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Table 1: Transitions of the anti-conformer of ethyl formate observed with the IRAM 30 m telescope toward Sgr B2(N). The horizontal lines mark discontinuities in the observed frequency coverage. Only the transitions associated with a modeled line stronger than 20 mK are listed.

Table 2: Transitions of the gauche-conformer of ethyl formate observed with the IRAM 30 m telescope toward Sgr B2(N). The horizontal lines mark discontinuities in the observed frequency coverage. Only the transitions associated with a modeled line stronger than 20 mK are listed.

Table 6: Transitions of anti-n-propyl cyanide, employed in the present fits, their frequencies (MHz), uncertainties Unc. (kHz), and residuals O-C (kHz) between frequencies measured in the laboratory and those calculated from the final spectroscopic parameters. Unresolved asymmetry splitting (two transitions having the same K_a and the same transition frequency) has been treated as intensity-weighted average of the two lines.

Table 7: Transitions of gauche-n-propyl cyanide, employed in the present fits, their frequencies (MHz), uncertainties Unc. (kHz), and residuals O-C (kHz) between frequencies measured in the laboratory and those calculated from the final spectroscopic parameters. Unresolved asymmetry splitting (two transitions having the same K_a and the same transition frequency) has been treated as intensity-weighted average of the two lines.

Table 9: Transitions of the anti-conformer of n-propyl cyanide observed with the IRAM 30 m telescope toward Sgr B2(N). The horizontal lines mark discontinuities in the observed frequency coverage. Only the transitions associated with a modeled line stronger than 20 mK are listed.

Table 10: Transitions of the gauche-conformer of n-propyl cyanide observed with the IRAM 30 m telescope toward Sgr B2(N). The horizontal lines mark discontinuities in the observed frequency coverage. Only the transitions associated with a modeled line stronger than 20 mK are listed.

$\begin{figure} {\resizebox{15cm}{!}{\includegraphics[angle=270]{11550f1a.ps}\inc... ...angle=270]{11550f1g.ps}\includegraphics[angle=270]{11550f1h.ps}} }\end{figure}$

Figure 1:

Transitions of the anti-conformer of ethyl formate (EtOCHO-a) detected with the IRAM 30 m telescope. Each panel consists of two plots and is labeled in black in the upper right corner. The lower plot shows in black the spectrum obtained toward Sgr B2(N) in main-beam brightness temperature scale (K), while the upper plot shows the spectrum toward Sgr B2(M). The rest frequency axis is labeled in GHz. The systemic velocities assumed for Sgr B2(N) and (M) are 64 and 62 km s^-1, respectively. The lines identified in the Sgr B2(N) spectrum are labeled in blue. The top red label indicates the EtOCHO-a transition centered in each plot (numbered like in Col. 1 of Table 3), along with the energy of its lower level in K ( $E_{\rm l}/k_{{\rm B}}$ ). The other EtOCHO-a lines are labeled in blue only. The bottom red label is the feature number (see Col. 8 of Table 3). The green spectrum shows our LTE model containing all identified molecules, including EtOCHO-a. The LTE synthetic spectrum of EtOCHO-a alone is overlaid in red, and its opacity in dashed violet. All observed lines which have no counterpart in the green spectrum are still unidentified in Sgr B2(N).

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$\begin{figure} \par {\resizebox{15.5cm}{!}{\includegraphics[angle=270]{11550f1i.... ...angle=270]{11550f1o.ps}\includegraphics[angle=270]{11550f1p.ps}} }\end{figure}$	Figure 1: continued.
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$\begin{figure} \par {\resizebox{15.5cm}{!}{\includegraphics[angle=270]{11550f1q.... ...angle=270]{11550f1s.ps}\includegraphics[angle=270]{11550f1t.ps}} }\end{figure}$	Figure 1: continued.
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$\begin{figure} \par {\resizebox{15.5cm}{!}{\includegraphics[angle=270]{11550f3a.... ...angle=270]{11550f3g.ps}\includegraphics[angle=270]{11550f3h.ps}} }\end{figure}$

