Dynamics studies of surface-induced dissociation of polyatomic
ions
EMSL Project ID
3612
Abstract
Ion- surface collisions have long been used for surface characterization and have recently been extended to the analysis of
projectile ions as well via their dissociations on surface impact, called
surface-induced dissociation (SID) [1]. This method has become important
with the development of new techniques for the ionization (such as
electrospray and matrix-assisted laser desorption ionization) of high mass
biological molecules and polymers by mass spectrometry. These ionization
techniques produce mainly (pseudo)molecular ions with very little
fragmentation that is needed for the structural characterization of the
molecular ion. The commonly used method to induce fragmentations of lower
mass ions in collision with a neutral gas is limited in energy transfer
from kinetic into internal modes following the conservation of momentum
principle. It has been demonstrated that collision of high mass ions
with a surface results in much higher energy transfer and extensive
fragmentation of the projectile ion is achieved [2]. This is specially the
case with modified surfaces such as self assembled monolayer (SAM)
surface of long chain fluorinated alkyl thiols on gold substrate which
reduces the dominant process of neutralization on metallic surfaces.
Although, early studies suggested that the mechanism of energy transfer and
dissociation is similar to gas phase collisions [1], detailed dynamics
studies have been performed only recently and only for smaller ions
[3-6]. These studies have demonstrated that ion excitation and dissociation
proceeds via several energetically distinct pathways. Also, the
scattering of fragment ions is non-specular and depends strongly on the
initial kinetic energy of the projectile ions. At the present time, there is
no clear understanding of these processes beyond a few small ions,
including the role played by the surface in the energy transfer and
dissociation processes. A better understanding of these aspects is necessary
to develop SID into a widely used method in tandem mass spectrometry.
I propose to use the beam scattering instrument developed recently at
the Environmental Molecular Sciences Laboratory within the PNNL to study
the detailed dynamics of surface-induced dissociations of a small
molecular ion, CF3+, using a variety of surfaces. Its SID has been studied
earlier [6]and the energetics of its dissociations is also known, thus
making it an ideal system to study its dissociation dynamics from
collisions with the CF3 group terminated SAM surface. By varying the ion's
kinetic energy, the role of kinetic energy on energy transfer,
dissociation characteristics and scattering of secondary ions will be explored.
These studies will be extended to include other surfaces (such as vapor
deposited diamond and LiF on Ti substrate) to better understand the
role played by the surface in the energy transfer and dissociation
processes. Another aspect of these collisions that will be explored is the
effective collision mass. Early studies have demonstrated that ions
collide with the end group or a small fraction of the total chain length of
the SAM surface [5, 7] or several atoms/chains simultaneously thus
creating the same effect as multiple collisions in gas phase collisions.
Hopefully, these studies will shed some light on the experimental
parameters or universality of this behavior as well.
Project Details
Project type
Exploratory Research
Start Date
2003-09-03
End Date
2005-08-09
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Journal of Chemical Physics