Nitrogen hydrate samples were synthesized using liquid nitrogen and powder ice at 16 MPa and 253 K. Confocal laser Raman spectroscopy was used to investigate the characteristics of nitrogen clathrate hydrates. The res...Nitrogen hydrate samples were synthesized using liquid nitrogen and powder ice at 16 MPa and 253 K. Confocal laser Raman spectroscopy was used to investigate the characteristics of nitrogen clathrate hydrates. The results show that the Raman peaks of N-N and O-H stretching vibration in nitrogen hydrates are observed at 2322.4 and 3092.1 cm^-1, respectively, which are very similar to those in natural air clathrate hydrates. For comparison, we measured the Raman peaks of N-N stretching vibration both in liquid nitrogen and nitrogen molecules saturated water, which appear at 2326.6 and 2325.0 cm^-1, respectively. The Raman spectroscopic observations on the dissociation process suggest that nitrogen molecules occupy both the large and small cages in nitrogen clathrate hydrates. However, only one Raman peak is observed for N N stretching vibration because the difference of the environment of nitrogen molecules between large and small cages is too small to be differentiated by Raman spectroscopy.展开更多
The infrared absorption and Raman scattering spectra were measured for the metallotriph- enylcorroles （MTPCs, M=Cu, Co, Ni, Mn）. The ground-state structures and vibrational spectra of MTPCs have been calculated with...The infrared absorption and Raman scattering spectra were measured for the metallotriph- enylcorroles （MTPCs, M=Cu, Co, Ni, Mn）. The ground-state structures and vibrational spectra of MTPCs have been calculated with the density functional theory. The observed Raman and IR bands have been assigned based on the calculation results. Due to the symmetry lowering, the vibrational spectra of MTPCs are much more complex than metal- loporphyrins, and several skeletal modes are found strongly coupled to the phenyl vibrations. The relationship between the Raman/IR frequencies and the structures of TPC ring is in-vestigated. It is found that the vibrations involving the Cα^I Cα^I stretch and CαCm stretchare sensitive to the size of corrole core. In particular, the frequency of v5, which is assigned to Cα^I Cα^I stretch in coupling with the CαCm symmetric stretch, increases linearly with the decrease of the corrole core-sizes and may be used as a mark band to evaluate the structural change of the metallocorroles.展开更多
The A-band resonance Raman spectra of thiourea were obtained in water and acetonitrile solution. B3LYP/6-311＋＋G（3df,3pd） and RCIS/6-311＋＋G（3df,3pd） calculations were done to elucidate the ultraviolet electroni...The A-band resonance Raman spectra of thiourea were obtained in water and acetonitrile solution. B3LYP/6-311＋＋G（3df,3pd） and RCIS/6-311＋＋G（3df,3pd） calculations were done to elucidate the ultraviolet electronic transitions, the distorted geometry structure and the saddle point of thiourea in 21A excited state, respectively. The resonance Raman spectra were assigned. The absorption spectrum and resonance Raman intensities were modeled using Heller＇s time-dependent wavepacket approach to resonance Raman scattering. The results indicate that largest change in the displacement takes place with the C--S stretch mode u6 （｜△｜=0.95） and noticeable changes appear in the H5N3H6＋H8N4H7 wag v5 （｜△｜=0.19）, NCN symmetric stretch^-C--S stretch＋N3H6＋H8N4 wag v4 （｜△｜=0.18）, while the moderate intensities of 2-15 and 4-15 are mostly due to the large excited state frequency changes of v15, but not due to its significant change in the normal mode displacement. The mechanism of the appearance of even overtones of the S-CN2 out of plane deformation is explored. The results indicate that a Franck-Condon region saddle point is the driving force for the quadric phonon mechanism within the standard A-term of resonance Raman scattering, which leads to the pyramidalization of the carbon center and the geometry distortion of thiourea molecule in 21A excited state.展开更多
