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1.
The fall in frequency on deuteration, by some 4 cm?1, of the intermolecular stretching mode vσ of hydrogen bonded complexes, is larger than can be accounted for by any reasonable harmonic force field. It is shown that this does not imply a different potential function for the deuterium bond; it may be quantitatively accounted for by anharmonicity in the vσ mode, together with anharmonic interaction with the AH stretching mode vs. 相似文献
2.
the intramolecular cyclisation of furans, 3, proceeds with the following activation characteristics: 3(R=Et) has EA=72.5, H=69.9 kJmol?1, S≠=62JK?1 mol?1, V≠=?25 cm3 mol?1. The results confirm the existence of a negative volume contribution from the approach of reagents in intermolecular analogues. 相似文献
3.
U. Buck X. J. Gu M. Hobein R. Krohne Ch. Lauenstein H. Linnartz A. Rudolph 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,20(1):177-180
Infrared photodissociation spectra of (CH3NH2) n clusters were measured fromn=2 ton=6 near the monomer absorption of the C-N stretching mode at 1044 cm?1 using a cw-CO2 laser. The clusters were size-selected by scattering from a helium beam. The spectrum of cold dimers shows a red (1038 cm?1) and a blue (1048 cm?1) shifted peak which is attributed to the non-equivalent position of the C-N in the open dimer structure. The larger clusters exhibit only one peak between 1045.4 cm?1 and 1046.0 cm?1 caused by the equivalent position of the C-N in the cyclic structures of the larger clusters. Structure calculations confirm these results. Secondly, the mixed complexes C2H4-CH3COCH3 and C2H4-(CH3COCH3)2 were investigated. The dimer spectrum, measured around the monomer frequency of the out-of-plane bending mode of C2H4 at 949 cm?1, shows two peaks at 946.2 cm?1 and 961.3 cm?1. This splitting is attributed to two different isomers that are found in configuration calculations. A similar behaviour is found for the trimer. 相似文献
4.
V. A. Marikhin E. I. Radovanova E. M. Ivan’kova L. P. Myasnikova B. Z. Volchek D. A. Medvedeva E. N. Vlasova 《Polymer Science Series A》2008,50(4):403-410
The IR absorption spectra of α,ω-alkanediols with different chain lengths, HO(CH2)22OH and HO(CH2)44OH, in the spectral range of 400–5000 cm?1 are analyzed. The assignment of numerous absorption bands to vibration modes in short methylene sequences and terminal hydroxyl groups is suggested. The splitting of IR absorption bands into doublets at 720–730 cm?1 (rocking vibrations of CH2 groups) and 1463–1473 cm?1 (bending vibrations of CH2 groups) testifies that the crystal unit subcells in the lamellae of alkanediols are orthorhombic with parameters typical of normal hydrocarbons. The specific features of absorption bands due to O-H stretching and C-O-H bending vibrations have been analyzed. These bands appear during formation of lengthy associates from hydrogen bonds formed by hydroxyl groups on the surface of elementary lamellae. A sharp increase in the intensity of the absorption bands in progression of C-C stretching and CH2 wagging vibrations due to the anharmonic Fermi resonance with the stretching vibrations of C-O groups in the terminal hydroxyl groups has been detected. 相似文献
5.
John F. Rabolt 《Journal of Polymer Science.Polymer Physics》1979,17(8):1457-1464
Raman spectra of stearyl alcohol (n-C18H37OH) indicate that vibrational bands in both the skeletal optical (1000-1200 cm?1) and longitudinal acoustical (0–500 cm?1) regions are considerably perturbed by intermolecular hydrogen bonding. The zone interior skeletal stretching mode reflecting phonon dispersion in the v4 branch of the infinite polyethylene chain is found at 1105 cm?1, approximately 20 cm?1 higher than in the corresponding n-alkane. Similarly the single nodal longitudinal acoustical mode (LAM-1) is found shifted by 12 cm?1 to higher frequency when the expected “mass effect” produced by the ? OH group is considered. This shift is further increased to 16 cm?1 at ?100°C indicating a further perturbation on this accordion mode due to the increased strength of the hydrogen bond at the low temperatures. The positions of the higher multinodal vibrations, LAM-3 and LAM-5, are also perturbed by the hydrogen bond but by differing amounts. The observation of a low-frequency Raman-active LAM in polytetrahydrofuran [(? CH2CH2CH2CH2O? )n] is discussed in conjunction with the expected effects of hydrogen bonding at the lamellar surface. 相似文献
6.
