I. IR Photodissociation Spectroscopy of Large van der Waals Clusters. II. UV Laser-Induced Photochemistry of Fe(CO)₅ on Single Crystal Surfaces

Citation

Celii, Francis Gabriel (1986) I. IR Photodissociation Spectroscopy of Large van der Waals Clusters. II. UV Laser-Induced Photochemistry of Fe(CO)₅ on Single Crystal Surfaces. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/nz14-wz74. https://resolver.caltech.edu/CaltechTHESIS:11042019-153133005

Abstract

Chapter 2 is a summary of vibrational predissociation spectra of weakly bound clusters containing either CF₃I or CF₃Br. Spectra indicative of ArCF₃I, KrCF₃I, (CF₃I)₂, ArCF₃Br and (CF₃Br)₂ clusters are presented with comparison to the matrix-isolation spectra of CF₃I and CF₃Br.

The infrared photodissociation technique can be applied to the study of weakly bonded clusters which do not absorb in the infrared by attaching an IR chromophore; this work is presented in Chapter 3. Vibrational predissociation spectra of large clusters of Ar, Kr, N₂ and CH₄ containing a single CH₃F or C₂H₄ chromophore are obtained as a function of cluster size. The IR spectra distinguish three regimes of cluster size in the CH₃F case. The dissociation profiles yield information on the chromophore environment and the lifetime of the excited vibration. The clusters are gas-phase analogies to the matrix-isolation technique, although differences between the two are consistent with the presumed icosahedral cluster geometry, and "matrix" and "surface" sites are distinguishable.

Chapter 4 presents the application of a simple two-level-with-decay model to the photodesorption of weakly bound adsorbates on crystal surfaces. Feasibility estimates are reported and establish that vibrational predissociation of the excited adsorbes can be induced in the infrared, where energy quenching mechanisms on surfaces can be quite fast. The effect of these quenching mechanisms on the lineshapes present the opportunity to probe the processes with the use of the photodesorption technique. Extraction of the phenomenological rate constants is described. Also reported are attempts to observe photodesorption induced by low-power lasers.

The photodecomposition of Fe(CO)₅ on three single crystal surfaces, sapphire (Al₂O₃), Si(100) and Ag(110), using UV irradiation is described in Chapter 5. The quenching of excited electronic states of adsorbates is expected to be quite different on the surfaces, yet dissociation of the Fe(CO)₅ is observed in all cases. The results allow determination of the dissociation mechanism and also imply that the Fe(CO)₅ dissociation rate is ultra-fast (< 10^-13). Extensions of this initial investigation are discussed.

Thesis Files