We have prepared the 2-（quinolin-8-yloxy）-acetic acid and characterized it by infrared and Raman spectroscopies in the solid phase. The Density Functional Theory （DFT） method, together with the 6-31G^＊ and 6-311...We have prepared the 2-（quinolin-8-yloxy）-acetic acid and characterized it by infrared and Raman spectroscopies in the solid phase. The Density Functional Theory （DFT） method, together with the 6-31G^＊ and 6-311＋＋ G^＊＊ basis sets, show that three stable molecules, for the anhydrous and monohydrated compounds were theoretically determined in the gas phase, and that probably the two more stable conformations are present in the solid phase of the monohydrated compound. The harmonic vibrational wavenumbers for the optimized geometries were calculated at B3LYP/6-31G^＊and B3LYP/6-311＋＋G^＊＊ levels. For a complete assignment of all the observed bands in the vibrational spectra the DFT calculations were combined with Pulay＇s scaled quantum mechanical force field （SQMFF） methodology in order to fit the theoretical Wavenumber values to the experimental ones. The characteristics of the electronic delocalization of all structures of both forms were performed by using natural bond orbital （NBO）, while the corresponding topological properties of electronic charge density are analysed by employing Bader＇s atoms in molecules theory （AIM）.展开更多
The excited state structural dynamics of phenyl absorbing S2（A＇）, S3（A＇）, and S6（A＇） states were troseopy and complete active space self-consistent and the UV absorption bands were assigned on azide （PhN3） ...The excited state structural dynamics of phenyl absorbing S2（A＇）, S3（A＇）, and S6（A＇） states were troseopy and complete active space self-consistent and the UV absorption bands were assigned on azide （PhN3） after excitation to the light studied using the resonance Raman specfield calculations. The vibrational spectra the basis of the Fourier transform （FT）- Raman, FT-infrared measurements, the density-functional theory computations and the normal mode analysis. The A-, B-, and C-bands resonance Raman spectra in cyclohex- ane, acetonitrile, and methanol solvents were, respectively, obtained at 273.9, 252.7, 245.9, 228.7, 223.1, and 208.8 nm excitation wavelengths to probe the corresponding structural dynamics of PhN3. The results indicated that the structural dynamics in the S2 （A＇）, S3（A＇）, and S6（A＇） states were significantly different. The crossing points of the potential energy surfaces, S2S1（1） and S2S1（2）, were predicted to play a key role in the low-lying excited state decay dynamics, in accordance with Kasha＇s rule, and NT=N8 dissociation. Two decay channels initiated from the Franck-Condon region of the S2（A＇） state were predicted： the radiative S2,min→S0 radiative decay and the S2→S1 internal conversion through the crossing points S2S1 （1）/S2S1（2）.展开更多
The decay dynamics of N, N-dimethylthioacetamide after excitation to the S3（ππ＊） state was studied by using the resonance Raman spectroscopy and complete active space self- consistent field method calculations. T...The decay dynamics of N, N-dimethylthioacetamide after excitation to the S3（ππ＊） state was studied by using the resonance Raman spectroscopy and complete active space self- consistent field method calculations. The UV-absorption and vibrational spectra were as- signed. The A-band resonance Raman spectra were obtained in acetonitrile, methanol and water with the laser excitation wavelengths in resonance with the first intense absorption band to probe the Franck-Condon region structural dynamics. The CASSCF calculations were carried out to determine the excitation energies and optimized structures of the lower- lying singlet states and conical intersection point. The A-band structural dynamics and the corresponding decay mechanism were obtained by the analysis of the resonance Raman in- tensity pattern and the CASSCF calculated structural parameters. The major decay channel of S3,FC （ππ＊）→S3（ππ＊）/S1 （nπ＊）→S1（nπ＊） is proposed.展开更多
The structural and vibrational properties of two-dimensional hexagonal silicon （silicene） and germanium （germanene） are investigated by means of first-principles calculations. It is predicted that the silicene （g...The structural and vibrational properties of two-dimensional hexagonal silicon （silicene） and germanium （germanene） are investigated by means of first-principles calculations. It is predicted that the silicene （germanene） structure with a small buckling of 0.44 ,~ （0.7/k） and bond lengths of 2.28 ,~ （2.44 .