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1.
The differential cross-sections (DCS) of the low-energy electron–N 2 scattering are studied using the vibrational close-coupling (VCC) method and vibrational scattering potentials which include static, exchange and polarization contributions. The polarization is obtained based on the ‘better than adiabatic dipole’ (BTAD) and the ‘distributed spherical Gaussian’ (DSG) respectively. The converged (0 → 0, 0 → 1, 0 → 2, 0 → 3) DCS are obtained with the impact energies being the resonance's first two elastic scattering peaks?–?approximately 1.90 eV and 2.10 eV. Calculations from both polarization potentials agree with experimental results. 相似文献
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5.
F. Liu W. Wang W. Zheng Y. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(3):435-440
In this study, spatially resolved measurements of the
emission intensity of OH (A2Σ↦X2Π, 0-0) and the
vibrational temperature of N2 (C) have been performed during a positive
pulsed streamer discharge with a wire-plate electrode configuration at
atmospheric pressure. The effects of pulse peak voltage, pulse repetition
rate and the added O2 flow rate on the spatial distributions of the
emission intensity of OH (A2Σ↦X2Π, 0-0) and the
vibrational temperatures of N2 (C) perpendicular to the wire in the
direction towards the plate (in the radial direction) are investigated. It
has been found that the emission intensity of OH (A2Σ↦X2Π, 0-0) increases with increasing pulse peak voltage and pulse
repetition rate and decreases with increasing the distance from the wire
electrode. When the different oxygen flows are added in N2 and H2O
mixture gas, the emission intensity of OH (A2Σ↦X2Π, 0-0) decreases with increasing the flow rate of oxygen. The
vibrational temperature of N2 (C) is nearly independent of pulsed peak
voltage and pulsed repetition rate, but increases with increasing the added
O2 flow rate and keeps almost constant in the radial direction under
the present experimental conditions. This measurement plays a crucial role
in understanding the discharge characters of pulsed streamer discharge and
establishing the molecule reaction dynamics model of pulsed streamer
discharge. 相似文献
6.
C.M. Marian F. Schneider M. Kleinschmidt J. Tatchen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):357-367
Electronic spectra of uracil in its diketo (lactam) form and five enol (lactim) tautomeric forms have been investigated by
means of combined density functional and configuration interaction methods. We have simulated the effects of hydrogen bonding
with a protic solvent by recomputing the spectrum of uracil in the presence of two, four, or six water molecules. Geometries
of the electronic ground state and several low-lying excited states have been optimized. Spin-orbit coupling has been determined
for correlated wavefunctions employing a non-empirical spin-orbit mean-field approach. In accord with experiment, we find
the diketo tautomer to be the most stable one. The calculations confirm that the first absorption band arises from the 1( π↦π*) S
0↦S
2 excitation. The experimentally observed vibrational structure in this band originates from a breathing mode of the six ring.
Complexation with water molecules is seen to cause a significant blue shift of n↦π* excitations while leaving π↦π* excitations nearly uninfluenced. Computed radiative lifetimes are presented for the experimentally known weak phosphorescence
from the π↦π* excited T1 state. Among the uracil lactim tautomers, one is particularly interesting from a spectroscopic point of view. In this tautomer,
the π↦π* excitation gives rise to the S1 state.
Received 18 February 2002 / Received in final form 5 June 2002 Published online 13 September 2002 相似文献
7.
Y. Y. Zeng H. Feng W. G. Sun 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2012,66(1):4
Distributed spherical Gaussian (DSG) correlation-polarization model potentials with higher-order terms and exact exchange
effects in single-configuration Slater determinant are taken into account for low-energy vibrational excitation e-N2 scattering system. The integrodifferential coupled channel equations are solved using a combination of linear-algebraic and
R-matrix-propagator algorithms. Analytic Born completion is used to calculate high-order scattering matrix elements in order
to obtain convergent differential cross sections. The energy range is set to 4–15 eV which is not tested by the present theoretical
method before. The overall agreement of theoretical results with the latest experiments emphasizes the importance of higher-order
correlation-polarization potentials and rigorous exchange effects in vibrational excitation scattering. 相似文献
8.
The collisional excitation of the lower vibrational levels of
H2(1Σg+) molecules by low-energy electron impact is
computed using an empirical model potential and by solving the
coupled-channels scattering equations within a space-fixed (SF)
frame of reference formulation. Numerically converged partial,
integral inelastic and elastic cross-sections are obtained from what
is an essentially exact treatment of the dynamics and the results
are compared with measurements and with earlier calculations on the
same system. The usefulness of the SF method for handling excitation
processes at near-threshold collision energies is discussed and
analyzed through the calculations of collisional superelastic
partial cross-sections down to 10-2 meV of collision energy. 相似文献
9.
