Table 1
Collisional processes included in the CH4 non-LTE model.
| No. | Process | Col. partner | Rate† (cm3 s−1) | Reference |
|---|---|---|---|---|
| 1a | CH4(v1,v3,vb)+M⇋ | M=H2, He | kg,a = 2.45 × 10−11 (0.237 + 2.58 × 10−3T) | 1 |
| CH4(v1+1,v3-1,vb)+M | M=CH4 | kg,a,CH4 = 1.0 × 10−11(1.157 + 7.48 × 10−3T) | 1 | |
| 1b | CH4(vS,v2,v4)+M ^ | M=H2, He | kg,b = 3.68 × 10−11(0.313 + 2.32 × 10−3T) | 1 |
| CH4(vs,v2-1,v4+1)+M | M=CH4 | kg,b,CH4 = 1.0 × 10−11(1.146 + 18.9 × 10−3T) | 1 | |
| 1c | CH4(v3,vb)+M ⇋ | M=H2, He | kg,c = 3.53 × 10−11(-0.57 + 5.31 × 10−3T) | 1 |
| CH4(v3 -1,vb+v2+v4)+M | M=CH4 | kg,c,CH4 = 1.0 × 10−11(1.726 + 9.71 × 10−3T) | 1 | |
| 1dw | CH4(v3,vb)+M ⇋ | M=H2, He, CH4 | kg,d = 1.0 × 10−12(0.976 + 5.49 × 10−3T) | 2 |
| CH4(v3 -1, vb+2v4)+M | ||||
| 2 |  |
M=H2 |  |
1 |
 |
M=He | kv t,CH4 = vb 6.37 × 10−16exp(0.01111 T) | 1 | |
| M=CH4 | kvt,CH4 = vb 10−16 exp(0.0347 T - 5.14 × 10−5T2) | 1 | ||
| 3a | CH4(vs,v4)+CH4 ⇋ CH4(vs,v4-1)+CH4(v4) | kvv,4 = v4 1.1 × 10−11 | 1 | |
| 3b | CH4(vs,v2)+CH4 ⇋ CH4(vs,v2-1)+CH4(v2) | kvv,2 = v2 1.1 × 10−11 | 3 | |
| 3c | CH4(vs,vb)+CH4 ⇋ CH4(v3-1,vb)+CH4(v3) | kvv,3 = v3 2.6 × 10−12 | 1 | |
| 4a |  |
kvv4,iso = 1.1 × 10−11 | 3 | |
| 4b |  |
kvv3,iso = 2.6 ×10−12 | 3 | |
Notes. †Rate coefficient for the forward direction of the process. Backward values are computed assuming detailed balance (see e.g. Eq. (3.54) of López-Puertas & Taylor 2001). vb is the bending quantum (v2 or v4). vs is the stretching quantum (v1 or v3). (*)Not considered in the nominal model. i and j refer to isotopologues 12CH4 and 13CH4, respectively. Rates at temperatures below 160 K and above 350 K are fixed to the values at those temperatures, respectively.
References. (1) Menard-Bourcin et al. (2005); (2) Hess & Moore (1976); (3) this work.
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