Internal energy distributions deposited in doubly and singly charged tungsten hexacarbonyl ions generated by charge stripping, electron impact, and charge exchange.

The distribution Pε of internal energies deposited in W(CO)6 (+•). ions upon charge stripping (that is, electron detachment to yield the doubly charged ion in the course of a single kiloelec-tronvolt energy collision) was estimated by a thermochemical method from the measured relative abundances of the doubly charged fragment ions produced. The thermochemical information needed to estimate P/ge was obtained by measuring the threshold translational energy losses associated with charge stripping of the singly charged fragment ions, W(CO) n (+) (n = 0-5). The P(/ge) curve falls exponentially with increasing internal energy. The average energy transferred to W(CO)6 (+•) upon a 7.8-keV collision with O2 is 19 eV, yielding W(CO)6 (2•) ions with an average of 4 eV of internal energy. In its general appearance, the P(ε) distribution associated with charge stripping is similar to the curves obtained from simple collisional activation of either W(CO) 6 (+•). or W(CO)6 (2+•) in kiloelectronvolt energy gaseous collisions. Given that charge stripping occurs by way of an electronic excitation process, this similarity in the energy deposition function is taken to indicate that electronic excitation is also the major mechanism for simple collisional activation in this system at zero scattering angle in the kiloelectronvolt energy regime. The internal energy distribution associated with a related charge-stripping process, charge inversion from the metal carbonyl anions to yield the corresponding cations, was also recorded. This reaction shows a large (∼7 eV) average internal energy deposition with a distribution that indicates near-zero probability of formation of unexcited ions. These data are tentatively interpreted in terms of vibrationalelectron detachment. The internal energy distribution associated with an exothermic process, charge exchange [W(CO)6 (2+•) + O2 → W(CO) + (6•)+O2 (+•)], was also characterized. Unexpectedly strong coupling of translational to internal energy is observed, and there is a large probability of depositing internal energies in excess of 10 eV, even though the exothermicity is only 3 eV. Finally, the internal energy distributions associated with the formation of doubly charged W(CO)6 (2+•) ions by electron ionization have been measured. Unlike the distribution for charge stripping, but like that for singly charged ions generated by electron impact, this distribution shows considerable structure, presumably due to Franck-Condon factors.