Sucrose clusters exhibiting a magic number in dilute aqueous solutions

We report clustering of sucrose molecules in dilute aqueous solutions, based on measurements of the electrical mobility spectrum of singly charged airborne clusters produced by electrospraying the solution. The spectrum contains peaks with a smooth envelope, except for one peak which has about twice the amplitude of the envelope. The mobility at this peak is found to be somewhat higher than would be expected based on the rest of the sequence, suggesting a more compact structure for this cluster. This "magic" peak is prominent for basic, but not acidic, solutions. It is argued that these observations demonstrate the existence of clusters of many sizes in the solution prior to electrospraying, including the "magic" cluster. A simplified model is presented which reproduces the observed features.