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1.
Raman spectra of deuterated L ‐alanine have been obtained at high‐pressure conditions. A phase transition at ∼1.5 GPa associated with the splitting of some internal modes and increase of the wavenumber of the external modes was observed. Similarly to the hydrogenated L ‐alanine crystal, this first transition was related to a symmetry change. Moreover, further modifications of the Raman spectra were observed at 4.4 GPa, which may be associated to conformational changes of the molecule. To give further support to such a hypothesis, neutron powder diffraction measurements were performed. Information about the cell parameter at atmospheric pressure gave valuable information about the N D distances, shedding light on the behavior of the torsional vibration of ND3+. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

2.
Raman spectra of a crystal of L ‐leucine, an essential amino acid, were obtained for pressures between 0 and 6 GPa. The results show anomalies at three pressure values, one between 0 and 0.46 GPa, another between 0.8 and 1.46 GPa, and a third at P ∼ 3.6 GPa. The first two anomalies are characterized by the disappearance of lattice modes (which can indicate occurrence of phase transitions), the appearance of several internal modes, or the splitting of modes of high wavenumbers. The changes of internal modes are related to CH and CH3 unit motions as well as hydrogen bonds, as can be inferred from the behavior of bands associated with CO2 moieties. The third anomaly is a discrete change of the slopes of the wavenumber versus pressure plots for most modes observed. Further, decompression to ambient pressure generates the original Raman spectrum, showing that the pressure‐induced anomalies undergone by L ‐leucine crystals are reversible. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

3.
Raman spectra of an L ‐methionine (C5H11NO2S) crystal were obtained in the spectral region between 50 and 3200 cm−1 for pressures up to 5 GPa. Pronounced changes of the Raman spectra were observed for bands associated to rocking of CO2; wagging of CO2; deformations of CO2, CH3, and NH3+; and stretching vibrations of SC, CC, CH, CH2, and CH3. Upon decompression to ambient pressure the original Raman spectrum prior to compression is recovered. These modifications were associated to a reversible phase transition undergone by the L ‐methionine crystal at about 2.2 GPa, with a hysteresis of ∼0.8 GPa. Pressure coefficients for most of the internal modes of the crystal are given. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

4.
The first high pressure study of solid hydrazinium monochloride has been performed by in situ Raman spectroscopy and synchrotron X‐ray diffraction (XRD) experiments in diamond anvil cell (DAC) up to 39.5 and 24.6 GPa, respectively. The structure of phase I at room temperature is confirmed to be space group C2/c by the Raman spectral analysis and Rietveld refinement of the XRD pattern. A structural transition from phase I to II is observed at 7.3 GPa. Pressure‐induced position variation of hydrogen atoms in NH3+ unit during the phase transition is attributed to the formation of N―H…Cl hydrogen‐bonds, which play a vital role in the stability and subsequent structural changes of this high energetic material under pressure. This inference is proved from the abnormal pressure shifts and obvious Fermi resonance in NH stretching mode of N2H5+ ion in the Raman experiment. Finally, a further transition from phase II to III accompanied with a slight internal distortion in the N2H5+ ions occurs above 19.8 GPa, and phase III persists up to 39.5 GPa. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

5.
A concentration‐dependent Raman study of the ν(C Br) stretching and trigonal bending modes of 2‐ and 3‐Br‐pyridine (2Br‐p and 3Br‐p) in CH3OH was performed at different mole fractions of the reference molecule, 2Br‐p/3Br‐p, from 0.1 to 0.9 in order to understand the origin of blue/red wavenumber shifts of the vibrational modes due to hydrogen‐bond formation. The appearance of additional Raman bands in these binary systems at ∼617 cm−1in the case of 2Br‐p and at ∼618 cm−1 in the case of 3Br‐p compared to neat bromopyridine derivatives were attributed to specific hydrogen‐bonded complexes formed in the mixtures. The interpretation of experimental results is supported by density functional calculations on optimized geometries and vibrational wavenumbers of 2Br‐p and 3Br‐p and a series of hydrogen‐bonded complexes with methanol. The parameters obtained from these calculations were used for a qualitative explanation of the blue/red shifts. The wavenumber shifts and linewidth changes for the ν(C Br) stretching and trigonal bending modes as a function of concentration reveal that the caging effects leading to motional narrowing and diffusion‐causing line broadening are simultaneously operative, in addition to the blue shift caused due to hydrogen bonding. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