严格交换势用于研究低能电子与H2分子的弹性和非弹性散射截面,线性代数方法和R-矩阵传播子相结合求解基于振动密耦合方法的积分-微分耦合方程组,由此得到收敛的(0→0,0→1,0→2)散射微分截面和积分截面.理论计算结果与目前优秀的实验值和其他理论计算值进行了比较,表明基于振动密耦合方程的严格交换势在低能电子与H2分子振动激发散射中有重要作用.
关键词:
严格交换势
2分子振动激发')" href="#">H2分子振动激发
微分截面
积分截面 相似文献
10.
The effects of the rovibrational excitation of reactants in the N(2D) + D2(X1Σg+) → ND(X3Σ+) + D(2S) reaction are calculated in a collision energy range from the threshold to 1.0 eV using the time-dependent wave packet approach and a second-order split operator. The reaction probability, integral cross-section, differential cross-section and rate constant of the title reaction are calculated. The integral cross-section and rate constant of the initial states v = 0, j = 0, 1, are in good agreement with experimental data available in the literature. The rotational excitation of the D2 molecule has little effect on reaction probability, integral cross-section and the rate constant, but it increased the sideways and forward scattering signals. The vibrational excitation of the D2 molecule reduced the threshold and broke up the forward–backward symmetry of the differential cross-section; it also increased the forward scattering signals. This may be because the vibrational excitation of the D2 molecule reduced the lifetime of the intermediate complex. 相似文献
11.
N.?A.?Borisevich A.?L.?Ivanov S.?M.?Kazakov A.?V.?Kukhto A.?I.?Mit'kovets D.?V.?Murtazaliev V.?A.?Povedailo O.?V.?Khristoforov 《Journal of Applied Spectroscopy》2005,72(4):503-508
The electron energy loss spectra (EELS) of indole, 3-indolyl propionic acid, 3-indolealdehyde, 3-dimethylaminomethylindole,
tryptophan, and N-acetyl-L-tryptophan in the gas phase upon excitation by monokinetic electrons with an energy of E0 = 11–50 eV are obtained. The structure of EELS is determined in the main by the indole chromophore; the side groups, except
for the C=O group of 3-indolealdehyde, exert an insignificant influence. The energy of the lower triplet level 3La is 3.3 eV for indole and its derivatives and 3.2 eV for tryptophan and N-acetyl-L-tryptophan. Four singlet transitions in
the region of 4.4–7.2 eV have been identified. The molecules studied, except for tryptophan, fluoresce in the gas phase on
excitation by electrons. At low values of E0 (10–25 eV), the fluorescence spectra are similar and are due to the indole fluorophore. Just as in the case of optical excitation,
fluorescence on excitation by electrons is associated with the 1Lb-S0 transitions. An increase in the energy E0 up to 60–80 eV leads to dissociation of a portion of the indole molecules and to the appearance of additional bands in the
fluorescence spectrum.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 468–472, July–August, 2005. 相似文献
12.
Tunneling electrons in a scanning tunneling microscope were used to excite specific vibrational quantum states of adsorbed water and hydroxyl molecules on a Ru(0 0 0 1) surface. The excited molecules relaxed by transfer of energy to lower energy modes, resulting in diffusion, dissociation, desorption, and surface-tip transfer processes. Diffusion of H2O molecules could be induced by excitation of the O-H stretch vibration mode at 445 meV. Isolated molecules required excitation of one single quantum while molecules bonded to a C atom required at least two quanta. Dissociation of single H2O molecules into H and OH required electron energies of 1 eV or higher while dissociation of OH required at least 2 eV electrons. In contrast, water molecules forming part of a cluster could be dissociated with electron energies of 0.5 eV. 相似文献
13.
