共查询到20条相似文献,搜索用时 15 毫秒
1.
Sven Thorwirth Michael C. McCarthy John B. Dudek Patrick Thaddeus 《Journal of Molecular Spectroscopy》2004,225(1):93-95
The carbon chain molecules vinylcyanoacetylene and cyanovinylacetylene have been investigated between 8 and 41 GHz by Fourier transform microwave spectroscopy of a supersonic molecular beam. Owing to the high spectral resolution of the present technique, significantly more accurate rotational and centrifugal distortion constants have been derived for both molecules. In addition, the dipole moments have been calculated at the B3LYP/cc-pVTZ level of theory. Because these carbon chains are similar in structure and composition to known astronomical molecules and because of their high polarity, both species are good candidates for radioastronomical detection. 相似文献
2.
D. Porezag G. Jungnickel T. Frauenheim G. Seifert A. Ayuela M.R. Pederson 《Applied Physics A: Materials Science & Processing》1997,64(3):321-326
\chem{[C_{60}]_{\chemindex{n}}} -oligomers (, , and ) as well as dimers partially bridged by oxygen atoms or a group. The applicability of the scheme for finding the ground state of these systems was carefully checked against more sophisticated
methods including an all-electron, self-consistent (SCF) scheme based on the local-density-approximation (LDA), and the recently
developed generalized-gradient approximation (GGA). We present Raman intensities for the vibrations of the oligomers, obtained in the framework of the bond polarization model, and compare with recent experimental data.
Received: 26 September 1996/Accepted: 16 December 1996 相似文献
3.
H. Khosroabadi A. Tavana M. Akhavan 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(2):161-165
Ab initio total energy calculations have been performed for superconducting
GdBa2Cu3O7 and insulating PrBa2Cu3O7 using the
full-potential linear augmented plane-wave method in the local density
approximation (LDA) and generalized gradient approximation (GGA). The
comparison of the calculated unit cell volume and lattice parameters with
the experimental data indicates the improvement of these parameters in the
GGA relative to LDA. LDA and GGA give the equilibrium unit cell volume about
6% smaller and 1.25% larger than the experimental data, respectively
for both systems. Thus frozen phonon calculations have been performed to
determine the eigenvalues and eigenvectors of the k=0 Ag modes of the
two systems in equilibrium structure have been obtained in GGA. The
calculated frequencies in the GGA are in good agreement with the other LDA
calculations for similar systems. Comparison of computational data with
experimental data indicates that calculations determine the frequencies
about ten percent below the experimental data. Even by improving LDA to GGA
in these calculations, the calculated phonon frequencies have remained
almost ten percent below the experimental data, even though the calculated
unit cell volumes are nearly equal to the experimental data. So, applying
GGA has not considerably decreased the difference between the computational
and experimental data. The effect of Pr doping on the eigenvalues and
eigenvectors have also been investigated. 相似文献
4.
The conductance of SnO2 small nanowires: A study based on density functional and scattering theories
A.M. Mazzone 《Solid State Communications》2007,143(10):481-486
This study is motivated by the recent advances in the fabrication of oxide nanostructures and its purpose is the assessment of the relationship between their structural properties and the conductance. The structures considered are small SnO2 nanowires whose size and shape reproduce on a smaller scale the structures produced by current technologies. Their electronic configuration and the conductance are evaluated using the density functional and scattering theories with a simplified modelling of the external leads. The study of the electronic configuration shows that the structure of the allowed energy levels and of the charges responds to the details of the nanowire structure and composition. These effects are important in the context of the conductance. In fact, deep resonances are produced by the alignment of the allowed energy levels in the nanowire with the ones in the external leads. For these conductive channels the relationship between the size and the conductance parallels the one between the size and the binding energy. 相似文献
5.
R. L. Zhou B. C. Pan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(3):367-372
We extensively search for the endohedral silicon-fullerene
structures of Si31–Si39 using the combination of a
tight-binding potential with the density functional theory. The
resulting structures of our best candidates characterize more
compact features comparing to previous isomers [J. Am. Chem. Soc. 126, 13845 (2004); J. Chem. Phys. 124, 164311 (2006)]. Most of our best candidates belong to new families
featuring different core/cage combinations or different original
carbon fullerene cages with respect to those of previous isomers.
