Laser control over the ultrafast Coulomb explosion of N22+ after Auger decay: A quantum-dynamics investigation (original) (raw)
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Rate equations for nitrogen molecules in ultrashort and intense x-ray pulses
Journal of Physics B: Atomic, Molecular and Optical Physics, 2016
We study theoretically the quantum dynamics of nitrogen molecules (N 2) exposed to intense and ultrafast x-rays at a wavelength of 1.1 nm (1100 eV photon energy) from the Linac Coherent Light Source (LCLS) free electron laser. Molecular rate equations are derived to describe the intertwined photoionization, decay, and dissociation processes occurring for N 2. This model complements our earlier phenomenological approaches, the single-atom, symmetric-sharing, and fragmentationmatrix models of J. Chem. Phys. 136, 214310 (2012). Our rate-equations are used to obtain the effective pulse energy at the sample and the time scale for the dissociation of the metastable dication N 2+ 2. This leads to a very good agreement between the theoretically and experimentally determined ion yields and, consequently, the average charge states. The effective pulse energy is found to decrease with shortening pulse duration. This variation together with a change in the molecular fragmentation pattern and frustrated absorption-an effect that reduces absorption of x-rays due to (double) core hole formation-are the causes for the drop of the average charge state with shortening LCLS pulse duration discovered previously.
Ultraintense X-Ray Induced Ionization, Dissociation, and Frustrated Absorption in Molecular Nitrogen
Physical Review Letters, 2010
Sequential multiple photoionization of the prototypical molecule N 2 is studied with femtosecond time resolution using the Linac Coherent Light Source (LCLS). A detailed picture of intense x-ray induced ionization and dissociation dynamics is revealed, including a molecular mechanism of frustrated absorption that suppresses the formation of high charge states at short pulse durations. The inverse scaling of the average target charge state with x-ray peak brightness has possible implications for singlepulse imaging applications.
The Journal of …, 2010
The NO 2 ion pair photodissociation dynamics leading to NO + (X 1 Σ + ,V) + O-(2 P 3/2 or 2 P 1/2), induced by a 1 kHz femtosecond laser with wavelengths near 400 nm, has been characterized using the coincidence vector correlation method. The ion pair production after four-photon absorption reaches more than 15% of the primary ionization. The kinetic energy release of the fragments demonstrates a significant vibrational excitation of the NO + (X 1 Σ + ,V) molecular fragment. Recoil ion fragment emission is strongly aligned along the polarization axis of linearly polarized light or preferentially emitted in the plane perpendicular to the propagation axis of circularly polarized light. The formalism describing the recoil anisotropy for bound-to-bound n-photon transition inducing prompt axial recoil dissociation of a nonlinear molecule has been developed to interpret the measured anisotropies in terms of excitation pathways via near-resonant intermediate states of specific symmetries. Possible reaction pathways are discussed that are consistent with the data and supported by calculations of potential energy surfaces and transition moments.
Ultrafast X-ray Auger probing of photoexcited molecular dynamics
Molecules can efficiently and selectively convert light energy into other degrees of freedom. Disentangling the underlying ultrafast motion of electrons and nuclei of the photoexcited molecule presents a challenge to current spectroscopic approaches. Here we explore the photoexcited dynamics of molecules by an interaction with an ultrafast X-ray pulse creating a highly localized core hole that decays via Auger emission. We discover that the Auger spectrum as a function of photoexcitation-X-ray-probe delay contains valuable information about the nuclear and electronic degrees of freedom from an element-specific point of view. For the nucleobase thymine, the oxygen Auger spectrum shifts towards high kinetic energies, resulting from a particular C-O bond stretch in the pp* photoexcited state. A subsequent shift of the Auger spectrum towards lower kinetic energies displays the electronic relaxation of the initial photoexcited state within 200 fs. Ab-initio simulations reinforce our interpretation and indicate an electronic decay to the np* state.
