| 1. |
- Hansen, Klavs, 1958, et al.
(författare)
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Influence of thermal radiation on hot cluster decay rates and abundances
- 2019
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Ingår i: Chinese Journal of Chemical Physics. - : AIP Publishing. - 1674-0068 .- 2327-2244. ; 32:2, s. 167-174
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Tidskriftsartikel (refereegranskat)abstract
- The influence of radiative cooling on the unimolecular decay rates of free, hot clusters and molecules with unspecified excitation energies is quantified. Two different regimes, defined by the magnitude of the energy of the photons emitted, are identified and the boundary between them is given. The boundary is determined in terms of the photon emission rate constants and thermal properties of the particles. Also the abundance spectra are calculated for the continuous cooling case, corresponding to small photon energies. The two regimes correspond to continuous cooling and single photon quenching of the unimolecular decay. The radiative effect can be parametrized by a redefinition of the time each individual cluster has available to undergo evaporation, expressed by an effective radiative time constant.
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| 2. |
- Yu, De-quan, et al.
(författare)
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Hermiticity of Hamiltonian Matrix using the Fourier Basis Sets in Bond-Bond-Angle and Radau Coordinates
- 2016
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Ingår i: Chinese Journal of Chemical Physics. - : AIP Publishing. - 1674-0068 .- 2327-2244. ; 29:1
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Tidskriftsartikel (refereegranskat)abstract
- In quantum calculations a transformed Hamiltonian is often used to avoid singularities in a certain basis set or to reduce computation time. We demonstrate for the Fourier basis set that the Hamiltonian can not be arbitrarily transformed. Otherwise, the Hamiltonian matrix becomes non-hermitian, which may lead to numerical problems. Methods for correctly constructing the Hamiltonian operators are discussed. Specific examples involving the Fourier basis functions for a triatomic molecular Hamiltonian (J=0) in bond-bond angle and Radau coordinates are presented. For illustration, absorption spectra are calculated for the OClO molecule using the time-dependent wavepacket method. Numerical results indicate that the non-hermiticity of the Hamiltonian matrix may also result from integration errors. The conclusion drawn here is generally useful for quantum calculation using basis expansion method using quadrature scheme.
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| 3. |
- Li, Hong-bao, et al.
(författare)
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Local Structures and Chemical Properties of Deprotonated Arginine
- 2012
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Ingår i: Chinese Journal of Chemical Physics. - : AIP Publishing. - 1674-0068 .- 2327-2244. ; 25:6, s. 681-686
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Tidskriftsartikel (refereegranskat)abstract
- The potential energy surface of gaseous deprotonated arginine has been systematically investigated by first principles calculations. At the B3LYP/6-31G(d) level, apart from the identification of several stable local structures, a new global minimum is located which is about 6.56 kJ/mol more stable than what has been reported. The deprotonated arginine molecule has two distinct forms with the deprotonation at the carboxylate group (COO-). These two forms are bridged by very high energy barrier and possess very different IR spectral profiles. Our calculated proton dissociation energy and gas-phase acidity of arginine molecule are found to be in good agreement with the corresponding experimental results. The predicted geometries, dipole moments, rotational constants, vertical ionization energies and IR spectra of low energy conformers will be useful for future experimental measurements.
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| 4. |
- Lian, Ke-yan, et al.
(författare)
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Stable High-Energy Density Super-Atom Clusters of Aluminum Hydride
- 2012
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Ingår i: Chinese Journal of Chemical Physics. - : AIP Publishing. - 1674-0068 .- 2327-2244. ; 25:2, s. 147-152
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Tidskriftsartikel (refereegranskat)abstract
- With the concept of super-atom, first principles calculations propose a new type of super stable cage clusters AlnH3n that are much more energetic stable than the well established clusters, AlnHn+2. In the new clusters, the aluminum core-frame acts as a super-atom with n vertexes and 2n Al-Al edges, which allow to adsorb n hydrogen atoms at the top-site and 2n at the bridge-site. Using Al12H36 as the basic unit, stable chain structures, (Al12H36)(m), have been constructed following the same connection mechanism as for (AlH3)(n) linear polymeric structures. Apart from high hydrogen percentage per molecule, calculations have shown that these new clusters possess large heat of formation values and their combustion heat is about 4.8 times of the methane, making them a promising high energy density material.
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| 5. |
- Lin, Ke, et al.
