COLLISION-INDUCED ELECTRIFICATION OF LARGE WATER CLUSTERS

The paper present the results of the molecular beam studies of the collisional electrification of water clusters. Both positive and negative ions were observed in scattered flow when clusters (H2O)n > 300 collided with various solid surfaces at the velocity about 1.3 km/s. In measurements of total ion currents the probability of charge removal from the surface was determined in dependence on the incident angle, on the mean sluster size (up to 3 000 molecules), and on the target material. The proposed model includes 1) the formation of an ion pair during ionic dissociation of a vibrationally excited molecule in water cluster colliding with surface; 2) asymmetric neutralization of an ion pair by surface; 3) inertial removal (recoil) of cluster ion from the surface. However some suprising features observed in the measurement of angular and energetic distributions of emitted charged particles, viz. rainbow spatial pattern of emission and the correlation between mean energy and scattered angle reversed to usual scattering, show that the emission of charged particles may be only partially determined by inertial removal.