A MULTICHANNEL QUANTUM DEFECT HALF-COLLISION ANALYSIS OF K2 PHOTODISSOCIATION THROUGH THE B1-PI-U STATE

Recent experiments by Zafiropulos et al. [Phys. Rev. Lett. 61, 1485 (1988)] indicate that K2 photodissociation through the B 1-PI-u state results in fluorescence polarization which is strongly dependent on excitation wavelength. To understand these results, we have studied the K2 system quantum mechanically using a half-collision analysis derived from the generalized form of multichannel quantum defect theory. This analysis factors the transition amplitudes into separate term representing absorption and final state interactions. An approximation called the adiabatic (a --> c)/recoil (c --> e) approximation is developed for the half-collision matrix which reproduces quantitatively the exact half-collision results projected from the close-coupled wave function. This specific approximation applies to the homonuclear molecule K2 because of the very long range of the excited state potential, which varies as 1/R3. The quantum mechanical expression for the polarization as a function of initial rotational quantum number J0 and total energy E is found to be extremely simple in this approximation, depending only on J0 and the single-channel P, Q, and R phase shifts for the adiabatic reference states corresponding to the B 1-PI-u state at short distance. In the high J limit, the quantum expression is in exact agreement with a semiclassical expression which is derived in the accompanying paper by Kleiber et al.