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Table D.2

Main grain reactions involved in the formation and destruction of H2 and HD.

Reaction Comment
1 H H# Physisorption, barrierless
2 D D#
3 H + * *H# = = (400) 900–15 900 K
                 
4 H# + * *H# =
                 
5 D + * *D# = + ΔEH-D
                 
6 D# + * *D# = + ΔEH-D

7 H# H = 600 K
                 
8 D# D = + ΔEH-D
                 
9 H# + H Photodesorption
10 D# + D
11 H# + CR H
12 D# + CR D
13 *H# H + * = 10,000–25 000 K
                 
14 *D# D + * = + ΔEH-D
15 *H# + H + *
16 *D# + D + *
17 *H# + CR H + * Via CR induced UV
18 *D# + CR D + *

19 H + H# H2 Eley–Rideal (ER) mechanism, barrierless
20 D + H# HD
21 H + D# HD
22 H# + H# H2 = 0–250 K (Navarro-Ruiz et al. 2014)
                 
23 H# + D# HD = + ΔEH-D = 0–308 K

24 H + *H# H2 + * ER mechanism, barrierless
25 H + *D# HD + *
26 D + *H# HD + *
27 H# + *H# H2 + * =
                 
28 H# + *D# HD + * = + ΔEH-D
                 
29 D# + *H# HD + * = + ΔEH-D
                 
30 *H# + *H# H2 + 2* =
                 
31 *H# + *D# HD + 2* = + ΔEH-D

32 H2 + * *H# + H# = 3481 K (Diño et al. 2004)
                 
33 HD + * *D# + H# = + ΔEH-D, 1/2 of the total dissociation rate
                 
34 HD + * *H# + D# , 1/2 of the total dissociation rate

Notes. The energies are expressed in units of Kelvin. ΔEH-D = 58 K (5 meV), = 970 K (83 meV), ΔEH2 −HD = 415.8 K.

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