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https://hdl.handle.net/2142/77313
Description
Title
Photodissociation Dynamics of Small Molecules
Author(s)
Eres, Djula
Issue Date
1985
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Language
eng
Abstract
Energy disposal into CN (product) degrees-of-freedom following photolysis of BrCN and NC=CN (cyanogen) upon absorption of a single 193 nm photon was investigated. Supersonic expansion in a molecular beam was utilized to obtain a narrow distribution of initial parent states. Laser induced fluorescence under collisionless conditions was used in determining the product internal state distributions. It was found that for both BrCN and cyanogen the disposal of energy into the product degrees-of-freedom is strongly influenced by the initial parent rovibrational excitation. Relative rotational state population of 0.15 for the v = 1 state of CN and no significant population of the v = 2 state in photolysis of cyanogen was observed. The population of rotational states of CN in the v = 0 and v = 1 vibrational states follows the prediction of a phase space theory model, while the vibrational state populations are nonstatistical and believed to be governed by the Franck-Condon factors. Angular and velocity distributions of state resolved (single rotational state) fragments were obtained with a uniquely designed detector array in conjunction with laser induced fluorescence. The obtained angular distributions are isotropic for rotational states in both v = 0 and v = 1 vibrational states of the CN fragments indicating long lifetime of the parent cyanogen state compared to the molecular rotation period. With the increase of internal energy (higher rotational state) of the fragment which is being detected the corresponding velocity distributions become narrower and the maximum in the distributions shifts towards lower velocities. The experimentally obtained velocity distributions were fitted to a phase space theory model assuming that the excess energy and the total angular momentum are conserved. It was necessary to allow for symmetric as well as non-symmetric disposal of the angular momentum into the two CN fragments in order for the experimental velocity distributions to fit the model.
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