1
|
Deprotonated sulfamic acid and its homodimers: Does sulfamic acid adopt zwitterion during cluster growth? J Chem Phys 2024; 160:054303. [PMID: 38341690 DOI: 10.1063/5.0190757] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2023] [Accepted: 01/15/2024] [Indexed: 02/13/2024] Open
Abstract
We present a joint experimental and computational study on the geometric and electronic structures of deprotonated sulfamic acid (SA) clusters [(SA)n-H]- (n = 1, 2) employing negative ion photoelectron spectroscopy and high-level ab initio calculations. The photoelectron spectra provide the vertical/adiabatic detachment energy (VDE/ADE) of the sulfamate anion (SM-) H2N●SO3- at 4.85 ± 0.05 and 4.58 ± 0.08 eV, respectively, and the VDE and ADE of the SM-●SA dimer at 6.41 ± 0.05 and 5.87 ± 0.08 eV, respectively. The significantly increased electron binding energies of the dimer confirm the enhanced electronic stability upon the addition of one SA molecule. The CCSD(T)-predicted VDEs/ADEs agree excellently with the experimental data, confirming the identified structures as the most stable ones. Two types of dimer isomers possessing different hydrogen bonding (HB) motifs are identified, corresponding to SM- binding to a zwitterionic SA (SM-●SAz) and a canonical SA (SM-●SAc), respectively. Two N-H⋯O HBs and one superior O-H⋯O HB are formed in the lowest-lying SM-●SAc, while SM-●SAz has three moderate N-H⋯O HBs, with the former being 4.71 kcal/mol more stable. Further theoretical analyses reveal that the binding strength advantage of SM-●SAc over SM-●SAz arises from its significant contributions of orbital interactions between fragments, illustrating that sulfamate strongly interacts with its parent SA acid and preferably chooses the canonical SA in the subsequent cluster formations. Given the prominent presence of SA, this study provides the first evidence that the canonical dimer model of sulfamic acid should exist as a superior configuration during cluster growth.
Collapse
|
2
|
On The Nature of the Chemical Bond in Valence Bond Theory. J Chem Phys 2022; 157:090901. [DOI: 10.1063/5.0095953] [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
This perspective outlines a panoramic description of the nature of the chemical bond according to valence bond theory. It describes single bonds, and charge-shift bonds (CSBs) in which the entire/most of the bond energy arises from the resonance between the covalent and ionic structures of the bond. Many CSBs are homonuclear bonds. Hypervalent molecules are CSBs. Then we describe multiply bonded molecules with emphasis on C2 and 3O2. The perspective outlines an effective methodology of peeling the electronic structure to the necessary minimum: a structure with a quadruple bond, and two minor structures with double bonds, which stabilize the quadruple bond by resonance. 3O2 is chosen because it is a persistent diradical. The persistence of 3O2 is due to the large CSB resonance interaction of the π-3-electron bonds. Subsequently, we describe the roles of π vs. σ in the geometric preferences in unsaturated molecules, and their Si-based analogs. Then, the perspective discusses bonding in clusters of univalent metal-atoms, which possess only parallel spins, and are nevertheless bonded due to multiple resonance interactions. The bond energy reaches ~40 kcal/mol for a pair of atoms (in n+1Cun; n~10-12). The final subsection discusses singlet excited states in ethene, ozone and SO2. It demonstrates the capability of the breathing-orbital VB method to yield an accurate description of a variety of excited states using 10 or less VB structures. Furthermore, the method underscores covalent structures which play a key role in the correct description and bonding of these excited states.