(författare)
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Identification of Free OH and its Implication on Structural Changes of Liquid Water
- 2013
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Ingår i: Chinese Journal of Chemical Physics. - : AIP Publishing. - 1674-0068 .- 2327-2244. ; 26:2, s. 121-126
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Tidskriftsartikel (refereegranskat)abstract
- The molecular structure of liquid water has been an outstanding issue for many years. The identification of free -OH holds the key in differentiating structure models for liquid water. By analyzing the relative changes of the intensity and depolarization ratio in temperature dependent Raman spectra, the occurrence of free -OH in liquid water is unambiguously determined. Furthermore, upon the increase of temperature from 5 degrees C to 85 degrees C, the structure of liquid water undergoes significant change, but the relative proportion of free -OH is considerably small and remains almost unchanged. This implies that the breaking of hydrogen bond from the tetrahedral structure prefers to occur at the site of the hydrogen acceptor. The energetic favoring of the structural change for liquid water is thus clearly revealed from experiments.
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| 6. |
- Lin, Ke, et al.
(författare)
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Quantum Effects on Global Structure of Liquid Water
- 2013
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Ingår i: Chinese Journal of Chemical Physics. - : AIP Publishing. - 1674-0068 .- 2327-2244. ; 26:2, s. 127-132
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Tidskriftsartikel (refereegranskat)abstract
- The structure difference between light and heavy liquid water has been systematically investigated by high precision Raman. spectroscopy over the temperature range of 5-85 degrees C. Distinct difference between the Raman spectral profiles of two different liquid waters is clearly observed. By analyzing the temperature-dependent Raman spectral contour using global fitting procedure, it is found that the micro-structure of heavy water is more ordered than that of light water at the same temperature, and the structure difference between the light and heavy water decreases with the increase of the temperature. The temperature offset, an indicator for the structure difference, is determined to vary from 28 degrees C to 18 degrees C for the low-to-high temperature. It indicates that quantum effect is significantly not only at low temperature, but also at room temperature. The interaction energy among water molecules has also been estimated from van't Hoff's relationship. The detailed structural information should help to develop reliable force fields for molecular modeling of liquid water.
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| 7. |
- Ma, Yong, et al.
(författare)
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Density Functional Theory Study on Raman Spectra of Rhodamine Molecules in Different Forms
- 2014
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Ingår i: Chinese Journal of Chemical Physics. - : AIP Publishing. - 1674-0068 .- 2327-2244. ; 27:3, s. 291-296
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Tidskriftsartikel (refereegranskat)abstract
- Rhodamine molecules are one of the most used dyes for applications related to Raman spectroscopy. We have systematically studied Raman spectra of Rhodamine 60, Rhodamine 123, and Rhodamine B (RhB) molecules using density functional theory. It is found that with BP86 functional the calculated Raman spectra of cationic Rhodamine molecules are in good agreement with corresponding experimental spectra in aqueous solution. It is shown that the involvement of the counter ion, chlorine, and the specific hydrogen bonds has noticeable effects on the Raman spectra of RhB that can partially explain the observed difference between Raman spectra of RhB in solution and on gold surfaces. It also indicates that an accurate description of surface enhanced Raman scattering for Rhodamine molecules on metal surface still requires to take into account the changes induced by the interfacial interactions.
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| 8. |
- Mohammed, Abdelsalam, et al.
(författare)
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Raman Scattering at Resonant or Near-Resonant Conditions : A Generalized Short-Time Approximation
- 2012
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Ingår i: Chinese Journal of Chemical Physics. - : AIP Publishing. - 1674-0068 .- 2327-2244. ; 25:1, s. 31-47
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the dynamics of resonant Raman scattering in the course of the frequency detuning. The dephasing in the time domain makes the scattering fast when the photon energy is tuned from the absorption resonance. This makes frequency detuning to act as a camera shutter with a regulated scattering duration and provides a practical tool of controlling the scattering time in ordinary stationary measurements. The theory is applied to resonant Raman spectra of a couple of few-mode model systems and to trams-1,3,5-hexatriene and guanine-cytosine (G-C) Watson-Crick base pairs (DNA) molecules. Besides some particular physical effects, the regime of fast scattering leads to a simplification of the spectrum as well as to the scattering theory itself. Strong overtones appear in the Raman spectra when the photon frequency is tuned in the resonant region, while in the mode of fast scattering, the overtones are gradually quenched when the photon frequency is tuned more than one vibrational quantum below the first a,absorption resonance. The detuning front the resonant region thus leads to a strong purification of the Raman spectrum from the contamination by higher overtones and soft modes and purifies the spectrum also in terms of avoidance of dissociation and interfering fluorescence decay of the resonant state. This makes frequency detuning a very useful practical tool in the analysis of the resonant Raman spectra of complex systems and considerably improves the prospects for using the Raman effect for detection of foreign substances at ultra-low concentrations.
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