Knowledge Bank

Matrix isolation spectroscopy is a technique which enables highly reactive species to be trapped in a host environment and studied spectroscopically. Solid parahydrogen ($p$H$2$) has been employed as a matrix host because of its interesting quantum mechanical properties and also because of its general inertness towards trapped dopants. However, in some cases $p$H$2$ can react with impurities yielding new product molecules and providing insight into non-classical reaction pathways. In this talk I will present the results from a series of experiments where molecular chlorine (Cl$2$) doped $p$H$2$ crystals were exposed to two different irradiation schemes (namely $UV$ only or $IR+UV$ conditions) that gave rise to very different products. Cl$2$ doped $p$H$2$ crystals irradiated with $355nm$ $UV$ light produced almost exclusively ($99\%$) isolated Cl-atom photofragments, indicating the reaction Cl+H$2(\nu =0,J=0)\to$ HCl+H is not readily occurring. Cl$2$ doped $p$H$2$ exposed simultaneously to $355nm$ $UV$ irradiation and broadband $cwIR$ light yielded HCl photoproducts indicating that the following reaction is playing a significant ($15\%$) role in the \emph{in situ} photochemistry: Cl+H$2(\nu =1,J=0)\to$ HCl+H. The kinetic analysis of these experiments with two very different reaction pathways for $UV$ only or $IR+UV$ conditions will be presented. Further, the results of current investigations involving spin-orbit excited Cl-atoms generated using $416nmUV$ photons will be discussed in order to explore the intriguing possibility of non-Born Oppenheimer reaction dynamics in the simple Cl+H$2$ reaction.