Table 4: Selected gas-phase fractional abundances with respect to H2, determined at the time of maximum HCOOCH3 abundancea.
Species Model
  $t_{\rm f}=5 \times 10^{4}$ yr $t_{\rm f}=2 \times 10^{5}$ yr $t_{\rm f}=1 \times 10^{6}$ yr $t_{\rm f}=2 \times 10^{5}$ yr
  T=T2(t) T=T2(t) T=T2(t) T=T1(t)
HCOOCH3 (all reactions) 1.9(-9) 7.8(-9) 1.9(-8) 5.3(-9)
HCOOCH3 (no gas-phase routes) 1.0(-10) 5.5(-9) 1.9(-8) 3.2(-9)
HCOOH 5.5(-8) 1.1(-7) 1.2(-7) 1.2(-7)
CH3OCH3 6.1(-9) 1.4(-8) 1.1(-9) 2.2(-8)
H2CO 2.3(-5) 2.3(-7) 3.9(-10) 1.5(-8)
CH3OH 3.2(-5) 1.7(-5) 5.9(-7) 1.8(-5)

$\textstyle \parbox{13cm}{ $^{a}$\space $a(b) = a \times 10^{b}$ .}$


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