MOLECULAR-BEAM STUDY OF THE COLLISION-INDUCED INTRAMOLECULAR ENERGY-TRANSFER CO(A(3)PI-]A('3)SIGMA(+), D(3)DELTA)

The collision-induced intramolecular energy transfer from CO(a(3) Pi) to CO(a'(3) Sigma(+)) and CO(d(3) Delta) was studied under single-collision conditions in a beam/gas-cell arrangement. CO molecules were excited into the long-lived a(3) Pi state in a de discharge burning in the expansion region of the CO(X) supersonic beam. The relative vibrational distribution of CO(a(3) Pi) was obtained from the spontaneous beam afterglow (AG) emission spectrum of the CO(a --> X) Cameron bands. Additional emission of the CO(a'3 Sigma(+)) and CO(d(3) Delta) states was observed to result from collisions with a target gas (He, Ne, Ar, Kr, and Xe) in a cell. This collision-induced afterglow (CIAG) is due to near-resonant intramolecular energy transfer CO(a --> a', d). From the CIAG spectra absolute state-to-state cross sections for populating various vibrational states in both CO(a') and CO(d) were deduced. They were obtained by normalizing the emission intensities of the product CO(a') and CO(d) levels to those of the CO(a) reactant levels. Spectral overlaps of the d(3) Delta and a'(3) Sigma(+) emissions were deconvoluted by means of computer simulation. The role of the energy gap between the reactant and the product states in the intramolecular transfer processes is discussed. The CO(d,upsilon=2) level is populated to a large extent via perturbations with the CO(a,upsilon(a)=9) level, according to the gateway mechanism. As a result, the emission from this particular level exhibits a very irregular band contour, with intense superimposed spikes marking the perturbed rotational states.