Theoretical methods for attosecond electron and nuclear dynamics: applications to the H₂molecule

Abstract

Attosecond science, born at the beginning of this century with the generation of the first bursts of light with durations shorter than a femtosecond, has opened the way to look at electron dynamics in atoms and molecules at its natural timescale. Thus controlling chemical reactions at the electronic level or obtaining time-resolved images of the electronic motion has become a goal for many physics and chemistry laboratories all over the world. The new experimental capabilities have spurred the development of sophisticated theoretical methods that can accurately predict phenomena occurring in the sub-fs timescale. This review provides an overview of the capabilities of existing theoretical tools to describe electron and nuclear dynamics resulting from the interaction of femto- and attosecond UV/XUV radiation with simple molecular targets. We describe one of these methods in more detail, the time-dependent Feshbach close-coupling (TDFCC) formalism, which has been used successfully over the years to investigate various attosecond phenomena in the hydrogen molecule and can easily be extended to other diatomics. In addition to describing the details of the method and discussing its advantages and limitations, we also provide examples of the new physics that one can learn by applying it to different problems: from the study of the autoionization decay that follows attosecond UV excitation to the imaging of the coupled electron and nuclear dynamics in H2 using different UV-pump/IR-probe and UV-pump/UV-probe schemes.

Imaging the square of the correlated two-electron wave function of a hydrogen molecule

“…The ab initio method used to obtain the dissociative ionization spectra and the corresponding angular distributions has been described elsewhere [22,23]. It has been successfully applied to evaluate photoionization cross sections and MFPADs of the H 2 molecule in both timedependent and time-independent scenarios [22][23][24][25]. Due to the high photoelectron energies produced in the experiment, we have made use of the Born-Oppenheimer approximation, which allows us to describe the initial and final continuum wave functions as products of an electronic wave function and a nuclear wave function.…”

Control of H2 Dissociative Ionization in the Nonlinear Regime Using Vacuum Ultraviolet Free-Electron Laser Pulses

“…We performed two calculations to get a better understanding of the experimental findings. First, in order to analyze the dependence of the results on the pulse duration, we solved the TDSE to second order of the perturbation theory [34] for pulses up to 40 fs (total duration). The use of this methodology is justified, as for the short wavelengths and peak intensities used in the experiment we are clearly in the perturbative regime.…”

The quantum chemistry of attosecond molecular science

“…Equation is a nonseparable differential equation of second order in the 3 N and 3 M electronic and nuclear coordinates and of first order in time. By solving this equation in a grid, nearly exact solutions have been obtained in the center‐of‐mass frame for the molecular ion ( N = 1, M = 2) and H 2 ( N = 2, M = 2), in the latter case for specific molecular orientations (i.e., by neglecting molecular rotations) . However, such methods are inapplicable to larger molecular systems due to their high computational cost.…”