Angular and internal state distributions of H2 (+) generated by (2 + 1) resonance enhanced multiphoton ionization of H2 using time-of-flight mass spectrometry (original) (raw)
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Physical Review Applied, 2020
We report on the production of cold, state-selected H + 2 molecular ions in a linear RF trap. The ions are produced by (3+1) resonance-enhanced multi-photon ionisation (REMPI) of H2, and sympathetically cooled by laser-cooled Be + ions. After demonstrating and characterizing the REMPI process, we use photodissociation by a deep UV laser at 213 nm to verify the high vibrational purity of the produced H + 2 ion samples. Moreover, the large difference between the photodissociation efficiencies of ions created in the v = 0 and v = 1 levels provides a way to detect a v = 0 → 1 transition. These results pave the way towards high-resolution vibrational spectroscopy of H + 2 for fundamental metrology applications.
Very low energy photoelectron spectroscopy in multiphoton ionization of H 2
Le Journal de Physique IV, 1994
We apply a novel photoelectron imaging spectrometer [I] to the energy and angular analysis of photoelectrons resulting from resonantly enhanced multiphoton ionization of H2. Photoelectron images with well resolved individual rotational saucture of the resulting H2+ ion are obtained, demonstrating the capability of this technique for analyzing photoelectrons in the meV energy range.
Enhanced ionization of hydrogen molecular ions in an intense laser field via a multiphoton resonance
Physical Review A, 2010
Multiphoton ionization of hydrogen molecular ions in a 480-nm intense laser field is investigated by solving the time-dependent Schrödinger equation numerically in prolate spheroidal coordinates. We discretize space on a generalized pseudospectral grid and propagate the electronic wave function using a second-order split-operator method. By including and excluding the 2pσ u state in the basis expansion, we confirm that the observed 10-eV peak in a recent experiment [Litvinyuk et al., New J. Phys. 10, 083011 (2008)] comes from the enhanced ionization via three-photon resonant excitation of the molecular ions. By folding the calculated ionization rates with the vibrational density distribution, the kinetic energy release spectra are obtained, which are in reasonable agreement with the experimental measurement. Furthermore, using this enhanced ionization, a pump-probe experiment is suggested to trace the vibrational wave packet.
International Journal of Quantum Chemistry, 2010
The delayed autoionization of H2 doubly excited states into channels of different inversion symmetry gerade and ungerade is investigated by using pulses of attosecond duration (isolated or packed in trains), linearly polarized along the molecular axis. It has been shown in previous work, by using XUV laser pulses with durations of 4 fs or longer, that the molecular frame photoelectron angular distributions (MFPAD) associated with the dissociative channel H+ + H(nℓ) are not symmetric with respect to the inversion center of the molecule. In contrast, the MFPADs become symmetric for shorter fs pulses. Here we show that, although this is still the case for pulses of attosecond duration, the combination of two of these pulses with a controlled time delay may still lead to asymmetric MFPADs. From the analysis of the time evolution of the calculated MFPADs, we propose a way to elucidate autoionization lifetimes of molecular resonant states. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2462–2471, 2010
Photo-double ionization of molecular hydrogen
Journal of Physics B: Atomic, Molecular and …, 1999
The angular distribution of the correlated electron pair emitted in single-photon double ionization of the hydrogen molecule is analysed and calculated using a variety of approximations. Attention is directed particularly towards the differences between the molecular angular distribution and that of the corresponding 'united atom', i.e. that arising from the double ionization of helium. Qualitative agreement is obtained with recent experiments on photo-double ionization of the hydrogen molecule. The major effects arising from the two-centre nuclear field of the molecule and the orientation of the axis at the moment of photon absorption are exposed in the simpler problem of photoionization of the H + 2 ion.
Direct multi-photon ionizations of H + 2 in intense laser fields
Journal of Physics B: Atomic, Molecular and Optical Physics, 2012
We have discussed a weak ionization channel characterized by the kinetic energy release spectra of the protons from Coulomb explosion with the sum energy over 10 eV from a hydrogen molecular ion for various vibrational states in infrared pulses. After Franck-Condon averaging of the contributions for various vibrational states, a 'shoulder'-like cutoff structure has been obtained which is consistent with the experiment. For longer pulses, a multi-peak structure is obvious for the v = 0 state and attosecond extreme-ultraviolet pulses were adopted to search the essential physical dynamics. The reproductions of the kinetic energy release spectra from extreme-ultraviolet light indicate that the high kinetic energies of the protons must be due to the direct multi-photon ionizations. The origin of the multi-peak structure has also been investigated by the extreme-ultraviolet pulses. Time-dependent spectra reveal the nuclear wavepacket motion and the time region when charge-resonance-enhanced ionization takes place. Competitions between direct multi-photon ionizations and charge-resonance-enhanced ionizations have also been discussed for various intensities and pulse durations for the v = 0 state.
Two-photon double ionization of H_{2} in intense femtosecond laser pulses
Physical Review A, 2010
Triple-differential cross sections for two-photon double ionization of molecular hydrogen are presented for a central photon energy of 30 eV. The calculations are based on a fully ab initio, nonperturbative, approach to the time-dependent Schrödinger equation in prolate spheroidal coordinates, discretized by a finite-element discrete-variable-representation. The wave function is propagated in time for a few femtoseconds using the short, iterative Lanczos method to study the correlated response of the two photoelectrons to short, intense laser radiation. The current results often lie in between those of Colgan et al [J. Phys. B 41 (2008) 121002] and Morales et al [J. Phys. B 41 (2009) 134013]. However, we argue that these individual predictions should not be compared directly to each other, but preferably to experimental data generated under well-defined conditions. PACS numbers: 33.80.-b, 33.80.Wz, 31.15.A-
Physical Review A, 2011
The dynamics of hydrogen molecular ions in intense laser pulses (100 fs, I = 0.77 × 10 14 W/cm 2 to 2.5 × 10 14 W/cm 2 ) has been studied, and the kinetic-energy-release spectra of Coulomb explosion channel have been calculated by numerically solving the time-dependent Schrödinger equation. In a recent experiment, a multipeak structure from charge-resonance-enhanced ionization is interpreted by a vibrational "comb" at a critical nuclear distance. We found that the peaks could not be attributed to a single vibrational level but a collective contribution of some typical vibrational states in our calculated Coulomb explosion spectra, and the main peak shifts toward the low-energy region with increasing vibrational level, which is also different from the explanation in that experiment. We have also discussed the proton's kinetic-energy-release spectra for different durations with the same laser intensity.
Alignment-dependent ionization of H_{2}^{+}: From multiphoton ionization to tunneling ionization
Physical Review A, 2012
We investigate the strong-field ionization for the ground state of H 2 + by numerically solving the threedimensional (3D) time-dependent Schrödinger equation (TDSE), and comparisons have been made among the TDSE, the different versions of molecular strong-field approximation (MO-SFA) and the molecular Ammosov-Delone-Krainov (MO-ADK) approximation. The study shows that, for the TDSE results, the ratio of ionization rates between perpendicular and parallel alignments displays a step-like structure against the Keldysh parameter γ. For small internuclear distances, the transition between the steps are found to be around γ ≈ 1 and is recognized as the competition between the multiphoton ionization (MPI) and tunneling ionization (TI). The ionization is more isotropic in the MPI regime. For large internuclear distances, the transition position shifts to larger γ due to the charge-resonance-enhanced ionization (CREI). Different versions of strong-field ionization theories are compared against the TDSE results.