Vibrationally resonant laser induced desorption of n-heptane /
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1993.
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| Subjects: | |
| Online Access: | ProQuest, Abstract Link to OAKTrust copy |
| Abstract: | Vibrationally resonant laser induced desorption of n-heptane from condensed films was studied by exciting the fundamental C-H stretching modes between 2800 and 3000 cm^-1. By measuring time resolved desorption signals, both the total photodesorption yield (PDY) and the velocity distributions of the desorbing molecules were determined. The PDY depended strongly on wavelength. Two local maxima, at 2918 and 2955 cm^-1, were observed and were assigned to the IR absorption maxima of the CH2 and CH3 antisymmetric stretching modes, respectively. No signals were observed in the region of the C-H symmetric stretches. At a given wavelength, the desorption yield increased with increasing laser intensity and the degree of crystallinity of the film. The PDY also increased with film thickness, from just over a single layer to approximately 400. No signals were obtained from monolayer or submonolayer films. The average kinetic energies of the desorbing molecules were determined from the velocity distributions. The energies depended on wavelength, laser intensity, and film thickness, and ranged from approximately 14 to 55 kJ/mol. Conditions which resulted in high desorption yields generally also gave high kinetic energies. The kinetic energies were too high to be consistent with a thermal desorption mechanism resulting from resonant substrate heating. A non-thermal mechanism, in which intermolecular vibrational energy transfer plays a role, is proposed instead. |
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| Item Description: | Vita. "Major subject: Chemistry." |
| Physical Description: | xvi, 175 leaves : illustrations ; 28 cm |
| Bibliography: | Includes bibliographical references. |