PROBING THE DYNAMICS OF WEAKLY-BOUND COMPLEXES USING HIGH-RESOLUTION LASER SPECTROSCOPY

A combination of high-resolution infrared spectroscopy and photofragme nt detection methods has been used to study the vibrational predissoci ation of a number of weakly bound complexes at the state-to-state leve l. The goal of this research is to provide detailed information on the dissociation of these highly non-statistical systems that can be used to make comparisons with the results of emerging theoretical methods and to gain new insights into the nature of bond rupture. In this pape r we discuss results for several systems which illustrate some of the new methods we have developed. In the case of the HF dimer, the photof ragment angular distributions provide sufficient information to assign the internal state distributions of the fragments. The experimental r esults are compared with recently reported theoretical calculations. P reliminary experimental results are also reported for the HF-DF and DF -HF complexes which, when combined with previously reported theoretica l calculations and the HF dimer results, reveal deficiencies in the ex isting potential-energy surfaces that are not evident from the availab le spectroscopy. For systems where the fragments have smaller rotation al constants or accessible excited vibrational states, the angular dis tributions no longer provide a unique assignment of the internal state quantum numbers. Without such, the detail with which the photofragmen tation process can be studied is greatly reduced. For this reason we h ave developed two new methods that greatly aid in determining such inf ormation. The first involves the use of a second infrared laser to pro be the fragments spectroscopically, while the second method involves o rienting the parent molecular complex using a large de electric field prior to dissociating it. In this way the two fragments can be detecte d separately, reducing the congestion in the angular distribution. The se methods will be illustrated with several examples.