~） is energetically the most favorable, and it does not exhibit imaginary phonon mode. The calculated non-resonance Raman spectra of silicene are characterized by a main peak at about 575 cm-1, namely the G-like peak. For germanene, the highest peak is at about 290 cm-1. Extensive calculations on armchair silicene nanoribbons and armchair germanene nanoribbons are also performed, with and without hydrogenation of the edges. The studies reveal other Raman peaks mainly distributed at lower frequencies than the G-like peak which could be attributed to the defects at the edges of the ribbons, thus not present in the Raman spectra of non-defective silicene and germanene. Particularly the Raman peak corresponding to the D mode is found to be located at around 515 cm-1 for silicene and 270 cm-1 for germanene. The calculated G-like and the D peaks are likely the fingerprints of the Raman spectra of the low-buckled structures of silicene and germanene.展开更多
文摘Nitrogen hydrate samples were synthesized using liquid nitrogen and powder ice at 16 MPa and 253 K. Confocal laser Raman spectroscopy was used to investigate the characteristics of nitrogen clathrate hydrates. The results show that the Raman peaks of N-N and O-H stretching vibration in nitrogen hydrates are observed at 2322.4 and 3092.1 cm^-1, respectively, which are very similar to those in natural air clathrate hydrates. For comparison, we measured the Raman peaks of N-N stretching vibration both in liquid nitrogen and nitrogen molecules saturated water, which appear at 2326.6 and 2325.0 cm^-1, respectively. The Raman spectroscopic observations on the dissociation process suggest that nitrogen molecules occupy both the large and small cages in nitrogen clathrate hydrates. However, only one Raman peak is observed for N N stretching vibration because the difference of the environment of nitrogen molecules between large and small cages is too small to be differentiated by Raman spectroscopy.
文摘The infrared absorption and Raman scattering spectra were measured for the metallotriph- enylcorroles （MTPCs, M=Cu, Co, Ni, Mn）. The ground-state structures and vibrational spectra of MTPCs have been calculated with the density functional theory. The observed Raman and IR bands have been assigned based on the calculation results. Due to the symmetry lowering, the vibrational spectra of MTPCs are much more complex than metal- loporphyrins, and several skeletal modes are found strongly coupled to the phenyl vibrations. The relationship between the Raman/IR frequencies and the structures of TPC ring is in-vestigated. It is found that the vibrations involving the Cα^I Cα^I stretch and CαCm stretchare sensitive to the size of corrole core. In particular, the frequency of v5, which is assigned to Cα^I Cα^I stretch in coupling with the CαCm symmetric stretch, increases linearly with the decrease of the corrole core-sizes and may be used as a mark band to evaluate the structural change of the metallocorroles.
基金This work was supported by the National Natural Science Foundation of China （No.21033002 and No.20803066） and the National Basic Research Program of China （No.2007CB815203）.
文摘The A-band resonance Raman spectra of thiourea were obtained in water and acetonitrile solution. B3LYP/6-311＋＋G（3df,3pd） and RCIS/6-311＋＋G（3df,3pd） calculations were done to elucidate the ultraviolet electronic transitions, the distorted geometry structure and the saddle point of thiourea in 21A excited state, respectively. The resonance Raman spectra were assigned. The absorption spectrum and resonance Raman intensities were modeled using Heller＇s time-dependent wavepacket approach to resonance Raman scattering. The results indicate that largest change in the displacement takes place with the C--S stretch mode u6 （｜△｜=0.95） and noticeable changes appear in the H5N3H6＋H8N4H7 wag v5 （｜△｜=0.19）, NCN symmetric stretch^-C--S stretch＋N3H6＋H8N4 wag v4 （｜△｜=0.18）, while the moderate intensities of 2-15 and 4-15 are mostly due to the large excited state frequency changes of v15, but not due to its significant change in the normal mode displacement. The mechanism of the appearance of even overtones of the S-CN2 out of plane deformation is explored. The results indicate that a Franck-Condon region saddle point is the driving force for the quadric phonon mechanism within the standard A-term of resonance Raman scattering, which leads to the pyramidalization of the carbon center and the geometry distortion of thiourea molecule in 21A excited state.
