Applying resonant Doppler-free 2-photon laser spectroscopy with thermionic diode detection, the cross sections for the excitation energy transfer of the collisional process7Li*(2P1/2+Cs(6S1/2)→7Li*(2P3/2)+Cs(6S1/2) have been measured. The experimental cross sections, σLi-Cs (1/2→3/2)=890 Å2 and σLi-Cs (3/2→1/2)=430 Å2, are compared with theoretical data obtained by a sudden impact approximation approach taking into account the long-range interaction potentials only. The calculated cross sections show an excitation mixing process at large internuclear distances where Li-Cs dipole-dipole and dipole-quadrupole interaction forces are predominant. 相似文献
The cross section for the fine-structure excitation transfer Cs(6P1/2) → Cs(6P3/2), induced by collisions with the ground state potassium atoms, has been measured by resonant Doppler-free two-photon spectroscopy. The population densities of caesium 6PJ (J=1/2, 3/2) levels were probed by thermionic detection of the collisionally ionized caesium atoms from the Cs(6PJ) → Cs(10S1/2) excitation channel. The cross section for the transfer process at the temperatureT=503 K has been found to be σ(1/2 → 3/2)=45 Å2 ± 20%. The result is compared with previously published experimental cross sections for fine-structure transfer in resonance states of other alkali elements perturbed by potassium and a thoeretical value of the Li(2PJ)-K system calculated in a simple approach. 相似文献
Cross sections of the transition 3P13P0 for the atoms Zn, Cd, Hg upon collisions with inert gas atoms are calculated. It is shown that the transitions between fine structure components induced by nonadiabatic interaction are due to rotation of the molecule. A numerical estimation of the cross sections is performed.
Zusammenfassung Es werden Wirkungsquerschnitte für den Übergang 3P13P0 für die Atome Zn, Cd, Hg bei Stößen mit Edelgasatomen berechnet. Es wird gezeigt, daß die Übergänge zwischen Feinstrukturkomponenten, induziert durch nicht-adiabatische Wechselwirkung, durch Rotation des Moleküls bewirkt werden. Es wird eine numerische Abschätzung der Wirkungsquerschnitte durchgeführt.
Résumé Calcul des sections efficaces pour la transition 3P13P0 dans les atomes Zn, Cd, Hg par collision avec des atomes de gaz rare. On montre que les transitions entre les composantes de structure fine induites par interaction non adiabatique sont dues à la rotation de la molécule. Estimation numérique des sections efficaces.
The authors are indebted to Dr. E. E. Nikitin for very valuable discussions. 相似文献
Electron attachment to SO2 clusters is studied in a pulsed crossed beam apparatus, using laser-excited nf Rydberg atoms as a low energy electron source. The results are interpreted as an attachment to a dimer subcluster followed by a rapid impulsive dissociation of the nascent dimer anion. The remaining cluster anions possess a large amount of internal energy. At low principal quantum numbersn, the influence of the Rydberg ionic core leads to an important evaporation process interpreted with simple model calculations. 相似文献
We investigate collisions of ultracold polar LiCs molecules and ultracold caesium atoms. LiCs molecules are formed in an optical dipole trap by photoassociation of caesium and lithium atoms via the B(1)Π excited state followed by spontaneous emission to the X(1)Σ(+) ground state and the lowest triplet state a(3)Σ(+). The molecules are then stored together with caesium atoms in the same optical trap. Rate coefficients for the loss of molecules induced by collisions with surrounding Cs atoms are measured for molecular ensembles produced via different photoassociation resonances. The results are analyzed in terms of the unitarity limit for the inelastic rates and predictions from the universal model of Idziaszek and Julienne (Phys. Rev. Lett., 2010, 104, 113202). 相似文献
Excimer laser (ArF) photolysis of diatomic and triatomic hydrides produces hydrogen atoms with translational energies in excess of 15000 cm?1 per atom. Subsequent collisions of these “hot” atoms with CO2 and N2O produces vibrationally excited molecules which can be detected by their characteristic infrared emission. 相似文献
Fine-structure mixing of excited114Cd 53PJ atoms induced by collisions with various molecular gases (N2, H2, D2, CO, CH4, C2H6) has been investigated by a combined method of absorption and fluorescence spectroscopy. After pulsed optical excitation of the Cd(53P1) level, the time dependence of the population densities has been measured simultaneously both for the 53P1 state and for the collisionally populated 53P0 state. By analyzing the signal curves at different molecular gas pressures cross sections for collisional transfer between the114Cd 53P1 and 53P0 levels as well as the quenching cross sections for the 53P levels have been obtained. 相似文献
Excitation cross sections for the potassium 42P and 42P states produced in collisions with rare gases are reported. They have been measured by the lightly yield as a function of the energy from 100 to 2500 eV. In addition to this, a spectral analysis from 3300 to 8600 Å of the light is given for some energies. This spectral analysis gives experimental evidence that the excited and ionized states of both potassium and the rare gases are involved in the collision process. 相似文献
