UNDERSTANDING THE ORIGIN OF ROTATIONAL DISTRIBUTIONS IN TRIATOMIC PHOTODISSOCIATION - A K-J WAVE PACKET STUDY OF ICN

In this paper, we analyze in detail the results of a quantum mechanical, time-dependent wave packet calculation of ICN photodissociation in the A continuum. Using the model potentials of Goldfield et al., the CN(X2SIGMA+) rotational final product distributions are calculated for all excitation frequencies. In a previous paper [J. Chem. Phys. 95, 1721 (1991)], we presented the details of the methodology of the calculation. The results are in good agreement with the time-independent close-coupling calculation by Guo and Schatz [J. Chem. Phys. 92, 2397 ( 1990)]. In the present paper, the connection between the final product state distribution and the wave packet reaction dynamics is discussed. In particular, the bimodal rotational distribution in the (I(P3/2))-P-2 final products channel, with its superimposed oscillatory structure, is analyzed in detail. By focusing on the time evolution of the wave packet in k-j space, i.e., the conjugate space in the coordinate of I-CN relative translation and CN rotational motion, respectively, it is possible to determine completely the origin of these features. The bimodal distribution in the (I(P3/2))-P-2 final products' channel arises from the abrupt angle dependence of the coupling of the two surfaces. The high j distribution is enhanced relative to the low j distribution by selective recrossing of the low j amplitude to the (I(P1/2))-P-2 surface at later times. The superimposed oscillations are the signature of a rotational rainbow which arises from the angular well of the bent potential surface. They are associated unambiguously with the high j portion of the distribution and are not due to the interference of the two modes of the "doorway state." These observations allow for some speculation on the dynamical origin of the experimental distributions.