Collapse
|
3
|
Theoretical Investigations on the Detecting Mechanism of a Typical 2,4,6-Trinitrophenol Fluorescence Sensor and Its Design Strategy. J Phys Chem A 2022; 126:230-238. [PMID: 34995455 DOI: 10.1021/acs.jpca.1c08151] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Fluorescence sensors based on small organic molecules are drawing increasing attention. In this contribution, the underlying detection mechanism of a typical fluorescence sensor for 2,4,6-trinitrophenol (TNP) based on fluorescence quenching is comprehensively investigated. The TNP molecule is proved to plant an intermolecular electron transfer state (dark state) below the bright state. Strong π-π interaction is observed between the sensor and TNP, which provides considerable orbital overlaps between the sensor and analyte. Electron transfer from the sensor to analyte is facilitated by such a strong interaction, which quenches the sensor's fluorescence. The design strategy for such TNP sensors is proposed based on the detection mechanism, and a series of new sensors is designed, which is likely to have better sensitivity than the original sensor.
Collapse
|
4
|
Exploring Dyson's Orbitals and Their Electron Binding Energies for Conceptualizing Excited States from Response Methodology. J Phys Chem Lett 2021; 12:9963-9972. [PMID: 34617764 DOI: 10.1021/acs.jpclett.1c02494] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The molecular orbital (MO) concept is a useful tool, which relates the molecular ground-state energy with the energies (and occupations) of the individual orbitals. However, analysis of the excited states from linear response computations is performed in terms of the initial state MOs or some other forms of orbitals, e.g., natural or natural transition orbitals. Because these orbitals lack the respective energies, they do not allow developing a consistent orbital picture of the excited states. Herein, we argue that Dyson's orbitals enable description of the response states compatible with the concepts of molecular orbital theory. The Dyson orbitals and their energies obtained by mixed-reference spin-flip time-dependent density functional theory (MRSF-TDDFT) for the response ground state are remarkably similar to the canonical MOs obtained by the usual DFT calculation. For excited states, the Dyson orbitals provide a chemically sensible picture of the electronic transitions, thus bridging the chasm between orbital theory and response computations.
Collapse
|
5
|
Simulation of Negative Ion Photoelectron Spectroscopy Using a Nuclear Ensemble Approach: Implications from a Nuclear Vibration Effect. J Phys Chem A 2021; 125:6621-6628. [PMID: 34318668 DOI: 10.1021/acs.jpca.1c04246] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The negative ion photoelectron spectroscopy (NIPES) has been proven to be a powerful technique to reveal the electronic structures and spectroscopic properties of various cluster anions/radicals with very high precision. However, direct comparisons of the theoretical NIPES with experimental measurements remain challenging. Particularly the nuclear vibration effect and the ionization probability are typically ignored in reproducing NIPES. In this work, the NIPES of three representative anions (NaS5-, P2N3-, and HCPN3-) with significantly different spectral features were simulated by combining the nuclear ensemble approach (NEA) and Dyson orbitals (DOs). Overall, the simulated NIPES are in good agreement with the experimentally determined ones, confirming the robustness of such a strategy. The analysis of frontier molecular orbitals (MOs) and DOs further suggests the similar mixed characters for the first ionized doublet (D0) and adjacent D1 states of NaS5- with distributions on the side sulfur atoms. And the D0 of P2N3* is confirmed as the lowest energy σ radical state; however, the D0 of HCPN3* should possess a mixture of π and σ electrons by taking into account the nuclear vibration effect. Next, the broader vibrational distribution and stronger main vibration modes of P2N3- and HCPN3- explain why the nuclear vibration possesses a more pronounced influence in reproducing their NIPES while it has little effect on NaS5-. Last, the limitations based on the double-harmonic approximation model and density of state method were also discussed, highlighting that the ionization probability and orbital relaxation effect during the ionization process should be reasonably considered.
