Collisional and thermal ionization of sodium Rydberg atoms: II. Theory for nS, nP and nD states with n = 5 25 (original) (raw)
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Journal of Physics B-atomic Molecular and Optical Physics, 2005
The results of experimental and theoretical studies of collisional ionization of Na Rydberg atoms in nS and nD (n = 8-20) states are presented. Molecular and atomic ions from associative ionization and photoionization by blackbody radiation were detected after pulsed laser excitation of Rydberg states in crossed Na atomic beams. An original method of determination of associative ionization rate constants based on the measurement of ratios of molecular and atomic ion signals was used, which did not require the determination of absolute number density of Rydberg atoms. The measured rate constants of associative ionization of Rydberg atoms in collisions with ground-state Na atoms are compared with the results of our earlier single-beam experiment and theoretical calculations. It is shown that the stochastic ionization model, which describes the collisional ionization of Rydberg atoms in terms of chaotic migration of highly excited electron induced by the motion of the colliding nuclei, yields a significantly better agreement with the experimental results than the earlier Duman-Shmatov-Mihajlov-Janev model.
Journal of Physics B-atomic Molecular and Optical Physics, 2005
Collisional and thermal ionization of sodium nS and nD Rydberg atoms with n=8-20 has been studied. The experiments were performed using a two-step pulsed laser excitation in an effusive atomic beam at atom density of about 2 10^{10} cm^{-3}. Molecular and atomic ions from associative, Penning, and thermal ionization processes were detected. It has been found that the atomic ions were created mainly due to photoionization of Rydberg atoms by photons of blackbody radiation at the ambient temperature of 300K. Blackbody ionization rates and effective lifetimes of Rydberg states of interest were determined. The molecular ions were found to be from associative ionization in Na(nL)+Na(3S) collisions. Rate constants of associative ionization have been measured using an original method based on relative measurements of Na_{2}^{+} and Na^{+} ion signals.
Experimental and theoretical study of the chemi-ionization in thermal collisions of Ne Rydberg atoms
Physical Review A, 2012
The state dependence of associative ionization of the ns and nd Rydberg series of Ne atoms with 5 < n < 18 at thermal collision energies is investigated experimentally using a combination of synchrotron radiation and mass spectrometry in a single-beam experiment. The n dependence of the collisional and associative ionization of the Ne Rydberg atoms have been calculated using the dipole resonant mechanism, in particular the associative ionization rates for 5 < n eff < 20 have been calculated for cell, single beam, and crossed beam conditions. Refinements of the theory implemented previously have been necessary in order to apply the theory to the collisions of rare gas atoms. The results of the theoretical model for the n dependency of the associative ionization rates of the Ne Rydberg atoms are compared to the experimental data.
The non-stationary multistep (diffusion-like) ionisation of Rydberg atoms is considered theoretically. The investigation is based on the time-dependent Fokker-Planck equation and is related to collisional and microwave ionisation of Rydberg atoms. Analytical expressions for the mean time and the higher moments of the distribution of the diffusive ionisation times are derived. The conditions for the occurrence of diffusive ionisation are obtained. The relation of the present study to stationary diffusive ionisation and the experimental investigation of the ionisation of Rydberg atoms is discussed.
Journal of Cluster Science, 2012
In this paper the history and the current state of research of the chemi-ionization processes in atom-Rydberg atom collisions is presented. The principal assumptions of the model of such processes based on the dipole resonance mechanism, as well as the problems of stochastic ionization in atom-Rydberg atom collisions, are exposed. The properties of the collision kinetics in atom beams of various types used in contemporary experimentations are briefly described. Results of the calculation of the chemi-ionization rate coefficients are given and discussed for the range of the principal quantum number values 5 ≤ n ≤ 25. The role of the chemi-ionization processes in astrophysical and laboratory low-temperature plasmas, and the contemporary methods of their investigation are described. Also the directions of further research of chemi-ionization processes are discussed in this paper.
Physical Review A, 1988
The absolute values of cross sections for the collisional ionization of low-Rydberg-state He atoms in the n 'I' state (n= 14) by the polar molecules NH3, SO» and acetone (C3H60) are measured in a crossed-beam experiment at thermal kinetic energies, for a well-defined relative velocity. Simultaneous Penning ionization of NH, by metastable He(2 S) atoms is carried out in situ for calibration. Experimental collisional-ionization cross sections 0', " '(u"), for u"=2400 m/s, as large as 9X 10 cm for NH3, 5)&10 "cm for SO» and 10 ' cm for C3H60 at 300 K, are obtained. These large cross sections cannot be explained by the "free-electron model" usually used in Rydbergatommolecule collisions: This model predicts no ionization of Rydberg levels as low as n=14, since the amount of energy available from rotational b,J =-1 5K=0 relaxation transitions of the molecule is insufficient. Our hypothesis of large l b,J l rotational transitions is strengthened by comparison of the results for the three studied molecules.
Ionization experiments involving Na Rydberg atoms
1995
Ionization by blackbody radiation of a beam of sodium atoms, prepared in Rydberg states by two-step laser excitation, has been investigated. Ionization by absorption of an additional laser photon was also present, although these ionization channels take place on very different time scales. For atom densities in the range 1-4× l0 H cm-3 and power density of the laser used for the second step excitation of the order of MW/cm 2, we have found evidence of space-charge interactions in the laser-light focus region.
Kinetics of diffusive ionization of the potassium Rydberg atoms
The non-stationary multistep (diffusion-like) ionisation of Rydberg atoms is considered theoretically. The investigation is based on the time-dependent Fokker-Planck equation and is related to collisional and microwave ionisation of Rydberg atoms. Analytical expressions for the mean time and the higher moments of the distribution of the diffusive ionisation times are derived. The conditions for the occurrence of diffusive ionisation are obtained. The relation of the present study to stationary diffusive ionisation and the experimental investigation of the ionisation of Rydberg atoms is discussed.
Ionization of Rydberg atoms by blackbody radiation
New Journal of Physics, 2009
We have studied ionization of alkali-metal Rydberg atoms by blackbody radiation (BBR). The results of theoretical calculations of ionization rates of Li, Na, K, Rb and Cs Rydberg atoms are presented. The calculations have been performed for nS, nP and nD states for principal quantum numbers n=8-65 at ambient temperatures of 77, 300 and 600 K. The calculations take into account the contributions of BBR-induced redistribution of population between Rydberg states prior to photoionization and field ionization by extraction electric field pulses. The obtained results show that these phenomena affect both the magnitude of the measured ionization rates and their ndependence. A Cooper minimum for BBR-induced transitions between bound Rydberg states of Li has been found. The calculated ionization rates are compared with our earlier measurements of BBR-induced ionization rates of Na nS and nD Rydberg states with n=8-20 at 300 K. A good agreement for all states except nS with n > 15 is observed. Useful analytical formulas for quick estimates of BBR ionization rates of Rydberg atoms are presented. Application of BBR-induced ionization signal to measurements of collisional ionization rates is demonstrated.
n-changing collisions of Rydberg atoms with ground-state atoms
Physics Letters A, 1985
The inelastic transitions between hydrogenic energy levels of a Rydberg atom induced in collisions with ground-state atoms are considered. The corresponding transition probability and cross section are calculated using the Fermi pseudopotential to describe the atom-Rydberg-atom interaction and a quasiclassical expression for the density distribution of the Rydberg electron.