Vibrational excitation of SF6 molecules in collisions with He atoms is studied using a vibrational close-coupling, rotational infinite-order-sudden method of calculation. Integral and differential cross sections for excitation of the triply degenerate ν6 and ν5 vibrational modes of SF6 are reported for thermal collisional energies. Excitation of the ν6 mode is found to be particularly efficieny. The cross sections are much larger than those calculated previously for the excitation of the bending mode in the He + CO2 system. The differential cross sections are backward peaked. 相似文献
Collisional 5 1P1 → 5 3PJ spin changing fine structure transfer as well as 5 3PJ intramultiplet mixing induced by various molecular gases (H2, D2, N2, CO, CO2, CH4, C2H6, C3H8, C2H4) have been investigated using a combined method of fluorescence and absorption spectroscopy. After pulsed optical excitation of the Cd(5 1P1) level the time dependence of the population densities has been measured both for the Cd(5 1P1) level as well as the three collisionally populated Cd(5 3PJ) levels. By analyzing the signal curves at different molecular gas pressures not only the ratios of 5 1P1 → 5 3PJ population transfer cross sections but also the Cd(5 1PJ), Cd(5 3PJ) quenching cross sections and the Cd(5 3PJ) intramultiplet population transfer cross sections have been obtained. 相似文献
The thermal decomposition of diatomic molecules in a light inert gas was examined within the scope of the diffusion theory with allowance for interaction between vibration and rotation. It was shown that molecular rotation changes the value of the dissociation constant within an order of magnitude and appreciably affects its temperature dependence. The results, obtained by computer, can be applied directly to the dissociation of I2, Br2, and Cl2.In conclusion, we express our gratitude to A. I. Vol'pert and L. N. Stesik for the possibility of carrying out the computer calculation. 相似文献
Using a crossed molecular-beam technique, electron transfer is studied in collisions of fast potassium atoms with benzene and fluorobenzene molecules. The negative fragment ions formed in the collision region are extracted by a pulsed voltage, and their masses and energy release distributions analyzed by a time-of-flight (TOF) method. The dominant fragment from C6H5F is F-. The phenyl ring fragments CH- and C2H- are also observed but with lower intensities. In the case of C6H6 the dominant anionic specie is C2H-. The kinetic-energy release distributions of the various fragments are derived from the width and shapes of the TOF peaks in the spectrum. 相似文献
For processes of the type K + M K+ + M? at eV collision energies, measurements are reported of the population of excited states of the product negative ions. For M = Br2 and SF6 only a small excitation (0.5 – 3 eV) is found. For M = O2, the products can be excited up to higher energies (? 5 eV); this is ascribed to a second electronic channel of the process. 相似文献
NaI molecules predissociate after excitation with ultrashort pulses at a peak wavelength of 320 nm. In rare gas environments
at higher pressures the process of geminate recombination is likely to occur. We studied the dynamics of these processes under
various pressure conditions and for different collision partners. The calculations were performed within a three-dimensional
statistical model which simulates the NaI wave-packet dynamics with classical trajectories and the collisions via an instantaneous
hard-sphere scattering.
Received: 4 May 1998 / Accepted: 27 July 1998 / Published online: 28 September 1998 相似文献
In connection with recent experiments on the observation of the metastable 2s state of muonic boron (μB)4+ formed in helium with a small admixture of diborane (B2H6) we estimated the cross-section of the electron transfer from helium to the muonic ion. The collisions energy T was considered to lie between the thermal energy and 1 a. u. The muonic ion (μB)4+ was treated as a heavy beryllium isotope Be4+. It was found that the main reaction responsible for the electron transfer at the energies specified above was: Be4+ + He → Be3+(1s) + He2+ + e-. . Its mechanism is the Auger effect in the two-electron quasi-molecule (Be-He)4+. In our estimation of its cross-section we used adiabatic quasi-molecular terms obtained by diagonalizing the electronic Hamiltonian on a basis of several diabatic states constructed from two-centre orbitals. The electronic wavefunctions built with this way were employed to calculate Auger effect rates. The outgoing electron was treated to be free. The relative motion of the nuclei was considered classically. It was found that in the region 0.001 ≤ T ≤ 0.01 (in atomic units) the cross-section was a decreasing function of T and it was small (~ 10-2 Å2). Then it starts to increase and mounts to typical atomic values (1 Å2) at T = 1 ÷ 2. The comparison of the reaction rate constant estimated on the basis of the obtained cross-section with experimental results establishes the upper limit of the energy of muonic boron during the 2s state lifetime (≈ 40 ns). It proves to be about 25 eV. This limit is in agreement with the typical value of 1 eV resulting from the energy transfer in the muon capture by the diborane molecule and the recoil energy acquired in the cascade. However, it does not exclude the possibility of an additional acceleration of muonic boron during its formation in the molecule. 相似文献
