Ground State In Gas Phase Research Articles

An Isolated Molecule of Iron(II) Phthalocyanin Exhibits Quintet Ground-State: A Nexus between Theory and Experiment.

Iron(II) phthalocyanine (FePc) is an important member of the phthalocyanines family with potential applications in the fields of electrocatalysis, magnetic switching, electrochemical sensing, and phototheranostics. Despite the importance of electronic properties of FePc in these applications, a reliable determination of its ground-state is still challenging. Here we present combined state of the art computational methods and experimental approaches, that is, Mössbauer spectroscopy and Superconducting Quantum Interference Device (SQUID) magnetic measurements to identify the ground state of FePc. While the nature of the ground state obtained with density functional theory (DFT) depends on the functional, giving mostly the triplet state, multi-reference complete active space second-order perturbation theory (CASPT2) and density matrix renormalization group (DMRG) methods assign quintet as the FePc ground-state in gas-phase. This has been confirmed by the hyperfine parameters obtained from 57 Fe Mössbauer spectroscopy performed in frozen monochlorobenzene. The use of monochlorobenzene guarantees an isolated nature of the FePc as indicated by a zero Weiss temperature. The results open doors for exploring the ground state of other metal porphyrin molecules and their controlled spin transitions via external stimuli.

Structural and spectroscopic characterization, reactivity study and charge transfer analysis of the newly synthetized 2-(6-hydroxy-1-benzofuran-3-yl) acetic acid

The title compound 2-(6-hydroxy-1-benzofuran-3-yl) acetic acid (abbreviated as HBFAA) has been synthetized and characterized by FT-IR, FT-Raman and NMR spectroscopic techniques. Solid state crystal structure of HBFAA has been determined by single crystal X-ray diffraction technique. The crystal structure features O-H⋯O and C-H⋯O intermolecular interactions resulting in a two dimensional supramolecular architecture. The presence of various intermolecular interactions is well supported by the Hirshfeld surface analysis. The molecular properties of HBFAA were performed by Density functional theory (DFT) using B3LYP/6-311G++(d,p) method at ground state in gas phase, compile these results with experimental values and shows mutual agreement. The vibrational spectral analysis were carried out using FT-IR and FT-Raman spectroscopic techniques and assignment of each vibrational wavenumber made on the basis of potential energy distribution (PED). And also frontier orbital analysis (FMOs), global reactivity descriptors, non-linear optical properties (NLO) and natural bond orbital analysis (NBO) of HBFAA were computed with same method. Efforts were made in order to understand global and local reactivity properties of title compound by calculations of MEP, ALIE, BDE and Fukui function surfaces in gas phase, together with thermodynamic properties. Molecular dynamics simulation and radial distribution functions were also used in order to understand the influence of water to the stability of title compound. Charge transfer between molecules of HBFAA has been investigated thanks to the combination of MD simulations and DFT calculations.

Supramolecular architecture of 5-bromo-7-methoxy-1-methyl-1H-benzoimidazole.3H2O: Synthesis, spectroscopic investigations, DFT computation, MD simulations and docking studies

Crystal and molecular structure of newly synthesized compound 5-bromo-7-methoxy-1-methyl-1H-benzoimidazole (BMMBI) has been authenticated by single crystal X-ray diffraction, FT-IR, FT-Raman, 1H NMR, 13C NMR and UV–Visible spectroscopic techniques; compile both experimental and theoretical results which are performed by DFT/B3LYP/6-311++G(d,p) method at ground state in gas phase. Visualize nature and type of intermolecular interactions and crucial role of these interactions in supra-molecular architecture has been investigated by use of a set of graphical tools 3D-Hirshfeld surfaces and 2D-fingerprint plots analysis. The title compound stabilized by strong intermolecular hydrogen bonds N⋯HO and O⋯HO, which are envisaged by dark red spots on dnorm mapped surfaces and weak Br⋯Br contacts envisaged by red spot on dnorm mapped surface. The detailed fundamental vibrational assignments of wavenumbers were aid by with help of Potential Energy distribution (PED) analysis by using GAR2PED program and shows good agreement with experimental values. Besides frontier orbitals analysis, global reactivity descriptors, natural bond orbitals and Mullikan charges analysis were performed by same basic set at ground state in gas phase. Potential reactive sites of the title compound have been identified by ALIE, Fukui functions and MEP, which are mapped to the electron density surfaces. Stability of BMMBI have been investigated from autoxidation process and pronounced interaction with water (hydrolysis) by using bond dissociation energies (BDE) and radial distribution functions (RDF), respectively after MD simulations. In order to identify molecule's most important reactive spots we have used a combination of DFT calculations and MD simulations. Reactivity study encompassed calculations of a set of quantities such as: HOMO-LUMO gap, MEP and ALIE surfaces, Fukui functions, bond dissociation energies and radial distribution functions. To confirm the potential of title molecule in the area of pharmaceutics, we have also calculated a series of drug likeness parameters. Possibly important biological activity of BMMBI molecule was also confirmed by molecular docking study.

