PHOTOINDUCED CHARGE-TRANSFER DISSOCIATION IN VAN-DER-WAALS COMPLEXES .4. NA(FCH3)(N) (N=1-4)

Complexes Na ...(FCH3)(n) were produced in crossed beams of Na and FCH3 and were monitored by photoionization (L(2) at 193 or 248 nm) together with time-of-flight mass spectrometry. The photoionization efficiencies of these van der Waals complexes were measured for n = 1-5. The ionization potentials decreased rapidly from rt = 1-3 and slowly thereafter; the first three FCH3 are thought to cluster directly around Na, whereas the fourth and fifth enter an outer solvation shell. Photoinduced charge-transfer dissociation in the complexes with n less than or equal to 4 was studied by measuring the action spectra, i.e., the photodepletion of the complexes by-tunable visible radiation from L(1) = 450-750 nm, using 248 nm ionization to measure the concentration of complexes with and without L(1). The action spectra for n = 1-4 consisted of three broad peaks corresponding to excitation to three electronically excited states of Na ...(FCH3)(n). Vibrational structure was evident in the action spectra of n 3 and 4, but not n 1 and 2. The measured peak cross sections, sigma(max), varied with the excited state and the size of complex, the largest being sigma(max) = 1.2 Angstrom(2) for Na ... FCH3 (n = 1). Based on these experimental results, some dynamical features of the reaction in Na ... FCH3, as well as properties of the ground-state complexes, are discussed.