**Table 8:** Comparison with fractional abundances in other PPNe, arranged in order of decreasing stellar temperature.
C-rich PPNe:	IRAS 16594-4656		M1-16		CRL618		CRL2688		IRAS 19500-1709		IRC+10216
¹³CO	3.3 (-5)^a				2.4 (-5)^b		5.2 (-5)^b		2.0 (-5)^k
HCN	6.1 (-7)^a		1.0 (-7)^j		4.4 (-6)^b-5.0 (-7)^d		2.1 (-5)^b-4.0 (-7)^d		1.5 (-7)^k		1.3 (-5)^r
CN	6.0 (-6)^a		8.5 (-7)^j		2.1 (-6)^c		1.0 (-6)^c				2.2 (-6)^r
H¹³CN	<2.4 (-8)^a				6.3 (-8)^e		>4.0 (-6)^g-5.1 (-7)^e				2.8 (-7)^r
HNC	<1.8 (-7)^a				1.9 (-6)^b-1.9 (-7)^e		1.8 (-7)^h-5.0 (-8)^g				5.5 (-8)^r
HC₃N	<2.7 (-7)^a				4.4 (-7)^e-1.9 (-7)^b		1.5 (-7)^e,g				1.0 (-6)^r
HCO⁺	<1.2 (-7)^a		9.3 (-8)^j		2.0 (-7)^d
CS	<6.5 (-8)^a		<8.8 (-8)^j		4.1 (-7)^b-6.0 (-8)^d		2.1 (-6)^b				8.8 (-7)^r
C₂H	<3.1 (-6)^a				2.0 (-6)^d		9.3 (-6)^f				2.6 (-6)^r
C₄H	<4.5 (-5)^a				2.9 (-6)^b-8.0 (-8)^d						3.2 (-6)^r
SiO	<5.1 (-8)^a		<2.4 (-8)^j		<5.5 (-7)^b						1.1 (-7)^r
SiS	<3.2 (-7)^a		<4.2 (-8)^j				4.0 (-8)^g				9.5 (-7)^r
O-rich PPNe:	IRAS 17150-3224		M1-92		HD101584		IRAS 19114+0002		OH17.7-2.0		OH231.8+4.2
¹³CO	2.9 (-5)^a				5.0 (-4)^q		3.8 (-4)^b		4.2 (-6)^b		1.0 (-4)^l-2.2 (-5)^b
HCN	3.8 (-7)^a		<2.0 (-7)^o,p		<1.7 (-6)^q		<4.5 (-6)^b		<1.6 (-7)^b		4.4 (-6)^b-5.2 (-8)^m
CN	<1.1 (-8)^a										<2.0 (-7)^c,l
H¹³CN	<1.3 (-8)^a										4.8 (-8)^l
C₄H	<1.4 (-6)^a		<3.6 (-7)^q				<1.4 (-6)^b		<4.7 (-8)^b

^a This work, ^b Bujarrabal et al. (1994), ^c Bachiller et al. (1997b), ^d Bujarrabal et al. (1988), ^e Sopka et al. (1989), ^f Fuente et al. (1998), ^g Nguyen-Q-Rieu & Bieging (1990), ^h Kasuga et al. (1997), ^j Sahai et al. (1994), ^k Using the results of Bujarrabal et al. (2001,1992), ^l Morris et al. (1987), ^m Sanchez Contreras et al. (1997), ⁿ Omont et al. (1993), ^o Lindqvist et al. (1992), ^p Nercessian et al. (1989), ^q Using the results of Olofsson & Nyman (1999), ^r Woods et al. (2003b).

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