Theoretical calculations of intramolecular hydrogen bond of the 2-Amino-2, 4, 6-cycloheptatrien-1-one in the gas phase and solution: Substituent effects and their positions

The density functional theory (DFT) method with 6-311[Formula: see text]G[Formula: see text] basis set has been used to calculate the intramolecular hydrogen bond, molecular structure, vibrational frequencies, nuclear quadrupole resonance (NQR) parameters, 1HNMR, and resonance parameters of 2-Amino-2, 4, 6-cycloheptatrien-1-one (2-amino tropone) and its 18 derivatives in 5 positions. The natural bonding orbital (NBO) and quantum theory of atoms in molecules (QTAIM) analyses have been studied. The strongest and weakest hydrogen bonds exist for NO2 substituent in R3 position and OH in R7 position, respectively. In general, the substituted systems in position 3 indicate the stronger hydrogen bond in comparison with the parent molecule (R[Formula: see text]H), while, it is comparatively weaker for position 5. The energy of the N-H[Formula: see text]O interaction is found to be medium in strength ([Formula: see text][Formula: see text]kJ mol[Formula: see text] to [Formula: see text][Formula: see text]kJ mol[Formula: see text]). The low [Formula: see text], positive [Formula: see text] values and [Formula: see text] show that the nature of O [Formula: see text] H bonding is electrostatic. Also, our theoretical results show that the hydrogen bond strength in solution phase and the first singlet excited state is weaker in comparison with the gas phase ground state.

Geometric, electronic and intrinsic chemical reactivity properties of mono- and bi-substituted quinoline derivatives for the ground state in gas phase

The study of geometric, electronic properties and intrinsic chemical reactivity is presented for the case of Quinoline and three-derived molecules (4-Amino-Quinoline, 3- Phenyl-Quinoline, 4-Amino-3-phenylquinoline). The study was carried for the ground state in gas phase in the context of the functional theory density using B3LYP/6 31+G (d) model. The purpose of the study is aimed for identifying a compound derived from quinoline, on based to mono- or bi-substitution, using the amino fragment and the phenyl group.

Noble Gas Matrices May Change the Electronic Structure of Trapped Molecules: The UO2(Ng)4 [Ng=Ne, Ar] Case

