共查询到20条相似文献,搜索用时 31 毫秒
1.
S.V. Ivanov 《Journal of Molecular Spectroscopy》2005,233(1):60-67
Semiclassical approaches to the computation of spectral line parameters stay up to nowadays one of the working tools complementary to refined but costly quantum-mechanical methods. Using of the trajectory concept together with quantum treatment of internal molecular motions imposes however the hypothesis of rotation-translation decoupling and translational motion governed by the isotropic potential. When a posteori justified for small heavy colliders, this hypothesis appears as doubtful for long polyatomic molecules. At the same time, purely classical methods, even requiring the artificial procedure of the correspondence principle with quantum mechanics, easily take into account the rototranslational energy transfer through the trajectory governed by the full anisotropic potential. The infrared line broadening of a typically classical C2H2-Ar system at various temperatures is analyzed here from these two different points of view. When a refined ab initio potential is chosen to represent the interaction energy, the semiclassical approach leads to a visible overestimation of the line broadening for all values of the rotational quantum number and for all temperatures studied whereas the fully classical treatment gives a quite satisfactory prediction. These fully classical computations show that even for C2H2-Ar the rototranslational coupling is quite important, and variations of the translational motion parameters during collisions produce detectable changes in rotation. When, for the sake of a meaningful comparison with the semiclassical approach, the isotropic trajectories are imposed within the classical method, this leads to smaller line widths; the effect strongly depends, however, on the peculiarities of potential energy surface, temperature, and rotational quantum number value. 相似文献
2.
Laura Gomez Oleg G. Buzykin 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(12):1942-1949
We use an accurate N2-H2ab initio potential energy surface (PES) in order to inter-compare various methods commonly employed to calculate pressure broadening coefficients. Close-coupling (CC) calculations of the collisional linewidths of the isotropic Raman lines of N2 perturbed by H2 are performed for temperatures between 77 and 2000 K. The CC results compare well with available experimental values. Three less exact methods of calculation are also used: the full classical (FC) model of Gordon, the semiclassical (SC) formalism of Robert and Bonamy and the quantum dynamical coupled states (CS) method. The CS method provides good agreement with CC calculations for all studied temperatures, FC calculations can be considered as accurate above room temperature while the SC method gives overestimated values by about 20-30% in all cases. The temperature dependences of pressure broadening coefficients provided by each method are very similar at elevated (above room) temperatures. 相似文献
3.
Comparison of classical, semiclassical and quantum methods in hydrogen broadening of acetylene lines
Franck Thibault Sergey V. Ivanov Laura Gomez Pierre Joubert 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(9):1429-1437
Quantum close coupling (CC) calculations of H2-broadening coefficients of infrared and isotropic Raman lines of acetylene (C2H2) are performed for temperatures between 77 and 2000 K. They are used to test three more approximate methods, the quantum coupled states (CS) theory, the semiclassical Robert-Bonamy (RB) formalism and the full classical (FC) model of Gordon. In order to allow a clear and well founded comparison, all the dynamical calculations were performed employing the same ab initio potential energy surface free of any adjustable parameters. It is shown that below room temperature both the coupled states method and full classical method fail at reproducing the close coupling pressure broadening coefficients while above room temperature they are correct and predict comparable accurate values for temperatures greater than about 1000 K. The values provided by the RB method are clearly not satisfactory even at the highest temperature examined. However, the temperature dependence of the RB results follows the functional form used for interpolating and extrapolating CC, CS and FC pressure broadening coefficients. 相似文献
4.
The 3s vacancy production in Ar+-He and Ar+-Ar collisions has been studied at impact energies of 100 keV to 550 keV. A comparison is made for the Ar+-He system with theoretical calculations based on the quasi-molecular model. 相似文献
5.