6.
Polarized Raman spectra of single crystals of the α‐polymorphs of protonated and deuterated oxalic acid dihydrate were recorded. The interpretation of the spectra is assisted by periodic DFT calculations using the CRYSTAL06 program and by comparison with the infrared spectra of the polycrystalline material. The agreement between the calculated and observed band wavenumbers is fair in the case of low‐anharmonicity modes, but marked differences appear for the stretching modes that are strongly anharmonic. A very broad feature, extending between ∼2000 and 1200 cm−1, is attributed to OH stretching. Notable is the topping of this feature by distinct bands that can be attributed to CO stretching, H2O scissoring and COH bending coupled to C O stretching. The assignments are supported by isotope effects. However, deuteration does not notably affect the wavenumber limits of the broad OH stretching band, which suggests that the potential governing the proton dynamics is of the asymmetric double‐minimum type with a very low barrier. The calculated normal coordinates show a strong participation of the bending modes of water molecules in almost all internal acid motions, as well as in the external phonons. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

7.
The ―NH2, ―NO2, ―NHNO2, ―C(NO2)3 and ―CF(NO2)2 substitution derivatives of 4,4′,5,5′‐tetranitro‐2,2′‐1H,1′H‐2,2′‐biimidazole were studied at B3LYP/aug‐cc‐pVDZ level of density functional theory. The crystal structures were obtained by molecular mechanics (MM) methods. Detonation properties were evaluated using Kamlet–Jacobs equations based on the calculated density and heat of formation. The thermal stability of the title compounds was investigated via the energy gaps (?ELUMO ? HOMO) predicted. Results show that molecules T5 (D = 10.85 km·s?1, P = 57.94 GPa) and T6 (D = 9.22 km·s?1, P = 39.21 GPa) with zero or positive oxygen balance are excellent candidates for high energy density oxidizers (HEDOs). All of them appear to be potential explosives compared with the famous ones, octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetraazocane (HMX, D = 8.96 km·s?1, P = 35.96 GPa) and hexanitrohexaazaisowurtzitane (CL‐20, D = 9.38 km·s?1, P = 42.00 GPa). In addition, bond dissociation energy calculation indicates that T5 and T6 are also the most thermally stable ones among the title compounds. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

8.
The crystal and local atomic structure of monoclinic ReO2 (α‐ReO2) under hydrostatic pressure up to 1.2 GPa was investigated for the first time using both X‐ray absorption spectroscopy and high‐resolution synchrotron X‐ray powder diffraction and a home‐built B4C anvil pressure cell developed for this purpose. Extended X‐ray absorption fine‐structure (EXAFS) data analysis at pressures from ambient up to 1.2 GPa indicates that there are two distinct Re—Re distances and a distorted ReO6 octahedron in the α‐ReO2 structure. X‐ray diffraction analysis at ambient pressure revealed an unambiguous solution for the crystal structure of the α‐phase, demonstrating a modulation of the Re—Re distances. The relatively small portion of the diffraction pattern accessed in the pressure‐dependent measurements does not allow for a detailed study of the crystal structure of α‐ReO2 under pressure. Nonetheless, a shift and reduction in the (011) Bragg peak intensity between 0.4 and 1.2 GPa is observed, with correlation to a decrease in Re—Re distance modulation, as confirmed by EXAFS analysis in the same pressure range. This behavior reveals that α‐ReO2 is a possible inner pressure gauge for future experiments up to 1.2 GPa.  相似文献   