文摘We have prepared the 2-（quinolin-8-yloxy）-acetic acid and characterized it by infrared and Raman spectroscopies in the solid phase. The Density Functional Theory （DFT） method, together with the 6-31G^＊ and 6-311＋＋ G^＊＊ basis sets, show that three stable molecules, for the anhydrous and monohydrated compounds were theoretically determined in the gas phase, and that probably the two more stable conformations are present in the solid phase of the monohydrated compound. The harmonic vibrational wavenumbers for the optimized geometries were calculated at B3LYP/6-31G^＊and B3LYP/6-311＋＋G^＊＊ levels. For a complete assignment of all the observed bands in the vibrational spectra the DFT calculations were combined with Pulay＇s scaled quantum mechanical force field （SQMFF） methodology in order to fit the theoretical Wavenumber values to the experimental ones. The characteristics of the electronic delocalization of all structures of both forms were performed by using natural bond orbital （NBO）, while the corresponding topological properties of electronic charge density are analysed by employing Bader＇s atoms in molecules theory （AIM）.
基金This work is supported by the National Natural Science Foundation of China （No.21473163, No.21033002, No.21202032） and the National Basic Research Program of China （No.2013CB834604）.
文摘The excited state structural dynamics of phenyl absorbing S2（A＇）, S3（A＇）, and S6（A＇） states were troseopy and complete active space self-consistent and the UV absorption bands were assigned on azide （PhN3） after excitation to the light studied using the resonance Raman specfield calculations. The vibrational spectra the basis of the Fourier transform （FT）- Raman, FT-infrared measurements, the density-functional theory computations and the normal mode analysis. The A-, B-, and C-bands resonance Raman spectra in cyclohex- ane, acetonitrile, and methanol solvents were, respectively, obtained at 273.9, 252.7, 245.9, 228.7, 223.1, and 208.8 nm excitation wavelengths to probe the corresponding structural dynamics of PhN3. The results indicated that the structural dynamics in the S2 （A＇）, S3（A＇）, and S6（A＇） states were significantly different. The crossing points of the potential energy surfaces, S2S1（1） and S2S1（2）, were predicted to play a key role in the low-lying excited state decay dynamics, in accordance with Kasha＇s rule, and NT=N8 dissociation. Two decay channels initiated from the Franck-Condon region of the S2（A＇） state were predicted： the radiative S2,min→S0 radiative decay and the S2→S1 internal conversion through the crossing points S2S1 （1）/S2S1（2）.
基金This work was supported by the National Natu- ral Science Foundation of China （No.21033002 and No.21202032） and the National Basic Research Pro- gram of China （No.2013CB834604）.
文摘The decay dynamics of N, N-dimethylthioacetamide after excitation to the S3（ππ＊） state was studied by using the resonance Raman spectroscopy and complete active space self- consistent field method calculations. The UV-absorption and vibrational spectra were as- signed. The A-band resonance Raman spectra were obtained in acetonitrile, methanol and water with the laser excitation wavelengths in resonance with the first intense absorption band to probe the Franck-Condon region structural dynamics. The CASSCF calculations were carried out to determine the excitation energies and optimized structures of the lower- lying singlet states and conical intersection point. The A-band structural dynamics and the corresponding decay mechanism were obtained by the analysis of the resonance Raman in- tensity pattern and the CASSCF calculated structural parameters. The major decay channel of S3,FC （ππ＊）→S3（ππ＊）/S1 （nπ＊）→S1（nπ＊） is proposed.
文摘The structural and vibrational properties of two-dimensional hexagonal silicon （silicene） and germanium （germanene） are investigated by means of first-principles calculations. It is predicted that the silicene （germanene） structure with a small buckling of 0.44 ,~ （0.7/k） and bond lengths of 2.28 ,~ （2.44 .~） is energetically the most favorable, and it does not exhibit imaginary phonon mode. The calculated non-resonance Raman spectra of silicene are characterized by a main peak at about 575 cm-1, namely the G-like peak. For germanene, the highest peak is at about 290 cm-1. Extensive calculations on armchair silicene nanoribbons and armchair germanene nanoribbons are also performed, with and without hydrogenation of the edges. The studies reveal other Raman peaks mainly distributed at lower frequencies than the G-like peak which could be attributed to the defects at the edges of the ribbons, thus not present in the Raman spectra of non-defective silicene and germanene. Particularly the Raman peak corresponding to the D mode is found to be located at around 515 cm-1 for silicene and 270 cm-1 for germanene. The calculated G-like and the D peaks are likely the fingerprints of the Raman spectra of the low-buckled structures of silicene and germanene.
