Photodepletion spectra (415–763 nm, 10 Å effective resolution) were obtained for LiNa3 and Li2Na2 and compared to previous Na4 and Li4 measurements as well as to model calculations ranging from classical electrostatic to ab initio molecular orbital. Findings include (i) the assignment of planar rhombic singlet ground states for both molecules; (ii) in Li2Na2, the possibleobservation of predominantly one of three energetically close-lying planar rhombic or near rhombic substitution isomers; and (iii) in the sodium/lithium tetramer series, evidence for increasing localization of itinerant valence electrons with increasing cluster lithium content.

Collinear molecular beam photodepletion was used to obtain particle specific electronic absorption information for Na 3 , Na 4 , and Na s in a wavelength range from 370-835 nm. We critically discuss the experimental method used and the deconvolution procedure applied to the resulting data to yield absolute absorption cross sections. The spectra contain much information on the cluster-size-dependent transition from molecular to bulk-like optical response and are interpreted in terms of various computational approaches ranging from classical electrostatic to ab initio large scale configuration interaction.