# Which way did it go? Revisiting the time-resolved study of bromine atom and iodine molecule

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 Title: Which way did it go? Revisiting the time-resolved study of bromine atom and iodine molecule Author(s): Tuchler, Matthew Frederick Doctoral Committee Chair(s): McDonald, J. Douglas Department / Program: Chemistry Discipline: Chemistry Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Chemistry, Physical Abstract: The low collision energy interaction of Br($\rm\sp 2P\sb {3/2}$) (Br) or Br($\rm\sp 2P\sb {1/2}$)(Br$\sp {*}$) and I$\sb 2$ is studied in real time. The method of detection, Resonance Enhanced Multiphoton Ionization (REMPI)-Time of Flight Mass Spectroscopy (TOFMS), allows unambiguous identification of products. The interaction is initiated in a restricted region of phase space defined by the geometry of the precursor dimer, H(D)Br$\rm\sp {*}I\sb 2$. The photodissociation of H(D)Br provides both Br and Br$\sp {*}$. The combination of low collision energy and narrow distribution of initial conditions results in a metastable intermediate complex, $\rm I\sb 2Br\sp {*}$. We simultaneously detect two transients, one of which is consistent with the above mentioned complex undergoing an internal conversion to either the ground or 1$\rm\sp {st}$ excited state. The second transient may contain a contribution from the ground state reaction, Br+I$\sb 2$, but interference from other channels makes this transient difficult to assign. Both transients' risetimes vary as a function of precursor constitution, i.e. H(D)Br$\rm\sp {*}I\sb 2$, a feature that is readily explained by a simple 1$\rm\sp {st}$ order kinetic model.An estimate of the precursor structure is provided and used as a starting point for a series of trajectory calculations run on standard LEPS surfaces. The trajectory calculations were used to study the process initiated on the spin-orbit excited (SO) surface, Br$\sp {*}$+I$\sb 2$. At various times during the evolution on the SO surface, the trajectory is allowed to internally convert to a lower electronic surface. The trajectory is followed to completion, at which point a thorough analysis of the products is conducted. The results of these trajectory studies are presented and discussed in detail, including a prediction that the method of detection may result in a signal arising from more than one dynamic feature of the complex evolution. Issue Date: 1995 Type: Text Language: English URI: http://hdl.handle.net/2142/22275 Rights Information: Copyright 1995 Tuchler, Matthew Frederick Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9624521 OCLC Identifier: (UMI)AAI9624521