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Fortenberry RC. Picking up Good Vibrations through Quartic Force Fields and Vibrational Perturbation Theory. J Phys Chem Lett 2024; 15:6528-6537. [PMID: 38875074 DOI: 10.1021/acs.jpclett.4c01089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2024]
Abstract
Quartic force fields (QFFs) define sparse potential energy surfaces (compared to semiglobal surfaces) that are the cheapest and easiest means of computing anharmonic vibrational frequencies, especially when utilized with second-order vibrational perturbation theory (VPT2). However, flat and shallow potential surfaces are exceedingly difficult for QFFs to treat through a combination of numerical noise in the often numerically computed derivatives and in competing energy factors in the composite energies often utilized to provide high-level spectroscopic predictions. While some of these issues can be alleviated with analytic derivatives, hybrid QFFs, and intelligent choices in coordinate systems, the best practice is for predicting good molecular vibrations via QFFs is to understand what they cannot do, and this manuscript documents such cases where QFFs may fail.
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Affiliation(s)
- Ryan C Fortenberry
- Department of Chemistry & Biochemistry, University of Mississippi, University, Mississippi 38677-1848, United States
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Tsegaw YA, Li H, Andrews L, Cho HG, Voßnacker P, Beckers H, Riedel S. (Noble Gas) n -NC + Molecular Ions in Noble Gas Matrices: Matrix Infrared Spectra and Electronic Structure Calculations. Chemistry 2021; 28:e202103142. [PMID: 34897851 PMCID: PMC9299772 DOI: 10.1002/chem.202103142] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2021] [Indexed: 11/12/2022]
Abstract
An investigation of pulsed‐laser‐ablated Zn, Cd and Hg metal atom reactions with HCN under excess argon during co‐deposition with laser‐ablated Hg atoms from a dental amalgam target also provided Hg emissions capable of photoionization of the CN photo‐dissociation product. A new band at 1933.4 cm−1 in the region of the CN and CN+ gas‐phase fundamental absorptions that appeared upon annealing the matrix to 20 K after sample deposition, and disappeared upon UV photolysis is assigned to (Ar)nCN+, our key finding. It is not possible to determine the n coefficient exactly, but structure calculations suggest that one, two, three or four argon atoms can solvate the CN+ cation in an argon matrix with C−N absorptions calculated (B3LYP) to be between 2317.2 and 2319.8 cm−1. Similar bands were observed in solid krypton at 1920.5, in solid xenon at 1935.4 and in solid neon at 1947.8 cm−1. H13CN reagent gave an 1892.3 absorption with shift instead, and a 12/13 isotopic frequency ratio–nearly the same as found for 13CN+ itself in the gas phase and in the argon matrix. The CN+ molecular ion serves as a useful infrared probe to examine Ng clusters. The following ion reactions are believed to occur here: the first step upon sample deposition is assisted by a focused pulsed YAG laser, and the second step occurs on sample annealing: (Ar)2++CN→Ar+CN+→(Ar)nCN+.
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Affiliation(s)
- Yetsedaw A Tsegaw
- Anorganische Chemie, Institut fur Chemie und Biochemie, Freie Universitat Berlin, Fabeckstrasse 34-36, 14195, Berlin, Germany
| | - Hongmin Li
- Anorganische Chemie, Institut fur Chemie und Biochemie, Freie Universitat Berlin, Fabeckstrasse 34-36, 14195, Berlin, Germany
| | - Lester Andrews
- Department of Chemistry, University of Virginia, Charlottesville, Virginia, 22904, USA
| | - Han-Gook Cho
- Department of Chemistry, Incheon National University, 119 Academy-ro, Yeonsu-gu, Incheon, 22012, South Korea
| | - Patrick Voßnacker
- Anorganische Chemie, Institut fur Chemie und Biochemie, Freie Universitat Berlin, Fabeckstrasse 34-36, 14195, Berlin, Germany
| | - Helmut Beckers
- Anorganische Chemie, Institut fur Chemie und Biochemie, Freie Universitat Berlin, Fabeckstrasse 34-36, 14195, Berlin, Germany
| | - Sebastian Riedel
- Anorganische Chemie, Institut fur Chemie und Biochemie, Freie Universitat Berlin, Fabeckstrasse 34-36, 14195, Berlin, Germany
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Fortenberry RC, Lee TJ. Computational vibrational spectroscopy for the detection of molecules in space. ANNUAL REPORTS IN COMPUTATIONAL CHEMISTRY 2019. [DOI: 10.1016/bs.arcc.2019.08.006] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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Fortenberry RC, Ascenzi D. ArCH 2 + : A Detectable Noble Gas Molecule. Chemphyschem 2018; 19:3388-3392. [PMID: 30370986 DOI: 10.1002/cphc.201800888] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Revised: 10/23/2018] [Indexed: 11/07/2022]
Abstract
The noble gas molecular cation, ArCH2 + , has been observed in mass spectrometry experiments, and the present work is providing high-level quantum chemical predictions for the vibrational and rotational spectroscopic data necessary to observe this molecule in situ in other laboratory conditions. The Ar-C stretch in this cation is a bright fundamental vibrational frequency that should be observable in the early regions of the far-infrared at 421.2 cm-1 for the universally most common 36 Ar isotope. The near-prolate nature of this molecule and its 2.91 D dipole moment should also make it distinguishable for submillimeter detection, as well. Furthermore, the Ar-C bond strength in ArCH2 + is greater than the global minimum for the dissociation of the experimentally known ArOH+ cation. As a result, the infrared spectrum of this simple organo-noble gas molecule is likely waiting to be observed and may already exist in the spectra of hydrocarbon cations in argon-matrix condensed phase experiments.
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Affiliation(s)
- Ryan C Fortenberry
- University of Mississippi, Department of Chemistry & Biochemistry, University, MS 38677-1848, U.S.A
| | - Daniela Ascenzi
- University of Trento, Department of Physics, Via Sommarive 14, 38050, Povo Trento, Italy
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