Pressure-broadening parameters of six lines belonging to the ν5 band of C2H2 in collision with N2 have been measured with a tunable diode-laser spectrometer in order to complete up to J = 33 our earlier measurements (D. Lambot, G. Blanquet, and J. P. Bouanich, J. Mol. Spectrosc.136, 86–92 (1989)) on the broadening of C2H2 by N2 and O2 at 297 K. These N2- and O2-broadening coefficients have been first calculated on the basis of the Anderson-Tsao-Curnutte theory; in this approach, we show that the short-range interactions which contribute significantly to the linewidths are not correctly treated. Next, we consider the improved semiclassical model proposed by Robert and Bonamy. The intermolecular potential consists in the addition of the atom-atom interaction model to the quadrupolar interactions. The limited radial spherical harmonics expansion of the atom-atom potential, from which expressions for the differential cross section were derived, appears to be quite insufficient at short intermolecular distances. Therefore, we use a more accurate representation of this potential, avoiding an inadequate truncation and keeping the analytic expressions obtained by Bonamy and Robert. In the calculations we take into account the contributions derived from the radial functions U000(r), U200(r), and U220(r), as well as from U400(r). A theoretical expression is obtained for the U400 contribution to the differential cross section. The results of the calculations arising from the exact radial expansion of the atom-atom potential appear to be significantly larger for high J lines than those arising from the truncated expansion. The latter results, which do not include adjustable atom-atom parameters, are in good agreement with experimental broadening coefficients for C2H2---O2 and in reasonable agreement (except at large J values) for C2H2---N2. It is also shown that the contributions to the linewidths derived from U400 are rather small for C2H2---N2 and more important for C2H2---O2. Finally, by calculating the collisional linewidths of C2H2---N2 and C2H2---O2 at 200 K, we have predicted their temperature dependences. 相似文献
6.
P.L. Lijnse 《Journal of Quantitative Spectroscopy & Radiative Transfer》1974,14(12):1195-1198
Doublet mixing cross sections for K(42P)-Ar and He and for Rb(52P)-He collisions have been measured, in flames at 1720 K. The ratio σ12/σ21 was measured separately and was found to agree within 2 per cent with predictions derived from detailed balance. The experiments are compared with available semiclassical theoretical results. 相似文献
7.
J.P. Bouanich A. Predoi-Cross R.L. Sams C.P. Rinsland V. Malathy Devi 《Journal of Molecular Spectroscopy》2005,231(1):85-95
A semiclassical theory based upon the Robert-Bonamy formalism has been developed to explain the experimental measurements of self-broadening, self-induced pressure shift coefficients in the ν1,ν2, 2ν2 bands of H12C14N and the 2ν1 band of H13C14N, as well as the temperature dependences of these parameters with special emphasis on the ν2 band. Our calculations include only electrostatic interactions and neglect the vibrational dependence of the isotropic part of the intermolecular potential, which probably has a weak contribution to the HCN self-shifts for the bands investigated in this study. The agreement between theory and measurements is good in the cases of self-broadening coefficients and their variation with temperature, as well as the self-shift coefficients determined at room temperature. However, the observed temperature dependence of self-shift coefficients in the ν2 band is different from that derived theoretically. 相似文献
8.
A.P. Hitchcock C.E. Brion 《Journal of Electron Spectroscopy and Related Phenomena》1977,10(3):317-330
Energy loss spectra of 2.5 keV electrons in the region of the carbon K-edge in C2H2, C2H4, C2H6 and C6H6 are report 相似文献
9.
M.C. McCarthyP. Thaddeus 《Journal of Molecular Spectroscopy》2002,211(2):235-240
The microwave rotational spectra of the carbon-13 isotopic species of H2C3, H2C4, and H2C5 have been observed in a pulsed supersonic molecular beam by Fourier transform microwave spectroscopy. At high resolution all of the rotational lines exhibit hyperfine structure produced by the magnetic interaction between the nuclear spin of 13C and the overall rotation of the molecule. The component of the nuclear spin-rotation tensor along the a-inertial axis is large for most isotopic species, especially at the carbene carbon; at this position Caa is two to three times larger than at other substituted positions along the chain. In contrast to both H2C3 and H2C3, in H2C4Caa exhibits a pronounced alternation along the carbon chain backbone. Following detection of the five carbon-13 isotopic species and D2C5, an experimental structure (r0) has been determined to high accuracy for H2C5. 相似文献
10.
