DEPENDENCE ON SCATTERING ANGLE OF THE INTERNAL ENERGY-DISTRIBUTION OFPRODUCTS OF CHARGE-CHANGING COLLISIONS

The internal energy distributions arising from charge-changing collisi ons were measured as a function of scattering angle, theta, for the 't hermometer' molecule W(CO)6. The experiments were performed by modifyi ng a reverse-geometry mass-analyzed ion kinetic energy (MIKE) spectrom eter by adding angle-resolving slits which allow measurement of the sc attering angle in the non-focusing plane of the instrument. Charge exc hange of W(CO)62+ with benzene to give W(CO)6+., and charge stripping of W(CO)6+. on collision with that, to give W(CO)62+, were studied at 6 keV with the product ions being collected over laboratory scattering angles selected in the range 0-0.60-degrees. The results show that ch arge-changing collisions accompanied by scattering have the potential for depositing extremely large internal energies. The observation of t he W(CO)2+ ion formed in dissociative charge stripping of W(CO)6+. sho ws that it is possible to deposit at least 27 eV into the colliding W( CO)6+. ion; of this energy, 15 eV is used for the charge-stripping pro cess, leaving 12 eV of internal energy in the nascent W(CO)62+. Even greater internal energies (more than 15 eV) can be deposited into scat tered W(CO)6+. produced by charge exchange of the doubly charged ion. The availability of such high internal energies has potential use in causing dissociation of refractory ions such as those of biomolecules. The average internal energy, epsilon(AVE), deposited increases with t he scattering angle at a rate of 10 eV degree-1 for charge exchange, a nd at approximately 5 eV degree-1 for charge stripping and for simple collision-induced dissociation (CID). This observation suggests that n on-zero angle charge stripping and CID may occur vis similar mechanism s in which direct vibrational activation occurs in small impact parame ter collisions which also lead to angular scattering. The higher inter nal energies and larger epsilon(AVE) vs. theta dependence observed for charge exchange are consistent with the formation of the products upo n a highly repulsive surface associated with coulombic repulsion betwe en the separating products.