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Table F.1
Variables used in the manuscript.
Variable | Symbol | Units and remarks |
---|---|---|
Species i mass | m_{i} | gram |
Dust grain radius squared | r^{2} | cm^{2}, input parameter |
Dust number density | n_{d} | cm^{−3} |
Number density of gas-phase species i | n_{i} | cm^{−3} |
Surface density of adsorption sites | N_{surf} | 1.5 × 10^{15} cm^{−2}, input parameter |
Number of adsorption sites per ice monolayer | nb_{site} | no units, nb_{site} = 4πN_{surf}r^{2} |
Surface site cross-section | σ_{surf,site} | σ_{surf,site} = 1∕N_{surf} cm^{2} |
Total number density of chemisorption sites | n_{surf,chem} | n_{surf,chem} = nb_{site}n_{d} = 4πN_{surf}r^{2}n_{d} cm^{−3} |
Number density of physisorbed species i | n_{#,i} | cm^{−3} |
Number density of chemisorbed species i | n_{*,i} | cm^{−3} |
Number density of unoccupied chemisorption sites | n_{*} | n_{*}= n_{surf,chem} − ∑_{i}n_{*,i} cm^{−3} |
Number density of chemically active physisorbed species i | cm^{−3} | |
Number of chemically active physisorption layers | N_{act} | no units, an input parameter with typical value 1–10 |
Total number of density of physisorbed species (ice) | n_{#,tot} | n_{#,tot} = ∑_{i}n_{#,i} cm^{−3} |
Number of physisorbed ice layers per grain | N_{layer} | no units, N_{layer} = n_{#,tot}∕(n_{d} nb_{site}) |
Fraction of available adsorption sites | f_{avail} | 1 for physisorption |
for chemisorption = n_{*}∕n_{surf,chem} if N_{layer} < 1, = 0 if N_{layer} ≥1 | ||
Gas temperature | T_{g} | K |
Dust temperature | T_{d} | K |
General activation barrier width | a_{Å} | Å |
Activation barrier | E_{act} | K |
Species mass in atomic mass units | m_{amu} | amu |
General adsorption rate | s^{−1} | |
General sticking coefficient | S_{i} | no units, between 0 and 1 |
General Bell’s formula | Q_{Bell} | no units |
Physisorption rate | s^{−1} | |
Physisorption sticking coefficient | S_{phys} | no units, between 0 and 1 |
Species i thermal speed | cm s^{−1} | |
Chemisorption activation energy | erg | |
Chemisorption rate | s^{−1} | |
Chemisorption Bell’s function | no units | |
Chemisorption sticking coefficient | S_{chem} | no units, between 0 and 1 |
Chemisorption activation barrier width | cm, assuming a rectangular-shaped barrier | |
Desorption energy | erg | |
Binding energy | erg, physisorption and chemisorption | |
Desorption activation energy | erg, non-null for desorption from chemisorption sites | |
Surface vibration frequency | ν_{0,i} | Hz |
Activation barrier for desorption | erg, non null for chemisorption | |
Desorption energy | erg, for either the physisorbed (=) chemisorbed (=) | |
Total desorption rate from a physisorption site | s^{−1} | |
Thermal desorption rate from a physisorption site | s^{−1} | |
Photodesorption rate from a physisorption site | s^{−1} | |
Photodesorption yield | Y_{i} | no units |
UV flux enhancement w.r.t. to the ISM value | χF_{Draine} | 1 χF_{Draine} =1.9921 × 10^{8} photons cm^{−2} s^{−1} |
Cosmic-Ray induced desorption rate from a physisorption site | s^{−1} | |
Activation barrier width for desorption from a chemisorption site | cm | |
Total desorption rate from a chemisorption site | s^{−1} | |
Thermal desorption from a chemisorption site | s^{−1} | |
Photodesorption rate from a chemisorption site | s^{−1} | |
Cosmic-ray induced desorption from a chemisorption site | ≃0 s^{−1} | |
Fraction of time a grain remains at 70 K up upon a cosmic-ray hit | f(70K) | no units |
Thermal desorption rate for a dust grain at 70 K | s^{−1} | |
Thermal diffusion rate for a dust grain at 70 K | s^{−1} | |
Thermal surface diffusion rate | s^{−1}, includes quantum tunnelling effect | |
Cosmic-Ray induced surface diffusion rate | s^{−1} | |
Bell’s formula for the diffusion processes | no units | |
Diffusion activation energy | erg | |