Using a coupled interferometer—spectrometer with a resolution of 0.02 cm?1 we have measured the Raman band profiles of the four low-frequency anthracene phonons ω1(ag), ω2(ag), ω6(bg) and ω7(bg) in the temperature range 2–70 K. These phonons possess very narrow bandwidth at low temperature which are convinently measured under high resolution. In particular the two lowest-frequency phonons ω1(ag) and ω6(bg) have a bandwidth at 2 K of 0.045 cm?1. The other two phonons ω7(bg) and ω2(ag) have bandwidths at 2 K of 0.165 and 0.4 cm?1, respectively. A detailed analysis of the bandwidth variation with temperature was made in terms of three-phonon decay processes. The exrerimental variation of the bandwidth with temperature was correctly reproduced assuming a single down-and up-process. The following results were obtained: ω1(ag): 49.45 cm?1 = 2×24.72 cm?1, 49.45 cm?1 = 98.45 cm?1 ?49.0 cm?1; ω6(bg): 57.50 cm?1 = 2×28.75 cm?1, 57.50 cm?1 = 108.50 cm?1 ?51.0 cm?1; ω7(bg): 71.20 cm?1 = 2×35.6 cm?1, 71.20 cm?1 = 120.20 cm?1 ?49.0 cm?1: ω2(ag): 82.40 cm?1 = 57.50 cm?1 +24.9 cm?1, 82.40 cm?1 = 138.4 cm?1 ?56 cm?1. The efficiency of the down- and up-processes is discussed in terms of the two-phonon density of states. The bandwidths at 2 K follows very closely the variation of the two-phonon sum density of states, whereas the relative importance of the up-processes follows well the two-phonon difference density of states. The anharmonic frequency shifts are corrected for the thermal expansion of the crystal using the Grüneisen single-phonon parameters and the thermal expansion coefficients given in the literature. This permits an estimation of the variation of the anharmonic shifts in the temperature range studied. 相似文献
7.
The vibrational spectroscopy of lithium dichloride anions microhydrated with one to three water molecules, [LiCl2(H2O)1–3]−, is studied in the OH stretching region (3800–2800 cm−1) using isomer-specific IR/IR double-resonance population labelling experiments. The spectroscopic fingerprints of individual isomers can only be unambiguously assigned after anharmonic effects are considered, but then yield molecular level insight into the onset of salt dissolution in these gas phase model systems. Based on the extent of the observed frequency shifts ΔνOH of the hydrogen-bonded OH stretching oscillators solvent-shared ion pair motifs (<3200 cm−1) can be distinguished from intact-core structures (>3200 cm−1). The characteristic fingerprint of a water molecule trapped directly in-between two ions of opposite charge provides an alternative route to evaluate the extent of ion pairing in aqueous electrolyte solutions. 相似文献
8.
Molecular beam depletion spectroscopy has been employed to study the dissociation of small methanol clusters in the spectral region between 1000 and 1100 cm?1 which covers thev 8 CO stretch (1033.5 cm?1) and thev 7 CH3 rock (1074.5 cm?1) monomer vibrations. Size selection has been achieved by dispersing the (CH3OH) n cluster beam by a secondary He beam. Aside from the recently published CH3OH dimer absorption bands at 1026.5 and 1051.6 cm?1 which are assigned to the excitation of the CO stretching vibrations in the non-equivalent subunits of the hydrogen-bonded complex, a previously unobserved band was found at 1071.3 cm?1. This absorption band is attributed to the excitation of the CH3 rocking vibration in the dimer. It appears that this transition which is very weak in the free methanol monomer receives substantial oscillator strength due to the intermolecular interaction in the complex. A splitting of this band could not be observed. The trimer and tetramer spectra feature single peaks for the CO stretching vibration being centered at 1042.2 cm?1 and 1044.0 cm?1, respectively. This observation is consistent with the cyclic structures of these species. The trimer and tetramer rocking vibrations are observed near 1060.5 cm?1 but cannot be localized exactly, due to a gap in the CO2 laser tuning range. 相似文献
9.