Collapse
|
6
|
Description of Sudden Polarization in the Excited Electronic States with an Ensemble Density Functional Theory Method. J Chem Theory Comput 2021; 17:5123-5139. [PMID: 34319730 DOI: 10.1021/acs.jctc.1c00479] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Sudden polarization (SP) is one of the manifestations of electron transfer in the electronically excited states of molecules. Proposed initially to explain the unusual reactivity of photoexcited olefins, SP often occurs in the excited states of molecules possessing strongly correlated diradical ground state. Theoretical description of SP involves mixing between the singly excited and the doubly excited zwitterionic states, which makes it inaccessible with the use of the popular linear-response time-dependent density functional theory methods. In this work, an extended variant of the state-interaction state-averaged spin-restricted ensemble-referenced Kohn-Sham (SI-SA-REKS, or SSR) method is applied to study SP in a number of organic diradical systems. To this end, the analytical derivative formalism is derived and implemented for the SSR(3,2) method (see the main text for explanation of the acronym), which enables the automatic geometry optimization and obtains the relaxed density matrices as well as the electron binding energies and respective Dyson's orbitals. Application of the new method to SP in the lowest singlet excited state of ethylene agrees with the results obtained previously with the use of multireference methods of wavefunction theory. A number of interesting manifestations of SP are observed, such as the charge transfer in photoexcited tetramethyleneethene (TME) diradical mediated by the vibrational motion and conductivity switching in the excited state of a donor-acceptor dyad placed in an external electric field.
Collapse
|
7
|
Atomic and Electronic Structure of Pilus from Geobacter sulfurreducens through QM/MM Calculations: Evidence for Hole Transfer in Aromatic Residues. J Phys Chem B 2021; 125:8305-8312. [PMID: 34292748 DOI: 10.1021/acs.jpcb.1c01185] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Long-range electron transport has been widely and experimentally reported in Geobacter sulfurreducens pilus protein. However, a better understanding of the still undefined molecular arrangement can bring to light the role of key residues in this phenomenon. We propose a theoretical investigation of the electronic structure of aromatic residue groups in the protein through a classical molecular dynamics (MD) simulation, followed by a quantum mechanics/molecular mechanics (QM/MM) electronic study of different frames sampled from MD trajectories, an electrostatic potential and electron density analysis, an analysis of the density of states, and an investigation of hole formation through Dyson orbital calculations. We observe a highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap in the ranges of 1.4-2.3 eV and 2.9-3.3 eV and a less intense dipole moment along the aromatic residues in the presence of water in comparison to the system in vacuum. HOMO and LUMO electron densities highlight the occupation of one tyrosine residue in every representation for HOMO and a delocalization along two to three rings for LUMO. The results show how the electronic structure of the aromatic residues is sensitive to the ring arrangement and the surrounding environment. In our study, we observe that slight rearrangements in the fiber geometry can create temporary conditions for hole transfer.
Collapse
|
8
|
Pauling's Conceptions of Hybridization and Resonance in Modern Quantum Chemistry. Molecules 2021; 26:4110. [PMID: 34299384 PMCID: PMC8303469 DOI: 10.3390/molecules26144110] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 06/30/2021] [Accepted: 07/02/2021] [Indexed: 12/05/2022] Open
Abstract
We employ the tools of natural bond orbital (NBO) and natural resonance theory (NRT) analysis to demonstrate the robustness, consistency, and accuracy with which Linus Pauling's qualitative conceptions of directional hybridization and resonance delocalization are manifested in all known variants of modern computational quantum chemistry methodology.
Collapse
|
9
|
Combined experimental and theoretical study on photoionization cross sections of benzonitrile and o/m/p-cyanotoluene. J Chem Phys 2021; 154:244301. [PMID: 34241365 DOI: 10.1063/5.0053119] [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
Photoionization cross sections (PICSs) for the products of the reaction from CN with toluene, including benzonitrile and o/m/p-cyanotoluene, were obtained at photon energies ranging from ionization thresholds to 14 eV by tunable synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Theoretical calculations based on the frozen-core Hartree-Fock approximation and Franck-Condon simulations were carried out to cross-verify the measured PICS. The results show that the photoionization cross sections of benzonitrile and cyanotoluene isomers are similar. The generalized charge decomposition analysis was used to investigate the components of the highest occupied molecular orbital (HOMO) and HOMO-1. It was found that the HOMO and HOMO-1 of benzonitrile and cyanotoluene isomers are dominated by the features of the benzene ring, indicating that the substitution of CN and methyl has a minor influence on the PICS of the studied molecules. The reported PICS on benzonitrile and cyanotoluene isomers in the present work could contribute to the near-threshold PIMS experiments and determine the ionization and dissociation rates in interstellar space for these crucial species. The theoretical analysis on characteristics of molecular orbitals provides clues to estimating the PICS of similar substituted aromatic compounds.
