| 531. |
- Minaeva, Valentina, et al.
(författare)
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Hirshfeld and AIM Analysis of the Methylone Hydrochloride Crystal Structure and Its Impact on the IR Spectrum Combined with DFT Study
- 2023
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Ingår i: Crystals. - : MDPI. - 2073-4352. ; 13:3
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Tidskriftsartikel (refereegranskat)abstract
- Herein, the Hirshfeld surfaces analysis of the crystalline methylone hydrochloride was performed in order to analyze NHMIDLINE HORIZONTAL ELLIPSISCl, CHMIDLINE HORIZONTAL ELLIPSISCl, and CHMIDLINE HORIZONTAL ELLIPSISO intermolecular interactions and study the formation of the NH2+-Cl- salt fragment in methylone hydrochloride crystal. There are two isomeric dimers with parallel and side-by-side orientation extracted from the crystal packing to model the IR spectrum of the crystalline methylone hydrochloride within the framework of density functional theory (DFT) and B3LYP/6-31G(d,p) method. We have assigned and interpreted all observed IR bands in the experimental spectrum of the 3,4-methylenedioxymethcathinone hydrochloride standard crystal sample that is important for forensic-medical examination. It was shown that intermolecular interactions between the NH2+ and Cl- ionic moieties occur in crystalline samples that confirm the presence of the ionized form of the methylone hydrochloride compound with the NH2+Cl- fragment.
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| 532. |
- Minkov, Ivaylo, et al.
(författare)
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Core-excitations of biphenyl
- 2005
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 109:7, s. 1330-1336
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution C(1s) near-edge X-ray absorption and X-ray photoionization spectra of the free biphenyl molecule are presented and theoretically analyzed in order to allow an assignment of the observed spectral features. Finite lifetime broadening, a high density of vibrational states, and a strong overlap of contributions from chemically different carbon atom sites only partially allow resolving the vibrational fine structure. However, the shape and width of the spectral profiles are strongly determined by both chemical shifts and vibronic effects. In particular, different from photoionization of valence levels, both types of core level spectra do not contain contributions from dihedral modes which are related to the twisting motion of the two phenyl rings. Contrary to naphthalene, C-H stretching modes are significantly enhanced in the core excitation spectra of biphenyl while the contributions from C-C stretching modes are reduced.
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| 533. |
- Minkov, Ivaylo, et al.
(författare)
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Core-excitations of naphthalene : Vibrational structure versus chemical shifts
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 121:12, s. 5733-5739
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Tidskriftsartikel (refereegranskat)abstract
- The initial state chemical shifts and vibrational fine structure of core excitations of naphthalene were analyzed using high-resolution x-ray photoelectron emission (XPS) and near-edge x-ray absorption fine structure (NEXAFS) spectra. The carbon atoms at peripheral sites were found to experience a small chemical shift and exhibit similar charge-vibrational coupling. The C-H stretching modes provide significant contributions to overall shape of spectra in the XPS spectra. The results show that vibrational fine structure dominates by particular C-C stretching modes, and in XPS of C2 and C3 sites also by high-energy C-H stretching modes.
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| 534. |
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| 535. |
- Minkov, Ivaylo
(författare)
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Theoretical studies of X-ray induced nuclear dynamics
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis is a theoretical study of several x-ray spectroscopies { x-ray absorption, xray photoelectron, radiative and non-radiative resonant Raman scattering spectroscopy. The main focus point is investigating the role of the nuclear dynamics in molecules (naphthalene, biphenyl, the water dimer, HCl) on these spectra. The theoretical tools we use consist of the basic equations of the relevant x-ray spectroscopy. Wave packet methods are also used. The molecular parameters needed for our simulations are obtained through suitable quantum chemical calculations, mainly based on either wave function or density functional methods. Our simulations are compared with experimental data, where available. Simulations of x-ray absorption and x-ray photoionization spectra for naphthalene and biphenyl show that the spectral shapes are heavily inuenced by the joint e ect of two factors { chemical shifts and excitations of vibrational progression. In both of the studied molecules, similar vibrational modes are excited, giving rise to a signi cant vibrational broadening of the spectra. Comparison between the two molecules and also comparison to the reference case { benzene, provides useful insight into the molecular behavior under core excitation. In a further step, we consider the O1s x-ray photoelectron spectrum of the water dimer. A substantial broadening of the two bands originating from the donor and the acceptor oxygen is found. It is caused by excitations of soft intermolecular vibrational modes, associated with the hydrogen bond. Another strong inuence of the nuclear dynamics is clearly seen in the resonant x-ray Raman scattering of HCl. Vibrational collapse is observed experimentally and con rmed theoretically for two cases: resonant excitation of the K line and o -resonant excitation of the elastic peak. These two collapses can be strictly realized for excitations in the hard x-ray region. Our considerations show that using this technique, one can eliminate the broadenings caused by the lifetime of the core excited state and the vibrational broadening, and hence, considerably increase the spectral resolution. Finally, we predict an interference e ect in the resonant Auger scattering from xed-inspace molecules. By exciting a molecule to a dissociative state and measuring the angular distribution of the Auger electrons in coincidence with the molecular ion, one can observe this e ect. The interference pattern can be used after Fourier transformation for extracting structural data about the studied system.
