Table Of Contents

XSAMS Process Codes


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.

Process Codes

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.

Atomic and Molecular Collisions

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

Particle Solid Interactions

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

States class involved in process

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

Combination of Processes

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    
Compton scattering