Comparison of PDR model predictions and observed line intensities from the negative-v_LSR globules. Error bars show the 1σ uncertainty to the measured intensities obtained from a Gaussian fit to the observed lines. Globule #6 lies close in LSR velocity and shows similar emission properties to the negative-v_LSR globules. The velocity centroid of each globule increases from left to right in the x-axis (see Fig. 5). Left panelshows variations in the gas density whereas the right panel shows variations in G₀.