Excitation and desorption of physisorbed H 2 via theΣu2 electron scattering resonance

• Published in: The Journal of chemical physics 2017-09, Vol.147 (11), p.114703
• Main Authors: Andersson, Stig, Svensson, Krister
• Format: Article
• Language: English
• ISSN: 1089-7690
• DOI: 10.1063/1.5003069

Our high-resolution electron energy-loss measurements concern physisorbed H and comprise differential cross sections for the excitation of the internal H modes and the H -surface bonding mode and their combinations and extend over the electron impact energy range of the classical low-energy H Σu2 resonance. Comparison with corresponding data for the excitation of the internal modes of gas phase H reveals that strong elastic electron reflectivity from the Cu(100) substrate profoundly distorts the inelastic scattering pattern for physisorbed H . We find that this influence can be corrected for and that the resulting peak cross sections agree with the H gas phase data, in accordance with theoretical predictions for the excitation of the internal H vibration. We have used corrected cross sections for the rotational mode spectra of physisorbed H , HD, and D in a model concerning electron induced desorption via rotation-translation energy conversion. These spectra include transitions from the ground state as well as excited levels of the physisorption potential well. H and HD can desorb from all levels while D , for energetic reason, can only desorb from the excited levels. This model gives a satisfactory account of the observed desorption cross sections and predicts characteristic velocity distributions of the desorbing molecules. The cross section data for H and HD reveals that direct bound-free transitions also contribute to the electron induced desorption.