Carbon-13 frequency shifts for C2H4, C2D4, and as-C2H2D2 have been measured in isotopic solid solutions in crystalline films at 60 K. All but two of the shifts (for as-C2H2D2) are compatible with recently determined ζ data for C2H4, with 13C frequency shifts for C2H4 and C2D4 in the gas phase and with conventional frequency data. Together, these data completely determine with precision all 18 parameters of the GHFF for ethylene, the previous ambiguity in choice between two sets of Ag species force constants being removed. The force field reproduces closely the observed centrifugal distortion constants for C2H4, a ζ constant observed for trans-C2H2D2, and the inertia defects for C2H4, C2D4, and as-C2H2D2. Vibration and rotation constants for all isotopically deuterated ethylenes are calculated.Possible explanations for the two anomalous crystal shifts in as-C2H2D2 involve the effects of the crystal field, and failure of the use of Dennison's rule for making anharmonic corrections to the shifts. The former explanation is preferred as a result of thorough analysis of the anharmonicity constants for as-C2H2D2 determined from many overtone and combination bands in the gas and crystal spectra. 相似文献
11.
Yoshio Tatamitani 《Journal of Molecular Spectroscopy》2007,242(2):150-155
The results of molecular beam Fourier transform microwave (FTMW) investigations of the van der Waals complexes of difluoromethane with 1,1-difluoroethene (DFE) and trifluoroethene (TFE) are reported. The rotational parameters of the complexes have been interpreted in terms of a Cs geometry with the two H or F atoms of CH2F2 lying out of the σv symmetry plane of the complexes. The complexes are bound by three hydrogen bonds, of which one is the stronger C-F?H-C type, and two are the weaker C-H?F?H-C or C-F?H?F-C types for DFM-DFE or DFM-TFE, respectively. The most notable difference in the two complexes is that the out of plane atoms are two hydrogens for DFM-DFE, but are two fluorines for DFM-TFE. Additional information on the structure and hydrogen bonding has been obtained from ab initio calculations. 相似文献
12.
Line broadening coefficients have been calculated, at room temperature, for lines in the P and R branches of the ν2 band of monodeuterated methane. A properly symmetrized semiclassical model with parabolic relative trajectories has been used. Two interaction potential models have been considered. The first is a Lennard-Jones type atom-atom potential, while the second one was derived from ab initio calculations. The calculated line widths were compared to the available experimental data and a satisfactory agreement was found, although the model contains no other adjustable parameters than the four atomic Lennard-Jones ones. Nonetheless, failures of calculations have also been evidenced for the highest rotational quantum numbers. 相似文献
13.
The spectra of the gaseous mixtures CH4-He and CH4-Ar were obtained in the spectral region 1400-1750 cm−1 with a resolution up to 0.003 cm−1. Helium and argon pressure broadenings for the vibration-rotation lines of the ν2 band of CH4 have been estimated at room temperature for some lines in the P, Q, and R branches. These values were also calculated using the theoretical approach developed by Robert and Bonamy, extended to the case of tetrahedral molecules. The helium data have been found to be in a satisfactory agreement whereas a divergence of calculated and measured broadening coefficients has been evidenced in the case of argon. Simulations of the ν2 band shapes of methane perturbed by helium have also been performed. 相似文献
14.
The rotational spectra of formaldehyde, H212C16O and its isotopic species H213C16O, H212C18O, and H213C18O have been investigated in the ground vibrational state in the frequency region between 8 and 460 GHz. For most cases in which measurements of the a-type R- and Q-branch transitions already existed the accuracy of the line position has been improved to about 10 kHz. For H212C16O and H213C16O a large number of ΔKa = ±2 transitions were measured with similar accuracy. These new data when combined with all other available data and appropriate weightings lead to a set of ground state parameters which for the first time are compatible with infrared and ultraviolet data. The rotational constants (and 3σ standard deviations) obtained using Watson's A-reduced Hamiltonian are:
H212C16O | H213C16O | H212C18O | H213C18O | |
A/MHz | 281 970.572 (24) | 281 993.258(135) | 281 961.94 (39) | 281 985.00 (93) |
B/MHz | 38 836.0456(13) | 37 811.0887(25) | 36 904.1693(66) | 35 859.256(10) |
C/MHz | 34 002.2034(12) | 33 213.9790(25) | 32 511.5311(63) | 31 697.868(10) |