20 research outputs found
Vibrational level population of H and H in the early Universe
We formulate a vibrationally resolved kinetics for molecular hydrogen and its
cation in the primordial Universe chemistry. Formation, destruction and
relaxation processes for each vibrational level are studied and included as
chemical pathways of the present model. The fractional abundance of each
vibrational level as a function of the redshift is given: a strong deviation
from the Boltzmann distribution is found at low . A discussion of the
results is provided, also evaluating the effects of relaxation processes on the
level populations. Analytical fits for some LTE rate coefficients are given in
the Appendix.Comment: 12 pages, 14 figures, 3 tables; published on ApJS 2011, 193,
Electron detachment from negative ions in bichromatic laser field
Negative ion detachment in two-colour laser field is considered within the
recent modification of Keldysh model which makes it quantitatively reliable.
The general approach is illustrated by calculation of angular differential
detachment rates, partial rates for particular ATD (Above Threshold Detachment)
channels and total detachment rates for H ion in bichromatic field with 1:2
frequency ratio. Both perturbative and strong field regimes are examined. Polar
asymmetry and phase effects are quantitatively characterized with some new
features revealed. Phase effects are found to result in a huge anisotropy
factor in the electron angular distribution in the perturbative
regime.Comment: 13 pages, 8 figures in separate files which are not incorporated in
the latex file of the pape
Adiabatic Theory of Electron Detachment from Negative Ions in Two-Color Laser Field
Negative ion detachment in bichromatic laser field is considered within the
adiabatic theory. The latter represents a recent modification of the famous
Keldysh model for multiphoton ionization which makes it quantitatively
reliable. We calculate angular differential detachment rates, partial rates for
particular ATD (Above Threshold Detachment) channels and total detachment rates
for the Hydrogen ion in a bichromatic field with 1:3 frequency ratio and
various phase differences. Reliability of the present, extremely simple
approach is testified by comparison with much more elaborate earlier
calculations.Comment: 22 pages, 6 Postscript figure
Azimuthal angular distributions for two-colour three-photon ionization of hydrogen
We study in some detail the photoelectron angular distributions in two-colour
three-photon ionization of the ground state hydrogen atom in its dependence
on the polarizations
of the two electromagnetic fields.
We treat the particular
case of photons propagating in the same direction and having elliptic
polarizations with the same axes.
The azimuthal distributions presented refer to the electrons emitted with
momenta orthogonal to the photons direction.
The calculations are done in nonrelativistic dipole approximation,
in velocity gauge, using third-order perturbation theory.
We show that the photoelectron azimuthal angular distributions have a fourfold
symmetry only for identical linear or circular polarizations.
In all the other cases the distribution has a twofold symmetry
Dissociation and vibrational excitation of cold HD
We have investigated the competition between dissociative excitation, dissociative recombination and vibrational excitation processes taking place in the reactive collisions of vibrationally cold HD+ with electrons. The energy range 1–12 eV has been considered
Ionization of a hydrogen atom from its ground state by a coherent bichromatic laser field
We study the "coherent phase control" between the three-photon ionization
by a fundamental laser field and the one-photon ionization by its third
harmonic for a hydrogen atom in its ground state. The relative phase of the harmonic field with respect to the fundamental laser radiation
"modulates" the interference between the two ionization channels, which is
important near the crossing points between the ionization rates of the two
individual processes. Numerical results for the total ionization rate and
for the angular distribution of the photoelectrons as a function of the
phase are presented for frequencies located in the vicinity of the
atomic resonances corresponding to the absorption of two laser photons
Elliptic dichroism in hydrogen ionization by a coherent superposition of two harmonics
The two-photon ionization of the hydrogen atom from its ground state by a
two-colour electromagnetic field consisting of two odd harmonics of the same
IR laser is analyzed. The influence of the state of polarization of the
bichromatic field on the azimuthal angular distribution and the dependence
of the elliptic dichroism on the photon frequencies are reported