Dissociation of ethyl chloride ions, 1-propanol ions, and acetylene cluster ions: Test cases for the statistical theory of unimolecular dissociation

Thesis/Dissertation · Tue Dec 31 23:00:00 EST 1991

OSTI ID:7205388

Booze, J A

The dissociation dynamics of three chemical systems are studied with the photoelectron-photoion coincidence technique. The rates of HCl loss from CH[sub 3]CH[sub 2]Cl[sup +] near threshold were on the order of 10[sup 5]-10[sup 7] s[sup [minus]1] despite a relatively small activation energy of 0.3 eV. The rates spanned this range over the relatively small internal energy range of 130 meV. Also, for a given internal energy, the rate of DCl loss from CD[sub 3]CH[sub 2]Cl[sup +] was several orders of magnitude slower than the CHl loss from CH[sub 3]CH[sub 2]Cl[sup +]. These results are accounted for by a statistical rate calculation which has been modified to include tunneling through an H-atom transfer barrier. The dissociation of 1-propanol via H loss and H[sub 2]O loss is also presented. Like the ethyl chloride, the 1-propanol dissociation is slow despite a small activation energy (0.3 eV). However, there is not a large isotope effect for HDO loss from CD[sub 3]CH[sub 2]CH[sub 2]OH[sup +], demonstrating that H-atom tunneling is not the explanation for the slow rates. Ab initio calculations are presented which indicate that there is a very stable [sigma]-type ion structure of 1-propanol which dictates the dynamics, but is not directly accessible via photoionization due to poor Franck-Condon overlap with the neutral. Using the statistical theory, this structure gives a very good account of the dissociation rates. Finally, the photoionization and dissociation dynamics of acetylene clusters are presented. Upon ionization, the trimer and tetramer are observed to isomerize to C[sub 4]H[sub 4][sup +]-C[sub 2]H[sub 2] and C[sub 6]H[sub 6][sup +]-C[sub 2]H[sub 2] and then to evaporate one monomer unit. The kinetic energy release distributions indicate that the dissociations are statistical. The core ion of the trimer is either vinylacetylene, butatriene, or cyclobutadiene, and the core of the tetramer ion is benzvalene.

• Research Organization: North Carolina Univ., Chapel Hill, NC (United States)
• OSTI ID: 7205388
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ACETYLENE
ALCOHOLS
ALKYNES
CHARGED PARTICLES
DISSOCIATION
HYDROCARBONS
HYDROXY COMPOUNDS
IONS
ISOTOPE EFFECTS
MATHEMATICAL MODELS
MOLECULAR IONS
ORGANIC COMPOUNDS
PROPANOLS
STATISTICAL MODELS