All Figures

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{1013fg01.eps}\end{figure}$ Figure 1: The 1+1-D model. The disk is divided into annuli, each of which is treated as a 1-dimensional PDR problem for the chemistry and the cooling rates.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{1013fg02.eps}\end{figure}$ Figure 2: The photodissociation rate of ${\rm C_2H}$ at a radius of 105 AU. The solid line gives the rate found in this work, the dotted line the rate by van Zadelhoff et al. (2003).
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{1013fg03.eps}\end{figure}$ Figure 3: Settling times in years for 0.1 $\mu$ m-sized dust particles. The dashed lines give the boundaries between which the $m_{\rm gas}/m_{\rm dust}$ ratio is interpolated from a value of 10⁴ to 10².
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In the text

$\begin{figure} \par\includegraphics[width=14cm,clip]{1013fg04.ps}\end{figure}$ Figure 4: The temperature structure of the disk. The colorscale and the white contours give the gas temperature, the black contours give the dust temperature for the well-mixed model a) and the dust settling model b). The dominant cooling rates are also shown for the well-mixed c) and settled d) models, as well as the dominant heating rates in e) and f).
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In the text

$\begin{figure} \par\includegraphics[width=14cm,clip]{1013fg05.ps}\end{figure}$ Figure 5: The vertical temperature distribution at a radius of 105 AU for the well-mixed a) and the settled b) models. Figures c) and d) give the cooling rates at this radius, where the solid line denotes cooling by gas-dust collisions, the dashed line [C I] cooling, the dotted line CO cooling, the dash-dot line [C II] cooling and the dash-triple dot line [O I] cooling. Figures e) and f) give the heating rates: the solid line gives the photoelectric heating rates on large grains, the dotted line on PAHs; the dashed and dash-dot lines gives the heating rates due to the formation and dissociation of ${\rm H_2}$ , respectively, the dash-triple dot line gives the cosmic ray heating rate, and the grey solid line gives the heating rate due to gas-grain collisions.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{1013fg06.ps}\end{figure}$ Figure 6: The normalized distribution of the temperature over total disk mass. The solid line shows the dust temperature, the dashed line the gas temperature of the well-mixed model, and the dotted line the gas temperature of the settled model.
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In the text

$\begin{figure} \par\includegraphics[width=14cm,clip]{1013fg07.ps}\end{figure}$ Figure 7: Chemical abundances for the well-mixed ( left column) and settled ( right column) models. In a) and b), the density profile of the disk is shown, as well as the $A_{\rm V}=$ 1 surface denoted by the dashed line. In c) and d), the surface of the disk is shown as a dotted line, the H/H₂ transition as a dashed line, and the O/O₂ transition as a solid line. The shaded area denotes the C⁺/C/CO transition.
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In the text

$\begin{figure} \par\includegraphics[width=14cm,clip]{1013fg08.ps}\end{figure}$ Figure 8: The vertical distribution of several chemical species in the disk at 105 AU for the well-mixed ( left column) and settled ( right column) models. Figures a) and b) show the abundances of H and ${\rm H_2}$ ; Figs. c) and d) of ${\rm C^+}$ , C and CO.
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In the text

$\begin{figure} \par\includegraphics[width=15.7cm,clip]{1013fg09.ps}\end{figure}$ Figure 9: The emission lines of C, O, ${\rm C^+}$ and CO for three scenarios: $T_{\rm gas}=T_{\rm dust}$ (dotted line), and $T_{\rm gas}$ calculated explicitly in the well-mixed (solid line) and settled (dashed line) model. Units are in Kelvins, assuming that the disk fills the beam precisely; this corresponds to a beam size of $5\hbox {$^{\prime \prime }$ }$ when the disk is at 150 pc.
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In the text

$\begin{figure} \par\includegraphics[width=7.55cm,clip]{1013fg10.ps}\end{figure}$ Figure 10: Vertical distribution of gas and dust temperatures in the disk at a radius of 105 AU. The solid line gives the gas temperature when gas-dust collisions are ignored, the dashed line gives the gas temperature when these collisions are included in the thermal balance. The dotted line gives the dust temperature. The inset shows the region around $T_{\rm gas}=20~{\rm K}$ .
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{1013fg01.eps}\end{figure}$	Figure 1: The 1+1-D model. The disk is divided into annuli, each of which is treated as a 1-dimensional PDR problem for the chemistry and the cooling rates.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{1013fg02.eps}\end{figure}$	Figure 2: The photodissociation rate of ${\rm C_2H}$ at a radius of 105 AU. The solid line gives the rate found in this work, the dotted line the rate by van Zadelhoff et al. (2003).
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$\begin{figure} \par\includegraphics[width=7.8cm,clip]{1013fg03.eps}\end{figure}$	Figure 3: Settling times in years for 0.1 $\mu$ m-sized dust particles. The dashed lines give the boundaries between which the $m_{\rm gas}/m_{\rm dust}$ ratio is interpolated from a value of 10⁴ to 10².
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$\begin{figure} \par\includegraphics[width=14cm,clip]{1013fg04.ps}\end{figure}$	Figure 4: The temperature structure of the disk. The colorscale and the white contours give the gas temperature, the black contours give the dust temperature for the well-mixed model a) and the dust settling model b). The dominant cooling rates are also shown for the well-mixed c) and settled d) models, as well as the dominant heating rates in e) and f).
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$\begin{figure} \par\includegraphics[width=8cm,clip]{1013fg06.ps}\end{figure}$	Figure 6: The normalized distribution of the temperature over total disk mass. The solid line shows the dust temperature, the dashed line the gas temperature of the well-mixed model, and the dotted line the gas temperature of the settled model.
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$\begin{figure} \par\includegraphics[width=14cm,clip]{1013fg08.ps}\end{figure}$	Figure 8: The vertical distribution of several chemical species in the disk at 105 AU for the well-mixed ( left column) and settled ( right column) models. Figures a) and b) show the abundances of H and ${\rm H_2}$ ; Figs. c) and d) of ${\rm C^+}$ , C and CO.
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$\begin{figure} \par\includegraphics[width=15.7cm,clip]{1013fg09.ps}\end{figure}$	Figure 9: The emission lines of C, O, ${\rm C^+}$ and CO for three scenarios: $T_{\rm gas}=T_{\rm dust}$ (dotted line), and $T_{\rm gas}$ calculated explicitly in the well-mixed (solid line) and settled (dashed line) model. Units are in Kelvins, assuming that the disk fills the beam precisely; this corresponds to a beam size of $5\hbox {$^{\prime \prime }$ }$ when the disk is at 150 pc.
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$\begin{figure} \par\includegraphics[width=7.55cm,clip]{1013fg10.ps}\end{figure}$	Figure 10: Vertical distribution of gas and dust temperatures in the disk at a radius of 105 AU. The solid line gives the gas temperature when gas-dust collisions are ignored, the dashed line gives the gas temperature when these collisions are included in the thermal balance. The dotted line gives the dust temperature. The inset shows the region around $T_{\rm gas}=20~{\rm K}$ .
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