Hyperthermal Energy Collisions of CF3 + Ions with Modified Surfaces: Surface-Induced Dissociation

Journal Article · Thu Jan 01 04:00:00 EST 2004 · Journal of Undergraduate Research

OSTI ID:1051672

Rezayat, T; Shukla, A

Collisions of low-energy ions, especially polyatomic ions, with surfaces have become an active area of research due to their numerous applications in chemistry, physics and material sciences. An interesting aspect of such collisions is the dissociation of ions which has been successfully exploited for the characterization of colliding ions, especially high mass ions from biological molecules. However, detailed studies of the energy transfer and dissociation have been performed only for a few simple systems and hence the mechanism(s) of ions’ excitation and dissociation are not as well understood even for small ions. We have therefore undertaken a study of the dissociation of a small polyatomic ion, CF3+, at several collision energies between 28.8 eV and 159 eV in collision with fluorinated alkyl thiol on gold 111 crystal and a LiF surface. These experiments were performed using a custom built tandem mass spectrometer where the energy and intensity distributions of the scattered fragment ions were measured as a function of the fragment ion mass and scattering angle. In contrast with the previous studies of the dissociation of ethanol and acetone cations where the inelastically scattered primary ions dominated the collision process (up to ~50 eV maximum energy used in those experiments), we did not observe a measurable abundance of inelastically scattered undissociated CF3+ ions at all energies studied here. We observed all fragment ions, CF2+, CF+, F+ and C+ at all energies studied with the relative intensity of the highest energy pathway, C+, increasing with collision energy. Also, the dissociation efficiency decreased significantly as the collision energy was increased from to 159 eV. The energy distributions of nearly all the fragment ions showed two distinct components, one corresponding to the loss of nearly all of the kinetic energy and scattered over a broad angular range while the other corresponding to smaller kinetic energy losses and scattered closer to the surface parallel. The latter process is due to delayed dissociation of excited ions after they have passed the collision region.

• Research Organization: DOESC (USDOE Office of Science (SC) (United States))
• Sponsoring Organization: USDOE Office of Science (SC)
• OSTI ID: 1051672
• Journal Information: Journal of Undergraduate Research, Journal Name: Journal of Undergraduate Research Vol. 4
• Country of Publication: United States
• Language: English