrates that CH3 substitution substantially reduces the acidity of the OH protons, so that only clusters up to n = 2 can be observed. The structure of the solvation sub-shells is visible in both the binding energies and the predicted vibrational OH stretch and bend frequencies.
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Affiliation(s)
- David Müller
- Institut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany.
| | - Otto Dopfer
- Institut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany.
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9
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Davies JA, Yang S, Ellis AM. Infrared spectra of carbocations and CH 4+ in helium. Phys Chem Chem Phys 2021; 23:27449-27459. [PMID: 34870649 DOI: 10.1039/d1cp03138d] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Infrared (IR) spectra of several hydrocarbon cations are reported, namely CH3+, CH4+, CH5+, CH5+(CH4) and C2H5+. The spectra were generated from weakly-bound helium-cation complexes formed by electron ionization of helium nanodroplets doped with a neutral hydrocarbon precursor. Spectroscopic transitions were registered by photoexcitation of the complexes coupled with mass spectrometric detection of the bare ions. For CH3+, we provide evidence showing that the helium-bound complexes contain 10-20 helium atoms (on average) and have a rotational temperature of ∼5 K. We show that this technique is well-suited to the study of highly symmetric or fluxional ionic species, as these intrinsic properties are preserved in the helium environment. This is in contrast to conventional tagging methods that use a single atom or molecule, which can change the point group or rigidity of the core ion and therefore the spectral profile. We demonstrate this for the highly fluxional molecular ion CH5+, whose spectrum in the current study matches that of the gas phase ion, whereas the fluxionality is lost when a methane tag is added. Finally, we present the first IR spectrum of methane cation, CH4+. The spectrum of this fundamental organic ion shows CH stretching bands consistent with a non-tetrahedral structure, a consequence of Jahn-Teller distortion.
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Affiliation(s)
- Julia A Davies
- Department of Chemistry, University of Leicester, University Road, Leicester, LE1 7RH, UK.
| | - Shengfu Yang
- Department of Chemistry, University of Leicester, University Road, Leicester, LE1 7RH, UK.
| | - Andrew M Ellis
- Department of Chemistry, University of Leicester, University Road, Leicester, LE1 7RH, UK.
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10
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Schiller A, Meyer M, Martini P, Zappa F, Krasnokutski SA, Calvo F, Scheier P. Adsorption of Helium on Small Cationic PAHs: Influence of Hydrocarbon Structure on the Microsolvation Pattern. J Phys Chem A 2021; 125:7813-7824. [PMID: 34436885 PMCID: PMC8450901 DOI: 10.1021/acs.jpca.1c05150] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Revised: 08/11/2021] [Indexed: 11/29/2022]
Abstract
The adsorption of up to ∼100 helium atoms on cations of the planar polycyclic aromatic hydrocarbons (PAHs) anthracene, phenanthrene, fluoranthene, and pyrene was studied by combining helium nanodroplet mass spectrometry with classical and quantum computational methods. Recorded time-of-flight mass spectra reveal a unique set of structural features in the ion abundance as a function of the number of attached helium atoms for each of the investigated PAHs. Path-integral molecular dynamics simulations were used with a polarizable potential to determine the underlying adsorption patterns of helium around the studied PAH cations and in good general agreement with the experimental data. The calculated structures of the helium-PAH complexes indicate that the arrangement of adsorbed helium atoms is highly sensitive toward the structure of the solvated PAH cation. Closures of the first solvation shell around the studied PAH cations are suggested to lie between 29 and 37 adsorbed helium atoms depending on the specific PAH cation. Helium atoms are found to preferentially adsorb on these PAHs following the 3 × 3 commensurate pattern common for graphitic surfaces, in contrast to larger carbonaceous molecules like corannulene, coronene, and fullerenes that exhibit a 1 × 1 commensurate phase.
