**Table 1:** Initial gas phase abundances of He, C, O, Si, Fe, and CO.
Element/	Abundance^a
molecule	[n(X)/n(H)]
He	0.1
C	$7.1\times10^{-9}$
O	$1.8\times10^{-4}$
Si	$8.0\times10^{-9}$
Fe	$3.0\times10^{-9}$
CO	$1.5\times10^{-4}$

^a From the low metal case for dense cloud chemistry (Prasad & Huntress 1982;
Herbst & Leung 1989; Graedel et al. 1982).

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