Free Access
Table F.1
Variables used in the manuscript.
| Variable | Symbol | Units and remarks |
|---|---|---|
| Species i mass | mi | gram |
| Dust grain radius squared | r2 | cm2, input parameter |
| Dust number density | nd | cm−3 |
| Number density of gas-phase species i | ni | cm−3 |
| Surface density of adsorption sites | Nsurf | 1.5 × 1015 cm−2, input parameter |
| Number of adsorption sites per ice monolayer | nbsite | no units, nbsite = 4πNsurfr2 |
| Surface site cross-section | σsurf,site | σsurf,site = 1∕Nsurf cm2 |
| Total number density of chemisorption sites | nsurf,chem | nsurf,chem = nbsitend = 4πNsurfr2nd 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*= nsurf,chem − ∑in*,i cm−3 |
| Number density of chemically active physisorbed species i |  |
cm−3 |
| Number of chemically active physisorption layers | Nact | no units, an input parameter with typical value 1–10 |
| Total number of density of physisorbed species (ice) | n#,tot | n#,tot = ∑in#,i cm−3 |
| Number of physisorbed ice layers per grain | Nlayer | no units, Nlayer = n#,tot∕(nd nbsite) |
| Fraction of available adsorption sites | favail | 1 for physisorption |
| for chemisorption = n*∕nsurf,chem if Nlayer < 1, = 0 if Nlayer ≥1 | ||
| Gas temperature | Tg | K |
| Dust temperature | Td | K |
| General activation barrier width | aÅ | Å |
| Activation barrier | Eact | K |
| Species mass in atomic mass units | mamu | amu |
| General adsorption rate |  |
s−1 |
| General sticking coefficient | Si | no units, between 0 and 1 |
| General Bell’s formula | QBell | no units |
| Physisorption rate |  |
s−1 |
| Physisorption sticking coefficient | Sphys | 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 | Schem | 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 | ν0,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 | Yi | no units |
| UV flux enhancement w.r.t. to the ISM value | χFDraine | 1 χFDraine =1.9921 × 108 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 | kij | cm3 s−1 |
| Surface reaction probability | κij | 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 H2 formation rate (physisorption site) |  |
s−1 |
| Eley-Rideal H2 formation rate (chemisorption site) |  |
s−1 |
| H2 formation rate after encounter between a physisorbed and a chemisorption H-atom | RH #, *H# | cm3 s−1 |
| PAH effective radius | aPAH | cm |
| PAH number of carbon atoms | NC | no units |
| PAH number of hydrogen atoms | NH | no units |
| PAH ionisation potential | IPPAH | erg |
| Hydrogenated PAH hydrogen association rate coefficient |  |
cm3 s−1 |
| Hydrogen association on PAH-Hx activation energy |  |
erg |
| Hydrogenated PAH hydrogen abstraction rate coefficient |  |
cm3 s−1 |
| Effective temperature upon absorption of a photon of energy hν | Te | K |
| PAH internal temperature | TPAH | K |
| Unimolecular PAH thermal dissociation rate at Te |  |
s−1 |
| Hydrogen binding energy on PAH-Hx | E0 | erg, ~1–2 eV |
| Yield for PAH-Hx photodissociation |  |
no units, = 0 for hν < E0 |
| Typical PAH IR photon emission rate | RIR | ~1 s−1 |
| Thermal unimolecular dissociation rate |  |
s−1 |
| Hydrogen association rate coefficient for (hydrogenated) PAHs cations |  |
cm3 s−1 |
| Activation energy for hydrogen association for PAH cations |  |
erg |
| Hydrogenated ionised PAH hydrogen abstraction rate coefficient |  |
cm3 s−1 |
| Energetic particle induced photoionisation rate coefficient | kpi,MeV | cm3 s−1 |
| Energetic particle induced photodetachment rate coefficient | kpd,CR | cm3 s−1 |
| Singly-ionised PAH cations electron recombination rate coefficient | ker | cm3 s−1 |
| Multiply-ionised PAH cations electron recombination rate coefficient |  |
cm3 s−1 |
| PAH shape correction factor | ϕPAH | ϕPAH = σdisk ∕σsphere |
| PAH electron attachment rate coefficient | kea | cm3 s−1 |
| Electron sticking coefficient on PAHs | SPAH (e −) | no units |
| Mutual neutralisation rate coefficient | kmn | cm3 s−1 |
| Electron collisional detachment rate coefficient | knd | cm3 s−1 |
| Neutral PAH charge-exchange reactions | kce,0 | cm3 s−1 |
| Charged PAH charge-exchange reactions | kce,n | cm3 s−1 |
| Double charge transfer reaction | kdi | cm3 s−1 |
| PAH adsorption/desorption energy | EPAH,des | cm3 s−1 |
| Total H2 formation rate according to Cazaux & Tielens (2002, 2004) |  |
s−1 |
| H2 recombination efficiency | ɛ | Cazaux & Tielens (2002) |
| Total H2 formation rate according to Jura (1974, 1975a,b) |  |
s−1 |
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.