In the last two decades matrix isolation techniques have achieved a notable success for several types of spectroscopy, ranging from infrared, optical absorption, laser-induced fluorescence and electron-spin resonance spectroscopy. Their major accomplishment lies on the possibility of embedding a guest molecule inside a host that acts as spectator and is inert towards any type of chemical interaction at very low temperatures (4–12 K). The most successful isolations occur when the gas used to trap the guest molecule is a light noble gas, known for its reluctance to form any type of chemical bond. The recent discoveries of stable noble gas complexes, such as HArF and NgAuF (Ng=Ar, Kr, Xe), have spurred new questions regarding the actual inertness of Ng hosts in matrix isolation, especially when actinide molecules, capable of forming bonds possibly involving the close-lying 5f, 6d, and 7s orbitals, are trapped. In particular, the molecules CUO and UO2 have challenged this paradigm, having shown in recent years a very probable noble-gas-induced ground state reversal going from Ne to Ar as the isolating gases. On investigating the UO2 molecule in more detail, Andrews et al. in 2000 noticed a large frequency shift for the asymmetric stretching mode at n=776 cm!1 in solid Ar, as compared to solid Ne at n=915 cm!1.[8] Such a significant shift can only be explained with the help of highly accurate calculations by exploring several electronic states and matching the measured asymmetric U!O stretch vibration with the computed ones. Following this procedure, the two possible candidates to the ground-state reversal have been recognized in the F2u (ground state in gas phase) and the H4g states, with their values being computed at n=919 and 824 cm!1, respectively, by using density functional theory (DFT). Subsequently, Heaven et al. have recorded fluorescence spectra attributed to UO2 in solid Ar and concluded that the pattern of low-lying electronic excited states is consistent with their previous gas-phase measurements, where they established the F2u as the ground state and stated that reversal of the ground state in solid Ar is unlikely. As a consequence of this contradicting situation, theoretical chemists carried out state-of-the-art calculations pinpointing the F2u state as the ground state and describing with great precision the excitation spectrum of the UO2 molecule. However, the calculations have been done for the bare molecule, certainly a good approximation for the gas phase, but not for the matrix. Now with improvement of computer architecture, we can use computationally intensive methods to study the electronic excited states of the UO2 molecule with a shell of noble gas atoms. In this work, we decided to run CASSCF/ CASPT2 calculations on the UO2(Ng)4 [Ng=Ne, Ar] complex, where the four noble gas atoms are displaced along the equatorial plane at a fixed equal U!Ng bond length, thus enforcing a D4h symmetry (D2h in the calculations). We decided to keep the inversion center to distinguish between the ungerade and gerade states and to allow maximum computational advantage. See the Supporting Information for more details. In Figure 1, the SO-CASPT2 potential energy surface (PES) computed with MOLCAS is depicted for the most [a] Prof. Dr. L. Gagliardi Department of Chemistry University of Minnesota and Supercomputing Institute 207 Pleasant St. SE, Minneapolis, MN 55455 (USA) Fax: (+1)6126 267 541 E-mail : gagliard@umn.edu [b] Dr. I. Infante Kimika Fakultatea Euskal Herriko Unibertsitatea and Donostia International Physics Center (DIPC) P.K. 1072, 20080 Donostia, Euskadi (Spain) [c] Prof. Dr. L. Andrews Department of Chemistry, University of Virginia Charlottesville, Virginia 22904-4319 (USA) [d] Dr. X. Wang Department of Chemistry, Tongji University 200092 Shanghai (China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201002549.

Local alkali-metal-promoted oxidation of Si(100)-(2 x 1) surfaces: A generalized-Hubbard-model calculation.

In order to study the local regime in the alkali-metal-promoted oxidation of silicon, we consider the coadsorption of an oxygen molecule and a potassium atom on the dimerized Si(100)-(2\ifmmode\times\else\texttimes\fi{}1) surface. Antiferromagnetic (singlet) spin correlations within the Si dimers are taken into account from the outset by working with a generalized Hubbard Hamiltonian. In this background, the adsorption of a K atom strongly polarizes the medium creating a local charge-spin bag, around the ${\mathrm{K}}^{+}$ ion, which sets the scenario for promoted oxidation. When an ${\mathrm{O}}_{2}$ molecule in its ground state ${(}^{3}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}$) approaches this region of the surface, it is influenced by the attractive electrostatic field of the ${\mathrm{K}}^{+}$ ion, with the corresonding lowering of its affinity level. This eventually crosses the Fermi level and captures the excess electron charge in the bag. A superoxide ${\mathrm{O}}_{2}$ ion, the $^{2}\mathrm{\ensuremath{\Pi}}_{\mathit{g}}$ state, is thereby formed, ionicly bonded to ${\mathrm{K}}^{+}$ and covalently bonded to the Si dimer. In the absence of potassium, the oxygen molecule simply physisorbs in a state adiabatically connected to its gas-phase ground state.

Excited state bromine atom and molecule reactions

Excitation of bromine at wavelengths near the dissociation limit of the B 3Π+0u electronic state is shown to produce substitution and extraction reactions of excited bromine with olefins. These reactions are produced by drastically shortening free-radical chains in contrast to more conventional photochemical experiments which yield addition products only. Shortening of radical chains is accomplished by irradiating a flowing gas mixture in a capillary optical reactor. Wavelength selective photochemical reactions of excited 2P1/2 bromine atoms are found to occur simultaneously with gas phase ground state 2P3/2 atom reactions and with surface reactions. Evidence for reactions of electronically excited molecules of bromine in the B 3Π+0u state is also found.