The HCO Potential Energy Surface; Probes Using Molecular Scattering and Photodissociation

The results from three recent types of experiment investigating the interaction potential between a hydrogen atom and a carbon monoxide molecule are summarized and compared to theoretical predictions based on an ab initio HCO potential energy surface. In the first experiment, energetic hydrogen atoms generated in the photolysis of H2S collisionally excite CO molecules to high rotational levels of v = 0, 1, and 2. The product state distributions are compared with the predictions of classical trajectory calculations. In the second experiment, HCO is excited to an upper RennerTeller component that is degenerate with the ground potential energy surface in the linear configuration. Coupling between the states leads to dissociation, and the CO product distribution is again measured and compared to the predictions of classical trajectory calculations. In the third experiment, HCO is prepared by stimulated emission pumping (SEP) in highly excited vibrational levels above the dissociation limit on the ground state potential energy surface. The SEP linewidths provide information about the rate of dissociation, and a measurement of the CO product distribution provides information about the dynamics. Both experimental observations are compared to results from recent wave packet calculations. The HCO Potential Energy Surface Page 2 Figure 1 Contour plot of the BBH potential energy surface of HCO for a fixed C-O bond length of 2.25 a.u. The contours are spaced every 0.25 eV with the dashed contours indicating energy below the energy of the H+CO asymptote.