Rotational population distribution of KH (v=0, 1, 2, and 3) in the reaction of K(5(2)P(j), 6(2)P(j) and 7(2)P(j)) with H-2: Reaction mechanism and product energy disposal

Using a pump-probe method, we have systematically studied the rotational distribution of KH (v =0-3) produced in the reaction of K (5P, 6P, and 7P) with H-2 The resulting rotational states fit roughly a statistical distribution at the system temperature, while the vibrational populations are characterized by a Boltzmann vibrational temperature of 1800, 3000, and 3100 K for the 5p, 6P, and 7P states, respectively. These results provide evidence that the reaction follows a collinear collisional geometry. This work has successfully probed KH from the K(5P) reaction, and confirms that a nonadiabatical transition via formation of an ion-pair K+H2- intermediate should account for the reaction pathway. The available energy dissipation was measured to be (68 +/- 4)%, (26 +/- 2)%, and (6 +/- 3)% into the translation, vibration, and rotation of the KH product, respectively. The energy conversion into vibrational degree of freedom generally increases with the principal quantum number, indicating that the electron-jump distance elongates along the order of 5P<6P<7P. The result is different from the Cs(8P,9P)-H-2 case, in which the electron-jump distances were considered roughly the same. Furthermore, a relatively large distance is expected to account for highly vibrational excitation found in the KH product. According to the classical trajectory computation reported by Polanyi and co-workers, the strong instability of the H-2(-) bond, inducing a large repulsion energy, appears to favor energy partitioning into the translation. (C) 1996 American Institute of Physics.