Dynamical studies of UV-laser-induced NO-desorption from the polar NiO(111) versus the nonpolar NiO(100) surfaces

Abstract

We have studied the UV-laser-induced desorption of NO adsorbed on an epitaxial film of NiO(111) grown on Ni(111). The desorbing molecules were detected state selectively via a resonance enhanced ionization technique [REMPI(1+1)] using the A 2Σ(v′=0,1,2)←X 2Π(v″=0,1,2) transition as intermediate state. Our results are compared with our experiments on NO desorption from NiO(100). The similarities and differences of the results due to the different surface structure of the polar NiO(111) and the non polar NiO(100) are discussed. For both surfaces we observe bimodal velocity flux distributions independent of the rovibrational state. Due to a rotational temperature of about 400 K and a vibrational temperature of 1800 K thermal processes can be ruled out. The wavelength dependence of the desorption cross section strongly correlates with the electronic structure of the NiO indicating a surface mediated excitation process. The spin orientation in the NO molecules influences the life time of the excited state depending on the magnetic property of the NiO surface.

Surrogate Hamiltonian study of electronic relaxation in the femtosecond laser induced desorption of NO/NiO(100)

“…This is compatible with estimates from experiment. 9,11,62 Furthermore, the velocities are found to be in the experimentally observed range between 0 and 2000 m/s. 39 The population of the excited state was decreased from its maximum value of about 0.11 to about 0.005 ͑at best 0.0034 shown in Fig.…”

“…11,39,40 The desorption probability is obtained by weighting the population in the asymptotic region by the excitation probability. In a one-dimensional model, only average velocity distributions can be observed.…”

“…This can be seen in the linear dependence of the desorption cross section on the laser energy once the laser energy is larger than the band gap. 11 The excitation mechanism can, however, be thought of as direct within the substrate-adsorbate complex as will be discussed in Sec. II C. Then the full time-dependence of the pulse enters the theoretical model.…”

“…In particular, a microscopic description of the dissipation has not been attempted so far. We therefore combine the information from previous studies 4,11,39,40,42,43 with the surrogate Hamiltonian method 2,3 to develop a model which treats the nuclear dynamics as well as the excitation and relaxation mechanism on the same level of rigor.…”

Quantum Dynamical Approach to Ultrafast Molecular Desorption from Surfaces

“…The photodesorption of CO from Cr 2 O 3 (0001) in the DIET limit after direct excitation was experimentally studied in ref 437. In their theoretical work, Klüner et al assumed a Franck-Condon excitation of the ground-state wave function to a "representative" excited state in the right energy window.…”