Dynamics of Molecular Photodissociation Studied Using Coherent Vacuum Ultraviolet
Todt, Michael Aaron
A method is described for generating intense pulsed vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) laser radiation by resonance enhanced four wave mixing of commercial pulsed nanosecond lasers in laser vaporized mercury under windowless conditions. By employing noncollinear mixing of the input beams, the need of dispersive elements such as gratings for separating the VUV/XUV from the residual UV and visible beams is eliminated. A number of schemes are described, facilitating access to the 9.9 - 14.6 eV range. A simple and convenient scheme for generating wavelengths of 125 nm, 112 nm, and 104 nm (10 eV, 11 eV, and 12 eV) using two dye lasers without need for dye changes is described. The photodissociation dynamics of OIO radicals were studied at four visible wavelengths using photofragment translational energy spectroscopy with VUV photoionization detection of the I(2P3/2) products. A molecular beam containing OIO was produced through the reaction IO + IO -> OIO + I. Translational energy distributions of the ground state I(2P3/2) products indicate that O2 is produced in both the ground 3Sigma-g and electronically excited 1Δg states. The energy change for OIO → I(2P3/2) + O2 (3Σ-g) was measured to be -4.3 ± 2 kcal/mol, 1 kcal/mol more exoergic than the theoretically predicted value, but within the uncertainty of the current experiments. The photodissociation dynamics of 1- and 2- iodopropane was studied at 266 nm using photofragment translational energy spectroscopy. Whereas 1-iodopropane dissociates exclusively to produce propyl radicals plus I(2P3/2) and I(2P1/2), HI elimination forming propene was observed from 2-iodopropane, accounting for 9% of the products. The HI is produced vibrationally excited in v > 3, with translational energy and angular distributions similar to the dominant I(2P3/2) channel. Product velocity and angular distributions were measured for all dissociation pathways using state selective photoionization as well as using electron impact ionization. Our results are compared to those from previous studies.
Physical chemistry; Photodissociation; vacuum ultraviolet
Davis, Harry Floyd
Ezra, Gregory Sion; Petersen, Poul B.
Chemistry and Chemical Biology
Ph. D., Chemistry and Chemical Biology
Doctor of Philosophy
dissertation or thesis