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$\begin{figure} \par\includegraphics[angle=270,width=8.8cm,clip]{3849fig1.ps} \end{figure}$ Figure 1: Sample of molecular spectra obtained on comet C/1999 T1 (McNaught-Hartley).
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=8.8cm,clip]{3849fig2.ps} \end{figure}$ Figure 2: HCN J(3-2) line at 265.9 GHz observed on comet C/1999 T1 (McNaught-Hartley).
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=8.6cm,clip]{3849fig3.ps} \end{figure}$ Figure 3: Sample of molecular spectra obtained on comet C/2001 A2 (LINEAR).
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=8.6cm,clip]{3849fig4.ps} \end{figure}$ Figure 4: Quasi-simultaneous observations of HCN J(3-2) and HNC J(3-2) lines on comet C/2001 A2 (LINEAR). The HCN J(3-2) line (dotted lines) intensity has been divided by 5 to fit with the vertical intensity scale in main beam brightness temperature.
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=8.6cm,clip]{3849fig5.ps} \end{figure}$ Figure 5: Sample of molecular spectra obtained on comet C/2000 WM₁ (LINEAR).
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=8.6cm,clip]{3849fig6.ps} \end{figure}$ Figure 6: Simultaneous observations of HCN J(3-2) and HNC J(3-2) (not detected) lines on comet C/2000 WM₁ (LINEAR). TheHCN J(3-2) lines (dotted lines) intensities have been divided by 5 to fit with the vertical intensity scale.
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=8.6cm,clip]{3849fig7.ps} \end{figure}$ Figure 7: Sample of molecular spectra obtained on comet 153P/Ikeya-Zhang.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{3849fig8.ps} \end{figure}$ Figure 8: Simultaneous observations of the HCN J(3-2) line (dotted line, plotted with an intensity divided by 5) and HNC J(3-2) line (plain line) on comet 153P/Ikeya-Zhang. One can readily see that the HNC/HCN line ratio decreased from about 20% in March to 5% at the end of April.
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=8.2cm,clip]{3849fig9.ps} \end{figure}$ Figure 9: Detection of the HNCO line at 219.8 GHz on comet 153P/Ikeya-Zhang at IRAM.
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=8.8cm,clip]{3849figa.ps} \end{figure}$ Figure 10: Medium resolution spectra of three methyl-cyanide lines observed around 147 GHz in comets C/2001 A2 (LINEAR) and 153P/Ikeya-Zhang with IRAM. The velocity scale refers to the (8, 0)-(7, 0) line.
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=8.8cm,clip]{3849figb.ps} \end{figure}$ Figure 11: Methanol lines simultaneously observed with the same tuning at 304 GHz (lower sideband) and 307 GHz (upper sideband) on comets C/1999 T1 (McNaught-Hartley) and C/2000 WM₁ (LINEAR) with the CSO. Frequency scale is upper sideband.
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In the text

$\begin{figure} \par\includegraphics[origin=rb,angle=270,width=12cm,clip]{3849figc.ps} \end{figure}$ Figure 12: Wide-band, low resolution spectra of methanol lines observed at 157 GHz on comets C/1999 T1 (McNaught-Hartley) and C/2000 WM₁ (LINEAR) with IRAM.
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In the text

$\begin{figure} \par\includegraphics[origin=rb,angle=270,width=12cm,clip]{3849figd.ps} \end{figure}$ Figure 13: Wide-band, low resolution spectra of methanol lines observed at 157 GHz on comets C/2001 A2 (LINEAR) and 153P/Ikeya-Zhang with IRAM.
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In the text

