Transition
Metal Chemistry in Crossed Beams
Please see our publications
page for recent work
Introduction:
A crossed molecular beams apparatus is used to
measure the velocity and angular distributions of chemical products from
bimolecular reactions of transition metal atoms with small molecules.
The apparatus and its capabilities are described in recent publication.
We have recently focussed our attention on studies of the reactions of
ground state transition metal atoms with simple hydrocarbons such as ethane,
ethylene, and acetylene. The primary goal of our studies is to understand
the role of reactant electronic state, orbital occupancy, and collision
energy in chemical reactivity.
A beam of transition metal atoms is produced by laser vaporization using
a
Smalley-type source. A 0.25" diameter metal rod is rotated and
translated
in front of the pulsed inert gas beam from a piezoelectrically operated
valve.
Below, the pulsed valve, ablation source and skimmer is shown.
In the figure below, the pulsed valve is removed. A copper rod is in
place. Near skimmer the copper
deposited from the ablation source is evident.
We are using this apparatus to study the reaction dynamics of transition
metal atoms with
small molecules in crossed beams. The beams are crossed at right
angles in the main
scattering chamber. Chemical products from the reaction are scattered
over a relatively
wide laboratory angular range. A small fraction of the products
enter the detector, where
they are ionized by either electron impact or by photoionization.
A schematic of the apparatus
is shown below. Click here
to learn more about how we constructed this apparatus.
We have studied the reactions of a variety of atoms from the 2nd row
of the periodic table.
The reactions studied to date include those with alkanes such as methane
and ethane, alkenes such as
ethylene, alkynes such as acetylene, and carbonyl-containing molecules
such as formaldehyde and
acetaldehyde. For further information on recent work, please
see our publications
page.
This fall, we began investigating reactions of small transition metal
clusters with simple
hydrocarbons such as acetylene. A very interesting aspect of
this work is that the center of mass
angles associated with reactions of different-sized clusters is appreciably
different. It is therefore
possible to directly measure the size-dependent reactivity of Mx, where
x > 1. Since we have
good mass-resolution and fragmentation is minimal using single photon
VUV ionization, it is
possible to study the chemical products resulting from reactions of
different sized clusters as a function
of collision energy. Stay tuned for new results in this
area!