Chemical dynamics simulations are reported of energy transfer in collisions of O(3P) atoms with a 300 K 1-decanethiol self-assembled monolayer (H-SAM) surface. The simulations are performed with a nonreactive potential energy surface, developed from PMP2/aug-cc-pVTZ calculations of the O(3P) + H-SAM intermolecular potential, and the simulation results represent the energy transfer dynamics in the absence of O(3P) reaction. Collisions energies E(i) of 0.12, 2.30, 11.2, 75.0, and 120.5 kcal/mol and incident angles theta(i) of 15, 30, 45, 60, and 75 degrees were considered in the study (theta(i) = 0 degrees is the surface normal). The translational energy distribution of the scattered O(3P) atoms, P(E(f)), may be deconvoluted into Boltzmann and non-Boltzmann components, with the former fraction identified as f(B). The trajectories are also analyzed in terms of three types; that is, direct scattering from and physisorption on the top of the H-SAM and penetration of the H-SAM. There are three energy regimes in the scattering dynamics. For the low E(i) values of 0.12 and 2.30 kcal/mol, physisorption is important and both f(B) and the average final translational energy of the scattered O(3P) atom, E(f), are nearly independent of the incident angle. The dynamics is much different for hyperthermal energies of 75.0 and 120.5 kcal/mol, where penetration of the surface is important. For hyperthermal collisions, the penetration probability decreases as theta(i) is increased, with a significant transition between theta(i) of 60 and 75 degrees . Hyperthermal penetration occurs upon initial surface impact and is more probable if the impinging O(3P) atom may move down a channel between the chains. For E(i) = 120.5 kcal/mol, 90% of the trajectories penetrate at theta(i) = 15 degrees , while only 3% penetrate at theta(i) = 75 degrees. For the former theta(i), the energy transfer to the surface is efficient with E(f) = 4.04 kcal/mol, but for the latter theta(i), E(f) = 85.3 kcal/mol! Particularly interesting penetrating trajectories are those in which O(3P) is trapped in the H-SAM for times exceeding 60 ps, linger near the Au substrate, and strike the Au substrate and scatter directly. For E(i) = 11.2 kcal/mol, there is a transition between the scattering dynamics for the low and hyperthermal collision energies. Additional detail in the energy transfer dynamics is obtained from the final polar and azimuthal angles, the residence time on/in the H-SAM, the minimum height with respect to the Au substrate, and the number of inner turning points in the O-atom's velocity. Calculated values of E(f) vs the final polar angle, theta(f), are in qualitative agreement with experiment. The O(3P) + H-SAM nonreactive energy transfer dynamics, for E(i) of 11.2 kcal/mol and lower, are very similar to previously reported Ne + H-SAM simulations. 相似文献
Electron transfer to uracil (U), 5-chlorouracil (5-ClU) and 5-fluorouracil (5-FU) yielding anion formation has been investigated in 30-100 eV potassium-molecule collisions. The rich fragmentation patterns of all three molecules suggest that electron transfer in collisions with electronegative neutrals may cause efficient damage to RNA. The main ring fragment anion in all the mass spectra was NCO(-) while the production of X(-) (X = F, Cl) was a strong decomposition of the halouracil temporary negative ions. Cl(-) was the most intense fragment anion in the 5-chlorouracil measurements, whereas NCO(-) production dominated in the U and 5-FU data. Arguments based on energetics and vibrational dynamics have been proposed to explain these differences. Electronic coupling between dipole- and valence-bound states may play a particularly important role in the fragmentation pathways of the 5-ClU parent anion. The stabilizing influence of the potassium cation following electron transfer (ionic scattering) on the observed fragmentation patterns is discussed, notably in the context of comparisons with free electron attachment processes. 相似文献
Collision-induced dissociation, laser-induced dissociation and electron-capture dissociation are compared on a singly and doubly protonated pentapeptide. The dissociation spectrum depends on the excitation mechanism and on the charge state of the peptide. The comparison of these results with the conformations obtained from Monte Carlo simulations suggests that the de-excitation mechanism following a laser or an electron-capture excitation is related to the initial geometry of the peptide. 相似文献
The photoredox reaction of ferrioxalate after 266/267 nm excitation in the charge transfer band has been studied by means of ultrafast extended X-ray absorption fine structure (EXAFS) analysis, optical transient spectroscopy, and quantum chemistry calculations. The Fe-O bond length changes combined with the transient spectra and kinetics have been measured and in combination with ultrahigh frequency density functional theory (UHF/DFT) calculations are used to determine the photochemical mechanism for the Fe(III) to Fe(II) redox reaction. The present data and the results obtained with 266/267 nm excitations strongly suggest that the primary reaction is the dissociation of the Fe-O bond before intramolecular electron transfer occurs. Low quantum yield electron photodetachment from ferrioxalate has also been observed. 相似文献
Measurements of the distribution of rotational states in a nitrogen molecular beam before and after deflection by collision with rare gas atoms are interpreted in terms of the intermolecular potential. A potential of the form V(R, θ) = 4?(1 + b2P2(cosθ)| R*12 ? 4θ [1 + α2P2(cosθ)]/R*6 is used with semiclassical theory using the sudden approximation to fit the observations. As α2 is known, as well as ? and the size parameter, σ, the objective is to find b2. However, the calculated state distributions are found to systematically vary from those measured, irrespective of the value of b2. This result is tentatively explained as due to the inadequacies of the 12-6 potential. 相似文献