Energy calculations reveal that our best candidates are more
stable than the previous best ones at the PW91 level, except for
n = 34 and 38. The predicted relative stabilities of these isomers remain even at finite
temperatures. In addition, the densities of dangling-bond atoms in
the surfaces of our Si33 and Si39 isomers are
significantly lower than the previous best candidates, as well as
lower than those of their neighbors. This finding together with
the densities of the active sites in the surfaces of the previous best candidates
of Si34 and Si38 is roughly consistent with the observed relative reactivities of the silicon
clusters in the size range of n = 31-39. 相似文献
6.
We investigate the high resolution absorption spectroscopy of P2 radical, generated in ac glow discharge of PC13 buffered with helium, using optical heterodyne magnetic rotation enhanced concentration modulation spectroscopy in the visible region. The (1, 2), (1, 3) and (2, 3) bands of c^3Ⅱu- b^3Ⅱg in the range 16620-17860cm^-1 are observed and their 3II2 3II2 subbands are rotationally analysed. A set of effective molecular constants for the Ω= 2 component of the states involved are determined. 相似文献
7.
I. Bhattacharyya N. C. Bera A. K. Das 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(2):221-226
Geometrical parameters, harmonic frequencies and molecular properties of FCN, ClCN, their cations and the isomers of FCN and
ClCN are studied in detail using ab initio MP2, CCSD and CCSD(T) methods. The dissociation energy of FCN and ClCN in various
dissociation channels has been
investigated. Both ground and metastable state of the fragmented atoms are considered in their dissociation pathways. The
isomerization energy of FCN and ClCN and the NBO charges of FCN, ClCN, their cations and isomers are analyzed. 相似文献
8.
Cluster models were used to represent the β-type cationic sites of the protonated beta zeolite (H-BEA) and the loading of PdO on these sites. The properties of these clusters and the cleavage of methane CH bond over these clusters were studied using density functional theory (DFT) method. The stability of H-BEA was enhanced due to the formation of hydrogen bonds. After PdO loading, the Pd atom bonds to four oxygen atoms among which three H-BEA framework oxygen atoms are included to form an approximate planar structure with Pd in the centre. This structure is very similar to that of bulk PdO. The acidic proton of H-BEA and the oxygen atom of PdO participate in the cleavage of methane CH bond, indicating that PdO is the active species for the activation of methane. Over the clusters constructed in the present work, the calculated energy barriers for the cleavage of methane CH bond are in the region between 17.54 and 21.02 kcal mol−1. 相似文献
9.
Using first-principles density functional theory, we have investigated the electronic and field emission properties of carbon nanocones (CNCs) doped with N or B with 60° disclination. Our findings are that the emission properties for the doped CNCs depend on the doping species, position, and concentration. Compared to pristine CNC, N-doped CNCs exhibit better field emission properties, in which as the doping concentration increases from 1.25% to 2.5% the maximum emission current at applied electric field of 0.3 V/Å increases from 0.94 μA (one N atom is doped at the position adjacent to the pentagon) to 2.90 μA (two N atoms are doped at pentagon). As for pristine CNC the emission current is only 0.21 μA. However, B-doping has no significant influence on the emission properties of CNCs. Our findings suggest that N-doped CNCs can be used as a candidate for cold-emission electron sources. 相似文献
10.
We have investigated a high-resolution Fourier transform (FT) absorption spectrum of the 13CH3OH isotopomer of methanol from 400 to 950 cm−1 with the “Ritz” program. We present the assignments of 7160 transitions, 3021 of which belong to A-symmetry, and 4139 to E-symmetry. These transitions occur between states labeled by K quantum numbers up to 14, and by torsional quantum numbers n up to 4. The “Ritz” program evaluated the energies of the 4684 involved levels with an accuracy of the order of 10−4 cm−1. All of the assigned lines correspond to transitions involving torsionally excited levels within the ground small-amplitude vibrational state. 相似文献
11.
