Relaxation processes of translationally hot O(1D) by collisions with O2

The collisions of translationally hot O(D-1) with O-2 result in two processes, translational energy relaxation and electronic quenching to O(P-3). These two processes were studied in a gas cell at room temperature using the vacuum ultraviolet laser-induced fluorescence technique. The initial hot O(D-1) atoms were produced by the photodissociation of N2O at 193 nm, which have average translational energies of 18.1 kcal mol(-1) in the laboratory frame. Time-resolved measurements of the Doppler profiles for the hot O(D-1) atoms revealed the translational energy relaxation process, whereas the quenching process was investigated by measuring both the decrease of the O(D-1) concentration and the increase of the product O(P-3) concentration at various delay times after the photochemical formation of the hot O(D-1) atoms. From the simulation employing an elastic hard-sphere collision model with a Monte Carlo method, the hard-sphere diameter for the translational energy relaxation process of hot O(D-1) by collisions with O-2 was found to be 2.5 +/- 0.2 Angstrom. The cross section of the electronic quenching of O(D-1) by O-2 at the high collision energy of 8.7 +/- 6 kcal mol(-1) was found to be 3.3 +/- 0.7 Angstrom(2), which is a little smaller than that at the thermal collision energy at 298 K. The observed collision energy dependence is explained by a centrifugal barrier on the entrance attractive potential surface of the quenching reaction.