Open Access
Table 1.
Critical densities.
| Molecule | Transition | Frequency | Eu/k (a) | ncrit (a),(b) | neff (c) |
|---|---|---|---|---|---|
| (GHz) | (K) | (cm−3) | (cm−3) | ||
| (1) | (2) | (3) | (4) | (5) | (6) |
| CO | 1−0 | 115.271 | 5.5 | 4 (2) | ... |
| 2−1 | 230.538 | 16.6 | 5 (3) | ... | |
| 3−2 | 345.796 | 33.2 | 2 (4) | ... | |
| 4−3 | 461.041 | 55.3 | 2 (5) | ... | |
| HCN | 1−0 | 88.632 | 4.3 | 2 (5) | 3 (3) |
| 3−2 | 265.886 | 25.5 | 8 (6) | 1 (4) | |
| 4−3 | 354.506 | 42.5 | 2 (7) | 2 (5) | |
| HCO+ | 1−0 | 89.189 | 4.3 | 3 (4) | 4 (2) |
| 3−2 | 267.558 | 25.7 | 1 (6) | 4 (3) | |
| 4−3 | 356.734 | 42.8 | 3 (6) | 2 (4) | |
| HNC | 1−0 | 90.664 | 4.4 | 1 (5) | 2 (3) |
| 3−2 | 271.981 | 26.1 | 4 (6) | 3 (4) | |
| 4−3 | 362.630 | 43.5 | 9 (6) | 1 (5) | |
| C2H | 1−0 | 87.317 | 4.3 | 2 (5) | 2 (4) |
| CS | 2−1 | 97.981 | 7.1 | 9 (4) | 9 (3) |
| 3−2 | 146.969 | 14.1 | 3 (5) | 3 (4) |
Notes.
(c)
Shirley (2015), with log Nref = 14.0 (HCN, HCO+, and HNC) and log Nref = 13.5 (CS, C2H).
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