Figure 3:

Transitions of the anti-conformer of n-propyl cyanide (PrCN-a) detected with the IRAM 30 m telescope. Each panel consists of two plots and is labeled in black in the upper right corner. The lower plot shows in black the spectrum obtained toward Sgr B2(N) in main-beam brightness temperature scale (K), while the upper plot shows the spectrum toward Sgr B2(M). The rest frequency axis is labeled in GHz. The systemic velocities assumed for Sgr B2(N) and (M) are 64 and 62 km s^-1, respectively. The lines identified in the Sgr B2(N) spectrum are labeled in blue. The top red label indicates the PrCN-a transition centered in each plot (numbered like in Col. 1 of Table 11), along with the energy of its lower level in K ( $E_{\rm l}/k_{{\rm B}}$ ). The other PrCN-a lines are labeled in blue only. The bottom red label is the feature number (see Col. 8 of Table 11). The green spectrum shows our LTE model containing all identified molecules, including PrCN-a. The LTE synthetic spectrum of PrCN-a alone is overlaid in red, and its opacity in dashed violet. All observed lines which have no counterpart in the green spectrum are still unidentified in Sgr B2(N).

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$\begin{figure} \par {\resizebox{15.5cm}{!}{\includegraphics[angle=270]{11550f3i.... ...{7.5cm}{!}{\includegraphics[angle=270]{11550f3k.ps}}\hspace*{4cm}}\end{figure}$	Figure 3: continued.
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Appendix A: a-type and b-type lines of methyl formate

Both A and E symmetry species of methyl formate (CH₃OCHO) are easily detected in our spectral survey of Sgr B2(N) at 3 mm. Sixty four lines of the A species are detected in the form of 57 features in our 3 mm survey and 48 lines of the E species in the form of 43 features. We followed the same procedure as described in Sect. 3.2 for ethyl formate to compute the population diagrams shown in Fig. A.1. In these diagrams, the a-type lines of methyl formate (with $\Delta K_a$ = 0 [2] and $\Delta K_c$ = 1 [2]) are marked with an additional circle. As mentioned in Sect. 3.4, both a- and b-type lines are well fitted with the same physical model (see Table 5). Although many a-type transitions with $E_{\rm u}/k_{\rm B} < 50$ K look systematically too low in the population diagrams after removal of the contribution of contaminating lines (Figs. A.1b and d), this can be explained by the limitations of our radiative transfer modeling: these a-type transitions (of the A or E species) have optical depths on the order of unity, as indicated by the significant shift between the red and green crosses in the lower energy range, and overlap with a-type lines of the other symmetry species (E or A, respectively) that have significant optical depths too. Since our current complete model treats the two symmetry species as independent and our radiative transfer program computes the contributions of overlapping transitions of different species independently, the sum of the overlapping A and E transitions with significant optical depths is systematically overestimated. For a transition of, e.g., the A species, the ``contamination'' by the E species is overestimated and its removal in Fig. A.1b yields an underestimated residual flux. Our model could be improved by treating both symmetry species as a single molecule but this would not significantly change the physical parameters found for methyl formate and is beyond the scope of this article focused on ethyl formate and n-propyl cyanide.

$\begin{figure} \par\includegraphics[angle=270,width=16cm,clip]{11550a1a.eps}\vspace*{2mm} \includegraphics[angle=270,width=16cm,clip]{11550a1b.eps} \end{figure}$

Figure A.1:

Population diagrams of the A and E symmetry species of methyl formate presented in the same way as for ethyl formate in Fig. 2 (see the caption of that figure for details). The a-type lines are marked with a circle. Panels a) and c) show the population diagrams derived from the measured integrated intensities for the A and E species, respectively, while panels b) and d) present the respective population diagrams after removing the expected contribution from contaminating molecules. Features 4 and 42 with $E_{\rm u}/k_{\rm B} > 120$ K (see panel c)) are missing in panel d) because the removal of the contaminating lines yields negative residuals. This is due to the uncertain level of the baseline that looks overestimated for both features in the observed spectrum.

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