Collapse
|
10
|
Valence Bond Theory-Its Birth, Struggles with Molecular Orbital Theory, Its Present State and Future Prospects. Molecules 2021; 26:molecules26061624. [PMID: 33804038 PMCID: PMC8001733 DOI: 10.3390/molecules26061624] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Revised: 03/08/2021] [Accepted: 03/10/2021] [Indexed: 01/04/2023] Open
Abstract
This essay describes the successive births of valence bond (VB) theory during 1916–1931. The alternative molecular orbital (MO) theory was born in the late 1920s. The presence of two seemingly different descriptions of molecules by the two theories led to struggles between the main proponents, Linus Pauling and Robert Mulliken, and their supporters. Until the 1950s, VB theory was dominant, and then it was eclipsed by MO theory. The struggles will be discussed, as well as the new dawn of VB theory, and its future.
Collapse
|
11
|
Tracing orbital images on ultrafast time scales. Science 2021; 371:1056-1059. [PMID: 33602865 DOI: 10.1126/science.abf3286] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Accepted: 02/01/2021] [Indexed: 11/02/2022]
Abstract
Frontier orbitals determine fundamental molecular properties such as chemical reactivities. Although electron distributions of occupied orbitals can be imaged in momentum space by photoemission tomography, it has so far been impossible to follow the momentum-space dynamics of a molecular orbital in time, for example, through an excitation or a chemical reaction. Here, we combined time-resolved photoemission using high laser harmonics and a momentum microscope to establish a tomographic, femtosecond pump-probe experiment of unoccupied molecular orbitals. We measured the full momentum-space distribution of transiently excited electrons, connecting their excited-state dynamics to real-space excitation pathways. Because in molecules this distribution is closely linked to orbital shapes, our experiment may, in the future, offer the possibility of observing ultrafast electron motion in time and space.
Collapse
|
12
|
|
13
|
|
14
|
Visualizing the 30-Dimensional Antisymmetrized Electronic Structure of Water: The Emergence of Lone Pairs. J Phys Chem Lett 2020; 11:735-739. [PMID: 31917585 DOI: 10.1021/acs.jpclett.9b03528] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The electronic structure of water is typically thought of as exhibiting lone pairs of electrons, described by some as "rabbit ears". This is not the universal view, and it does not mesh with an interpretation based on the one-electron wave functions that emerge from molecular orbital theory. Here, we show, by analyzing the 30-dimensional antisymmetrized wave function (Slater determinant) rather than the Hartree product, that the water wave function indeed exhibits equivalent lone pairs. The observed photoelectron spectrum is reconciled with this view, in terms of a relaxation of this structure upon the loss of an electron. Therefore, the lone-pair viewpoint is shown to be completely consistent with both the experimental results and the calculated wave function.
Collapse
|
15
|
Abstract
We review the pre-quantum theories of electronic structure of Lewis and Langmuir, and how this relates to the post-quantum double-quartet theory of Linnett. Linnett’s ideas are put on a firm theoretical footing through the emergence of the wavefunction tile: The 3N-dimensional repeating structure of the N-electron wavefunction. Wavefunction tiles calculated by the dynamic Voronoi Metropolis sampling method are reviewed, and new results are presented for bent bonds of cyclopropane, and electron correlation in Be-O-Be.
Collapse
|