All Figures

$\begin{figure} \par\includegraphics[width=6cm,clip]{4246fig1.eps}\end{figure}$ Figure 1: The ratio of abundances of ortho- and para-H₂ as a function of time, t, from an assumed initial value of 3 through to the attainment of steady state. A constant gas density of $n_{\rm H} = 10^4$ cm^-3 and temperatures T = 10 K and T = 30 K were adopted. The ortho:para ratios in Boltzmann equilibrium are shown for both values of T.
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In the text

$\begin{figure} \par\includegraphics[width=6cm,clip]{4246fig2.eps} \end{figure}$ Figure 2: The fractional abundances of CO and selected isotopes of H₃⁺ as functions of the gas density, $n_{\rm H}$ , for a constant kinetic temperature, T = 10 K (our "reference'' model of collapse). The initial value of the ortho:para H₂ ratio is $2.7\times 10^{-3}$ .
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{4246fig3.eps}\end{figure}$ Figure 3: The fractional abundances, relative to $n_{\rm H}$ , of a) H⁺ (full curve), H₃⁺ (broken curve) and e^- (chain curve), and b) H₂D⁺ (full curve), D₂H⁺ (long-dashed curve) and D₃⁺ (short-dashed curve), as functions of $n_{\rm H}$ . The bold curves are the predictions of the free-fall model, the light curves are the corresponding results in steady-state.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{4246fig4a.eps}\par\includegraphics[width=8.8cm,clip]{4246fig4b.eps}\end{figure}$ Figure 4: The relative abundances of the two lowest nuclear spin states (in the sense of energetically higher:lower) of H₃⁺, H₂D⁺, D₂H⁺ and D₃⁺ as functions of $n_{\rm H}$ , as predicted by the free-fall model (bold curves). The corresponding values in steady-state are shown as the light curves joining the symbols (full circles for H₂, full squares for the other species).
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{4246fig5a.eps}\vspace*{2mm... ....eps}\vspace*{2mm} \includegraphics[width=8.8cm,clip]{4246fig5d.eps}\end{figure}$ Figure 5: The fractional abundances, relative to $n_{\rm H} \approx n({\rm H}) + 2n({\rm H}_2)$ , of H₃⁺, H₂D⁺, D₂H⁺ and D₃⁺ as functions of the gas density, $n_{\rm H}$ , at a constant temperature T = 10 K. Results are shown for five values of the ortho:para H₂ ratio, between the statistical value of 3 and $3.6\times 10^{-7}$ , the ratio in Boltzmann equilibrium at T = 10 K. The computed values of the relative populations of nuclear spin states of the same species are also shown, in the sense of the population of the energetically higher state divided by that of the lower.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{4246fig6.eps}\end{figure}$ Figure 6: The fractional abundances, relative to $n_{\rm H} \approx n({\rm H}) + 2n({\rm H}_2)$ , of ortho-H₂D⁺ and para-D₂H⁺ as functions of the gas density, $n_{\rm H}$ , at a constant temperature T = 10 K. Results are shown for five initial (i.e. at $n_{\rm H} = 10^4$ cm^-3) values of the ortho:para H₂ ratio, between the statistical value of 3 and $3.6\times 10^{-7}$ , the ratio in Boltzmann equilibrium at T = 10 K. The fractional abundance of ortho-H₂D⁺ in L1544 (Caselli et al. 2003) and IRAS 16293E (Vastel et al. 2004), and the fractional abundance of para-D₂H⁺ in IRAS 16293E (Vastel et al. 2004), areindicated, as are the densities believed to prevail in these cores.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{4246fig7a.eps}\par\includegraphics[width=8.8cm,clip]{4246fig7b.eps}\end{figure}$ Figure 7: The fractional abundances of a) H₃⁺ and b) its isotopes, as functions of $n_{\rm H}$ , as predicted by the free-fall model including (bold curves) and excluding (corresponding light curves) coagulation; see Sect. 3.5. The fractional abundances of H⁺ and of the free electrons are also plotted in panel a). The ortho:para ratios of H₂, H₃⁺ and H₂D⁺ are displayed in panels c) and d).
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In the text

$\begin{figure} \par\includegraphics[width=6cm,clip]{4246fig1.eps}\end{figure}$	Figure 1: The ratio of abundances of ortho- and para-H₂ as a function of time, t, from an assumed initial value of 3 through to the attainment of steady state. A constant gas density of $n_{\rm H} = 10^4$ cm^-3 and temperatures T = 10 K and T = 30 K were adopted. The ortho:para ratios in Boltzmann equilibrium are shown for both values of T.
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$\begin{figure} \par\includegraphics[width=6cm,clip]{4246fig2.eps} \end{figure}$	Figure 2: The fractional abundances of CO and selected isotopes of H₃⁺ as functions of the gas density, $n_{\rm H}$ , for a constant kinetic temperature, T = 10 K (our "reference'' model of collapse). The initial value of the ortho:para H₂ ratio is $2.7\times 10^{-3}$ .
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$\begin{figure} \par\includegraphics[width=7cm,clip]{4246fig3.eps}\end{figure}$	Figure 3: The fractional abundances, relative to $n_{\rm H}$ , of a) H⁺ (full curve), H₃⁺ (broken curve) and e^- (chain curve), and b) H₂D⁺ (full curve), D₂H⁺ (long-dashed curve) and D₃⁺ (short-dashed curve), as functions of $n_{\rm H}$ . The bold curves are the predictions of the free-fall model, the light curves are the corresponding results in steady-state.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{4246fig4a.eps}\par\includegraphics[width=8.8cm,clip]{4246fig4b.eps}\end{figure}$	Figure 4: The relative abundances of the two lowest nuclear spin states (in the sense of energetically higher:lower) of H₃⁺, H₂D⁺, D₂H⁺ and D₃⁺ as functions of $n_{\rm H}$ , as predicted by the free-fall model (bold curves). The corresponding values in steady-state are shown as the light curves joining the symbols (full circles for H₂, full squares for the other species).
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