On increasing the wavelength of excitation over the range 350–700 nm, Raman bands of pyridine adsorbed at a roughened silver electrode are found to increase in intensity, relative to bands of the bulk medium (aqueous perchlorate or liquid pyridine) in contact with the electrode. The increase is observed in the bands at 1000–1050 cm?1 and 1600 cm?1 due to ring stretching, and similar increases are observed in other bands of the surface species, notably those due to CH stretching (3076 cm?1), b2 ring deformation (669 cm?1, and AgN stretching (239 cm?1, which have not been reported previously. 相似文献
10.
高压下β-HMX热分解机理的ReaxFF反应分子动力学模拟 总被引:1,自引:0,他引:1
采用ReaxFF反应分子动力学方法研究了不同压缩态β-HMX晶体(ρ=1.89、2.11、2.22、2.46、2.80、3.20 g·cm-3)在T=2500 K时的热分解机理, 分析了压力对初级和次级化学反应速率的影响、高压与低压下初始分解机理的区别以及造成反应机理发生变化的原因. 发现HMX的初始分解机理与压力(或密度)相关. 低压下(ρ<2.80 g·cm-3)以分子内反应为主, 即N-NO2键的断裂、HONO的生成以及分子主环的断裂(C-N键的断裂). 高压下(ρ≥2.80 g·cm-3)分子内反应被显著地抑制, 而分子间反应得到促进, 生成了较多的O2、HO等小分子和大分子团簇. 初始分解机理随压力的变化导致不同密度下的反应速率和势能也有所不同. 本文在原子水平对高压下HMX反应机理的深入研究对于认识含能材料在极端条件下的起爆、化学反应的发展以及爆轰等具有重要意义. 相似文献
11.
The metal ion distribution on the two metal sites of monoclinic Mn1?xCux(HCOO)2 · 2(H,D)2O mixed crystals are studied by infrared and Raman spectroscopic methods. The spectral regions 3 200–3 400 cm?1 (vOH), 2 875–2 990 cm?1 (vCH), 2 330–2 500 cm?1 (vOD of matrix isolated HDO molecules), 1 350–1 400 cm?1 (symmetric CO2 stretching modes), 570–950 cm?1 (H2O librations), and 490 cm?1 (M? O lattice modes) are mostly sensitive to the metal ions present. The frequency shifts of these bands with increasing content of copper show that Cu2+ prefers the M(1) site, coordinated by HCOO? only. The strengths of the hydrogen bonds increase on going from manganese to copper formate, due to the increased synergetic effect of Cu2+. Solubility and X-ray data of the mixed crystals are included. Irrespective of the same crystal structure, two series of mixed crystals are formed: eutonic area at 0.65 ≥ x ≥ 0.5. 相似文献
12.
Two bands appear for each CN stretching and nitro deformation vibration in the infrared and Raman spectra of m-dinitrobenzene and m-dinitrobenzene-d4. The 907 cm?1 bending mode in the vibrational spectra of m-dinitrobenzene undergo 30 cm?1 upward shift upon d4 substitution. A normal coordinate analysis pointed out that the 937 cm?1 bending and 727 cm?1 CN stretching vibrations as well as 18b CD in-plane deformation are mixed to a great extent. The other nitro bending mode undergo also an inverse isotopic effect (2 cm?1 upward shift) due to coupling with the 18a CD in-plane deformation vibration. 相似文献
13.
Monte Carlo simulations are used, together with models of the intramolecular and intermolecular potential surfaces, to model liquid water and several phases of ice. Intramolecular relaxation makes important contributions to both thermodynamic and structural properties. A quantum local mode analysis of the Monte Carlo configurations is used to predict the density of states and infrared absorption intensities for the intramolecular bending and stretching vibrations. The large shifts from the gas phase OH stretch frequencies observed experimentally in the liquid and solid phases are due to anharmonic terms in the intramolecular surface rather than to harmonic intermolecular coupling. A significant contribution to observed changes in IR intensity on condensation arises from the large molecular polarisability. 相似文献
14.
