Table 7
Column density estimates of CH3CN, HNCO, and HCOOCH3 in NGC 7538 survey according to the partition function computed in the present study (rovibrational partition functions are computed as the product of the rotational contribution, given as a direct sum, the harmonic approximation of the vibrational partition function, and, for methyl formate, the torsional partition sum) and in the CDMS and JPL databases.
| Linear interpolation | Nonlinear interpolation | Present work (b) | |||||
|---|---|---|---|---|---|---|---|
| CH3 CN | Present work | CDMS | Rel. diff. (a) | Present work | CDMS | Rel. diff. (a) | |
| Q(T = 350 K) | 20 715.0 | 17 376.9 | 16 770.2 | 15 396.3 | 16 814.5 | ||
| N(cm−2) | (79.6 ± 5.3) × 1013 | (66.8 ± 4.5) × 1013 | 18% | (64.5 ± 4.3) × 1013 | (59.2 ± 3.9) × 1013 | 9% | (64.6 ± 4.3) × 1013 |
| HNCO | Present work | CDMS | Rel. diff. | Present work | CDMS | Rel. diff. | Present work |
| Q(T = 349 K) | 4700.25 | 3472.3 | 4169.83 | 3392.7 | 4183.4 | ||
| N(cm−2) | (21.8 ± 1.9) × 1013 | (16.1 ± 1.4) × 1013 | 30% | (19.3 ± 1.7) × 1013 | (15.7 ± 1.4) × 1013 | 21% | (19.4 ± 1.7) × 1013 |
| HCOOCH3 | Present work | JPL | Rel. diff. | Present work | JPL | Rel. diff. | Present work |
| Q(T = 182 K) | 66 091.3 | 42 769.4 | 59 265.8 | 41 801.6 | 59 302.1 | ||
| N(cm−2) | (18.4 ± 5.4) × 1014 | (11.9 ± 3.5) × 1014 | 43% | (16.5 ± 4.8) × 1014 | (11.6 ± 3.4) × 1014 | 35% | (16.5 ± 4.8) × 1014 |
Notes. The interpolated partition functions at the excitation temperatures deduced from Figs. 5–7 (350.33 K for CH3 CN, 349.23 K for HNCO and 182.46 K for HCOOCH3) are compared with the value computed inthe present study. (a)Relative difference between the column density estimates obtained from the partition functions computed in the present study and those given in CDMS and JPL catalogs, using the formalism Rel. diff. 
. (b) Partition function computed with Eq. (6) for the excitation temperatures deduced for NGC 7538 survey and provided in Tables D.1–D.3, available at the CDS.
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