Vibrational level population of H2_2 and H2+_2^+ 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 $z$. 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 $\sim 10^3$ 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 $\delta$ 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 $\delta$ 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