M. Vatasescu F. Masnou-Seeuws 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(2):191-204
The paper contains a time-dependent investigation of the tunneling effect observed in the photoassociation spectrum of Cs2 and attributed to the 0g
-(6s, 6p
3/2) double well. When by photoassociation of two cold cesium atoms a vibrational level of the outer well is populated, tunneling
is an efficient mechanism for transferring the population to the inner well (R < 15a
0), where spontaneous emission may lead to formation of cold molecules in low vibrational levels of the a
3Σ+
u(6s, 6s) electronic state. This tunneling effect is analyzed by wavepackets propagation, first considering the double well potential
alone, and following a packet made by a superposition of states initially located at large distances. Characteristic times
for the vibration dynamics, corresponding to a beating phenomenon between the two wells, to partial “revival” at large distances,
and to maxima in the population localized in the inner well are reported and discussed. Second, we simulate the two-channels
a
3Σ+
u(6s, 6s)↦0g
-(6s, 6p
3/2) photoassociation at detunings around 2.9 cm-1: the inner well can be populated either by the excitation of a vibrational level of the external well (resonant excitation),
or by tuning the photoassociation laser at the energy of the inner well level which displays tunneling (“off-resonance excitation”).
In the first case the photoassociation is efficient, while the tunneling probability is small; in the second, the tunneling
probability is large, so that despite the poor efficiency of the photoassociation process, more population can be transferred
to the inner well. This second choice is shown to be very sensitive to the laser intensity, which could be used to control
the population of the inner well and hence the formation of ultracold molecules in low vibrational levels.
Received 19 April 2002 Published online 1st October 2002
RID="a"
ID="a"e-mail: francoise.masnou@lac.u-psud.fr 相似文献
14.
N. Vujičić S. Vdović D. Aumiler T. Ban H. Skenderović G. Pichler 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(3):447-454
We present direct observation of the velocity-selective optical pumping of
the Cs ground state hyperfine levels induced by the femtosecond (fs) laser
oscillator centered at either D2 (6 2S1/2↦6 2P3/2,
852 nm) or D1 (6
P1/2, 894 nm) cesium
line. We utilized previously developed modified direct frequency comb
spectroscopy (DFCS) which uses a fixed frequency comb for the excitation and
a weak cw scanning probe laser centered at the 133Cs 6
2S1/2↦6 2P3/2 transition (D2 line) for ground
levels population monitoring. The frequency comb excitation changes the
usual Doppler absorption profile into a specific periodic, comblike
structure. The mechanism of the velocity selective population transfer
between the Cs ground state hyperfine levels induced by fs pulse train
excitation is verified in a theoretical treatment of the multilevel atomic
system subjected to a pulse train resonant field interaction. 相似文献
15.
A. Morozov T. Heindl J. Wieser R. Krücken A. Ulrich 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(1):51-57
Continuous and pulsed 12 keV electron beams were used to excite nitrogen
within a gas cell at pressures ranging from 10 to 1400 hPa. The pressure
dependence of the ratio of photon fluxes for emission from vibrational
levels v'=0 and 1 of the C 3Π u state has been studied. The
results confirm the presence of a collisional excitation mechanism
populating v'=0, 1 in addition to electron impact excitation. Rate constants
of (1.27 ±0.04)×10-11 cm3s-1 [ v'=0] and
(2.68 ±0.08)×10-11 cm3s-1 [ v'=1] were measured for
C 3Π u quenching by ground state nitrogen. For electron beam
conditions relative excitation efficiencies of 1:0.59:0.22 for
vibrational levels 0, 1 and 2 were calculated. The recorded flux ratios are
compared with the predictions given by a vibrational relaxation model. 相似文献
16.
V.Yu. Grishina L.A. Kondratyuk E.L. Bratkovskaya M. Büscher W. Cassing 《The European Physical Journal A - Hadrons and Nuclei》2000,9(2):277-285
We investigate the reactions πN↦a
0
N and pp↦da
0
+ near threshold and at medium energies. An effective Lagragian approach and the Regge pole model are applied to analyze different
contributions to the cross-section of the reaction πN↦a
0
N. These results are used to calculate the differential and total cross-sections of the reaction pp↦da
0
+ within the framework of the two-step model in which two nucleons produce an a0-meson via π-meson exchange and fuse to a deuteron. The necessity of new measurements on a0 production and branching fractions (of its decay to the K
and πη channels) is emphasized for clarifying the a0 structure. Detailed predictions for the reaction pp→da
0
+ are presented for the energy regime of the proton synchrotron COSY-Jülich.
Received: 4 August 2000 / Accepted: 17 September 2000 相似文献
17.
