Research descriptions

My research interests lie in the area of physical chemistry. I particularly enjoy studying reaction and dissociation dynamics of small molecules. Additionally, writing computer interfaces for data acquisition, analysis and visualization is also a passion of mine. Here I summarize some of the work that I have done, mostly in the area of reaction and dissociation dynamics. For information on computer programs, see the programs page.

• Current research interests
• Research performed for my PhD

Current research interests

Description, 13 May 2003

I am working in Peter Harland's lab at the University of Canterbury in Christchurch, New Zealand. Our goal is to examine the dynamics of collision processes through the use of photoion imaging.

There are two versions of this explanation. A non-technical version, which appears next, and a technical version which appears later.

The non-technical version

Our goal is to look at what happens when one molecule collides with another. To do this, we have a large apparatus that is essentially a very expensive vacuum. We need to have a vacuum so that we know that the molecules are colliding with one another, and not the air.

We make two beams of molecules (a beam meaning that we have molecules travelling all in one direction along a very thin line), one travelling in one direction and the other travelling perpendicular to the first one. At some point in the machine, these beams collide. When they collide, the molecules can react and form different molecules (technical aside: they don't have to form different molecules, they can just form different ions, or even the same ions. Something has to happen, though!). We then use a very sensitive camera to takes pictures of where those molecules go when they react.

The pictures that we get from the camera tell us what happened when the molecules react. Did they blow apart, or simply knock lightly into one another? We can also see in the pictures what direction the molecules went after they reacted. All of this information tells us a lot about these molecules and how they interact with one another.

Of course, the quintessential question then arises: "So, good for you that you can do that. What's the point?" The simple answer is that the more we know about molecules, the more we can do with them. As we increase our understanding of fundamental reactions of molecules, we can employ that knowledge to make new compounds, or make compounds in a cleaner or more efficient method than before. Is it likely that anyone is ever going to need to know details about the reaction of acetylene (C2H2) with methyl bromide (CH3Br) (the system I am working on at the moment)? Probably not. But by performing our experiment, we say that this experiment can be done, and then we can use it for something that someone might be interested in, or someone else might be able to. Additionally, knowledge we gain from studying this system may prove useful and generally applicable to many systems.

What we are doing is on the frontiers of science, and sometimes (even for me), it is difficult to see beyond the esoteric nature of the experiment to what might be done with it some day. But just doing new science and trying new techniques is useful in its own right. Who knows future applications of the techniques that I am developing today? I certainly don't, but if I don't try, who will?

The technical version

The interactions and reactions of ions are of fundamental importance in chemistry and physics. In our experiments, we are exploring the interactions of ions and neutrals using high vacuum crossed-beam experiments. The unique aspects of our experiment are the use of a velocity-focusing assembly to direct the ions to a CCD camera, and hexapole focusing of the parent neutral beam. The CCD setup allows us to collect all ions, regardless of recoil angle, unlike similar experiments which employ movable mass spectrometers to collect the products of reaction. The hexapole focusing of the neutral molecules allows us to explore changes in reaction products and distributions as a function of the orientation of the neutral molecule relative to the ion beam.

The systems we are currently studying are charge exchange with neutral methyl halides. Methyl halides are employed because they are easily obtained, and focus well in the hexapole field. The ion beam can consist of any molecule with a larger ionization energy than the methyl halide in question. Currently we are using acetylene (C2H2) owing to its inability to charge exchange with the background gases (N2, O2 and H2O primarily).

Ultimately, we want to examine reactions of the methyl halides:

CH₃X + A⁺ --> CH₃ + X⁺ + A

By changing the orientation of the methyl halide in the hexpole field, we can then examine how the energy and angular distribution of X+ changes based on which end of the molecule collides with the incident A+.

Currently, the success of this experiment is being hampered by the small signal levels (owing to the small reactive cross sections of the molecules, and the small intensities of the incident beams), and the large contribution from background gasses (this is where mass spectrometry has an advantage, being able to easily mass-select).

Research for my Ph.D.

The research I performed for my PhD involved the photodissociation dynamics of small molecular and cluster anions. We studied the two-, three-, and four-body dissociation dynamics of a variety of systems. Through the use of kinematically complete detection of the neutral products (as well as the photodetached electron), we are able to gain unique insight into the detailed dissociation dynamics and energetics of these systems.

The experiments I performed, and a bibliography, can be found on the group web site.