9.
Abstract

The L-cysteine zwitterions in the orthorhombic crystal structure and in aqueous solution, including the deuterated isotopologues HSCD2CH(NH3 +)COO?, DSCH2CH(ND3 +)COO?, and DSCD2CH(ND3 +)COO?, have been studied by mid-infrared, far-infrared, and Raman spectroscopy. Density functional theory (DFT) calculations were performed for an equilibrium molecular geometry of the cysteine zwitterion to obtain vibrational frequencies of fundamental modes, infrared (IR) and Raman intensities, and the depolarization ratio of the Raman bands and combined with normal coordinate force field analyses. The force field obtained for dissolved (in H2O and D2O) cysteine, based on the 4 × 36 experimental fundamental modes of the four isotopologues, was successfully transferred to the two conformers in the solid state. The experimentally observed multiple bands (generally doublets) of L-cysteine and its deuterated isotopologues in the solid state were interpreted based on the coexistence of two conformers in the unit cell. The calculated frequencies were used for full assignments of the fundamental IR and Raman vibrational transitions, including an attempt to interpret all low-frequency vibrations (below 400 cm?1) of the zwitterion also in the solid state. In particular, the hydrogen bonding effects on conformation, bond lengths, and force constants were studied, including those of the distorted NH3 + amino group. The –S-H and -S-D stretching vibrations were found to be local modes, not sensitive to deuterium substitution of the -CH2 and -NH3 + groups in the molecule or to the H(D)-S-C-C torsional angle. The two major -S-H or -S-D stretching bands observed in the solid state correspond to different S-H/D bond lengths and resulted in the force constants K SH = 3.618 N·cm?1 and 3.657 N·cm?1 for the SH S and SH O hydrogen-bonded interactions. A remarkable result was that the S(H) O interaction was weaker than the S(H) S interaction in the solid state and even weaker in aqueous solution, K SH = 3.715 N·cm?1, possibly due to intramolecular interactions between the thiol and amino groups. A general correlation between the S-H/D bond length and vibrational frequency was developed, allowing the bond length to be estimated for sulfhydryl groups in, for example, proteins. The C-S stretching modes were fitted with different C-S stretching force constants, K CS = 3.213 and 2.713 N·cm?1, consistent with the different CS bond lengths for the two solid-state conformers.  相似文献   

10.
Gas‐phase structure, hydrogen bonding, and cation–anion interactions of a series of 1‐(2‐hydroxyethyl)‐3‐methylimidazolium ([HOEMIm]+)‐based ionic liquids (hereafter called hydroxyl ILs) with different anions (X = [NTf2], [PF6], [ClO4], [BF4], [DCA], [NO3], [AC] and [Cl]), as well as 1‐ethyl‐3‐methylimizolium ([EMIm]+)‐based ionic liquids (hereafter called nonhydroxyl ILs), were investigated by density functional theory calculations and experiments. Electrostatic potential surfaces and optimized structures of isolated ions, and ion pairs of all ILs have been obtained through calculations at the Becke, three‐parameter, Lee–Yang–Parr/6‐31 + G(d,p) level and their hydrogen bonding behavior was further studied by the polarity and Kamlet–Taft Parameters, and 1H‐NMR analysis. In [EMIm]+‐based nonhydroxyl ILs, hydrogen bonding preferred to be formed between anions and C2–H on the imidazolium ring, while in [HOEMIm]+‐based hydroxyl ILs, it was replaced by a much stronger one that preferably formed between anions and OH. The O–H···X hydrogen bonding is much more anion‐dependent than the C2–H···X, and it is weakened when the anion is changed from [AC] to [NTf2]. The different interaction between [HOEMIm]+ and variable anion involving O–H···X hydrogen bonding resulted in significant effect on their bulk phase properties such as 1H‐NMR shift, polarity and hydrogen‐bond donor ability (acidity, α). Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

11.
Raman and infrared spectra are reported for rhodanine, 3‐aminorhodanine and 3‐methylrhodanine in the solid state. Comparisons of the spectra of non‐deuterated/deuterated species facilitate discrimination of the bands associated with N H, NH2, CH2 and CH3 vibrations. DFT calculations of structures and vibrational spectra of isolated gas‐phase molecules, at the B3‐LYP/cc‐pVTZ and B3‐PW91/cc‐pVTZ level, enable normal coordinate analyses in terms of potential energy distributions for each vibrational normal mode. The cis amide I mode of rhodanine is associated with bands at ∼1713 and 1779 cm−1, whereas a Raman and IR band at ∼1457 cm−1 is assigned to the amide II mode. The thioamide II and III modes of rhodanine, 3‐aminorhodanine and 3‐methylrhodanine are observed at 1176 and 1066/1078; 1158 and 1044; 1107 and 984 cm−1 in the Raman and at 1187 and 1083; 1179 and 1074; 1116 and 983 cm−1 in the IR spectra, respectively. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