An apparatus is described for measuring the inelastic differential cross section for vibrational excitation in collisions of diatomic molecules with monoenergetic ions at laboratory energies between 10 and 50 eV. The method consists of measuring the time of flight of single ions with a time amplitude converter and displaying the results on a 100 channel pulse height analyzer. From the shift in the time of flight relative to that expected for elastic scattering the final state of the molecule excited in a single collision is identified. By studying only central collisions with almost zero impact parameter rotational excitation is strongly suppressed. Measured times of flight after collisions of monoenergetic Li+ ions with H2 show that with increasing energy the most probable vibrational quantum jump increases from 0→1 to 0→2,0→3 etc. Contrary to the usual assumption of a small steric factor for vibrational excitation the results show that the inelastic cross section is larger than the elastic cross section. Using reported potential parameters the energy dependence of the most probable excited state is compared with the calculations of Secrest and Johnson for a one-dimensional collinear collision. The satisfactory agreement suggests that the steric factor is close to 1. From measurements at different scattering angles at 10 eV the integral inelastic cross section is found to be about 0.2 Å2 corresponding to a differential cross section of 0.4 Å2/sr. Measured values of integral and differential total cross sections for Li+-He andLi+-H2 are reported and compared with theory. Direct dissociation of D2 by Li+ in the energy range from 25 to 55 eV was not observed, yielding an upper limit for the cross section of 4 · 10?4 Å2/sr. 相似文献
18.
We consider one-dimensional (1D) interacting spinless fermions with a non-linear spectrum in a clean quantum wire (non-linear
bosonization). We compute diagrammatically the 1D dynamical structure factor, S(ω,q), beyond the Tomonaga approximation focusing
on it's tails, |ω| ≫vq,
i.e. the 2-pair excitation continuum due to forward scattering. Our methodology reveals three classes of diagrams: two “chiral”
classes which bring divergent contributions in the limits ω→±vq, i.e. near the single-pair excitation continuum, and a “mixed”
class (so-called Aslamasov-Larkin or Altshuler-Shklovskii type diagrams) which is crucial for the f-sum rule to be satisfied.
We relate our approach to the T=0 ones present in the literature. We also consider the
case and show that the 2-pair excitation continuum dominates the single-pair one in the range: |q|T/kF ≪ω±vq ≪T (substantial for q ≪kF). As applications we first derive the small-momentum optical conductivity due to forward scattering: σ∼1/ω for T ≪ω and σ∼T/ω2 for T ≫ω. Next, within the 2-pair excitation continuum, we show that the attenuation rate of a coherent mode of dispersion
Ωq crosses over from
, e.g. γq ∼|q|3 for an acoustic mode, to
, independent of Ωq, as temperature increases. Finally, we show that the 2-pair excitation continuum yields subleading curvature corrections
to the electron-electron scattering rate:
, where V is the dimensionless strength of the interaction. 相似文献
19.
The interpretation of High Resolution Electron Energy Loss Spectroscopy (HREELS) spectra recorded from polymers remains a difficult task because of (1) the relatively poor resolution achieved on these non-ordered systems, (2) the large number of vibrational features induced by the numerous chemical groups in the monomer unit, (3) the superposition of the dipole, impact and resonant scattering mechanisms. In this report, the study of the physical mechanisms responsible for the electron–molecular vibration coupling is investigated, using a simple model system consisting of a well-ordered film of eicosanoic acid adsorbed on a GeS substrate and an hypothesis supposing that dipole scattering is extinguished in non specular geometry. The ordered character of the molecular layer allowed to separate the dipole from the impact contributions in the signal recorded in specular geometry. The results support the idea that any vibrational mode of an organic compound induced by electron excitation contains both contributions with different relative extent, depending on the chemical nature of the molecular group involved in the vibration and their orientation. Cross section measurements for both interaction mechanisms are in agreement with theoretical prediction, confirming the validity of this new and original method suggested for the separation of the interaction mechanisms. Furthermore, we measured a resonance near 6 eV impact energy as the intensity of the ν(C–D) band is enhanced for this impact energy. This observation again is in agreement with our hypothesis that the impact scattering is the dominant interaction mechanism involved in the vibrational excitation of the C–D group. This study allowed for a model of the geometry of adsorption of the molecule on the substrate. It is confirmed that the eicosanoic acid adsorbs the COO group on the substrate, with the long hydrocarbon chain standing up and the CD3 terminating group pointing out of the surface. 相似文献
20.
Absolute measurements of elastic scattering and vibrational excitation of the NO molecule by low energy electron impact (0.4-2.5 eV) are presented. They show that previous estimates of these cross sections may be in error by as much as a factor of 3 and provide compelling evidence for a reassessment of the balance between elastic scattering and vibrational excitation at incident energies below 2 eV. They also confirm the critical contribution that intermediate negative ion resonances (NO-) make to the various scattering processes for this molecule at low incident energies. 相似文献