Bar plot showing the recurrence of the difference chemical species to the fit in IRAS 2A (top) and IRAS 23385 (bottom). Recurrences above 50% are considered essential to the fit and robust detection. CH₃COOH in IRAS 23385 does not occur in any of the solutions. In the case of IRAS 2A (top panel) we present hatched bars that show the recurrence of the solutions if the errors in optical depth are increased by a factor of three.