C. Oppenheimer P. Francis M. Burton A.J.H. Maciejewski L. Boardman 《Applied physics. B, Lasers and optics》1998,67(4):505-515
Received: 25 March 1998 相似文献
12.
A compact diode laser operating around 1.5 μm was used to measure cavity enhanced absorption spectra of hot water molecules
and OH radicals in radiative environments under atmospheric conditions. Spectra of air were measured in an oven at temperatures
ranging from 300 K to 1500 K. These spectra contained rovibrational lines from water and OH. The water spectra were compared
to simulations from the HITRAN and HITEMP databases. Furthermore, spectra were recorded in the flame of a flat methane/air
burner and in an oxyacetylene flame produced by a welding torch. The results show that cavity enhanced absorption spectroscopy
provides a sensitive method for rapid monitoring of species in radiative environments.
Received: 22 February 2001 / Revised version: 23 April 2001 / Published online: 7 June 2001 相似文献
13.
We investigate the configurations, electronic structures, and magnetic ordering of MnN (N = 2-13) clusters based on all-electron density functional theory. The Jahn-Teller effect plays an important role in determining the ground state of certain geometries. The magnetic ordering of the MnN dusters transits from ferromagnetic ordering for the smallest ( N = 2, 3) dusters to a near degeneracy state including ferromagnetic and ferrimagnetic ordering in the vicinity of N = 4-6 and to a clear ferrimagnetic ordering at N = 7 or beyond. N = 6 and 10 are the magic numbers for neutrai MnN (N = 2-13) dusters. 相似文献
14.
C.-K. Siu S. J. Reitmeier I. Balteanu V. E. Bondybey M. K. Beyer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):189-192
Pt4
- catalyses the conversion of CO and
N2O to CO2 and N2 in the gas phase, as observed by Fourier
transform ion cyclotron (FT-ICR) mass spectrometry. The partial pressures of
CO and N2O determine the extent of poisoning and the turnover numbers
that can be achieved. The catalytic conversion terminates as soon as two CO
are adsorbed on the cluster. With N2O, the reactivity of
Pt4O2
- and Pt4O3
- is reduced to 41% and
34% compared to Pt4O-, respectively, and with
Pt4O4
- this value is reduced to 1%. In contrast,
Pt4
+ shows no apparent catalytic activity. Density functional
theory calculations of Pt4
+/- with CO and N2O adsorbates
reveal significantly different stabilities of the reaction intermediates for
the different charge states. 相似文献
15.
Adsorption of acetylene and ethane molecules by water clusters has been investigated by the molecular dynamics method at T=233 K. With the help of determination of statistical weights the cluster systems are created. In the frequency range of 0?ω?1000 cm−1 the integral absorption coefficient of IR-radiation increases after the adsorption of acetylene or ethane molecules by the ultra disperse water system. The dissipation power of IR-radiation by cluster systems increases if C2H2 molecules are adsorbed, and it reduces in the case of C2H6 molecules' adsorption. 相似文献
16.
17.
K. Song H.K. Cha V.A. Kapitanov Yu.N. Ponomarev A.P. Rostov D. Courtois B. Parvitte V. Zeninari 《Applied physics. B, Lasers and optics》2002,75(2-3):215-227
The results of theoretical and experimental studies and the design of a multi-purpose differential Helmholtz resonant photoacoustic
detector (DHRD) and its applications to high-resolution spectroscopy of molecular gases and gas analysis with a room-temperature
diode laser in the near-IR region are summarized. The series of experiments and numerical analysis of the DHRD sensitivity
were performed for both types (single-pass and multi-pass) of DHRDs within a wide pressure range 0.1–101 kPa, including the
regime of a gas flowing through a DHRD cell. The hardware and electronic arrangement of DHRDs for diode laser spectrometers
and gas analyzers providing a limiting absorption sensitivity better than 10-7 Wm-1 are described. The results of measurements of spectral line parameters of H2O near 800 and 1390 nm and CH4 near 1650 nm (intensities, line broadening and shifting by atomic and molecular gases) are presented and discussed. The problems
and the ways of perfection of the methodology and accuracy of DHRD techniques with tunable diode lasers of near-IR and visible
spectral ranges are discussed.
