Publication: Excitación vibracional de moléculas adsorbidas por fotoelectrones de muy baja energía
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2016-07-06
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Universidad Complutense de Madrid
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Abstract
En esta Tesis Doctoral se demuestra, en primer lugar, la existencia de efectos catalíticos inducidos por láser en procesos de captura electrónica disociativa para las moléculas SF6, acrilonitrilo o 2-propenenitrilo (ACN) y CH3I adsorbidas en Ba y ACN adsorbida en Cu policristalino, detectándose como productos SF−5 y SF−6 para SF6/Ba, CN− para ACN/Ba y ACN/Cu y I− para CH3I/Ba. Para el sistema ACN/Cu, la medida del cociente CN−/e− en función de la longitud de onda del láser, demostró la selectividad vibracional del proceso al replicar el espectro de IR del ACN en fase gaseosa desplazado 20,17 cm−1 hacia el rojo. Estos experimentos se realizaron en un sistema experimental expresamente orientado a la espectroscopía en el infrarrojo. En un segundo sistema experimental especialmente diseñado para la detección y el análisis de electrones de baja energía generados en metal mediante luz láser visible, se estudiaron por primera vez las transiciones intrabanda entre estados sp de cobre generadas mediante 2PPE en Cu(100). Como resultado se consiguió identificar y medir la posición en energía del estado de volumen X′4 con alta precisión EX′4 =2,08±0,04 eV. En este sentido se desarrolló un modelo teórico para estudiar las transiciones intrabanda cerca del estado de alta simetría X. Los ajustes del modelo ofrecieron un valor de energía por fonón de ≈5 meV...
As a first task, the Thesis demonstrates the existence of clear catalytic effects in dissociative electron attachment processes induced by IR laser for SF6, acrylonitrile or 2-propenenitrile (named as ACN) and CH3I adsorbed on Ba and ACN adsorbed on policrystalline Cu. As a result SF−5 y SF−6 were detected as products for the SF6/Ba system, CN− for ACN/Ba and ACN/Cu, and I− for the CH3I/Ba system. In the ACN/Cu case the ratio CN−/e− as a function of laser wavelength resemble the ACN IR gas spectrum red-shifted 20,17 cm−1. Thus, these results demonstrate the vibrational selectivity of the dissociative electron attachment for the quimisorbed acrylonitrile. A second experimental setup was especially designed to detect and analyzed very low energy photoelectrons from metals induced by visible laser light. For the first time, intraband transitions generated by 2-Photon Photoemission Spectroscopy between sp states of Cu(100) were detected and studied. As main result, the identification and energy value of the volume state X′4 was measured with high precision EX′4 =2,08±0,04 eV. A theoretical model was developed to study intraband transitions near high simmetry state X, with fitting values for phonon energy ≈5 meV...
As a first task, the Thesis demonstrates the existence of clear catalytic effects in dissociative electron attachment processes induced by IR laser for SF6, acrylonitrile or 2-propenenitrile (named as ACN) and CH3I adsorbed on Ba and ACN adsorbed on policrystalline Cu. As a result SF−5 y SF−6 were detected as products for the SF6/Ba system, CN− for ACN/Ba and ACN/Cu, and I− for the CH3I/Ba system. In the ACN/Cu case the ratio CN−/e− as a function of laser wavelength resemble the ACN IR gas spectrum red-shifted 20,17 cm−1. Thus, these results demonstrate the vibrational selectivity of the dissociative electron attachment for the quimisorbed acrylonitrile. A second experimental setup was especially designed to detect and analyzed very low energy photoelectrons from metals induced by visible laser light. For the first time, intraband transitions generated by 2-Photon Photoemission Spectroscopy between sp states of Cu(100) were detected and studied. As main result, the identification and energy value of the volume state X′4 was measured with high precision EX′4 =2,08±0,04 eV. A theoretical model was developed to study intraband transitions near high simmetry state X, with fitting values for phonon energy ≈5 meV...
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Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de Materiales, leída el 08/02/2016