Results of the LVG models of Cesaroni & Walmsley (1991) showing only the predictions of excitation temperature and line intensity for the 1834 and 1837 GHz lines. The gray dashed area indicates the observed line intensity including the errors. Light green and blue lines correspond to the sum of the hfs lines in each component of the doublet. Upper panels: models with internal radiation field. Lower panels: models without internal radiation field.