In order to facilitate searching and sorting XSAMS files or blocks of data within a file, a classification scheme is defined to provide standard definitions for the fundamental process that is being described (e.g., the reflection of a particle from a surface or the excitation of an atomic state).
The process codes are “fundamental” in that they do not define the reactions to a great degree of detail that is carried out by specific elements of the overall schema. Rather, they provide a high level identification that can be used to aggregate similar data or provide a simple search point.
The following table defines the fundamental reactant codes. The process codes embody a high level description and a much more complete definition of the process that data pertain to is contained in the elements of the full schema. Processes are split into two categories: collisions (electron and heavy particle collisions) and particle surface interactions (PSI). Within each category, the codes are intended for use with any reactant. For example, a single process code is used to describe elastic scattering whatever is the projectile (electron, photon, atom, ion or molecule).
This approach has been taken not only for economy but because an exhaustive list of processes involving elementary particles, atoms, molecules, and solids is not likely possible. Even if it were, using it would be cumbersome in that some non-intuitive coding would be necessary, for example, to encode inverse bremstrahlung, sublimation of water from a dust grain, a production of an atomic inner shell vacancy with a subsequent Coster-Kronig decay, etc.
Multiple process codes can be given in order to build more complex descriptions from the fundamental processes, e.g., charge transfer + ionization in ion-atom collisions could be described by the code for ionization (liberation of an electron from the target or projectile to the continuum) and the code for charge transfer (the transfer of an electron from one collision partner to another). This combining of individual codes avoids the need for a code for all possible combinations of processes that are at least relatively common, e.g., dissociative recombination simply has the codes for dissociation and for recombination. Other examples of combinations of codes are given in the final table.
| Code | Name | Description |
|---|---|---|
| phem | Photon emission | Emission of a photon or photons from a reactant (e.g.,. atom, molecule, surface), fluorescence |
| phab | Photon absorption | Absorption of a photon or photons from a reactant (e.g., atom, molecule, surface) |
| phsc | Photon scattering | Scattering of a photon or photons by a reactant |
| elas | Elastic scattering | Scattering of one reactant from another without change of state or energy, including related processes such as momentum transfer |
| inel | Inelastic scattering | Scattering of one reactant from another with change of state or energy. This code is provided in case none of the other specific inelastic codes are applicable or appropriate (e.g., energy or spin transfer reactions, projectile energy loss) |
| exci | Excitation | Excitation from a lower to higher state of any fundamental reactant, e.g., electron-impact excitation of an atom, photoexcitation of a molecule to a higher ro-vibrational state |
| deex | De-excitation | Induced or spontaneous transition from a higher state to a lower state, e.g., vibrational de-excitation in atom-diatom scattering |
| ioni | Ionization | Removal of an electron from any reactant |
| tran | Charge transfer | Transfer of an electron from one “center” (atomic ion, atom, molecule, etc.) to another |
| exch | Electron exchange | The exchange of an electron with another electron (most commonly in electron-impact processes) |
| reco | Recombination | Capture of an electron by an atomic or molecular ion, e.g., in dissociative recombination, dielectronic recombination, or radiative recombination |
| elat | Electron attachment | The formation of a negative ion by electron attachment |
| eldt | Electron detachment | The removal of the weakly bound electron of a negative ion by photon impact or collision with another particle such as an electron or surface |
| asso | Association | Association of two (or more) reactants, typically neutrals, collisionally, or radiatively |
| diss | Dissociation | The splitting of two (or more) reactants e.g., via electron-impact of a molecule, photodissociation, molecular break-up on a surface |
| intr | Interchange | The exchange of a heavy particle (atom, ion) in a reaction, e.g., D + H2 \rightarrow DH + H |
| chem | Chemical reaction | The exchange of atoms or groups of atoms in chemical reactions, e.g., C + 2O \rightarrow CO2 + heat |
| Code | Name | Description |
|---|---|---|
| sore | Reflection | The elastic or inelastic reflection of a reactant from a surface |
| soem | Emission or erosion | Any form of erosion of a surface, e.g., physical or chemical sputtering, etching, sublimation, emission of particle or macroscopic pieces, desorption, secondary electron emission |
| sodp | Deposition | Absorption of particles by a surface, sticking, surface implantation |
| soch | Change | Change of the composition or properties of a surface induced by any reactant |
| sope | Penetration | The penetration of a reactant into a solid, characterized by the change of energy, e.g., stopping, straggling, energy loss, range, charge state equilibrium, or change of structure, e.g., trapping, diffusion, deep implantation |
| Code | Name | Description |
|---|---|---|
| rota | Rotational process | Characterizes processes involving transition between rotational states |
| vibr | Vibrational process | Characterizes processes involving transition between vibrational states |
| rvib | Ro-Vibrational process | Characterizes processes involving transition between ro-vibrational states |
| hype | Hyperfine process | Characterizes processes involving transition between hyperfine states |
| hyp1 | Hyperfine 1 process | Characterizes processes involving transition between hyperfine states when 1 nuclear spin coupling is resolved |
| hypN | Hyperfine N process | Characterizes processes involving transition between hyperfine states when N nuclear spin couplings is resolved (here N is a digit in range 1-9) |
| fine | Fine process | Characterizes processes involving transition between fine states |
| tors | Torsional process | Characterizes processes involving transition between torsional states |
| rtor | Ro-Torsional process | Characterizes processes involving transition between ro-torsional states |
The following table gives examples of the use of the fundamental process codes to describe more complex but still common processes. Some simply fall within the broad scope of one of the fundamental codes and others can be described by use of multiple codes.
| Common Name | Codes | Description |
|---|---|---|
| Penning ionization | asso + ioni | Association of atoms with ionization |
| Transfer ionization | tran + ioni | Charge transfer between and ion and an atom, for example, with ionization |
| Transfer excitation | tran + exec | Charge transfer with excitation |
| Stripping | ioni | Ionization of the projectile in a collision of an ion or atom with an atom, molecule, or solid |
| Dissociative recombination | diss + reco | |
| Dielectronic recombination | reco | |
| Auger ionization | exci + ioni | |
| Spin-flip | inel | |
| photoionization | ioni | |
| Three-body recombination | reco | |
| Superelastic scattering | inel | |
| Surface catalysis | sure + chem | |
| Stark shift | ||
| Line broadening | ||
| Bremsstrahlung | ||
| Compton scattering |