Stochastic approach to laser-induced ultrafast dynamics: the desorption of H2/D2 from Ru(0001)

Abstract

The desorption of molecular hydrogen and deuterium induced by femtosecond-laser pulses is studied theoretically for the so-called DIMET (Desorption Induced by Multiple Electronic Transitions) process. These investigations are based on nonadiabatic classical Monte Carlo trajectory (CMCT) simulations on a ground and an excited state potential energy surface, including up to all six adsorbate degrees of freedom. The focus is on the hot-electron mediated energy transfer from the surface to the molecule and back, and the energy partitioning between the different degrees of freedom of the desorbing molecules. We first validate for a two-mode model comprising the desorption mode and the internal vibrational coordinate, the classical Monte Carlo trajectory method by comparing with Monte Carlo wavepacket (MCWP) calculations arising from a fully quantum mechanical open-system density matrix treatment. We then proceed by extending the CMCT calculations to include all six nuclear degrees of freedom of the desorbing molecule. This allows for a detailed comparison between theory and experiment concerning isotope effects, energy partitioning (translational, vibrational, and rotational energies and their distributions), and the dependence of these properties on the laser fluence. The most important findings are as follows. (i) CMCT agrees qualitative with the MCWP scheme. (ii) The basic experimental features such as the large isotope effect, the non-linear increase of yield with laser fluence, translationally hot products (in the order of several 1000 K) and non-equipartitioning of translational and internal energies (E(trans) > E(vib) > E(rot)) are well reproduced. (iii) Predictions concerning a strong angular dependence of translational energies at large observation angles are also made.

Femtosecond-laser induced dynamics of CO on Ru(0001): Deep insights from a hot-electron friction model including surface motion

“…However, this goal has been achieved, for metal surfaces at least, only for reduced-dimensional models using open-system density matrix theory or stochastic wave-packet methods [15]. An alternative approach makes use of classical trajectories and either nonadiabatic surface hopping [3,16], or ground-state Langevin dynamics in which electronic friction and hotelectron excitation are included via a damping term and stochastic forces, respectively. The (quasi)classical approach allows for the treatment of multidimensional dynamics.…”

Optimal control of a Cope rearrangement by coupling the reaction path to a dissipative bath or a second active mode

“…While in this work, we focused on a density matrix formalism when modeling the environment, a stochastic approach in the Hilbert space, which mimics the surrounding by a fluctuating force is an interesting perspective, in particular, in the context of coherent control. 77,78 Future work will be directed along these lines.…”

Quantum Dynamical Simulations of the Femtosecond‐Laser‐Induced Ultrafast Desorption of H2 and D2 from Ru(0001)

“…The process has been widely investigated by experiment [36][37][38][39] and theory [40][41][42][43][44][45] and represents an example of nonadiabatic dynamics of an open-quantum system (adsorbate) that is coupled to a dissipative bath (surface). Experimentally, the reaction was initialized by 120-130 fs short laser pulses centered at a wavelength of 800 nm.…”

“…All experimental findings could be reasonably explained by a hot-electron-driven reaction mechanism, as shown in theoretical studies in refs. [40][41][42][43][44].…”

“…[46,49]) by using, for example, the classical Monte-Carlo trajectory (CMCT) method. [43] In the second approach, the dynamics of the adsorbate proceed on a single (ground-state) PES. The coupling of the adsorbate to the surface electrons is represented by a friction tensor, which dampens adsorbate vibrations and fluctuation forces that accelerate the motion of the adsorbate.…”