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Table 1

Important processes for the chemistry of carbon chains in IRC +10216.

Process α β γ ΔT (K) Notes and references
Bimolecular gas-phase chemical reactionsa
C2H + C2nH2 → C2n+2H2 + H 9.19 × 10-11 −0.29 0 15–295 Based on C2H + C2H2 (Chastaing et al. 1998)
C4H + C2nH2 → C2n+4H2 + H 1.82 × 10-10 −1.06 66 39–300 Based on C4H + C2H2 (Berteloite et al. 2010)
C2 + C2nH2 → C2n+2H + H 3.04 × 10-10 −0.14 0 24–300 Based on C2 + C2H2 (Páramo et al. 2008)
CN + C2nH2 → HC2n+1N + H 2.82 × 10-10 −0.54 22 25–295 Based on CN + C2H2 (Sims et al. 1993)
C3N + C2nH2 → HC2n+3N + H 3.21 × 10-10 −0.12 0 24–294 Based on C3N + C2H2 (Fournier 2014)
Photodissociation processesb
C2H2 + hν → C2H + H 4.40 × 10-9 2.46 Cooper et al. (1995)
C4H2 + hν → C4H + H 1.09 × 10-8 2.19 Ferradaz et al. (2009); 100% C4H + H (Silva et al. 2008)
C6H2 + hν → C6H + H 1.78 × 10-8 1.83 Kloster-Jensen et al. (1974); Shindo et al. (2003)
HCN + hν → CN + H 1.93 × 10-9 2.82 Nuth & Glicker (1982)
HC3N + hν → C3N + H 4.55 × 10-9 2.45 Ferradaz et al. (2009)
→ C2H + CN 3.43 × 10-9 2.47 Wavelength-dependent branching ratios (Silva et al. 2009)
HC5N + hν → C5N + H 8.84 × 10-9 1.94 Fray et al. (2010)
→ C4H + CN 6.66 × 10-9 1.94 Branching ratios of H and CN channels based on HC3N

Notes.

(a)

Rate constants have units of cm3 s-1 and are given by the expression k(T) = α(T/ 300)βexp(−γ/T). ΔT is the valid temperature range of the rate constant expression. The subindex n has values 1, 2, 3, 4, ....

(b)

Photodissociation rates have units of s-1 and are given by the expression K = αexp(−γAV).

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