Prof. Dr. Durga Nath Dhar Ved Prakash Gupta 《Monatshefte für Chemie / Chemical Monthly》1975,106(2):333-338
IR data of eight substituted flavanones and their isomeric hydroxychalkones have been recorded in order to assign the various absorption bands and to study the effect of substituents on C=C out-of-plane deformation (400–700 cm?1), C?H out-of-plane deformation (700–1000 cm?1), C?H in-plane deformation (1000–1300 cm?1), C?O stretch (≈1200 cm?1), OCH3 (1200–1300 cm?1), O?H deformation (1300–1400 cm?1), CH3 deformation (1300–1500 cm?1), benzene ring vibration (1400–1600 cm?1) and C=O stretch (≈1650 cm?1). The δC?H (ring A) in 2′,4′-dihydroxy-3-nitrochalkone appears at 826 cm?1 (s), while in the isomeric flavanone it shows up as three bands, viz., 807 (w), 833 (m) and 881 cm?1 (w). This difference principally arises due to the presence of the electron withdrawing nitro substituent. The C=O stretching vibration in flavanones appears at a higher frequency than in the corresponding hydroxychalkones. This is perhaps due to the lack of conjugation in the former class of compounds. Chloro substituents (ring B) in different positions exert differing effects on νC?O. These differences can be rationalized in terms of a field-effect exerted by the chlorine atom. 相似文献
15.
R. Ahlrichs S. Brode U. Buck M. DeKieviet Ch. Lauenstein A. Rudolph B. Schmidt 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1990,15(4):341-351
Optimized geometries and binding energies are calculated for ethene (ethylene) dimers, trimers, and tetramers based on a pairwise additive dimer potential. From these results intermolecular frequencies and relative abundancies (catchment areas) of the different isomers are obtained and compared with the results of accurate measurements of the photodissociation upon absorption of one photon of a CO2 laser in the region of thev 7 monomer absorption band at 949 cm?1. The clusters are size selected in a scattering experiment and show for a cluster size fromn=2 ton=6 a frequency maximum shifted by 3 cm?1 to the blue compared with the monomer. The result is explained by the predominance of chains and chain-like structures of the clusters in the photodissociation process. The chains consist of cross-like dimer sub-units. 相似文献
16.
Low-frequency Raman spectra of catechol (1,2-dihydroxybenzene) and catechol-d2 have been measured at 130 K. The stretching mode of the intermolecular hydrogen bond, νσ, has been assigned at 187 and 184 cm?1, respectively. A short discussion of this assignment and its implications with respect to the previously reported guaiacol (2-methoxyphenol) spectra is presented. 相似文献
17.
18.
Frequency dependence of intermolecular proton spin-lattice relaxation rate [(1/T1)inter(ω)] in neat acetonitrile-d2 was studied. From (1/T1)inter(ω) pair-diffusion constants were determined to be 0.281 × 10?5 and 0.237 × 10?5 cm2 s?1 at 22 and ?32.6°C, respectively. These values differ greatly from the self-diffusion constants. 相似文献
19.
Stephen Wilson 《International journal of quantum chemistry》1977,12(4):609-622
Diagrammatic many-body perturbation theory is used to calculate the potential energy function for the X1 σ+ state of the CO molecule near the equilibrium nuclear configuration. Spectroscopic constants are derived from a number of curves which are obtained from calculations taken through third order in the energy. By forming [2/1] Padé approximants to the constants we obtain: re = 1.125 Å (1.128 Å), Be = 1.943 cm?1 (1.9312 cm?1), aBe = 0.0156 cm?1 (0.0175 cm?1), We = 2247 cm?1 (2170 cm?1), WeXe = 12.16 cm?1 (13.29 cm?1), where the experimental values are given in parenthesis. 相似文献
20.
Kazunori Sakata Hidetoshi Tagami Mamoru Hashimoto 《Journal of heterocyclic chemistry》1989,26(3):805-809
The condensation reaction between tetraaza[14]annulene ( 1 ) and a series of para-substituted benzoyl chlorides led to the 16-benzoylated corresponding products in 13–21% yields, but 1 was unreactive with alkyl acid chlorides and easily cleaved in macrocyclic framework. The mass spectra show the presence of molecular ion peaks which support the 16-benzoylated products. A strong ir band due to the C = N stretching mode of the macrocyclic moiety was observed at 1610 cm?1 and shifted slightly toward higher energy upon benzoylation. An intense ir band which was associated with a C = 0 stretching mode was newly observed at 1640 cm1. The very strong absorption band about 29000 cm?1 was attributed to the π ? π* transition and gave a slight shift to higher frequency on benzoylation. All proton signals except for methyl protons exhibit downfield shifts due to the deshielding effect of the substituted benzene ring, but the methyl proton peaks show upfield shifts due to the shielding effect caused by the magnetic anisotropy of the substituted benzene ring. The 13C nmr result is also in accord with that of 1H nmr. 相似文献