The triple coincidence PEPIPICO technique was used to study the dynamics of fragmentation. The time differences of several masses can easily be derived. For example, when SF6 is irradiated with synchrotron radiation od about 200 eV, it gives the charged fragments F+ and S+. How can I derive the momenta of this step? For example, in the reaction SF6++ --> SF5+ + F SF5+ --> S+ +5F. The time differences will be about 0,1µs for fluorine-ion and 0,05µs for the sulfur-ion.
In principle I know how the shapes shall look like, according to different fragmentation processes. My problem is to calculate the kinetic energy released in the process of charge-separation. To calculate the kinetic energy one has to calculate the momenta first. To calculate the momenta, I have to do something with the time differences. But even several papers of Eland and other groups are not conclusive (at least not for my understanding).
Lets go back to the named example.
Maybe it will be better to show the real measured values: Undergoing initial charge separation SF6++ fragments to S+ and F+: The mechanism is supposingly: SF6++-- SF3++ + 3F, SF3++ --> S+ + F+ + 2F.
The slope of the resulting signal is about -0.35 . The time difference on the x-Axis (F+-flight time) is 0.16µs and on the y-Axis(S+ flight time) its about 0.05µs. The observed width is 0.073µs.
Calculation of momenta of the undetected neutrals will be another challenge.
Hello
I think I saw you ask this question a few months ago. No luck yet?
We'd have to know a bit more about your experiment. Is a time of flight the only information you have? Is there no position-sensitive detector?
We'd also have to know something about the necessary precision. With 200 eV photons, there would be an easily measurable recoil velocity, if you are talking about reasonably high precision.
And you mention PEPIPICO - what information do you have from the electron, or does it only serve as a start signal for the ion TOF? Is it a threshold electron or an energetic electron? If you have more than one undetected fragment, you can't get an absolutely unambiguous KER, since you can't invoke a "total momentum is zero" condition to solve for the undetected fragment.
If I assume you don't have a momentum measurement on either electron, the center of mass of the SF6++ ion has an unknown momentum of up to the negative of the momentum of both electrons leaving in the same direction, with (200ev - double ionization threshold of SF6) kinetic evergy. That gives you you first limitation, and any KER you calculate will reflect this uncertainty. If you calculate that out and it's a tolerable error bar, then we start talking details about the ion detection.
It's not really worth talking about the KER calculation until we know more about the ion detector.
Hello,
and first of all I want to thank you for answering my question. I did not find an answer to solve this problem of calculating the KER. The only information is the time of flight. There were two time of flight detectors mounted on opposite sides of the interaction region of photon beam and molecule. Maybe it would be easier to take a two-body-breakup. The picture is below this text. It displays the splitting of SF4: SF4++ -->SF3+ + F+. The photons had an energy of 210.18 eV. There was no position-sensitive detector or an "filter" to sort out appointed electrons. The previous plots were derives usind 210.18 eV photons as well. We used energies around the S 2p edge of the respective molecule. We found that the processes did not change using other energies.
What do you mean by "If you calculate that out and it's a tolerable error bar, then we start talking details about the ion detection."? How can I calculate the uncertainty?
Thank you for your help
Beate Kieling
We calculated a spectral resolution (at least of the cation-TOF) of deltaE/E=15000.
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