Crossed molecular beams experiments are designed to provide single-collision conditions for molecular reactions with strategically placed detectors to gather dynamical information. GMTHRASHpy is designed to process this dynamical information to get center-of-mass information on the reactions. An crossed molecular beams setup from Perugia is shown in the figure to the right, from https://doi.org/10.1080/01442350600641305.
These kind of setups can be used to study a vast number of elementary gas-phase bimoelcular reactions. For example, consider the reaction below:
The primary and secondary beams can be setup to produce CH and C4H6, and then the detector's mass-to-charge ratio (m/z) of 66 can be scanned for any product formation. Any measurement in the device is result of a long chain of events, namely: (1) a collision reacts and then dissociate to products, (2) the product flies in the direction of the detector, and (3) finally, the product successfully ionizes without fragmenting.
When the detector in the experiment is callibrated to pick up on different speeds for the same detected mass, time-of-flight distributions can be gathered which give an insight into how much translational energy products have after dissociating. An example for the reaction above is shown here:
where the black circles are the experimental raw data. To get a "simulated" fit, like the red line shown above, a long series of physical transformations have to be done to obtain the proper number and distribution of product velocities in what is called a "forward convolution". GMTHRASHpy does this convolution, using a candidate center-of-mass function to describe the reaction, and transforming that forward to get these set of lab intensities.
Details on the reaction above can be found here: https://doi.org/10.1039/D1CP04443E. Without further analysis, it can be difficult to distinguish what mechanisms are responsible for the the signals seen. In this example, the scan was done at a m/z of 65, assuming that electron impact ionization fragments the C6H6 product by one hydrogen. An example mechanism is shown below from molecular dynamics:
There are two usages for two different kinds of users:
Run the GMTHRASH.py python application with your favourite Python environment. You may need something with conda distributions. A window should pop up:
Click on "Import PAN file" to select your input file. It will populate the text box where you may edit the input. Then click on either "Forward Convolution" buttons to product the lab distributions as shown above. If you click "Full Forward Convolution", the images and data files will by default be saved in the background; they will be named the same as the input but with extra file suffixes attached.
From a terminal, using the command line interface (CLI) is usually easier. First, create a PAN input file that describes your experimental setup and data, like so:
Header portion of CH+C4H6.pan
ch + c4h6 ->
00001010110211
13 9 5 5
90. 1.6 0.8
0
18.4 12.0
8 9.5
13 54
1
65
3 0
1
0
-0.3
0.65 5.0 15 0
12 2500
0.1 0.1
and then give it to GMTHRASH_cli.py as an argument, like so:
GMTHRASH_cli.py CH+C4H6.pan
this produces the figure in the Introduction as well as the candidate center-of-mass (CM) functions.
GMTHRASH may also be imported as a module into another script's main program. The class resposible for all of the variables and functions is `crossedmolecularbeamsexperiment` and requires a few setup steps before calling for the forward convolution in `scanlabangles`. An example is shown below:
from gmthrash import crossedmolecularbeamsexperiment
experiment = crossedmolecularbeamsexperiment() # Step 0
experiment.readPAN("CH+C4H6.pan") # Step 1.1
experiment.setup_nonPANvariables() # Step 1.2
# Manipulate PAN variables here...
experiment.setup_postPANvariables() # Step 2
simANG, totalsimANG, simTOF, totalsimTOF = experiment.scanlabangles() # Step 3
# Plot!
experiment.plotLABfits(simANG,simTOF,"CH+C4H6.LAB.png")
experiment.plotCMfits("CH+C4H6.CM.png")
