The impact of attenuation on cosmic-ray chemistry - I. Abundances and chemical calibrators in molecular clouds

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Table 2

Important reactions and their rate coefficients, taken from UMIST2012 database.

Reaction no.	Reaction	Rate coefficient (cm³ s⁻¹)
(R2)	$H_{2}^{+} + H_{2} \to H_{3}^{+} + H$ $Mathematical equation: $\mathrm{H}_{2}^{+}+\mathrm{H}_{2} \rightarrow \mathrm{H}_{3}^{+}+\mathrm{H}$$	k₂ = 2.08 × 10⁻⁹
(R3)	$H_{2}^{+} + e^{-} \to H + H$ $Mathematical equation: $\mathrm{H}_{2}^{+}+e^{-} \rightarrow \mathrm{H}+\mathrm{H}$$	k₃ = 1.6 × 10⁻⁸(T/300)^−0.43
(R4)	$H_{2}^{+} + e^{-} \to H + H$ $Mathematical equation: $\mathrm{H}_{2}^{+}+\mathrm{e}^{-} \rightarrow \mathrm{H}+\mathrm{H}$$	k₄ = 6.4 × 10⁻¹⁰
(R5)	$H_{2}^{+} + H \to H_{2} + H^{+}$ $Mathematical equation: $\mathrm{H}_{2}^{+}+\mathrm{H} \rightarrow \mathrm{H}_{2}+\mathrm{H}^{+}$$	k₅=2.34 × 10⁻⁸(T/300)^−0.52
(R6)	$H_{3}^{+} + e^{-} \to H_{2} + H$ $Mathematical equation: $\mathrm{H}_{3}^{+}+\mathrm{e}^{-} \rightarrow \mathrm{H}_{2}+\mathrm{H}$$	k₆=4.36 × 10⁻⁸(T/300)^−0.52
(R7)	$H_{3}^{+} + CO \to {HCO}^{+} + H_{2}$ $Mathematical equation: $\mathrm{H}_{3}^{+}+\mathrm{CO} \rightarrow \mathrm{HCO}^{+}+\mathrm{H}_{2}$$	k₇=1.36 × 10⁻⁹(T/300)^−0.14 exp (3.4/T)
(R8)	$H_{3}^{+} + CO \to {HOC}^{+} + H_{2}$ $Mathematical equation: $\mathrm{H}_{3}^{+}+\mathrm{CO} \rightarrow \mathrm{HOC}^{+}+\mathrm{H}_{2}$$	k₈=8.49 × 10⁻¹⁰(T/300)^0.07 exp (−5.2/T)
(R9)	$H_{3}^{+} + O \to {OH}^{+} + H_{2}$ $Mathematical equation: $\mathrm{H}_{3}^{+}+\mathrm{O} \rightarrow \mathrm{OH}^{+}+\mathrm{H}_{2}$$	k₉=7.98 × 10⁻¹⁰(T/300)^−0.16 exp (−1.4/T)
(R10)	$H_{3}^{+} + O \to H_{2} O^{+} + H$ $Mathematical equation: $\mathrm{H}_{3}^{+}+\mathrm{O} \rightarrow \mathrm{H}_{2} \mathrm{O}^{+}+\mathrm{H}$$	k₁₀=3.42 × 10⁻¹⁰(T/300)^−0.16 exp (−1.4/T)
(R11)	$H_{3}^{+} + C \to {CH}^{+} + H_{2}$ $Mathematical equation: $\mathrm{H}_{3}^{+}+\mathrm{C} \rightarrow \mathrm{CH}^{+}+\mathrm{H}_{2}$$	k₁₁=2.00 × 10⁻⁹
(R12)	HCO⁺ + e⁻ → H+CO	k₁₂=2.40 × 10⁻⁷(T/300)^−0.69
(R13)	${He}^{+} + CO \to O + C^{+} + He$ $Mathematical equation: $\mathrm{He}^{+}+\mathrm{CO} \rightarrow \mathrm{O}+\mathrm{C}^{+}+\mathrm{He}$$	k₁₃ = 1.60 × 10⁻⁹
(R14)	He⁺+O₂ → O⁺+O+He	k₁₄ = 1.10 × 10⁻⁹
(R15)	C⁺+e⁻ → C+h ν	k₁₅ = 2.36 × 10⁻¹²(T/300)^−0.29 exp (17.6/T)
(R16)	C⁺+O₂ → CO⁺+O	k₁₆ = 3.42 × 10⁻¹⁰
(R17)	C⁺+O₂ → CO+O⁺	k₁₇ = 4.54 × 10⁻¹⁰
(R18)	$H_{3}^{+} + N_{2} \to N_{2} H^{+} + H_{2}$ $Mathematical equation: $\mathrm{H}_{3}^{+}+\mathrm{N}_{2} \rightarrow \mathrm{~N}_{2} \mathrm{H}^{+}+\mathrm{H}_{2}$$	k₁₈ = 1.80 × 10⁻⁹
(R19)	CO + N₂H⁺ → HCO⁺+N₂	k₁₉=8.80 × 10⁻¹⁰

Notes. Numerical subscripts on rate coefficients correspond to the reaction numbers stated in the text. The H₃⁺–electron recombination rate coefficient (k_e) is equal to k₅+k₆. The rate coefficient for proton transfer to CO, denoted as k_CO, is calculated as k₇+k₈. The rate coefficient for destruction via proton transfer to O, k_O, is equal to k₉+k₁₀. The rate coefficient for O₂ destruction via reaction with C⁺, $k_{C^{+}}$ $Mathematical equation: $k_{\mathrm{C}^{+}}$$ , is equal to k₁₆+k₁₇. Temperature-dependent coefficients are expressed in terms of gas kinetic temperature (T).

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