Double Ionization Of H2 Research Articles

Electro-Nuclear Dynamics of Single and Double Ionization of H2 in Ultrafast Intense Laser Pulses.

We present an efficient method for modeling the single and double ionization dynamics of the H2 molecule in ultrashort, intense laser fields. This method is based on a semianalytical approach to calculate the time-dependent single and double molecular ionization rates and on a numerical approach to describe the vibrational motion that takes place in the intermediate molecular ion H2+. This model allows for the prediction of the single and double ionization probabilities of the H2 molecule to be made over a wide range of frequencies and laser intensities with limited computational time while providing a realistic estimate of the energy of the products of the dissociative ionization and of the Coulomb explosion of the H2 molecule. The effect of vibrational dynamics on ionization yields and proton kinetic energy release spectra is demonstrated and, in the case of the latter, is discussed in terms of basic strong-field molecular fragmentation mechanisms.

Studies of H2 photoionization by a strong ultrashort x-ray pulse on base of a trajectory method

Photoionization of the hydrogen molecule was studied using our previously developed semiclassical trajectory method. The focus was on the parameters of the field for which there are no other results, namely a short photo-pulse with photon energies from soft to hard x-rays and with intensities including superatomic values. We calculated photoionization probabilities for the single and double ionization of H2. In the superatomic field we observed the transient from single-photon to multiphoton double photoionization, the inversion of single and double ionization probabilities, and distinct stabilization effect for the single photoionization. We also observed a specific behavior in the single photoionization probability dynamics with a dip in the middle of the pulse, which becomes extremely deep for a field approaching relativistic intensity. The agreement of our previous results with independent data on the helium atom in superatomic field is an important argument in favor of the efficiency of the used method. This allows us to hope that the probabilities of photoionization of a hydrogen molecule in an atomic and superatomic x-ray field obtained in this work are not only the first, but also quite reasonable results on the indicated process.

The double ionization of H2 by fast electron impact: Influence of the final state electron-electron correlation

We have determined fully differential cross sections of the (e, 3e) double ionization of H2 by employing correlated initial- and final-state wave functions. We have constructed for the description of the two slow ejected electrons a symmetrized product of a correlation function and two-center continuum wave functions, which fulfill the correct boundary conditions asymptotically up to the order O((kr)−2). We have shown that the introduction of the correlated part of the final-state wave function improves the results on the (e, 3-1e) of H2.

Direct two-photon double ionization of H2

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The correlated two-centre double continuum and the double ionization of H2 and N2 by fast electron impact

A correlated product of two two-centre continuum Coulomb waves is constructed to describe the state of two ejected electrons in the (e, 3e) double ionization of the two most common and naturally existing diatomic molecules, H2 and N2, for which experiments are currently in progress. New computational approaches are introduced to overcome and improve the numerical precision of the calculations involved. We show that the introduction of correlation significantly modifies the outcome of the results.

Few-cycle laser pulses tested with double ionization of H2

Different compression schemes for the production of sub-10 fs laser pulses are tested using double ionization of H2. Compression schemes differ in the laser beam guiding modes which are necessary in order to get a spatially-homogeneous spectral broadening through self-phase modulation in argon. Guiding may take place in a hollow fibre waveguide or may be self-induced in a filament. We tested four set-ups: a single hollow fibre, two hollow fibres, a hollow fibre then a filament, and two filaments. The shortest pulses around 8 fs were recorded with the set-ups involving one or two filaments. Double ionization of H2 and the associated proton spectra give results in good agreement with the spectral and interferometric autocorrelation measurements. The two-filament set-up gives the shortest pulses. In addition, the H2 experiment reveals that the spectral phase induced with two filaments cannot be fully compensated with second-order chirped mirrors as for the other tested set-ups.

Molecular tunnelling ionization and rescattering induced double ionization of H2 and D2 molecules

We review the recently developed molecular tunnelling ionization theory, which is an extension of the well-known tunnelling model for atoms, by taking into account the characteristic of molecular orbitals. Employing the molecular tunnelling theory and the rescattering model, we have studied the double ionization of D2 and H2 molecules by intense lasers. Comparing our calculated kinetic energy release spectra of D+ with the measured data, we can derive the time duration between the first and second ionizations to sub-femtosecond accuracy and the breakup distance of D2 to within a fraction of one Angstrom.

Double ionization of H2 by electron impact: a second Born treatment

A second Born treatment is applied to study the (e, 3e) and (e, 3 − 1e) reactions for H2 targets. The results of this approximation are compared to the (e, 3 − 1e) experimental data obtained at about 600 eV impact energy. Several single-centre wavefunctions are used to describe the initial state and excited states of the molecule. Even if the second Born approximation is able to explain part of the experimental results the agreement is not good, similar to the case of the double ionization of helium (Götz et al 2003 J. Phys. B: At. Mol. Opt. Phys. 36 L77).

Single and double ionization of H2 by electrons and protons.

The single- and double-ionization cross sections of ${\mathrm{H}}_{2}$ produced by fast-electron bombardment have been measured. The electrons had selected energies between 750 and 3500 keV/amu. The results are compared to previously reported data from this laboratory for equivelocity protons on ${\mathrm{H}}_{2}$. The ratio R of double-to-single-ionization cross sections is about a factor of 2 greater for electrons than for protons. The difference occurs because of differences in both the single- and double-ionization cross sections. At 750 keV/amu, the single-ionization cross section produced by electrons is 0.83\ifmmode\pm\else\textpm\fi{}0.04 times that produced by protons. At the same velocity, the double-ionization cross section produced by electrons is 2.25\ifmmode\pm\else\textpm\fi{}0.35 times that produced by protons. The results from the ${\mathrm{H}}_{2}$ target are compared to results from a helium target, and marked similarities are observed.

Franck–Condon Calculations for Double Ionization of Molecular Hydrogen

The Franck–Condon radial overlap integral for transition from the ground vibronic state of H2 to a state in the H2++ continuum is expanded as an asymptotic series in powers of a small parameter. The initial semiconvergence of the series is sufficiently rapid to provide a convenient basis for computing the kinetic energy distribution for protons formed by double ionization of H2. The results of these computations are presented. The analysis includes a derivation of the reflection approximation for the particular case of transition to the repulsive Coulomb potential curve. Preliminary results of a more general study indicate that this approximation can be applied to a much larger class of repulsive potentials. Previous forms of the reflection approximation, which have heretofore lacked theoretical foundation, are classified and discussed in relation to the derived approximation.