Received: 1 April 2002 / Revised version: 20 June 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +7/382-225-8026, E-mail: kvan@asd.iao.ru 相似文献
18.
Spectroscopic sensing of gases can be performed with high sensitivity and photometric precision by cavity ringdown (CRD) absorption
spectroscopy. Our cavity ringdown spectrometer incorporates continuous-wave (cw) tunable diode lasers, fibre-optic coupling
and standard photonics and optical telecommunications components. It comprises a rapidly swept optical cavity in a single-ended
optical heterodyne transmitter–receiver configuration, enabling optical absorption of gases to be recorded either as single-frequency
scanned spectra or as simultaneous, multi-wavelength tailored spectra. By measuring weak near-infrared rovibrational spectra
of carbon dioxide gas (CO2), with high resolution in the vicinity of 1.53 μm, we have realised a noise-limited absorption sensitivity of 2.5×10-9 cm-1 Hz-1/2. Analytical sensitivity limits (both actual and projected) and prospective gas-diagnostic applications are discussed. Our
approach to cw-CRD spectroscopy offers high performance in a relatively simple, low-cost, compact instrument that is amenable
to chemical analysis of trace gases in medical, agricultural, industrial and environmental situations.
Received: 16 May 2002 / Revised version: 3 June 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +61-2/9850-8313, E-mail: brian.orr@mq.edu.au 相似文献
19.
A.?Giuliani P.?Lim?o-Vieira D.?Duflot A. R.?Milosavljevic B. P.?Marinkovic S. V.?Hoffmann N.?Mason J.?Delwiche M.-J.?Hubin-Franskin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,51(1):97-108
The electronic spectroscopy of isolated tetrahydrofuran (THF) in the gas phase has been investigated using high-resolution
photoabsorption spectroscopy in the 5.8–10.6 eV with absolute cross-section measurements derived. In addition, an electron
energy loss spectrum was recorded at 100 eV and 10° over the 5–11.4 eV range. The He(I) photoelectron spectrum was also collected
to quantify ionisation energies in the 9–16.1 eV spectral region. These experiments are supported by the first high-level
ab initio calculations performed on the excited states of the neutral molecule and on the ground state of the positive ion.
The excellent agreement between the theoretical results and the measurements allows us to solve several discrepancies concerning
the electronic state spectroscopy of THF. The present work reconsiders the question of the lowest energy conformers of the
molecule and its population distribution at room temperature.
Electronic supplementary material Supplementary Online Material 相似文献
20.
Alberto Milani Nur Aiman Fadel Luigi Brambilla Mirella Del Zoppo Chiara Castiglioni Giuseppe Zerbi Riccardo Stradi 《Journal of Raman spectroscopy : JRS》2009,40(9):1110-1116
The intermolecular interactions in amylose/dimethyl sulfoxide (DMSO) complexes are discussed both experimentally and theoretically by means of Raman and infrared spectroscopies. The study is based on a preliminary analysis of well known systems such as pure liquid DMSO or DMSO in mixture with water: for such systems, an analysis of the CS stretching region is carried out both by means of Raman and infrared spectra. In particular, Raman spectra reveal a high sensitivity to the strength and to the type of interaction involving the DMSO molecules. These results, applied to the investigation of amylose‐DMSO complexes, show the presence of different hydrogen‐bonded complexes which coexist in this compound. In particular, DMSO molecules are identified both on the external surface of the V‐amylose helix, where they can interact via one hydrogen bond and in the inner channel of the helix where they can interact via two hydrogen bonds. The present findings open the possibility of applying vibrational spectroscopy to the characterization of inclusion compounds of amylose which are currently being involved in many fields of nanosciences. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献