SPECTROSCOPY AND DISSOCIATION DYNAMICS OF THE 1-METHYLALLYL RADICAL

Abstract

\begin{wrapfigure}[7]{r}{3.5cm} \vspace{-.5cm} \hspace*{-0cm} \epsfig{file=mea.eps} \end{wrapfigure} The $\widetilde{A}\leftarrow\widetilde{X}$ band system of jet-cooled 1-methylallyl radical (C$_4$H$_7$) was observed for the first time using resonance-enhanced multiphoton ionization combined with electronic ground state depletion spectroscopy. Analysis of the vibronic structure reveals transitions to the non-planar $\widetilde{A}$ valence excited state with an electronic origin for the $Z$-isomer of 1-methylallyl at 23~979~cm$^{-1}$. Time- and frequency-resolved photoionization of the hydrogen atom product from electronically excited 1-methylallyl radical and its isotopologue CH$_3$C$_3$D$_4$ provides information on the dissociation dynamics. The measured dissociation rates and kinetic energy release combined with results from high level \emph{ab initio} calculations suggests unimolecular decompostion to 1,3-butadiene and hydrogen with no evidence for nonstatistical behavior in dissociation.