Influence of surface charge field on the electron impact fragmentation pattern of KCl molecules in the free surface vaporization of single crystals

A mass-spectrometric method was used to investigate the temperature depende nce of the electron impact fragmentation pattern of KCI molecules [ion curr ent ratio I(K+)/I(KCl+)] vaporizing from a free surface of a potassium chlo ride single crystal. In the temperature range 766-945 K a very good correla tion is observed between the variation in fragmentation pattern with temper ature and the pattern of the curve E versus T, where E is the strength of s urface charge field. It is concluded that molecules desorbing from an open crystal surface may possess excessive vibrational and rotational energy com pared to that characteristic of thermal excitation. (C) 2000 Elsevier Scien ce B.V.