**Table 6:** Calculated fractional abundances, with respect to n(H₂).
			IRAS 16594-4656			IRAS 17150-3224
Molecule	Transition	$r_{\rm i}$	$r_{\rm e}$	$f_{\rm X}$	$r_{\rm i}$	$r_{\rm e}$	$f_{\rm X}$
		cm	cm		cm	cm
¹³CO^a	-	-	2.9 (17)	3.3 (-5)	-	2.4 (17)	2.9 (-5)
HCN	J=1-0	-	2.3 (16)	1.0 (-6)	-	4.4 (16)	3.8 (-7)
HCN	J=3-2	-	2.3 (16)	1.9 (-7)	-	4.4 (16)	-
CN	N=1-0	1.7 (16)	5.1 (16)	9.6 (-6)	3.9 (16)	9.8 (16)	U.L.^b
CN	N=2-1	1.7 (16)	5.1 (16)	2.5 (-6)	3.9 (16)	9.8 (16)	U.L.^b

$% latex2html id marker 7703 $\textstyle \parbox{16cm}{ $^a$\space $^{13}$ CO fr... ...limit to the fractional abundance has been made (see Table~\ref{upperlimits}).}$$

Source LaTeX | All tables | In the text

	1 Introduction
	2 Observations
	3 Sources
	4 CO observations
	5 CO line modelling
	6 Molecular evolution
	7 Discussion
	8 Conclusions
	References
	Online Material
	Appendix A: Molecular line spectra