Table 8
Peak gas-phase fractional abundances with respect to H2 and temperatures at which the peak abundance values are achieved, for models based on model M4, that is, with an activation energy barrier of 1250 K for the grain-surface reaction NH + CO → HNCO.
| M4A | M4B | M4C | M4D | M4E | |||||||||||
| EA = 1390 K | EA = 2000 K | EA = 2500 K | EA = 3000 K | EA = 3500 K | |||||||||||
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| Species | n[i]/n[H2] | T (K) | n[i]/n[H2] | T (K) | n[i]/n[H2] | T (K) | n[i]/n[H2] | T (K) | n[i]/n[H2] | T (K) | |||||
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| CH3NHCHO | 1.2(−8) | 139 | 5.3(−9) | 139 | 1.2(−9) | 139 | 6.0(−10) | 139 | 5.1(−10) | 139 | |||||
| CH3NCO | 7.0(−11) | 398 | 4.1(−9) | 74 | 6.5(−9) | 74 | 6.9(−9) | 74 | 6.9(−9) | 74 | |||||
| NH2CHO | 5.1(−7) | 157 | 5.1(−7) | 157 | 5.1(−7) | 157 | 5.1(−7) | 157 | 5.1(−7) | 157 | |||||
| HNCO | 2.2(−8) | 56 | 2.2(−8) | 56 | 2.2(−8) | 56 | 2.2(−8) | 56 | 2.2(−8) | 56 | |||||
| CH3CONH2 | 3.2(−8) | 138 | 3.2(−8) | 138 | 3.2(−8) | 138 | 3.2(−8) | 138 | 3.2(−8) | 138 | |||||
Notes. The models (M4A–E) vary from model M4 in two ways: (i) the OH + NH2CHO → NHCHO + H2O reaction pathway has been switched off; (ii) the reaction H + CH3NCO → CH3NHCO is switched on, with an activation energy barrier, EA, as indicated. Model M4A uses the value assumed for the H + HNCO → NH2CO reaction (1390 K, Nguyen et al. 1996), while the other models use larger values. X(Y) means X × 10Y.
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