193 research outputs found
Vibrational states of the triplet electronic state of H3+. The role of non-adiabatic coupling and geometrical phase
Vibrational energies and wave functions of the triplet state of the H3+ ion
have been determined. In the calculations, the ground and first excited triplet
electronic states are included as well as the non-Born-Oppenheimer coupling
between them. A diabatization procedure transforming the two adiabatic ab
initio potential energy surfaces of the triplet-H3+ state into a 2x2 matrix is
employed. The diabatization takes into account the non-Born-Oppenheimer
coupling and the effect of the geometrical phase due to the conical
intersection between the two adiabatic potential surfaces. The results are
compared to the calculation involving only the lowest adiabatic potential
energy surface of the triplet-H3+ ion and neglecting the geometrical phase. The
energy difference between results with and without the non-adiabatic coupling
and the geometrical phase is about a wave number for the lowest vibrational
levels
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.Comment: 10 figure
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)).Comment: 23 pages, 10 figure
Geometrical phase driven predissociation: Lifetimes of 2^2 A' levels of H_3
We discuss the role of the geometrical phase in predissociation dynamics of
vibrational states near a conical intersection of two electronic potential
surfaces of a D_{3h} molecule. For quantitative description of the
predissociation driven by the coupling near a conical intersection, we
developed a method for calculating lifetimes and positions of vibrational
predissociated states (Feshbach resonances) for X_3 molecule. The method takes
into account the two coupled three-body potential energy surfaces, which are
degenerate at the intersection. As an example, we apply the method to obtain
lifetimes and positions of resonances of predissociated vibrational levels of
the 2^2 A' electronic state of the H_3 molecule. The three-body recombination
rate coefficient for the H+H+H -> H_2+H process is estimated.Comment: 4 pages, 4 figure
Formation of H by radiative association of H and H in the interstellar medium
We develop the theory of radiative association of an atom and a diatomic
molecule within a close-coupling framework. We apply it to the formation of
H after the low energy collision (below 0.5 eV) of H with H.
Using recently obtained potential energy and permanent dipole moment surfaces
of H, we calculate the lowest rovibrational levels of the H
electronic ground state, and the cross section for the formation of H by
radiative association between H and ortho- and para-H. We discuss the
possibility for the H ion to be formed and observed in the cold and dense
interstellar medium in an environment with a high ionization rate. Such an
observation would be a probe for the presence of H in the interstellar
medium
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.Comment: 11 page
Theory of dissociative recombination of highly-symmetric polyatomic ions
A general first-principles theory of dissociative recombination is developed
for highly-symmetric molecular ions and applied to HO and CH,
which play an important role in astrophysical, combustion, and laboratory
plasma environments. The theoretical cross-sections obtained for the
dissociative recombination of the two ions are in good agreement with existing
experimental data from storage ring experiments
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