Experimental and Theoretical Studies of van der Waals Molecule Photodissociation

• Main Author: Hair, Sally Reid
• Format: Others
• Language: en
• Published: 1988
• Online Access: https://thesis.library.caltech.edu/7413/1/Hair_sr_1988.pdf; Hair, Sally Reid (1988) Experimental and Theoretical Studies of van der Waals Molecule Photodissociation. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/anb1-sr68. https://resolver.caltech.edu/CaltechTHESIS:01182013-160624319 <https://resolver.caltech.edu/CaltechTHESIS:01182013-160624319>

<p>Three studies are reported on the vibrational predissociation of polyatomic van der Waals complexes. In the first, the ethylene dimer and rare gas-ethylene complexes are treated theoretically, using a local mode quantum mechanical technique. The ethylene dimer exhibits extensive mixing between the initially excited ν₇ vibration and nearby combinations of the ν₁₀ and van der Waals vibrations, while the rare gas- ethylene complexes do not. Mixing is extensive enough in the ethylene dimer to spread the oscillator strength of the ν₇ vibration over a 10 cm⁻¹ region of the spectrum, in agreement with the experimentally observed band.</p> <p>The second study is a low resolution photodissociation experiment on the ethylene-methane complex. The spectra observed by exciting the ν₇ ethylene vibration of C₂H₄-CH₄, C₂H₄-CH₂D₂, and C₂H₄-CD₄ all exhibit the same width. This indicates that the shapes and widths of the observed spectra are not determined by unresolved or power-broadened rotational structure. This result underscores the importance of vibrational coupling in the dissociation process.</p> <p>The final study is a laser pump-probe experiment on the Ne₂Cl₂ and Ne₃Cl₂ complexes. The Ne₂Cl₂ complex has a distorted tetrahedral geometry, as determined from high resolution, excitation spectra. Excitation shift arguments suggest a structure for Ne₃Cl₂ with the three neon atoms encircling the Cl₂ bond axis. The total van der Waals bond energy of the Ne₂Cl₂ complex is found to be between 145.6 and 148.6 cm⁻¹. When energetically possible, the Ne₂Cl₂ complex can dissociate by losing a single quantum of Cl₂ stretching energy. This indicates that the two neon atoms do not dissociate by two independent "half-collisions." The Cl₂ fragment rotational excitation is found to depend only weakly on the energy available to the fragments.</p>