12.
We report surface‐enhanced Raman scattering (SERS) spectra from 4‐mercaptopyridine (4‐Mpy) adsorbed on sub‐monolayers of α‐Fe2O3 nanocrystals (sphere, spindle, cube). The maximum enhancement factor has been estimated to be about 104 compared to that of 4‐Mpy in solution. A possible mechanism has been proposed that the charge transfer between the α‐Fe2O3 nanocrystals and the 4‐Mpy molecules is most likely responsible for the observed enhancement of Raman intensity of adsorbed 4‐Mpy molecules as surface plasmon resonances have not occurred. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

13.
Raman spectroscopy investigations of L-isoleucine crystals under high pressures have been carried out up to 7.3 GPa. From this study it was possible to observe modifications on bands associated to both rocking vibrations of r(NH3+) and r(CO2) as well as to lattice modes at about 2.3 and 5.0 GPa. These modifications were correlated to either conformational change of molecules or to a solid–solid phase transition undergone by the crystals involving the hydrogen bonds that maintain the molecules held in the unit cell. A comparison with a few results on other amino acid crystals is also given.  相似文献   

14.
As a probe of local structure, the vibrational properties of the 1‐butyl‐3‐methylimidazolium tetrafluoroborate [bmim][BF4] ionic liquid were studied by infrared (IR), Raman spectroscopy, and ab initio calculations. The coexistence of at least four [bmim]+ conformers (GG, GA, TA, and AA) at room temperature was established through unique spectral responses. The Raman modes characteristic of the two most stable [bmim]+ conformers, GA and AA, according to the ab initio calculations, increase in intensity with decreasing temperature. To assess the total spectral behavior of the ionic liquid both the contributions of different [bmim]+ conformers and the [bmim]+− [BF4] interactions to the vibrational spectra are discussed. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

15.
The isotropic and anisotropic parts of the Raman spectra of NH2 bending and ν(CO) stretching modes of HCONH2 in a hydrogen‐bonding solvent, methanol, at different concentrations have been analyzed carefully in order to study the noncoincidence effect (NCE). In neat HCONH2, the experimentally measured values of noncoincidence Δνnc are ∼11 and ∼18 cm−1 for the NH2 bending and ν(CO) stretching modes, which reduce to 0.45 and 1.14 cm−1, respectively at the concentration of HCONH2 in mole fraction, χm = 0.1. The experimental results have been explained on the basis of two models, namely, the microscopic prediction of Logan and the macroscopic model of Mirone and Fini. The relative success of the two models in explaining the experimental data for both the modes have been discussed. It has been observed that in case of the ν(CO) stretching vibrational mode the Logan model can reproduce the experimental data rather precisely, whereas in the case of the NH2 bending mode, Mirone and Fini model yields more accurate results. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

16.
Raman spectroscopy complemented by infrared spectroscopy was used to characterise both gallium oxyhydroxide (α‐GaO(OH)) and gallium oxide (β‐Ga2O3) nanorods synthesised with and without the surfactants using a soft chemical methodology at low temperatures. Nano‐ to micro‐sized gallium oxyhydroxide and gallium oxide materials were characterised and analysed by both X‐ray diffraction and Raman spectroscopy. Rod‐like GaO(OH) crystals with average length of ∼2.5 µm and width of 1.5 µm were obtained. Upon thermally treating gallium oxyhydroxide GaO(OH) to 900 °C, β‐Ga2O3 was synthesised retaining the initial GaO(OH) morphology. Raman spectroscopy has been used to study the structure of nanorods of GaO(OH) and Ga2O3 crystals. Raman spectroscopy shows bands characteristic of GaO(OH) at 950 and ∼1000 cm−1 attributed to Ga OH deformation modes. Bands at 261, 275, 433 and 522 cm−1 are assigned to vibrational modes involving Ga OH units. Bands observed at 320, 346, 418 and 472 cm−1 are assigned to the deformation modes of Ga2O6 octahedra. Two sharp infrared bands at 2948 and 2916 cm−1 are attributed to the GaO(OH) symmetric stretching vibrations. Raman spectroscopy of Ga2O3 provides bands at 630, 656 and 767 cm−1 which are assigned to the bending and stretching of GaO4 units. Raman bands at 417 and 475 cm−1 are attributed to the symmetric stretching modes of GaO2 units. The Raman bands at 319 and 347 cm−1 are assigned to the bending modes of GaO2 units. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