The Journal of Physical Chemistry A, 2010
The NO 2 ion pair photodissociation dynamics leading to NO + (X 1 Σ + ,V) + O-(2 P 3/2 or 2 P 1/2), induced by a 1 kHz femtosecond laser with wavelengths near 400 nm, has been characterized using the coincidence vector correlation method. The ion pair production after four-photon absorption reaches more than 15% of the primary ionization. The kinetic energy release of the fragments demonstrates a significant vibrational excitation of the NO + (X 1 Σ + ,V) molecular fragment. Recoil ion fragment emission is strongly aligned along the polarization axis of linearly polarized light or preferentially emitted in the plane perpendicular to the propagation axis of circularly polarized light. The formalism describing the recoil anisotropy for bound-to-bound n-photon transition inducing prompt axial recoil dissociation of a nonlinear molecule has been developed to interpret the measured anisotropies in terms of excitation pathways via near-resonant intermediate states of specific symmetries. Possible reaction pathways are discussed that are consistent with the data and supported by calculations of potential energy surfaces and transition moments.
Physical chemistry chemical physics : PCCP, 2017
We investigate the multiphoton ionization of NO2 using tunable (430-375 nm) femtosecond pulses and photoelectron-photoion coincidence momentum spectroscopy. In order to understand the complex electronic and nuclear photodynamics at play following absorption of three to five photons, we also report extended photoionization calculations using correlated targets and coupled channels. Exploring the multiphoton dissociative ionization (MPDI) and multiphoton ionization (MPI) processes over such a broad energy range enables us to lend further support to our work carried out around 400 nm of a femtosecond laser [S. Marggi Poullain et al., J. Phys. B: At., Mol. Opt. Phys., 2014, 47, 124024]. Two excitation energy regions are identified and discussed in terms of the proposed reaction pathways, highlighting the significant role of Rydberg states, such as the [R*(6a1)(-1), 3pσ] Rydberg state, in the NO2 multiphoton excitation and photoionization. These new results support our previous assumptio...
Physical Review Letters, 2009
We present a combined theoretical and experimental study of ultrafast wave-packet dynamics in the dissociative ionization of H 2 molecules as a result of irradiation with an extreme-ultraviolet (XUV) pulse followed by an infrared (IR) pulse. In experiments where the duration of both the XUV and IR pulses are shorter than the vibrational period of H 2 þ , dephasing and rephasing of the vibrational wave packet that is formed in H 2 þ upon ionization of the neutral molecule by the XUV pulse is observed. In experiments where the duration of the IR pulse exceeds the vibrational period of H 2 þ (15 fs), a pronounced dependence of the H þ kinetic energy distribution on XUV-IR delay is observed that can be explained in terms of the adiabatic propagation of the H 2 þ wave packet on field-dressed potential energy curves.
Direct time resolved observation of molecular dynamics induced by soft-x-ray photoionization
Journal of Physics: Conference Series, 2007
We report the first direct observation of ultrafast dynamics in molecules induced by ionizing radiation. We use high harmonic upconversion process to generate soft-x-ray pulses of few femtoseconds duration, which photoionize N 2 molecule. This leads to the formation of highly excited N 2 + ions via inner-shell ionization and electron shakeup processes. We time resolve the unexplored fragmentation dynamics of the electron shakeup states with femtosecond resolution using a strong-field IR probe. The IR pulse promotes the dissociating N 2 + wavepacket to repulsive N 2 2+ potential. We obtain kinetic energy release of N + /N + channel as function of time delay and observe a rapid transition from spherically-symmetric molecular potential to a two-center potential within ~150 fs.
Resonant Auger decay of the core-excited C^{*}O molecule in intense x-ray laser fields
Physical Review A, 2011
The dynamics of the resonant Auger (RA) process of the core-excited C * O(1s −1 π * , v r = 0) molecule in an intense X-ray laser field is studied theoretically. The theoretical approach includes the analogue of the conical intersections of the complex potential energy surfaces of the ground and 'dressed' resonant states due to intense X-ray pulses, taking into account the decay of the resonance and the direct photoionization of the ground state, both populating the same final ionic states coherently, as well as the direct photoionization of the resonance state itself. The light-induced non-adiabatic effect of the analogue of the conical intersections of the resulting complex potential energy surfaces gives rise to strong coupling between the electronic, vibrational and rotational degrees of freedom of the diatomic CO molecule. The interplay of the direct photoionization of the ground state and of the decay of the resonance increases dramatically with the field intensity. The coherent population of a final ionic state via both the direct photoionization and the resonant Auger decay channels induces strong interference effects with distinct patterns in the RA electron spectra. The individual impact of these physical processes on the total electron yield and on the CO + (A 2 Π) electron spectrum are demonstrated.