Diffusion activation barrier width | cm | |
Total surface diffusion rate | s^{−1}, | |
Activation barrier width for diffusion | cm | |
Hydrogen diffusion barrier between physisorption sites | erg | |
Hydrogen diffusion barrier between chemisorption sites | erg | |
Deuterium diffusion barrier between physisorption sites | erg | |
Deuterium diffusion barrier between chemisorption sites | erg | |
Physisorbed hydrogen desorption energy | erg | |
Physisorbed deuterium desorption energy | erg | |
Chemisorbed hydrogen desorption energy | erg | |
Chemisorbed deuterium desorption energy | erg | |
Surface reaction rate coefficient between species i and j | k_{ij} | cm^{3} s^{−1} |
Surface reaction probability | κ_{ij} | no units, between 0 and 1 |
Surface reaction activation barrier | erg | |
Surface reaction activation barrier width | cm | |
Hydrogen thermal desorption rate from a physisorption site | s^{−1} | |
Hydrogen diffusion rate between physisorption sites | s^{−1} | |
Hydrogen transfer rate from a physisorption to a chemisorption site | s^{−1} | |
Activation barrier energy for H transfer from a physisorption to a chemisorption site | erg | |
Bell’s function for H transfer from a physisorption to a chemisorption site | no units | |
Hydrogen transfer rate from a chemisorption to a physisorption site | s^{−1} | |
Eley-Rideal H_{2} formation rate (physisorption site) | s^{−1} | |
Eley-Rideal H_{2} formation rate (chemisorption site) | s^{−1} | |
H_{2} formation rate after encounter between a physisorbed and a chemisorption H-atom | R_{H} #, *H# | cm^{3} s^{−1} |
PAH effective radius | a_{PAH} | cm |
PAH number of carbon atoms | N_{C} | no units |
PAH number of hydrogen atoms | N_{H} | no units |
PAH ionisation potential | IP_{PAH} | erg |
Hydrogenated PAH hydrogen association rate coefficient | cm^{3} s^{−1} | |
Hydrogen association on PAH-H_{x} activation energy | erg | |
Hydrogenated PAH hydrogen abstraction rate coefficient | cm^{3} s^{−1} | |
Effective temperature upon absorption of a photon of energy hν | T_{e} | K |
PAH internal temperature | T_{PAH} | K |
Unimolecular PAH thermal dissociation rate at T_{e} | s^{−1} | |
Hydrogen binding energy on PAH-H_{x} | E_{0} | erg, ~1–2 eV |
Yield for PAH-H_{x} photodissociation | no units, = 0 for hν < E_{0} | |
Typical PAH IR photon emission rate | R_{IR} | ~1 s^{−1} |
Thermal unimolecular dissociation rate | s^{−1} | |
Hydrogen association rate coefficient for (hydrogenated) PAHs cations | cm^{3} s^{−1} | |
Activation energy for hydrogen association for PAH cations | erg | |
Hydrogenated ionised PAH hydrogen abstraction rate coefficient | cm^{3} s^{−1} | |
Energetic particle induced photoionisation rate coefficient | k_{pi,MeV} | cm^{3} s^{−1} |
Energetic particle induced photodetachment rate coefficient | k_{pd,CR} | cm^{3} s^{−1} |
Singly-ionised PAH cations electron recombination rate coefficient | k_{er} | cm^{3} s^{−1} |
Multiply-ionised PAH cations electron recombination rate coefficient | cm^{3} s^{−1} | |
PAH shape correction factor | ϕ_{PAH} | ϕ_{PAH} = σ_{disk} ∕σ_{sphere} |
PAH electron attachment rate coefficient | k_{ea} | cm^{3} s^{−1} |
Electron sticking coefficient on PAHs | S_{PAH} (e ^{−}) | no units |
Mutual neutralisation rate coefficient | k_{mn} | cm^{3} s^{−1} |
Electron collisional detachment rate coefficient | k_{nd} | cm^{3} s^{−1} |
Neutral PAH charge-exchange reactions | k_{ce,0} | cm^{3} s^{−1} |
Charged PAH charge-exchange reactions | k_{ce,n} | cm^{3} s^{−1} |
Double charge transfer reaction | k_{di} | cm^{3} s^{−1} |
PAH adsorption/desorption energy | E_{PAH,des} | cm^{3} s^{−1} |
Total H_{2} formation rate according to Cazaux & Tielens (2002, 2004) | s^{−1} | |
H_{2} recombination efficiency | ɛ | Cazaux & Tielens (2002) |
Total H_{2} formation rate according to Jura (1974, 1975a,b) | s^{−1} |
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