17.
BH4, a well‐known and widely used reducing agent for carbonyl compounds, has been reported to have the ability to participate in dihydrogen bonding, an interaction with applications in catalysis, stereoselectivity and crystal engineering. Specifically, α‐hydroxycarbonyls are activated for reduction by dihydrogen bonding that occurs between BH4 and hydroxyl group. We explored the effect of the interaction on the mechanism of these reactions by examining their activation parameters. We found that dihydrogen bonding activates α‐hydroxycyclopentanone for reduction with NBu4BH4 by lowering the activation enthalpy by 6.6 kcal/mol. While the activation entropy is a significant component of the barrier, the changes resulting from the occurrence of dihydrogen bonding are manifested predominantly in the enthalpy term. Computational studies suggest that, while internal hydrogen bonding is allowed by the flexibility of the carbon backbone, that interaction is outweighed by dihydrogen bonding once BH4 is present in the system. Experimentally, a red shift of the hydroxyl frequency is observed upon addition of BH4 to the reaction mixture, suggesting a dihydrogen bonding interaction. The flexibility of the substrate's skeleton or the selectivity of the hydride sites in BH4 does not account for the lack of directing effect of the dihydrogen bonding. When a substrate with a rigid naphthalene backbone moiety, 2‐hydroxyacenaphthylen‐1(2H)‐one, is reduced, the stereochemical outcome is very similar to the one corresponding to the α‐hydroxycyclopentanone. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

18.
1,1,1‐Trichloro‐3‐(1‐phenethylamino‐ethylidene)‐pentane‐2,4‐dione is spectroscopically and structurally elucidated by means of linear‐polarized IR spectroscopy (IR‐LD) of oriented solids as a colloidal suspension in nematic liquid crystal. Structural information and IR‐spectroscopic assignment are supported by quantum chemical calculations at MP2 and B3LYP level of theory and 6‐311++G** basis set. The geometry is characterized with an inramolecular hydrogen bond of NHO?C with length of 2.526 Å and a NHO angle of 140.5(1)°. The NH? C(CH3)C?C? C?O(CH3) fragment is nearly flat with a maximal deviation of total planarity of 10.4°. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

19.
In this work, a set of derivatives of 2‐(5‐amino‐3‐nitro‐1,2,4‐triazolyl)‐3,5‐dinitropyridine (PRAN) with different energetic substituents (?N3, –NO2, –NH2, –NF2) have been studied at the Becke, three‐parameter, Lee–Yang–Parr/aug‐cc‐pvdz, Becke, three‐parameter, Lee–Yang–Parr/6‐31G(d), Becke, three‐parameter, Perdew 86/6‐31G(d), and Becke three‐parameter, Perdew–Wang 91/6‐31G(d,p) levels of density functional theory. The gas‐phase heats of formation were predicted with isodesmic reactions and the condensed‐phase HOFs were estimated with the Politzer approach. The effects of different functionals and basis sets were analyzed. –N3 and –NO2 greatly increase while –NH2 and –NF2 slightly decrease heats of formation. An analysis of the bond dissociation energies and impact sensitivity shows that all compounds have good stability. The crystal densities (1.82–2.00 g/cm3) computed from molecular packing calculations are big for all compounds and that of the –NF2 derivative is the largest. All derivatives have higher detonation velocity and detonation pressure than PRAN. Compounds 3 and 4 (R = NO2 and NF2) have better performance than hexahydro‐1,3,5‐trinitro‐1,3,5‐trizine and the performance of 4 is quite close to that of 1,3,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane, they are promising candidates of high energy compounds and worth further investigations. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

20.
The infrared spectra of ammonia-borane, BH3NH3, and two of its deuterated isotropic species, BD3ND3 and BH3ND3, isolated in argon matrix at liquid hydrogen temperature have been measured. Well resolved bands for these three isotopic species have been observed for all the fundamentals. A complete frequency assignment based on C3v molecular symmetry has been made. A set of force constants have been calculated from the data for the two isotopes BH3NH3 and BD3ND3 using a valence force field. The agreement between experiment and frequencies calculated from these force constants for the mixed isotopic species, BH3ND3, substantiates the present assignment.  相似文献   

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