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| 536. |
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| 537. |
- Miron, Catalin, et al.
(författare)
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Site-selective photoemission from delocalized valence shells induced by molecular rotation
- 2014
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 3816-
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Tidskriftsartikel (refereegranskat)abstract
- Due to the generally delocalized nature of molecular valence orbitals, valence-shell spectroscopies do not usually allow to specifically target a selected atom in a molecule. However, in X-ray electron spectroscopy, the photoelectron momentum is large and the recoil angular momentum transferred to the molecule is larger when the photoelectron is ejected from a light atom compared with a heavy one. This confers an extreme sensitivity of the rotational excitation to the ionization site. Here we show that, indeed, the use of high-energy photons to photoionize valence-shell electrons of hydrogen chloride offers an unexpected way to decrypt the atomic composition of the molecular orbitals due to the rotational dependence of the photoionization profiles. The analysis of the site-specific rotational envelopes allows us to disentangle the effects of the two main mechanisms of rotational excitation, based on angular momentum exchange between the molecule and either the incoming photon or the emitted electron.
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| 538. |
- Mitev, Pavlin D., et al.
(författare)
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Different structures give similar vibrational spectra : The case of OH- in aqueous solution
- 2013
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 138:6, s. 064503-
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Tidskriftsartikel (refereegranskat)abstract
- We have calculated the anharmonic OH-(aq) vibrational spectrum in aqueous solution with a "classical Monte Carlo simulation + QM/MM + vibrational" sequential approach. A new interaction model was used in the Monte Carlo simulations: a modified version of the charged-ring hydroxide-water model from the literature. This spectrum is compared with experiment and with a spectrum based on CPMD-generated structures, and the hydration structures and H-bonding for the two models are compared. We find that: (i) the solvent-induced frequency shift as well as the absolute OH- frequency are in good agreement with experiment using the two models; (ii) the Raman and IR bands are very similar, in agreement with experiment; (iii) the hydration structure and H-bonding around the ion are very different with the two ion-water interaction models (charged-ring and CPMD); (iv) a cancellation effect between different regions of the hydration shell makes the total spectra similar for the two interaction models, although their hydration structures are different; (v) the net OH- frequency shift is a blueshift of about + 80 cm(-1) with respect to frequency of the gas-phase ion.
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| 539. |
- Mochizuki, Y., et al.
(författare)
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Polarizability of silicon clusters
- 2001
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 336:06-maj, s. 451-456
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Tidskriftsartikel (refereegranskat)abstract
- The polarizability of hydrogen-terminated silicon dusters derived from the silicon diamond-lattice structure was evaluated by linear response calculations. The dependences on cluster size and basis set were systematically investigated. A convergence in calculated polarizability per silicon atom toward the bulk value was found. Frequency-dependent polarizabilities were also addressed.
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| 540. |
- Moghadam, Reza Zarei, et al.
(författare)
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Understanding the effect of Mn2+ on Yb3+/Er3+ co-doped NaYF4 upconversion and obtaining the optimal combination of these tridoping
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we investigated in detail the upconversion properties of several types of nanoparticles, including NaYF4:5%Yb3+/30%Mn2+, NaYF4:40%Mn2+/x%Yb3+ (x% = 1, 5, 10, 20, 30, and 40), NaYF4:2%Er3+/x%Mn2+ (x% = 20, 30, 40, 50, 60, and 70), NaYF4:40%Mn2+/x%Er3+ (x% = 1, 2, 5, and 10), and NaYF4:40%Mn2+/1%Yb3+/x%Er3+ (x% = 0, 2, 5, and 10). We studied their upconversion emission under 980 nm excitation in both pulsed and continuous wave modes at different synthesis temperatures. The nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and photoluminescence (PL) spectroscopy. The doping of Yb3+ and Mn2+ ions resulted in the nanoparticles assuming cubic and hexagonal crystal structures. The emission intensity increased (106.4 (a.u.*10(3)) to 334.4(a.u.*10(3))) with increasing synthesis temperature from 120 to 140 C-degrees, while a sharp decrease was observed when the synthesis temperature was increased to 200 C-degrees. The gradual decrease in peak intensity with increasing Mn2+ concentration from 20 to 70% was attributed to energy transfer from Mn2+ to Yb3+. In NaYF4:Mn2+/Yb3+/Er3+ UCNPs, increasing the Er3+ concentration from 0 to 10% led to the disappearance of the blue, orange, and green emission bands. The intense upconversion luminescence pattern with high spatial resolution indicates excellent potential for applications in displays, biological sensors, photodetectors, and solar energy converters.
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