**Table 1:** Column densities and ¹⁶OH/¹⁸OH ratios for the best fit carried out to the ¹⁶OH and ¹⁸OH ground state lines. Columns 1 and 2 show the Gaussian fit parameters from the H I observations of Garwood & Dickey (1989).
Velocity	FWHM	$N({\rm ^{16}OH})$	¹⁶OH/¹⁸OH
(km s^-1)	(km s^-1)	(10¹⁵ cm^-2)
$-108\pm2$	$7\pm4$	$0.56\pm0.39$	$\rm 460^{+90}_{-50}$
$-82\pm4$	$28\pm12$	$9.0\pm3.9$	$\rm 460^{+90}_{-50}$
$-44.0\pm0.6/(-52\pm6)^a$	$8\pm2$ ( $17\pm5$ )	$3.5\pm1.8$	$\rm 450^{+100}_{-60}$
$-24.4\pm0.8$	$14\pm2$	$5.4\pm1.8$	$\rm 370^{+110}_{-50}$
$+1.1\pm0.4$	$19\pm1$	$7.6\pm3.4$	$\rm 430^{+80}_{-40}$
$+15.7\pm0.3$	$7\pm1$	$3.6\pm2.3$	$\rm 360^{+80}_{-50}$
$+31\pm4$	$21\pm14$	$5.4\pm3.8$	$\rm 540^{+100}_{-50}$
$+66.7\pm0.5/(+52.8\pm0.9)^b$	$16\pm1$ ( $11\pm2$ )	$\rm 32^{+6}_{-4}$	$\rm 320^{+70}_{-30}$
Total		67.0

^a These two components are too close to separate in our model and the best fit line shape requires only the -44.0 km s^-1 component.
^b The H I data resolve 2 components in Sgr B2. However, our fit requires only one of these (at 66.7 km s^-1) to reproduce the ISO spectrum.

Source LaTeX | All tables | In the text

	1 Introduction
	2 Observations and data reduction
	3 Results
	4 Modelling of OH in the line of sight
	5 ¹⁶OH/¹⁸OH ratio
	6 Comparison with other species
	7 Summary
	Appendix A: Observations and wavelengths
	References