Spectroscopy and dynamics of hydroxyl radical complexes with argon and hydrogen

The intermolecular interaction potentials between OH radicals in the $A\ \sp2\Sigma\sp{+}$ and $X\sp2\Pi$ electronic states and Ar, H$\sb2,$ and D$\sb2$ have been characterized using laser-induced fluorescence (LIF), stimulated emission pumping experiments (SEP), and fluorescence depletion experiments. Stimulated emission spectroscopy was used to access nearly all of the intermolecular bending and stretching vibrations supported by the OH ($X\sp2\Pi$) + Ar ($\rm\sp1S\sb{0})$ potential energy surfaces. Intermolecular vibrational levels of the spin-orbit excited state and metastable levels lying above the dissociation limit were also detected. OH-Ar LIF experiments were performed in the OH A-X 0-0 spectral region. The experimental data was used to refine a semiempirical potential for OH $A\ \sp2\Sigma\sp{+}$ (v = 0) + Ar. The potential parameters were adjusted to increase the steepness of the radial part of the potential and increase the potential anisotropy. The calculated vibrational energies of the intermolecular levels supported by the adjusted potential agreed to within 1% of the experimental values. Binary complexes of OH $X\sp2\Pi$ and H$\sb2$/D$\sb2$ have been stabilized in a shallow well below the activation barrier to the hydrogen abstraction reaction and identified by LIF in the OH A-X 1-0 spectral region. LIF and fluorescence depletion experiments have accessed the strongly quenched intermolecular vibrational levels correlating with OH $A\ \sp2\Sigma\sp{+}$ (v$\sp\prime=0)$ + H$\sb2$/D$\sb2.$ The characteristics of the OH $(X\sp2\Pi$, $A\ \sp2\Sigma\sp{+})$ + H$\sb2$/D$\sb2$ potentials are in accord with ab initio predictions. OH-H$\sb2$/D$\sb2$ binding energies in the ground state correlating OH $(X\sp2\Pi$, $A\ \sp2\Sigma\sp{+})$ + H$\sb2$/D$\sb2$ were determined to be 54 cm$\sp{-1}$ and ${\u3e}$68 cm$\sp{-1},$ respectively. The OH $A\ \sp2\Sigma\sp{+}$ (v$\sp\prime=0)$ + H$\sb2$/D$\sb2$ excited state is found to be at least an order of magnitude more strongly bound, with lower limits placed at 631 and 706 cm$\sp{-1},$ respectively. The dynamics within the OH $A\ \sp2\Sigma\sp{+}$ (v$\sp\prime=0)$ and (v$\sp\prime=1)$ + H$\sb2$/D$\sb2$ potentials appear to be considerably different: the OH-H$\sb2$ (OH-D$\sb2)$ intermolecular levels correlating with OH $A\ \sp2\Sigma\sp{+}$ (v$\sp\prime=0)$ + H$\sb2$/D$\sb2$ have lifetimes of 3.2-4.5 ps (4.5 ps), while vibrational levels probed in the OH A-X 1-0 region live for 60-300 fs (110-240 fs). A cavity ring-down absorption apparatus has been constructed to probe the reaction dynamics of complexes via absorption