Mid-infrared spectra of IRAS 16029–5055, IRAS 17375–2759, IRAS 17393–2727, and IRAS 19176+1251, as seen by the IRS SL (left) and SH (right) modules of Spitzer. Narrow and broad emission lines (red color) from ionized gas and dust grains, respectively, are present in their spectra. The narrow emission lines of [Ar II], [Ar III], [S IV], [Ne II], [Ne III], and [Ne V] are observed at around 6.98, 8.98, 10.51, 12.84 μm, 15.55, and 14.32 μm, respectively. The broad emission lines are usually attributed to emission from PAHs, which present a different chemistry (C-rich) from that of the O-rich maser-emitting regions.