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Affiliation(s)
- Arne Schiller
- Institut
für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria
| | - Miriam Meyer
- Institut
für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria
| | - Paul Martini
- Institut
für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria
| | - Fabio Zappa
- Institut
für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria
| | - Serge A. Krasnokutski
- Laboratory
Astrophysics Group of the MPI for Astronomy at the University of Jena, Helmholtzweg 3, D-07743 Jena, Germany
| | - Florent Calvo
- CNRS,
LiPhy, Univ. Grenoble Alpes, F-38000 Grenoble, France
| | - Paul Scheier
- Institut
für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria
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11
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Erukala S, Feinberg A, Singh A, Vilesov AF. Infrared spectroscopy of carbocations upon electron ionization of ethylene in helium nanodroplets. J Chem Phys 2021; 155:084306. [PMID: 34470362 DOI: 10.1063/5.0062171] [Citation(s) in RCA: 2] [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 electron impact ionization of helium droplets doped with ethylene molecules and clusters yields diverse CXHY + cations embedded in the droplets. The ionization primarily produces C2H2 +, C2H3 +, C2H4 +, and CH2 +, whereas larger carbocations are produced upon the reactions of the primary ions with ethylene molecules. The vibrational excitation of the cations leads to the release of bare cations and cations with a few helium atoms attached. The laser excitation spectra of the embedded cations show well resolved vibrational bands with a few wavenumber widths-an order of magnitude less than those previously obtained in solid matrices or molecular beams by tagging techniques. Comparison with the previous studies of free and tagged CH2 +, CH3 +, C2H2 +, C2H3 +, and C2H4 + cations shows that the helium matrix typically introduces a shift in the vibrational frequencies of less than about 20 cm-1, enabling direct comparisons with the results of quantum chemical calculations for structure determination. This work demonstrates a facile technique for the production and spectroscopic study of diverse carbocations, which act as important intermediates in gas and condensed phases.
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Affiliation(s)
- Swetha Erukala
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
| | - Alexandra Feinberg
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
| | - Amandeep Singh
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
| | - Andrey F Vilesov
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
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12
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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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13
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Opoku E, Pawłowski F, Ortiz JV. Electron binding energies and Dyson orbitals of O nH 2n+1 +,0,- clusters: Double Rydberg anions, Rydberg radicals, and micro-solvated hydronium cations. J Chem Phys 2021; 154:234304. [PMID: 34241254 DOI: 10.1063/5.0053297] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Ab initio electron propagator methods are employed to predict the vertical electron attachment energies (VEAEs) of OH3 +(H2O)n clusters. The VEAEs decrease with increasing n, and the corresponding Dyson orbitals are diffused over exterior, non-hydrogen bonded protons. Clusters formed from OH3 - double Rydberg anions (DRAs) and stabilized by hydrogen bonding or electrostatic interactions between ions and polar molecules are studied through calculations on OH3 -(H2O)n complexes and are compared with more stable H-(H2O)n+1 isomers. Remarkable changes in the geometry of the anionic hydronium-water clusters with respect to their cationic counterparts occur. Rydberg electrons in the uncharged and anionic clusters are held near the exterior protons of the water network. For all values of n, the anion-water complex H-(H2O)n+1 is always the most stable, with large vertical electron detachment energies (VEDEs). OH3 -(H2O)n DRA isomers have well separated VEDEs and may be visible in anion photoelectron spectra. Corresponding Dyson orbitals occupy regions beyond the peripheral O-H bonds and differ significantly from those obtained for the VEAEs of the cations.
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Affiliation(s)
- Ernest Opoku
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849-5312, USA
| | - Filip Pawłowski
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849-5312, USA
| | - Joseph Vincent Ortiz
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849-5312, USA
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Abstract
Observation of the free rotation of molecules in helium droplets enabled microscopic study of interaction of quantum rotors with a superfluid environment at T = 0.4 K. This work extends studies of rotation in helium to molecular cations, such as methenium, CH3+. The spectrum of the v3 band of CH3+ around 3130 cm-1 has three prominent peaks assigned to the rotational structure of the band. While the free CH3+ is an oblate top, in helium it behaves as a prolate top. This effect is ascribed to the strong binding of two He atoms along the figure axis of the ion. Our results indicate that the other He atoms within the first solvation shell remain fluxional and in disparity with the widely accepted model of a rigid He "snowball" surrounding ions.
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Affiliation(s)
- Swetha Erukala
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Deepak Verma
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Andrey Vilesov
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, United States
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