$\begin{figure} \par\includegraphics[width=8.6cm,clip]{3849fige.ps} \end{figure}$ Figure 14: Evolution of post-perihelion production rates in comet 153P/Ikeya-Zhang. Water production rates are from Odin (black dots, Lecacheux et al. 2003) and from infrared observations (black squares, Dello Russo et al. 2004).
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{3849figf.ps} \end{figure}$ Figure 15: Plot of the abundances relative to water of 11 molecules observed in the four comets or searched for in at least two of them. Data are from Table 12. For HNC and CS, whose abundances relative to water vary with heliocentric distance, values at $r_{\rm h}\approx 1$ AU are plotted. Abundances measured in Hale-Bopp around perihelion are shown for comparison. Upper limits are drawn with $3-\sigma$ error bars in dashed lines.
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=8.6cm,clip]{3849figg.ps} \end{figure}$ Figure 16: The HNC/HCN production rate ratio as a function of heliocentric distance observed in 7 comets. The open symbols represent data previously published on comets of similar activity to those studied here: C/1996 B2 (Hyakutake) (Irvine et al. 1996), C/1999 H1 (Lee) (Biver et al. 2000) and C/1999 S4 (LINEAR) (Bockelée-Morvan et al. 2001). The dotted line corresponds to a weighted fit to all data yielding HNC/HCN = 0.06 $r_{\rm h}^{-2.1}$ .
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=8.8cm,clip]{3849figh.ps} \end{figure}$ Figure 17: Abundances of H₂S and CO relative to water in seven comets. Ellipses correspond to uncertainty domains ( $\pm 1\sigma$ on each axis). In the case of CO, $3-\sigma$ upper limits obtained in the radio are shown with light shaded ellipses. Circles (with comet number) correspond to the measured radio values, diamonds the infrared ones (Gibb et al. 2003; Mumma et al. 2002) and triangles the UV measurements (Weaver et al. 2003).
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=8.8cm,clip]{3849fig1.ps} \end{figure}$	Figure 1: Sample of molecular spectra obtained on comet C/1999 T1 (McNaught-Hartley).
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$\begin{figure} \par\includegraphics[angle=270,width=8.8cm,clip]{3849fig2.ps} \end{figure}$	Figure 2: HCN J(3-2) line at 265.9 GHz observed on comet C/1999 T1 (McNaught-Hartley).
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$\begin{figure} \par\includegraphics[angle=270,width=8.6cm,clip]{3849fig3.ps} \end{figure}$	Figure 3: Sample of molecular spectra obtained on comet C/2001 A2 (LINEAR).
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$\begin{figure} \par\includegraphics[angle=270,width=8.6cm,clip]{3849fig4.ps} \end{figure}$	Figure 4: Quasi-simultaneous observations of HCN J(3-2) and HNC J(3-2) lines on comet C/2001 A2 (LINEAR). The HCN J(3-2) line (dotted lines) intensity has been divided by 5 to fit with the vertical intensity scale in main beam brightness temperature.
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$\begin{figure} \par\includegraphics[angle=270,width=8.6cm,clip]{3849fig5.ps} \end{figure}$	Figure 5: Sample of molecular spectra obtained on comet C/2000 WM₁ (LINEAR).
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$\begin{figure} \par\includegraphics[angle=270,width=8.6cm,clip]{3849fig6.ps} \end{figure}$	Figure 6: Simultaneous observations of HCN J(3-2) and HNC J(3-2) (not detected) lines on comet C/2000 WM₁ (LINEAR). TheHCN J(3-2) lines (dotted lines) intensities have been divided by 5 to fit with the vertical intensity scale.
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$\begin{figure} \par\includegraphics[angle=270,width=8.6cm,clip]{3849fig7.ps} \end{figure}$	Figure 7: Sample of molecular spectra obtained on comet 153P/Ikeya-Zhang.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{3849fig8.ps} \end{figure}$	Figure 8: Simultaneous observations of the HCN J(3-2) line (dotted line, plotted with an intensity divided by 5) and HNC J(3-2) line (plain line) on comet 153P/Ikeya-Zhang. One can readily see that the HNC/HCN line ratio decreased from about 20% in March to 5% at the end of April.
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$\begin{figure} \par\includegraphics[angle=270,width=8.2cm,clip]{3849fig9.ps} \end{figure}$	Figure 9: Detection of the HNCO line at 219.8 GHz on comet 153P/Ikeya-Zhang at IRAM.
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$\begin{figure} \par\includegraphics[angle=270,width=8.8cm,clip]{3849figa.ps} \end{figure}$	Figure 10: Medium resolution spectra of three methyl-cyanide lines observed around 147 GHz in comets C/2001 A2 (LINEAR) and 153P/Ikeya-Zhang with IRAM. The velocity scale refers to the (8, 0)-(7, 0) line.
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$\begin{figure} \par\includegraphics[angle=270,width=8.8cm,clip]{3849figb.ps} \end{figure}$	Figure 11: Methanol lines simultaneously observed with the same tuning at 304 GHz (lower sideband) and 307 GHz (upper sideband) on comets C/1999 T1 (McNaught-Hartley) and C/2000 WM₁ (LINEAR) with the CSO. Frequency scale is upper sideband.
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$\begin{figure} \par\includegraphics[origin=rb,angle=270,width=12cm,clip]{3849figc.ps} \end{figure}$	Figure 12: Wide-band, low resolution spectra of methanol lines observed at 157 GHz on comets C/1999 T1 (McNaught-Hartley) and C/2000 WM₁ (LINEAR) with IRAM.
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$\begin{figure} \par\includegraphics[origin=rb,angle=270,width=12cm,clip]{3849figd.ps} \end{figure}$	Figure 13: Wide-band, low resolution spectra of methanol lines observed at 157 GHz on comets C/2001 A2 (LINEAR) and 153P/Ikeya-Zhang with IRAM.
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$\begin{figure} \par\includegraphics[width=8.6cm,clip]{3849fige.ps} \end{figure}$	Figure 14: Evolution of post-perihelion production rates in comet 153P/Ikeya-Zhang. Water production rates are from Odin (black dots, Lecacheux et al. 2003) and from infrared observations (black squares, Dello Russo et al. 2004).
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