arXiv subjects

Viatcheslav Kokoouline

Publications and source records attributed to Viatcheslav Kokoouline.

26 records · Page 2Linked to original sources

arXiv2008

Theoretical rate of dissociative recombination of HCO$^{+}$ and DCO$^{+}$ ions

The article presents an improved theoretical description of dissociative recombination of HCO$^+$ and DCO$^+$ ions with a low energy electron. In the previous theoretical study (Phys. Rev. A {\bf 74}, 032707) on HCO$^+$, the vibrational motion along the CO coordinate was neglected. Here, all vibrational degrees of freedom, including the CO stretch coordinate, are taken into account. The theoretical dissociative recombination cross-section obtained is similar to the previous theoretical result at low collision energies ($<$0.1 eV) but somewhat larger at higher ($>$0.1 eV) energies. Therefore, the present study suggests that motion along the CO coordinate does not play a significant role in the process at low collision energies. The theoretical cross-section is still approximately 2-3 times lower than the data from a recent merged-beam experiment.

physics.chem-ph↗

arXiv2007

Correlation diagrams in collisions of three identical particles

We discuss collision of three identical particles and derive scattering selection rules from initial to final states of the particles. We use either laboratory-frame, hyperspherical, or Jacobian coordinates depending on which one is best suited to describe three different configurations of the particles: (1) three free particles, (2) a quasi-bound trimer, or (3) a dimer and a free particle. We summarize quantum numbers conserved during the collision as well as quantum numbers that are appropriate for a given configuration but may change during the scattering process. The total symmetry of the system depends on these quantum numbers. Based on the selection rules, we construct correlation diagrams between different configurations before and after a collision. In particular, we describe a possible recombination of the system into one free particle and a dimer, which can be used, for example, to identify possible decay products of quasi-stationary three-body states

physics.atom-ph↗

arXiv2007

Dissociative recombination of H3+ in the ground and excited vibrational states

The article presents calculated dissociative recombination (DR) rate coefficients for H+3 . The previous theoretical work on H+3 was performed using the adiabatic hyperspherical approximation to calculate the target ion vibrational states and it considered just a limited number of ionic rotational states. In this study, we use accurate vibrational wave functions and a larger number of possible rotational states of the H3+ ground vibrational level. The DR rate coefficient obtained is found to agree better with the experimental data from storage-ring experiments than the previous theoretical calculation. We present evidence that excited rotational states could be playing an important role in those experiments for collision energies above 10 meV. The DR rate coefficients calculated separately for ortho- and para-H3+ are predicted to differ significantly at low energy, a result consistent with a recent experiment. We also present DR rate coefficients for vibrationally-excited initial states of H3+, which are found to be somewhat larger than the rate coefficient for the ground vibrational level.

physics.atom-ph↗

arXiv2007

Calculation of three-body resonances using slow-variable discretization coupled with complex absorbing potential

We developed a method to calculate positions and widths of three-body resonances. The method combines the hyperspherical adiabatic approach, slow variable discretization method (Tolstikhin et al., J. Phys. B: At. Mol. Opt. Phys. 29, L389 (1996)), and a complex absorbing potential. The method can be used to obtain resonances having short-range or long-range wave functions. In particular, we applied the method to obtain very shallow three-body Efimov resonances for a model system (Nielsen et al., Phys. Rev. A 66, 012705 (2002)).

physics.atom-ph↗

arXiv2006

Renner-Teller effects in HCO+ dissociative recombination

A theoretical description of the dissociative recombination process for the HCO+ ion suggests that the nonadiabatic Renner-Teller coupling between electronic and vibrational degrees of freedom plays an important role. This finding is consistent with a recent study of this process for another closed-shell molecule, the H3+ ion, where Jahn-Teller coupling was shown to generate a relatively high rate. The cross section obtained here for the dissociative recombination of HCO+exhibits encouraging agreement with a merged-beam experiment.

physics.atom-ph↗

arXiv2004

Photofragmentation of the H_3 molecule, including Jahn-Teller coupling effects

We have developed a theoretical method for interpretation of photoionization experiments with the H_3 molecule. In the present study we give a detailed description of the method, which combines multichannel quantum defect theory, the adiabatic hyperspherical approach, and the techniques of outgoing Siegert pseudostates. The present method accounts for vibrational and rotation excitations of the molecule, deals with all symmetry restrictions imposed by the geometry of the molecule, including vibrational, rotational, electronic and nuclear spin symmetries. The method was recently applied to treat dissociative recombination of the H_3^+ ion. Since H_3^+ dissociative recombination has been a controversial problem, the present study also allows us to test the method on the process of photoionization, which is understood better than dissociative recombination. Good agreement with two photoionization experiments is obtained.

physics.atom-ph↗

arXiv2003

Atom-Molecule Laser Fed by Stimulated Three-Body Recombination

Using three-body recombination as the underlying process, we propose a method of coherently driving an atomic Bose-Einstein condensate (BEC) into a molecular BEC. Superradiant-like stimulation favors atom-to-molecule transitions when two atomic BECs collide at a resonant kinetic energy, the result being two molecular BEC clouds moving with well defined velocities. Potential applications include the construction of a molecule laser.

cond-mat.soft↗

arXiv2003

Multichannel cold collisions between metastable Sr atoms

We present a multichannel scattering calculation of elastic and inelastic cold collisions between two low-field seeking, metastable ^{88}Sr [(5s5p) ^3P_2] atoms in the presence of an external magnetic field. The scattering physics is governed by strong anisotropic long-range interactions, which lead to pronounced coupling among the partial waves of relative motion. As a result, nonadiabatic transitions are shown to trigger a high rate of inelastic losses. At relatively high energies, T > 100 mkK, the total inelastic collision rate is comparable with the elastic rate. However, at lower collisional energy, the elastic rate decreases, and at T ~ 1mkK, it becomes substantially smaller than the inelastic rate. Our study suggests that magnetic trapping and evaporative cooling of ^{88}Sr [(5s5p) ^3P_2] atoms, as well as ^{40}Ca [(4s4p) ^3P_2], in low-field seeking states will prove difficult to achieve experimentally.

physics.atom-ph↗