Photodissociation studies of brominated neutral and ion species using ion velocity imaging
Abstract
The photodissociation dynamics of 1,2 dibromoethane and 1-bromopropane at 267 nm and 234 nm have been studied using time of flight mass spectrometry (TOF-MS) and ion velocity imaging techniques. The photochemical products were detected with resonance enhanced multiphoton ionization (REMPI) as well as single photon VUV ionization at 118 nm. REMPI at 267 nm and 234 nm was used to detect the ground Br (P3/2) and spin-orbit excited Br ( 2P1/2) atoms. Time-of-flight (TOF) mass spectroscopy and ion velocity imaging were also employed to study the formation and photodissociation of C2H4Br2+ and C3H 7Br+ ions that were observed in the TOF spectrum when the neutral species were irradiated with 118 nm and 355 nm lasers. The present results indicate that the thermodynamics data for the C2H 4Br fragment may be lower than that reported in literature by 1.8 kcal mol-1. The ionization energy of C2H4Br was calculated as 7.5 eV using a coupled cluster method, which confirms that C2H4Br+ must be formed from dissociative ionization of 1,2-DBE with 118 nm as opposed to neutral dissociation of 1,2-DBE. 1-bromopropane cations are produced via direct photoionization of C 3H7Br by 118 nm light, which is generated by frequency tripling a 355 nm laser. The TOF-MS show many dissociation products, including C 3H7+, C3H5+, C2H3+, and C2H3 +. Although secondary dissociation of C3H7 + produces C3H5+ and C2 H3+, photodissociation of C3H 7Br+ with a 355 nm photon produces C2H 5+. The major dissociation fragment from the 1-bromopropane neutral studies was Br. The beta and translational energy distributions for Br and Br* in the 234 nm and 267 nm dissociation studies suggests that Br + is formed primarily via a parallel transition with 234 nm and 267 nm. The possible dissociation pathways and the angular and translational distributions for the brominated neutral and ion species are discussed in the dissertation.
Degree
Ph.D.
Advisors
Francisco, Purdue University.
Subject Area
Physical chemistry
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