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

Abstract

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.

Leucine enkephalin—A mass spectrometry standard

“…Because the dissociation energy needed to lose CO molecules is well known, the number of CO units lost from the molecular ion brackets the internal energy (Kenttamaa & Cooks, 1985;Wysocki, Kenttamaa, & Cooks, 1987;Cooks et al, 1990). Although very useful and valuable, metal carbonyls have a chemical structure that is dissimilar to most organics, so they might behave differently in mass spectrometry.…”

“…Thermometer molecules are often used in mass spectrometrythe original idea goes back to the 1960s, to studies on energy dependence (Vekey, Brenton, & Beynon, 1986), and which has been developed further by Cooks and other researchers (Williams & Cooks, 1968;Kenttamaa & Cooks, 1985;Vekey, Brenton, & Beynon, 1986;Wysocki, Kenttamaa, & Cooks, 1987;Cooks et al, 1990;De Pauw, Pelzer, & Natalis, 1990;Derwa, De Pauw, & Natalis, 1991;Vekey, Somogyi, & Wysocki, 1995). The main idea is to use a compound that has a simple fragmentation pattern with known dissociation energetics.…”

Study of Ion Dynamics by Electron Transfer Dissociation: Alkali Metals as Targets

“…Whereas doubly-charged fragment ions resulting from CAD were dominant in the CID spectrum with the Xe target, singly-charged fragment ions result- 35) ing from ETD were dominant in the CID spectrum with the Cs target. e most intense peak resulting from ETD was estimated to be associated with a charge reduced ion in which H 2 had been abstracted from the precursor.…”

“…Using the same method, Cooks and coworkers determined the internal energy distributions, P(ε), in doubly charged ions following electron transfer in high-energy collisions by using a sector-type mass spectrometer and in low-energy collisions by using a triple quadrupole mass spectrometer with various atomic and molecular targets. 35) Di erences between the deposition of internal energy induced by collisional activation and electron transfer were investigated using W(CO) 6 2+ ions on collision with a rare gas and with an alkali metal target. 36,37) e internal energy deposition in collisionally activated dissociation (CAD) evaluated with a rare gas target was broad and decreased with increasing internal energy.…”

Potential crossing position in electron transfer of a doubly charged ion and an alkali metal target measured using thermometer molecule W(CO)6

“…Wysocki et al [20] have reported the use of so-called thermometer molecules to measure internal energy distributions P(ε) of gas-phase ions. By using the same method, Cooks and coworkers determined the internal energy distributions, P(ε), in doubly charged ions following electron transfer in high-energy collisions by using a sector-type mass spectrometer and in lowenergy collisions by using a triple quadrupole mass spectrometer with various atomic and molecular targets [21][22][23]. One of the authors have previously measured the internal energy distribution of neutral species formed through neutralization in charge-inversion mass spectrometry with alkali metal targets by using the thermometer molecule W(CO) 6 [24].…”