Photodissociation branching of NH3

NH3 partial cross sections.

We have estimated the wavelength dependent branching ratio of NH3 into its main astrochemically-significant photodissociation products, NH2 and NH. A discussion of these cross sections is given in Heays et al. 2017, and principal sources of data are Slanger & Black 1982 and Leach et al. 2005.

[Download the NH3 partial cross sections in hdf5 format.]

We have calculated the partial photodissociation rates generating these products when exposed to various kinds of interstellar and cosmic-ray-generated radiation fields.

NH3 ⟶ NH2 + H NH3 ⟶ NH + 2H/H2
Radiation field1 Rate2 Frac.3 Unc.4 Rate Frac. Unc.
ISRF 8.3e-10 0.58 B 6.1e-10 0.42 B
Blackbody 4000K 3.6e-09 1.00 A 2.3e-13 0.00 C
Blackbody 10000K 1.6e-09 0.95 A 9.0e-11 0.05 B
Lyman-alpha 6.6e-11 0.05 B 1.3e-09 0.95 A
Solar 4.0e-09 0.99 A 5.6e-11 0.01 C
TW-Hydra 4.9e-10 0.35 A 9.1e-10 0.65 A
Cosmic-ray induced 3.9e-14 0.39 B 6.2e-14 0.61 B
1 [Definition of radiation fields].
2 In units of s-1.
3 Estimated branching fraction between all channels producing OH and O (or NH2 and NH) regardless of excitation state or the chemical co-fragment.
4 Estimated rate uncertainties: accurate to within 30% (A), a factor of 2 (B), a factor of 10 (C).